Electron-emitting electrode, method of manufacturing the same, and light-emitting device having the same

The present invention relates to a cold cathode device and a method of manufacturing the device.

Electrodes are known which emit electrons when a high electric field is applied to them. These electrodes, commonly known as "electron-emitting electrodes," are shaped like a needle or plate, as opposed to hot cathodes that have coil-shaped filaments and emit electrons as current flows through them to heat them. An electron-emitting electrode emits electrons from its surface due to a tunneling effect when a high voltage of about 10 & sup7; V / cm or more is applied to them. These electrodes are used as cathodes in copying machines, in cold cathode fluorescent lamps which are used as backlight sources of non-self-emitting displays (e.g. Liquid crystal displays), used in monochromatic or color displays, in plasma displays, in VFDs (Vacuum Fluorescent Displays) and in similar devices.

A cold cathode fluorescent lamp equipped with an electron-emitting electrode comprises a tube having a fluorescent layer on its inner surface and filled with a mixture of inert gas and mercury vapor. The electrons emitted from the electrodes strike the mercury atoms in the tube so that ultraviolet rays are emitted. The ultraviolet rays stimulate the fluorescent layer. Excited in this way, the fluorescent layer emits visible light.

Electron-emitting electrodes are made of metal, which has a low work function or exit energy, such. Example of nickel (Ni), molybdenum (Mo) or the like. In general, the smaller the diameter of the cold cathode fluorescent lamp having an electron-emitting electrode made of such a metal, the higher the luminance (cd / m 2) of the light that generates the lamp. Fluorescent lamps with cold cathode can be thin and emit intense light radiation. They are therefore suitable for use as a backside light source in liquid crystal displays.

However, the voltage applied to the cold cathode fluorescent lamp must be increased to allow the lamp to emit higher luminance light. Therefore, the lamp will consume more power. When the lamp is used in a battery-powered portable display, the display can not be used for a long time. The cold cathode fluorescent lamp with electron-emitting electrodes is also disadvantageous in another respect. As the discharge progresses, the material of the electrode is gradually evaporated off, which inevitably results in contamination of the inner surface of the tube and a decrease in the life of the electron-emitting electrode.

Different materials have been proposed for the electron-emitting electrodes. However, there are various limitations on material selection for an electron-emitting electrode. For example, insulating materials that substantially prevent the tunneling effect used in a cold cathode can not be used.

A first object of the present invention is therefore to provide a cold cathode device which can be operated at a low discharge voltage and in which evaporation from an electrode of the cold cathode device can be prevented.

The first object is achieved by a cold cathode device having the features of claim 1.

Here, an "atomic group" means a group of different rare earth elements. Due to the one of the plurality of electrodes including R 2 O 3-z, the electrode may emit electrons at a lower voltage. The electrode is hardly sputtered during the emission of electrons. The electron-emitting electrode therefore has a long life.

A second object of this invention is to provide a method of manufacturing a cold cathode device in which sputtering, ie, sputtering of an electrode can be prevented.

The second object is achieved by a method having the features of claim 8.

Among the rare earth oxides are some that can hardly be reduced. It is difficult to control the crystal systems of such oxides. Nevertheless, the crystal system of a rare earth oxide film can be controlled when the film is formed by heating a rare earth element film in a gas atmosphere containing oxygen or oxide in a concentration of 1% by volume or less. Therefore, it is possible to provide a rare earth oxide film which emits electrons at a low discharge voltage and which has little tendency for sputtering by changing the rare earth oxide crystal system to one showing a high efficiency of discharge.

The present invention will become more apparent from the following detailed description when taken in conjunction with the following drawings, wherein:

Fig. 1 is a sectional view showing an electron-emitting electrode according to an embodiment of the present invention;

Fig. 2 is a sectional view showing an electron-emitting electrode according to another embodiment of the present invention;

Fig. 3 is a graph illustrating the intensities of elements of the electrode detected with respect to the direction of the depth of the electrode;

Fig. 4 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system is a body-centered cubic lattice and which has been oxidized in the atmosphere;

Fig. 5 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system is a body-centered cubic lattice and which has been oxidized in a hydrogen atmosphere;

Fig. 6 is a graph showing the optical characteristics of an electron-emitting electrode of this invention which has been oxidized in a hydrogen atmosphere;

Fig. 7 is a diagram illustrating the optical characteristics of an electron-emitting electrode of the present invention which has been oxidized in the atmosphere;

Fig. 8 is a diagram showing the absorption edge of the electron-emitting electrode which has been oxidized in the hydrogen atmosphere;

Fig. 9 is a graph showing the absorption edge of the electron-emitting electrode which has been oxidized in the atmosphere;

Fig. 10 is a schematic sectional view of a cold cathode fluorescent lamp according to the present invention;

Fig. 11 is a schematic plan view of an electron-emitting electrode included in the cold-cathode fluorescent lamp;

Fig. 12 is a graph showing the discharge characteristic of the electron-emitting electrode according to the invention and a known Ni-type electrode;

Fig. 13 is a sectional view showing a step of the method of manufacturing an electron-emitting electrode according to the present invention;

Fig. 14 is a sectional view explaining the step following the step explained with reference to Fig. 13;

Fig. 15 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system is a body-centered cubic lattice;

Fig. 16 is an enlarged portion of the X-ray diffraction analytical chart shown in Fig. 15;

Fig. 17 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system is a single-cubic lattice;

Fig. 18 is an enlarged portion of the X-ray diffraction analytical chart of Fig. 17;

Fig. 19 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system lies between those of a body-centered grating and a single-cubic grating;

Fig. 20 is an enlarged portion of the X-ray diffraction analytical chart shown in Fig. 19;

Fig. 21 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention, whose crystal system is a face-centered cubic lattice;

Fig. 22 is an enlarged portion of the X-ray diffraction analytical chart shown in Fig. 20;

Fig. 23 is an analytical diagram of X-ray diffraction of an electron-emitting electrode according to the invention whose crystal system lies between that of a body-centered cubic lattice and a single cubic lattice;

Fig. 24 is a graph showing the relationship between the time for heating an yttrium film and an yttrium compound and the thickness of the yttrium oxide film formed by heating the yttrium film;

Fig. 25 is a perspective view of another cold cathode fluorescent lamp according to the invention;

Fig. 26 is a view of still another cold cathode fluorescent lamp according to the invention;

Fig. 27 is a perspective view of a cold cathode fluorescent lamp according to the invention;

Fig. 28 is a perspective view of another cold cathode fluorescent lamp according to the invention;

Fig. 29 is a sectional view of a liquid crystal display panel incorporating a cold cathode fluorescent lamp according to the present invention;

Fig. 30 is a sectional view of a PDP containing electron-emitting electrodes according to the present invention; and

Fig. 31 is a sectional view of a FED including electron-emitting electrodes according to the present invention.

The best mode of carrying out the invention

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Fig. 1 shows an electron-emitting electrode 1 according to the invention, which performs a field emission of electrons. As shown in FIG. 1 1, the electrode 1 comprises a base plate 2, a rare earth film 3 mounted on the base plate 2, and an electron-emitting film 4 covering the rare earth film 3 and the exposed portion of the upper surface of the base plate 2. The base plate 2 (INCONEL 601, trademark) contains Ni and Cr.

The base plate 2 is either electrically conductive or made of a semiconductor. It is composed of a single element made of a material having a low leakage function or made of two or more elements made of different materials. To have a low tendency for sputtering, ie To have sputtering, the base plate 2 must be made of a material or materials having a liquid-to-solid interface below a low pressure of about 10 &min; Torr have. The plate 2 may be made of metals other than Ni and Cr, e.g. As molybdenum (Mo), aluminum (Al) and the like.

The rare earth movie 3 is essentially made of an element of a rare earth. The electron-emitting film 4 is made of an oxide R 2 O 3-z, where R is an atom or an atomic group of rare earth elements and O is oxygen and z is between 0.0 and 1.0.

FIG. 2 shows an electron-emitting electrode 11 according to the invention, which differs structurally from the electron-emitting electrode shown in FIG. The electrode 11 includes a base plate 12 and an electron-emitting film 13 provided on the base plate 12. The base plate 12 contains, for example, nickel (Ni). The electron-emitting film 13 is z. B. made of yttrium oxide.

FIG. 3 shows the relationship between the sputtering time and the intensities of the elements of the electrode 11 shown in FIG. 2, which were detected by Auger electron spectroscopy with respect to the direction of the depth of the electrode, while the elements of FIG the surface of the film 13 were atomized. The sputtering time and intensity of each element are plotted on the abscissa and ordinate in FIG. 3, respectively. It is shown in FIG. 3 It is clear that the base plate 12 contains Ni and that the electron-emitting film 13 provided on the base plate 12 is made of yttrium oxide.

The electron-emitting film 13 illustrated in FIGS. 1 and 2 made of yttria has a crystal system including a single-cubic lattice, a cubic face-centered lattice, a cubic body-centered lattice, a lattice between one cubic lattice and a cubic face-centered lattice, or a lattice between the simple cubic lattice and the cubic body-centered lattice.

Fig. 4 is an analytical diagram of X-ray diffraction at the yttria crystal lattice obtained by oxidizing the yttrium in the atmosphere. The yttria has a lattice constant of 10.60 Å. Its crystal system is identified as a cubic body-centered lattice, hereinafter referred to as the "lattice of the A-type" according to the usual custom. The Fig. 5 Fig. 10 is an analytical diagram of X-ray diffraction on an yttria crystal lattice obtained by oxidizing yttrium in a hydrogen atmosphere. This yttrium oxide has a lattice constant of 14.85 Å. The crystal system of this oxide is identified as a simple cubic lattice, which will hereinafter be referred to as the "B-type lattice" in the usual way. The present invention can use a material whose grid system lies between that of a body centered cubic lattice and a simple cubic lattice. The intervening crystal system will hereinafter also be referred to as "grating of the AB type".

An electron-emitting electrode having an electron-emitting film made of yttrium oxide of the A-type lattice and an electron-emitting electrode having an electron-emitting film made of yttrium oxide of the B-type lattice and an electron-emitting electrode having an electron-emitting film made of yttrium oxide of the AB-type lattice was measured for resistance across its thickness. They showed low resistances, such as 10 ohms, proving that they were electrically conductive. In other words, the films had electron-conducting properties.

An yttrium film of about 3000 Å in thickness was formed on a quartz substrate by electron beam vapor deposition and heated at about 600 ° C for 15 minutes in a hydrogen atmosphere of a predetermined concentration, thereby forming a first yttrium oxide film. Further, an yttrium film of about 3000 Å in thickness was formed on a quartz substrate by electron beam vapor deposition and heated at about 700 ° C for 30 minutes in the atmosphere, thereby forming a second film of yttria. The first and second yttrium films were examined for their optical properties.

The first film of yttria had a B-type grating and exhibited the transmission characteristics of Fig. 6. In Fig. 6, the transmittance and the reflectance are plotted on the ordinate and the wavelength of the light applied to the electron-emitting electrode containing the quartz substrate and the first yttrium oxide film. The transmittance is the ratio of the amount of light passing through both the quartz substrate and the yttrium oxide film to the amount (100%) of the light applied to the electron-emitting electrode. The reflectance is the ratio of the amount of light reflected by the quartz substrate and the yttria film to the amount of light reflected by an aluminum (Al) plate having smooth surfaces.

The second film of an yttrium oxide had an A-type lattice and exhibited the transmission property of Fig. 7. As shown in Fig. 7, the electron-emitting electrode having the second yttrium oxide (A-type) film exhibited a transmittance of over 50% for light whose wavelength ranges from 500 nm to 2500 nm. However, the electron-emitting electrode having the second film of yttrium oxide (B-type lattice) exhibited a transmittance of less than 20% for light having a wavelength in a range of 500 nm to 2500 nm.

Hereinafter, the first film of an yttrium oxide whose crystal system is of an A-type as an "A-type yttrium oxide film" and the second film of an yttrium oxide whose crystal system is a B-type will be referred to as a "B-type yttrium oxide film" become.

As shown in Fig. 7, the electron-emitting electrode having the A-type yttrium oxide film showed a reflectance of less than 40% for light whose wavelength is in a range of 500 nm to 2500 nm. In contrast, the electron-emitting electrode having the B-type yttrium oxide film had a reflectance ranging from a few percent to 75% for light of a wavelength in a range of 500 nm to 2500 nm. In particular, the maximum reflectance exceeded 60%.

As apparent from Figs. 6 and 7, yttrium oxides which are different in their crystal system differ greatly in their optical properties.

One of these optical properties of a substance is its absorption edge. The A-type and B-type yttrium oxide films were examined for their absorption edge. In a general definition, an absorption edge is a point or part in a continuous absorption spectrum in which the absorption for light rays of a longer wavelength decreases sharply. In the following, however, it is defined as a point where the transmittance drops to a value too small to be accurately measured.

Fig. 8 illustrates the absorption edge of the B-type yttrium oxide film obtained by oxidizing an yttrium film in the hydrogen atmosphere having the predetermined concentration. Fig. 9 shows the absorption edge of the A-type yttrium oxide film obtained by oxidizing an yttrium film in the atmosphere. The Y-type yttrium oxide film has an absorption edge at a little less than 4.0 eV, while the A-type yttrium oxide has an absorption edge at about 5.9 eV. Obviously, the B-type yttrium oxide is on a lower energetic side compared to the A-type yttrium oxide. Therefore, it is obvious that the different optical properties of the yttria depend on the crystal system of the oxide.

Furthermore, cold cathode discharge lamps were produced which were tested to determine their discharge characteristics. Each of these lamps comprises a cylindrical tube of glass and a pair of electron-emitting electrodes. Each electrode has an yttrium oxide film that can conduct cold emission of electrons.

The tube has an outer diameter of 2.6 mm and a length of 63.5 mm and was filled with a noble gas and silver vapor. The electron-emitting electrodes were positioned inside the tube while being spaced from each other and spatially spaced at a distance of 45 mm.

These cold cathode gas discharge lamps consist of three groups. The lamps of the first group had electrodes each having an electron-emitting film made of an A-type yttrium oxide. Those of the second group had electrodes each having an electron-emitting film made of B-type yttrium oxide. Those of the third group had electrodes having an electron-emitting film made of nickel (Ni) outside the scope of the present invention. The discharge cathodes with cold cathode from all groups were examined for their discharge voltages. The lamps of the first group, which had films made of A-type yttria, operated at a voltage of about 30 V, which was lower than the operating voltage of the lamps of the third group, which had an electron-emitting film made of Nickel was made. The lamps of the second groups, which had films made of B-type yttria, operated at a voltage of about 50 V, which was lower than the operating voltage of the lamps of the third group.

Further, cold cathode fluorescent lamps 21 of a type shown in Fig. 10 were produced. As can be seen from Fig. 10, the lamps 21 were identical in structure to the above described cold cathode gas discharge lamps, except that a fluorescent layer was deposited on the inner surface of the glass tube 23. The glass tube 23 was filled with a noble gas and mercury. A pair of electron-emitting electrodes 22 were oppositely positioned within the tube 23 and connected to two wires 24, respectively.

As shown in FIG. 11, the electron-emitting electrode 22 is bent at the middle part in the shape of the letter V. Each electrode is made of a Ni-Cr alloy (INCONEL 601), a base plate 25, an yttrium (Y) film 26 provided on the base plate 25, and an electron-emitting film 27 made of a B-type yttrium oxide is and is applied to the yttrium film 26. The electrodes 22 are positioned so that their electron-emitting films 27 face each other. Because the films 27 are made of a B-type yttrium oxide, the lamps 21 can be operated at a lower discharge voltage than cold-cathode fluorescent lamps having electron-emitting films of an A-type yttrium oxide.

The cold cathode 21 fluorescent lamps were examined for their light-emitting properties. In each lamp 21, the electrodes 22 emitted electrons. The electrons hit mercury atoms and produced ultraviolet radiation. The ultraviolet radiation excited the fluorescent layer on the inner surface of the tube 23. The thus-excited fluorescent layer emitted visible light within a predetermined wavelength range.

The result of the test is shown in the following Table 1 together with the emission characteristics of the conventional cold cathode fluorescent lamps comprising electron-emitting electrodes each having a nickel electron-emitting film. Table 1

From the results of Table 1, it can be understood that the lamps 21 having electrodes each having a B-type yttrium oxide film (hereinafter also referred to as "B-type electrode") are compared in terms of luminance and luminous efficiency were superior to conventional lamps with Ni-type electrodes, at least apart from the fact that the lamp voltage was about 23.5% lower than that of the conventional lamps. In addition, the lamps showed 21 after they have been operated for a long time, much lower atomization properties than conventional lamps with electrodes of the Ni-type, such as fluorescent lamps, cold-cathode, which have electrodes each comprise a yttrium oxide film of A-type (i m following also referred to as "A-type electrodes").

Further, cold cathode discharge lamps were prepared each comprising a cylindrical glass tube having an inner diameter of 12 mm and a pair of disc-shaped electron-emitting B-type electrodes having a diameter of 10 mm, which are disposed within the tube and spaced apart by 220 mm , These lamps were tested to determine how their discharge characteristics change over time. The results of the test were as shown in FIG. As apparent from Fig. 12, the cold cathode discharge lamps having B-type electrodes achieved a stable original discharge. After a continuous operating time of 200 hours, you did not show any noticeable voltage drop. They were found to have a discharge voltage about 15 to 20% lower than the discharge voltage of the conventional cold cathode gas discharge lamps having Ni-type electrodes. Furthermore, they showed less tendency to sputter than the conventional lamps having Ni-type electrodes. Cold-cathode gas discharge lamps, each comprising a tube with an inner diameter of 15 mm and B-type electron-emitting electrodes, exhibited a discharge life exceeding 3,000 hours.

The electron-emitting film has a resistance of 10000 Ω at least over most of the thickness of 45000 Å.

The yttria oxide films whose crystal system is a face centered cubic lattice and the yttria oxide films whose crystal system is between that of a single cubic lattice and a face centered cubic lattice work at a low discharge voltage. AB type yttrium oxide films whose crystal system lies between that of a cubic body centered lattice and a single cubic lattice also operated at a low discharge voltage.

In the present invention, yttrium can be replaced by other rare earth elements. In particular, instead of yttrium (Y), scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), Gadolium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb) or Lutetium (Lu).

The electron-emitting electrodes according to the invention having the structure described above exhibit good electron-emitting properties at a low discharge voltage. In addition, they show little tendency for atomization and therefore can continuously emit electrons for a long period of time.

Therefore, the electron-emitting electrodes of the invention can be used in cold-cathode fluorescent lamps used as rear-side light sources for emitting white light in non-self-emitting displays (for example, in liquid crystal displays). Furthermore, they can be used as cathodes in monochromatic or color displays, in a plasma display, and in FEDs (field emission displays) used as VFDs (Vacuum Fluorescent Displays).

A first method of manufacturing the electron-emitting electrodes of the type shown in Fig. 1 which performs field emission of electrons will be described below.

The first method comprises the following steps:

Washing a base plate; forming a metal film on the base plate; oxidizing the metal film in a hydrogen atmosphere to form an electron-emitting film; and the dehydrogenation of the electron-emitting film. These steps are carried out in the described sequence, thereby providing an electron-emitting electrode having an electron-emitting film having a predetermined crystal lattice. The base plate consists of an electrically conductive material or a semiconductor material. The electron-emitting film provided on the base plate contains R 2 O 3-z (wherein R is an atom or an atomic group of rare earth elements, O is oxygen and z is between 0.0 and 1.0) and performs field emission from cold electrons. In this example, the rare earth element is yttrium (Y).

The first method will now be explained in detail with reference to FIGS. 13 and 14.

First, the base plate 33 made of a Ni-Cr alloy (INCONEL 601) is washed. An yttrium film 34 is formed on the base plate 33 by vapor deposition (obtained by resistance heating or application of an electron beam) or by sputtering to a thickness in a range of 1,000 Å to 30,000 Å.

Subsequently, the resultant structure consisting of the base plate 33 and the yttrium 34 is placed on a table 32 in a reaction furnace 31, as shown in FIG. As shown in Fig. 13, the furnace 31 has a port 38 for gas inlet and a port 39 as a gas outlet. Hydrogen is introduced into the furnace 31 through the gas inlet port 38 into the furnace 31 so that the furnace 31 remains filled with hydrogen. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is less than 1% by volume, preferably 1000 ppm (parts per million) or less, or more preferably 100 ppm or less. The oxygen-containing substance is water which is in vapor form. The concentration may be achieved by using an oxygen adsorbing filter and a water adsorbing filter, each in the ports 38 and 38, respectively. 39 are present and controlled by adjusting the concentration of hydrogen introduced into the furnace 31.

Then, the hydrogen atmosphere is heated from room temperature (about 25 ° C) to about 600 ° C at a rate in the range of 10000/15 minutes to 100 ° C / 5 minutes. Thereafter, the structure is heated at about 600 ° C for 10 to 60 minutes, whereby the exposed surface portion of the yttrium film 34 is oxidized. As shown in Fig. 14, an yttrium oxide film 36 covering a body 35 of the yttrium film will thereby be formed. The temperature of the oxidation may range from 300 ° C to 1000 ° C, preferably 500 ° C to 700 ° C. The rate of temperature rise may range from 100 ° C / 20 minutes to 100 ° C / 5 minutes.

Thereafter, the film 36 of the yttrium oxide is dehydrated. To be more specific, the film 36 is heated at 300 ° C or more, preferably at 400 ° C to 800 ° C for 15 minutes in an atmosphere having a pressure of 1 x 10 &³ Torr or less, preferably 1 x 10 &min; 6 Torr or less, whereby the hydrogen is removed from the yttrium oxide film 36.

However, cold cathode fluorescent lamps produced by washing a base plate, forming an yttrium film, oxidizing the surface portion of the film but not dehydrating the generated yttria film emit bluish white light after one hundred hours of continuous discharge. This is caused by the hydrogen contained in the yttria film. Therefore, the yttrium oxide film formed in a hydrogen atmosphere should be dehydrated.

In producing a cold cathode fluorescent lamp, impurities such as water are usually removed from the glass tube before electrodes each having an yttrium oxide film are sealed in the tube. The removal of impurities is achieved by heating the glass tube at about 400 ° C in a reduced pressure atmosphere. The heating process may in fact serve to remove some of the hydrogen from the yttria film. However, since the temperature is relatively low (about 400 ° C), the fluorescent lamp can not achieve an initial discharge as quickly as a lamp containing electrodes each containing a dehydrated film of an yttrium oxide. Therefore, the yttria film 36 should be dehydrated in a reduced-pressure atmosphere at 450 ° C or more.

When an yttrium film of about 3000 Å thickness is heated and oxidized in a hydrogen atmosphere in which the concentration of oxygen and / or an oxygen-containing substance exceeds the order of 100 ppm, a film of yttria approximately 4500 Å thick is formed, which is a lattice of the A-type (cubic body-centered lattice). This yttrium oxide film shows an analytical pattern of X-ray diffraction as shown in FIG. The oxide film has a lattice constant of 10.60 Å and a peak in the intensity of X-ray which occurs at about 29 °, as shown in FIG.

When an yttrium film is about 3000 Å thick and heated and oxidized in a hydrogen atmosphere in which the concentration of oxygen and / or an oxygen-containing substance is on the order of 10 ppm, a film of yttria of about 4500 Å thickness is formed has a grid of B-type (simple cubic grid). This yttrium oxide film shows an analytical pattern of X-ray diffraction as shown in FIG. It has a lattice constant of 14.85 Å and a high intensity peak of X-ray at about 29 ° and a low intensity peak of X-ray at about 29.6 °, as shown in FIG.

When an yttrium film of about 3000 Å thick is heated and oxidized in a hydrogen atmosphere in which the concentration of oxygen and / or an oxygen-containing substance is on the order of 100 ppm, a film of yttria of about 4500 Å thickness is formed, the lattice thereof is of an AB type, ie of a crystal system between an A-type grating and a B-type grating (the concentration of the order of 100 ppm is higher than the concentration suitable for forming the B-type yttrium oxide film and lower than the concentration suitable for forming the A-type yttrium oxide film). The film of yttria thus formed shows the analytical pattern of X-ray diffraction as shown in FIG. It has a high intensity peak of X-ray at about 29 ° and a low intensity peak of X-ray at about 29.6 °, as shown in FIG.

When an yttrium film of about 3000 Å thick is heated and oxidized in a hydrogen atmosphere in which the concentration of oxygen and / or an oxygen-containing substance is of the order of 1 ppm, a film of yttria of about 4500 Å thickness is formed Lattice is a cubic face-centered lattice (hereinafter also referred to as "C-type lattice"). This oxide film shows the analytical pattern of X-ray diffraction, as shown in FIG. 21 is shown. It has a lattice constant of 5.21 Å and has a high intensity peak of X-radiation at about 29.6 °, as shown in FIG.

When an yttrium film of about 3000 Å in thickness is heated and oxidized in a hydrogen atmosphere in which the concentration of oxygen and / or an oxygen-containing substance is higher than the concentration suitable for forming a C-type yttrium oxide film and lower than the concentration which is suitable for forming a B-type yttrium oxide film, a film of yttria of about 4500 Å thick is formed, whose crystal system is identified as lying between a B-type lattice and a C-type lattice (hereinafter also referred to as "BC-type lattice"). This film of yttria shows the analytical pattern of X-ray diffraction shown in FIG. It has a low intensity peak of X-rays at about 29 ° and a high peak of X-rays at about 29.6 °, as shown in FIG. 23:

From the foregoing, it is understood that the crystal system of the yttrium oxide film can be changed by adjusting the oxygen concentration in the hydrogen atmosphere.

Three kinds of cold cathode fluorescent lamps each having a pair of electron-emitting electrodes produced by the first method were produced. The first type comprises electrodes each having a film of a B type yttria of about 4500 Å thick; the second type comprises electrodes each having a film of BC type yttria; and the third type includes electrodes each having a film of a C-type yttrium oxide. These lamps were examined for their emission properties. The results were as shown in Table 2 below. Further, Table 2 shows the emission characteristics of a conventional cold cathode fluorescent lamp including Ni-type electron-emitting electrodes to be compared with the emission characteristics of the three types of lamps according to the present invention. All of these fluorescent lamps, including the conventional one, had the same structure as shown in Fig. 10, each comprising a glass tube 21 and a pair of electron-emitting electrodes 22 positioned in the tube 21. The tube 21 was filled with a noble gas and mercury, and its inner surface was coated with a white light emitting fluorescent material. The glass tube 21 was 63.5 mm long and had an outer diameter of 2.6 mm, with the electrodes 22 being opposed to each other at a distance of 45 mm from each other. Table 2

Obviously, according to Table 2, the cold cathode fluorescent lamps having B-type, BC-type and C-type electrodes are superior to the conventional lamp despite their relatively low discharge voltage in luminance and luminous efficiency. Although these yttria films are over several hundred Å thick, these electrodes exhibit high electrical conductivity. The lamps having the B-type, BC-type and C-type electrodes had a much lower tendency for sputtering than the conventional lamp having the Ni-type electron-emitting electrodes. They continuously emitted light for a longer time than the conventional cold cathode fluorescent lamp.

The values ​​for the lamp with the B-type electrodes shown in Table 1 are different from those specified in Table 2. The same applies to the conventional lamp with the Ni-type electrodes. This occurs because an analyzer was used to achieve the results of Table 1 and because another analyzer was used to achieve the results of Table 2.

The lamp with the A-type electrodes and the lamp with the AB-type electrodes exhibited greater luminance and luminous efficiency than the conventional lamp with the Ni-type electrodes, although their discharge voltage was lower than that of the conventional lamp. Nevertheless, their luminance and luminous efficiency have been found to be lower compared to the C-type electrodes.

A second method of manufacturing the electron-emitting electrodes of the type illustrated in FIG. 1 which conduct cold emission of electrons will be described with reference to FIGS. 13 and 14.

The second method comprises the following steps:

Washing a base plate; forming a metal film on the base plate and oxidizing the metal film in a rare gas atmosphere to form an electron-emitting film. The three steps are carried out in the described sequence, thereby providing an electron-emitting electrode having an electron-emitting film having a predetermined crystal lattice. The base plate is made of an electrically conductive material or a semiconductor material. The electron-emitting film contains R 2 O 3-z (where R is an atom or an atomic group of rare earth elements, O is oxygen and z is between 0.0 and 1.0) and can emit cold electrons. Also in this example, the rare earth element is yttrium (Y).

First, the base plate 33 made of a Ni-Cr alloy (INCONEL 601) is washed. An yttrium film 34 is formed on the base plate 33 by vapor deposition (achieved by resistance heating or application of an electron beam) or by sputtering to a thickness in the range of 1000 Å to 30,000 Å.

Subsequently, the resultant structure consisting of the base plate 33 and the yttrium film 34 is positioned on the table 32 in the reaction furnace 31, as illustrated in FIG. Argon is admitted into the furnace 31 through the gas inlet port 38 so that the furnace 31 remains filled with argon. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is less than 1% by volume, preferably 1000 ppm or less, more preferably 100 ppm or less. The oxygen-containing substance is water, which is in vapor form. Concentration may be achieved by using an oxygen adsorbing filter and a water adsorbing filter which are provided in ports 38 and 38, respectively. 39 and adjusted by adjusting the concentration of argon introduced into the furnace 31.

Then, the argon atmosphere is heated from room temperature to about 600 ° C at a rate in a range of 100 ° C / 15 minutes to 100 ° C / 5 minutes. The structure is heated at about 600 ° C for 10 to 60 minutes, whereby the exposed surface region of the yttrium film 34 is oxidized. As shown in Fig. 14, an yttrium oxide film 36 is thereby formed covering a body 35 of the yttrium film. The rate of the temperature rise may be in a range of 100 ° C / 20 minutes to 100 ° C / 5 minutes.

The crystal system of the yttrium oxide film can be adjusted by adjusting the concentration of the oxygen and / or the oxygen-containing substance as in the first method. The second method was performed on an experimental basis. It has been found that films of yttria of A-type lattice, AB-type lattice, B-type lattice, BC type lattice and C-type lattice were formed by the second method.

In the second method, the yttrium film is oxidized in an argon atmosphere. Therefore, it is distinguished from the first method in which the film is oxidized in a hydrogen atmosphere. The yttrium oxide film formed in an argon atmosphere contains almost no hydrogen. The film of yttria does not need to be dehydrated at all. The second method therefore comprises one step less than the first method. Nevertheless, it is desirable to dehydrate the film as in the first method if hydrogen, even in a small amount, should be contained in the yttrium film.

A third method of manufacturing the electron-emitting electrodes that perform field emission of cold electrons will be explained with reference to Figs.

In the present invention, argon gas may be replaced by any other noble gas, e.g. As helium, neon, krypton or xenon gas can be replaced.

The third method comprises the following steps:

Washing a base plate; forming a metal oxide film on the base plate; heating the metal oxide film to form a desired crystal system; and dehydrating the electron-emitting film. These steps are carried out in the described sequence, thereby providing an electron-emitting electrode having an electron-emitting film having a predetermined crystal lattice. The base plate is made of an electrically conductive material or a semiconductor material. The electron emitting film provided on the base plate contains R 2 O 3-z (where R is an atom or atomic group of rare earth elements, O is oxygen and z is between 0.0 and 1.0), and can field emission of cold electrons To run. In the present example, the rare earth element is yttrium (Y).

The third method will now be described in detail with reference to FIGS. 13 and 14.

First, the base plate 33 made of a Ni-Cr alloy (INCONEL 601) is washed. An amorphous yttria oxide film is then formed on the base plate 33 by ion implantation with a thickness in the range of 1000 Å to 30,000 Å.

Thereafter, the generated structure consisting of the base plate 33 and the yttrium oxide film is positioned in the reaction furnace 31. Hydrogen is admitted into the furnace 31 through the gas inlet port 28 so that the furnace 31 remains filled with hydrogen. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is less than 1% by volume, preferably 1000 ppm or less, more preferably 100 ppm or less. The oxygen-containing substance is water, which is in vapor form. The concentration can be controlled by using an oxygen adsorbing filter and a water adsorbing filter respectively provided in the ports 38 and 39, respectively, and adjusting the concentration of the hydrogen introduced into the furnace 31.

Then, the hydrogen atmosphere is heated from room temperature to about 600 ° C at a rate in a range of 100 ° C / 15 minutes to 100 ° C / 5 minutes. The structure is heated at a temperature of about 600 ° C for 10 to 60 minutes, thereby forming a desired crystal lattice of the yttrium oxide film. The heating temperature may range from 300 ° C to 1000 ° C, preferably from 500 ° C to 700 ° C. The rate of temperature rise may range from 100 ° C / 20 minutes to 100 ° C / 5 minutes.

Thereafter, the desired yttrium oxide film is dehydrated. To be more specific, the film is heated at 300 ° C or more, preferably 450 ° C to 800 ° C, for 15 minutes in an atmosphere having a pressure of 1 x 10 &³ Torr or less, preferably 1 x 10 & & Torr. Torr or less, whereby the hydrogen is removed from the yttrium oxide film.

Cold-cathode fluorescent lamps produced by washing a base plate, forming a film of yttria and heating the film but not by dehydrating the produced yttria film emit a bluish-white light after 100 hours of continuous discharge. This is due to the hydrogen contained in the film of yttria. Therefore, the film of yttria formed in a hydrogen atmosphere should be dehydrated.

In manufacturing a cold cathode fluorescent lamp, impurities such as water are removed from the glass tube before electrodes each having a film of yttria are sealed in the tube. The removal of the impurities is carried out by heating the glass tube at about 400 ° C in a reduced-pressure atmosphere. The heating process may in fact serve to remove some of the hydrogen of the yttria film. However, since the temperature is relatively low (about 400 ° C), the fluorescent lamp can not achieve an initial discharge as directly as would be possible with a lamp including electrodes each having a dehydrated yttrium oxide film. Therefore, the yttrium oxide film 36 should be dehydrated in a reduced-pressure atmosphere at 450 ° C or more.

The third method described above was carried out on an experimental basis. It was confirmed that films of yttria of the A-type lattice, the AB-type lattice and the B-type lattice were formed by the third method.

A fourth method of manufacturing the electron-emitting electrodes that perform field emission of cold electrons will now be explained.

The fourth method comprises the following steps:

Washing a base plate; forming a lower layer on the base plate; forming a metal oxide film on the lower layer; heating the metal oxide film to have a desired crystal system; and dehydrating the electron-emitting film. The five steps are carried out in the described arrangement, thereby providing an electron-emitting electrode having an electron-emitting film having a predetermined crystal lattice structure. The base plate is made of an electrically conductive material or of a semiconductor material. The electron-emitting film contains R 2 O 3-z (where R is an atom or atomic group of rare earth elements, O is oxygen and z is between 0.0 and 1.0) and can emit cold electrons. Also in this example, the rare earth element is yttrium (Y).

The fourth method will now be described in detail with reference to Figs.

First, the base plate made of a Ni-Cr alloy (INCONEL 601) is washed. An yttrium film or a conductive underlayer, which serves to prevent the oxidation of the base plate and improve the physical and electrical connection to the yttria, is deposited on the base plate by vapor deposition (achieved by resistance heating or electron beam application) or sputtering of thickness Range from 20,000 Å to 40,000 Å deposited.

Thereafter, an amorphous film of yttria is formed on the yttrium film by ion implantation to a thickness in the range of 1000 Å to 10000 Å.

Subsequently, the resultant structure consisting of the base plate, the yttrium film and the amorphous film of yttrium oxide is placed on the table 32 in a reaction furnace 31, as shown in FIGS. 13 and 14. Hydrogen is admitted into the furnace 31 through the gas inlet port 38 so that the furnace 31 remains filled with hydrogen. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is less than 1% by volume, preferably 1000 ppm or less, more preferably 100 ppm or less. The oxygen-containing substance is water, which is in vapor form. The concentration may be determined by using an oxygen adsorbing filter and a water adsorbing filter, each in the ports 38 and 38, respectively. 39 are mounted, and regulated by adjusting the concentration of the hydrogen, which is introduced into the furnace 31.

The hydrogen atmosphere is heated from room temperature to about 600 ° C at a rate in the range of 100 ° C / 15 minutes to 100 ° C / 5 minutes. The structure is heated at 600 ° C for 10 to 60 minutes, thereby oxidizing the amorphous film of yttria. An yttrium oxide film is thereby formed covering the yttrium oxide film. The temperature of the oxidation may be between 300 ° C and 1000 ° C, preferably between 500 ° C and 700 ° C. The rate of the temperature rise may be in a range of 100 ° C / 20 minutes to 100 ° C / 5 minutes.

Cold-cathode fluorescent lamps prepared by washing a base plate, forming an yttrium film, and oxidizing the surface portion of the film, but not by dehydrating the resulting yttria film, emit bluish white light after 100 hours of continuous discharge. This is due to the hydrogen contained in the film of yttria. This is the reason why the film of yttria formed in a hydrogen atmosphere should be dehydrated.

When manufacturing a cold cathode fluorescent lamp, impurities such as water are removed from the glass tube before the electrodes, each having a film of yttria, are sealed in the tube. The removal of the impurities is carried out by heating the glass tube at a temperature of about 400 ° C in a reduced-pressure atmosphere. The heating process may in fact serve to remove some of the hydrogen from the yttria film. However, since the temperature is relatively low (about 400 ° C), the fluorescent lamp can not achieve a starting discharge as fast as a lamp containing electrodes each having a dehydrated yttrium oxide film. Therefore, the film 36 of yttria should be dehydrated in a reduced-pressure atmosphere at 450 ° C or more.

The fourth method described above was carried out on an experimental basis. It was confirmed that yttrium oxide films of the A-type lattice, the AB-type lattice and the B-type lattice were formed.

A fifth method of manufacturing the electron-emitting electrodes that perform field emission of cold electrons will be described below.

The fifth method comprises the following steps:

Washing a base plate; forming a lower layer on the base plate; forming a metal oxide film on the lower layer; and heating the metal oxide film to obtain a desired crystal structure. The four steps are performed in the described arrangement, thereby providing an electron-emitting electrode comprising an electron-emitting film having a predetermined crystal lattice structure. The base plate is made of an electrically conductive material or a semiconductor material. The electron-emitting film contains R 2 O 3-z (where R is an atom or atomic group of a rare earth element, O is oxygen and z is between 0.0 and 1.0) and can perform field emission of cold electrons. Also in this example, the rare earth element is yttrium (Y).

The fifth method will now be described in detail with reference to Figs.

First, the base plate 33 made of a Ni-Cr alloy (INCONEL 601) is washed. An yttrium film or a conductive lower layer, which serves to prevent the oxidation of the base plate and to improve the physical and electrical connection to the yttrium oxide, is deposited on the base plate by vapor deposition (achieved by resistance heating or electron beam application) or by sputtering of thickness Range from 20,000 Å to 40,000 Å deposited.

Then, a film of an amorphous yttrium oxide film is formed on the yttrium film by ion implantation in a thickness in a range of 500 Å to 2,000 Å.

After this is done, the resulting structure consisting of the base plate, the yttrium film and the amorphous yttrium oxide film is placed in the reaction furnace 31, as shown in FIGS. 13 and 14. Argon is admitted into the furnace 31 through the gas inlet port 38 so that the furnace 31 remains filled with argon. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is less than 1% by volume, preferably 1000 ppm or less, more preferably 100 ppm or less. The oxygen-containing substance is water, which is in vapor form. The concentration may be increased by the use of an oxygen adsorptive filter and a water adsorptive filter which may be present in the ports 38 and 38, respectively. 39 are respectively mounted, and controlled by adjusting the concentration of the argon, which is introduced into the furnace 31.

The argon atmosphere is heated from room temperature to about 600 ° C at a rate in the range of 100 ° C / 15 minutes to 100 ° C / 5 minutes. The structure is heated at about 600 ° C for 10 to 60 minutes, whereby the amorphous film of yttria is oxidized. Thereby, an yttrium oxide film (ie, an electron-emitting film) is formed. The temperature of the oxidation may range from 300 ° C to 1000 ° C, preferably from 500 ° C to 700 ° C. The rate of the temperature rise may be in a range of 100 ° C / 20 minutes to 100 ° C / 5 minutes.

Thereafter, the film of yttria (ie, the electron-emitting film) is dehydrated. To be more specific, the film is heated at 350 ° C or more, preferably at 450 ° C to 800 ° C for 15 minutes in an atmosphere having a pressure of up to 1 x 10 &³ Torr or less, preferably 1 x 10 &min; 6 Torr or less, whereby the hydrogen is removed from the yttrium oxide film.

In the fifth method, the yttrium film is oxidized in an argon atmosphere. Therefore, it differs from the fourth method in which the film was oxidized in a hydrogen atmosphere. Since the film is formed in an argon atmosphere, the yttrium oxide film contains almost no hydrogen. The yttrium oxide film does not need to be dehydrated at all. This method therefore comprises one step less than the first method. Nevertheless, it is desirable to dehydrate the film as in the first method if hydrogen should be contained in the yttrium film, albeit in a small amount.

The fifth method described above was carried out on an experimental basis. It was confirmed that yttrium oxide films of the A-type lattice, the AB-type lattice and the B-type lattice were formed. Which type is formed depends on the oxygen concentration in the oxygen atmosphere. An yttrium oxide film having a thickness of about 1000 Å became an yttrium oxide film of the A-type lattice when the oxygen concentration in the oxidation was on the order of 100 ppm and became an yttrium oxide film of the B-type lattice when the oxygen concentration in the oxidation was on the order of magnitude of 10 ppm.

Two types of cold cathode fluorescent lamps each comprising a pair of electron-emitting electrodes were manufactured by the fifth method. The first type comprises electrodes each having an A-type yttria oxide film, and the second type comprises electrodes each having an AB-type yttrium oxide film. These lamps were examined for their emission properties. The results were as specified in Table 3 below. Also shown in Table 3 is the emission characteristic of a conventional cold cathode fluorescent lamp containing Ni-type electron-emitting electrodes. Table 3

As is apparent from Table 3, the cold cathode fluorescent lamps having the A-type and AB-type electrodes are superior to the conventional lamp in luminance and luminous efficiency, despite the relatively low discharge voltage, and although they are slightly worse than lamps with B-type electrodes or as lamps with BC-type electrodes and lamps with C-type electrodes. Furthermore, both the lamps with the A-type electrodes and the lamps with the AB-type electrodes showed a high electrical conductivity. In addition, they had a much lower sputtering tendency than the conventional lamp which had the Ni-type electron-emitting electrodes. They continuously emitted light for a longer time than the conventional cold cathode fluorescent lamp.

The A-type electrode, the AB-type electrode and the B-type electrode, all made by the first and second methods described above, exhibited an emission characteristic similar to that of the A-type electrode, the AB-type electrode and the B-type electrode produced by the third, fourth and fifth methods, respectively.

From Tables 1, 2 and 3, it is apparent that the electron-emitting films containing yttria have somewhat of their electron-emitting properties according to their crystal system, ie, the A-type lattice, the AB-type lattice, the B-type Grid, the BC type grid or the C-type grid vary. The electron-emitting films had a resistance of 10,000 Ωcm or less.

In the second and fifth methods for producing the electron-emitting electrodes in argon gas, the crystal lattice of the rare earth element was affected by the presence of a small amount of hydrogen. Since the hydrogen gas tends to diffuse oxygen into the furnace, it is desirable to produce a single rare earth element film of a better crystal lattice. Therefore, the second and fifth methods can be performed in a mixture of hydrogen gas and a noble gas such as argon gas.

Fig. 24 illustrates the relationship between the time used to heat the yttrium films and the thickness of each of the yttrium oxide films formed by heating an yttrium film. The thickness of the oxide film is shown on the ordinate and the heating time on the abscissa. In Fig. 24, the solid line represents how an oxide film gradually grows, while an yttrium film is oxidized in the first method described above. The broken line shows how an yttria film grows as an yttria film deposited by ion implantation to a thickness of 3000 Å on an yttrium film of about 27000 Å thickness, which was oxidized in the atmosphere. The dot-dash line indicates how an yttrium oxide film grown as an yttrium oxide film deposited with a thickness of 3000 Å on an yttrium film of about 27000 Å thick by ion implantation in an atmosphere of a mixture of a gas of 79 vol% Argon and 21 vol.% Oxygen, was oxidized.

As shown in Fig. 24, although the oxygen concentration was very low, the yttrium film was oxidized at a high rate in the hydrogen atmosphere (according to the first method).

An yttrium film of 1000 Å to 3000 Å thick was formed on a base plate by resistive heating or by the application of an electron beam. The yttrium film was heated from room temperature to about 600 ° C at a rate in the range of 100 ° C / 15 min to 100 ° C / 5 min. In an atmosphere having a pressure up to a pressure of 1 x 10 &³ Torr to 1 x 10 & supmin; & sup6; Torr was reduced and in which the oxygen concentration was very low. Thereby, an yttrium oxide film of an A-type lattice is formed. An AB type yttria film, a BC type yttria film, and a C type yttria film having a good electron emission property were not formed at all. When an yttrium film was oxidized in an atmosphere of a mixture of gas consisting of 79% by volume of argon and 21% by volume of oxygen, an A-type yttrium oxide film was also formed.

The electron-emitting films formed with a thickness as shown in Fig. 24 exhibited a resistance of 10000 Ωcm or less. A method of manufacturing an electron-emitting electrode in which R is in "R₂O3-z" Lanthanum (La) is described with reference to FIGS. 13 and 14. First, the base plate made of a Ni-Cr alloy (INCONEL 601) is washed. A lanthanum film is deposited on the base plate by vapor deposition (achieved by resistance heating or electron beam application) or by sputtering in a thickness ranging from 3000 Å to about 6000 Å.

Subsequently, the resulting structure consisting of the base plate and the lanthanum film is introduced into the reaction furnace 31 shown in Figs. 13 and 14 and mounted on the table 23. Hydrogen is admitted into the furnace 31 through the gas inlet port 38 so that the furnace 31 remains filled with hydrogen. It is desirable that the concentration of oxygen and / or an oxygen-containing substance is 1% by volume or less, preferably 1000 ppm or less, more preferably 100 ppm or less. The oxygen-containing substance is water, which is in vapor form. The concentration can be determined by using an oxygen adsorptive filter and a water adsorbing filter connected respectively to the ports 38 and 38, respectively. 39 and adjusted by adjusting the concentration of hydrogen introduced into the furnace 31.

The hydrogen atmosphere is heated from normal temperature to about 600 ° C at a rate in the range of 100 ° C / 15 minutes to 100 ° C / 5 minutes. The structure is heated at about 600 ° C for 10 to 60 minutes, whereby the surface region of the lanthanum film is oxidized. A lanthanum oxide film (ie, an electron-emitting film) is thereby formed covering the lanthanum film. The temperature of the oxidation may range from 300 ° C to 1000 ° C, preferably from 500 ° C to 700 ° C. The rate of the temperature rise may be in a range of 100 ° C / 20 minutes to 100 ° C / 5 minutes.

Thereafter, the lanthanum oxide film (ie, the electron-emitting film) is dehydrated. To be more specific, the film is heated at 350 ° C or more, preferably at 450 ° C to 800 ° C for 15 minutes in an atmosphere having a pressure of up to 1 x 10 &³ Torr or less, preferably up to 1 x 10 &min; 6 Torr or less, whereby the hydrogen is removed from the lanthanum oxide film.

Cold cathode fluorescent lamps comprising electrodes each having a lanthanum oxide film were prepared and examined for their discharge characteristics. It was found that they are inferior to the cold cathode fluorescent lamps equipped with electrodes each having an yttrium oxide film. Nevertheless, they are superior to lamps having Ni-type electron-emitting electrodes not only in terms of their discharge characteristics but also in terms of luminance and luminous efficiency.

In the first to fifth methods described above, yttrium and lanthanum may be replaced by another rare earth element. Specifically, scandium (Sc), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolium (Gd), terbium (Tb), dysprosium ( Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or lutetium (Lu) instead of yttrium (Y) and lanthanum (La).

All cold cathode fluorescent lamps described above are straight tubes. Nevertheless, the present invention can also be applied to cold cathode fluorescent lamps having a different shape. For example, the invention can be applied to a planar lamp shown in FIG. As shown in FIG. 25 As shown, this cold cathode fluorescent lamp comprises a pair of glass plates 41 connected to each other one on top of each other so as to define a closed space therebetween. The closed space is filled with an inert gas (eg argon) and with mercury vapor. The inner surface of each of the glass plates 41 is coated with a fluorescent material. The fluorescent material emits visible light within a predetermined wavelength range when excited with ultraviolet radiation generated when electrons strike the mercury atoms. A pair of electron-emitting electrodes 42, both of which are strip-shaped, are disposed within the closed space opposite each other and connected to two wires 43, respectively.

Further, the present invention can also be applied to a cold cathode fluorescent lamp in the form of L, a cold cathode fluorescent lamp in the form of a U, and a cold cathode fluorescent lamp in the form of S shown in Figs. 28 are shown. The L-shaped lamp comprises an L-shaped glass tube 51, a pair of electron-emitting electrodes 52 formed at the end portions 50 of the tube 51, and two wires 53 respectively connected to the electrodes 52. The U-shaped lamp includes a U-shaped glass tube 61, a pair of electron-emitting electrodes 62 stored in the end portions 64 of the tube 61, and two wires 63 respectively connected to the electrodes 62. The S-shaped lamp comprises an S-shaped glass tube 71, a pair of electron-emitting electrodes 72 mounted on the end portions 74 of the tube 71, and two wires 73 respectively connected to the electrodes 72. The electrodes 52, 62 and 72 have an electron-emitting film which is a rare-earth oxide, so that the fluorescent layer mounted on the inner surface of the glass tubes can emit light.

The above-described cold cathode fluorescent lamps can be used as a white light emitting backlight in a liquid crystal display. Fig. 29 shows a liquid crystal display 81 incorporating a cold cathode fluorescent lamp 86 according to the invention. As shown in FIG. 29 is shown, the display 81 comprises two transparent substrates 82 and 83, which are spaced from each other, a frame-shaped seal 85, which is mounted between the substrates 81 and 83 and connects them at their edges and TN or STN liquid crystals 84, the are filled in the space defined by the two substrates 81 and 82 and the seal 85. Each of the transparent substrates is made of glass or an organic film and has one or more electrodes on the surface opposite to the other transparent substrate. The liquid crystal display 81 can be switched by switching elements such as TFTs.

On one side of the liquid crystal display 81, a straight cylindrical cold cathode fluorescent lamp 86 is positioned. A light guiding plate 87 is provided adjacent to the lamp 86 below the liquid crystal display 81 to guide the light from the lamp 86 to the back of the display 81. The plate 87 is made of an acrylic plastic. On the surrounding surface, apart from an upper surface and a surface opposite to the lamp 86 of the plate 87, there is a light-reflecting layer 88, and on the upper surface of the plate 87, a light-diffusing layer 89 is attached.

The electron-emitting electrodes according to the present invention may be used in a DC-powered PDP of the kind shown in FIG.

As shown in FIG. 30, the PDP 91 has red-emitting pixels, green-emitting pixels, and blue-emitting pixels attached in a plane in rows and columns. The pixels are separated from each other by barriers 101, between a transparent upper substrate 92 and a transparent lower substrate 93 are attached. The barrier 101 includes a material that is opaque to visible light rays and made of multiple strips or a grid. Auxiliary cathodes 94 are mounted on the lower substrate 93 in rows and columns, each positioned at the center of a pixel. Each auxiliary cathode 94 is a two-layer element comprising a base layer 95 and an electron-emitting film 96 mounted on the layer 95. The base layer 95 is at least of a conductive material with low leakage energy z. B. Y, Ni, Cr, Al and Mo made. The film 96 is made of yttrium oxide (a rare earth oxide). The yttria is one which in the crystal system is either an A-type lattice, AB-type lattice, B-type lattice, BC-type lattice or C-type lattice. Of these yttrium oxides, preferred are those whose crystal system is a B-type lattice, a BC-type lattice or a C-type lattice.

As shown in FIG. 30, data electrodes 97 are mounted on the lower substrate 93 surrounding the auxiliary cathodes 94. Further, current-controlling films 98 made of amorphous silicon or the like and surrounding the data electrodes 97 are provided on the lower substrate 93. In addition, cathodes 102 are mounted on the lower substrate 93 surrounding the current-regulating films 98 and covering the area of ​​their outer peripheral edge. Each cathode 102 is a two-layered element consisting of a base layer 103 and an electron-emitting film 104 formed on the layer 103. The base layer 103 is made of at least one conductive material such as Y, Ni, Cr, Al or Mo. The electron-emitting film 104 is made of yttrium oxide (a rare-earth oxide). The yttria is one having a crystal system having an A-type lattice, an AB-type lattice, a B-type lattice, a BC-type lattice, and a C-type lattice, respectively. Of these yttrium oxides, preferred are those having a B-type lattice, a BC-type lattice, and a C-type lattice, respectively.

The current regulating films 98 regulate the current supplied to the cathodes 102 to suppress the sputtering of the cathode 102. The films 98 may have any desired resistance by adjusting their thickness and length and by choosing a suitable impurity to be added to the amorphous silicon. As shown in FIG. 30 is shown, an insulating film 105 is substantially over the entire surface of the lower substrate 93 applied to those areas which are covered with the electron-emitting films 96 of the auxiliary cathodes 94 and the electron-emitting films of the cathodes 102. In the alternative, barriers 106 are applied to those regions of the insulating film which surround the auxiliary cathodes 94. A red-emitting fluorescent layer 107A, a green-emitting fluorescent layer 107G, and a blue-emitting fluorescent layer 107B are provided for each pixel on the barrier 101 and the auxiliary barrier 106.

The red-emitting fluorescent layer 107R is composed of (Y, Gd) BO 3: Eu 3+. or Y & sub2; O & sub3;: Eu & sub3; & spplus; made. The green-emitting fluorescent layer 107G is made of Zn₂SiO₄: Mn or BaAl₁₂O₁:: Mn. The blue-emitting fluorescent layer 107B is made of BaMgAl & sub4; O & sub2; & sub3;: Eu & spplus; & spplus; or SrMg (SiO₄) ₂: Eu² & spplus; made.

On the upper substrate 92, color filters 111R, 111G and 111B for transmitting only red light, green light and blue light, respectively, are mounted. The filters 111R, 111G and 111B are covered with transparent electrodes 112 made of ITO. The gaps defined by the upper substrate 92, the lower substrate 93 and the barriers 101 are filled with a rare gas such as He or Xe.

Now it will be explained how the PDP 91 is powered. First, a predetermined voltage is applied between the transparent electrode 112 and the auxiliary cathode 94 to generate an auxiliary plasma therebetween.

Subsequently, a data voltage is applied to the data electrode 97 of each pixel. As a result, a regulated current will flow from the current control film 98 to the cathode 102. Because of the aid of the auxiliary plasma, a plasma will readily be formed between the cathode 102 and the transparent electrode 112. The plasma stimulates the noble gas, which generates ultraviolet radiation. The ultraviolet rays act on the fluorescent layers deposited on the barriers 101 and the auxiliary barrier 106. The fluorescent layers then emit light having a predetermined wavelength range. The light passes through the upper substrate 92, whereby each pixel emits a beam of light to make a display.

When external light beams are incident on the PDP 91, they are externally emitted through the color filters 111R, 111G, and 111B as a red light beam, a green light beam, and a blue light beam, respectively. These light beams connect with the light beams emitted from the fluorescent layers 107R, 107G and 107B, respectively. As a result, the light beams emitted from the PDP 91 have a sufficiently intense hue. Further, since each of the color filters 111R, 111G and 111B absorbs the external light except for the light having the respective predetermined wavelength range, the external light is not reflected too much from the display surface of the PDP 91. This suppresses flicker on the display surface, allowing the PDP 91 to display clear color images.

The display surface of the PDP 91 may be covered with a liquid crystal display serving as a light shader. In this case, the PDP 91 can display images with a precise grayscale scale.

Also, in the PDP 91 having electron-emitting electrodes each comprising an yttrium oxide film, no fluorescent layers could be present. If this were the case, the pixels of the PDP 91 would emit orange light emerging from the plasma rather than light rays of different colors.

In the PDP 91, yttrium can be replaced by another element of a rare earth or more of these elements. In particular, scandium (Se), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolium (Gd), terbium (Tb ), Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or lutetium (Lu) instead of yttrium (Y). Furthermore, the material of the base layers 95 and 103 is not limited to Y, Ni, Cr, Al and Mo. Rather, they can be made of any other material having a lower exit energy than the transparent electrodes 112 of the anode.

As described above, the electrodes 94, 102 themselves can reduce the sputtering and emit a large amount of low-voltage electrons.

The electron-emitting electrodes according to the present invention can also be used in a FED of the type shown in FIG. 31.

As shown in Fig. 31, the FED 121 has red-emitting pixels, green-emitting pixels, and blue-emitting pixels arranged in a plane in rows and columns. The pixels are isolated from each other by barriers which are mounted between a transparent upper substrate 122 and a transparent lower substrate 123. The barrier are constructed of several strips or a grid. Data electrodes 124 to which voltages corresponding to the luminance data are applied are applied to the lower substrate 123. A current control film 125 made of amorphous silicon is deposited on the data electrodes 124. Conical cold cathodes 126 are deposited on the current control film 125 in columns and rows. About 2000 cold cathodes 126 are provided for each pixel. Each cold cathode 126 is a two-layered element consisting of a conical base 127 and an electron-emitting film 128 which completely covers the base 127 except for its bottom. The base 127 is made of at least one conductive material having a low work function (exit energy), e.g. Of Y, Ni, Cr, Al, and Mo, respectively. The electron-emitting film 128 is made of yttria (a rare-earth oxide). The cold cathodes 128 are electrically isolated from each other by insulating films 129. A gate electrode 130 is deposited on the insulating films 129. The gate electrode 130 has such openings that the tips of the conical cold cathodes 126 point to the upper substrate. The yttria is one whose crystal system is an A-type lattice, an AB-type lattice, a B-type lattice, a BC-type lattice, and a C-type lattice, respectively. Of these yttrium oxides, preferred are those whose crystal system is a B-type lattice, a BC-type lattice, and a C-type lattice, respectively.

The current control films 125 regulate the current supplied to the cold cathodes 126 to suppress the sputtering of the cathodes 126. The film 125 may have a suitable resistance which can be adjusted by adjusting its thickness and length and by selecting a suitable impurity to be added to the amorphous silicon.

On the transparent upper substrate 122 are applied transparent electrodes 131 made of ITO facing the respective conical cold cathodes 126. Red-emitting fluorescent layers 132R are mounted on some of the anodes 131, green-emitting fluorescent layers 132G are mounted on some other anodes 131, and blue-emitting fluorescent layers 132B are mounted on the remaining ones of the anodes 131.

In the following it will be described how the FED 121 is operated.

First, a data voltage for the pixels is applied between the transparent anodes 131 on one side and the data electrode 124 on the other side. The current regulated by the current regulation film 125 flows from the data electrode 124 to the conical bases 127 of the cold cathodes 126. At the same time, a selection voltage is applied to the gate electrode 130. The gate selects some of the cold cathodes 126. The electron-emitting film or films 128 of each of the cold cathodes 126 that have been selected emit electrons in accordance with the data voltage.

The transparent anodes 131, to which a prescribed voltage is applied, attract the electrons emitted from the selected cold cathodes 126. Therefore, the electrons strike the fluorescent layers 132R, 132G, and 132B deposited on the transparent anodes 131. Excited by the electrons, the fluorescent layers 132R, 132G, and 132B emit visible light rays. The visible light rays pass outwardly through the transparent upper substrate 122. As a result, the FED 121 displays a color image.

The display surface of the FED 121 may be covered with a liquid crystal display serving as a light shading member. In this case, the FED 121 can display images with an accurate gray scale.

The electron-emitting electrodes, each having an yttrium oxide film, can also be used in monochromatic FEDs.

In the FED 121, the yttrium may be replaced by another element of a rare earth. In particular, scandium (Sc), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolium (Gd), terbium ( Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) or lutetium (Lu) instead of yttrium (Y). Furthermore, the material of the bases 127 is not limited to Y, Ni, Cr, Al and Mo. Rather, it may be made of any other material having a leakage energy lower than that of the transparent anode 131.

As described above, the electrodes 126 can suppress their sputtering and emit a large amount of low-voltage electrons.