Double doped-layer, phosphorescent organic light emitting devices

The present invention relates to, for example, a double-doped layer capable of emitting blue light, a phosphorescent organic light emitting device. The present invention relates to, for example, an organic light emitting device (OLED) on a substrate, in which case the OLED is doped with an anode, a first hole transport layer (HTL), a phosphorescent-doped second hole transport layer, and a phosphorescent material. It has a first electron transport layer (ETL), a second electron transport layer, and a cathode.

Organic light emitting devices (OLEDs) that utilize thin film materials that emit light when excited by an electric current are expected to become an increasingly versatile form of flat panel display technology. It has a wide variety of potential OLEDs, including mobile phones, personal digital assistants (PDAs), computer displays, information displays in vehicles, television monitors, as well as light sources for general lighting. This is because it has a purpose. Due to their brilliant colors, viewing angle, compatibility with full-motion video, wide temperature range, thin and comfortable morphological factors, low power consumption, and low cost manufacturing potential, OLEDs are currently growing for years. It is seen as a future technology to replace cathode ray tubes (CRTs) and liquid crystal display devices (LCDs), which are sweeping the $ 40 billion electrical display market. Due to their high luminous efficiency, electrophosphorescent OLEDs are expected to have the potential to replace incandescent lamps, and perhaps fluorescent lamps and lamps for certain applications.

Emission from an OLED is typically due to fluorescence or phosphorescence. The term "phosphorescence" used here refers to light emission from a triplet excited state of an organic molecule, and the term "fluorescence" refers to light emission from a singlet excited state of an organic molecule.

Successful use of phosphorescence promises enormous promising prospects for OLED devices. For example, the advantage of phosphorescence is that all excitons (formed by the recombination of holes and electrons in the light emitting layer) are involved in light emission regardless of whether they are formed as singlet or triplet excited states. Is what you can do. This is because the lowest singlet excited state of an organic molecule is typically at a slightly higher energy than the lowest triplet excited state. This means that for a typical phosphorescent organometallic compound, the lowest singlet excited state rapidly decays to the lowest triplet excited state, from which phosphorescence occurs. In contrast, fluorescent devices can produce fluorescence luminescence obtained from the singlet excited state with only a small percentage (about 25%) of excitons. Residual excitons in a fluorescent device generated in the lowest triplet excited state of an organic molecule are typically unable to convert to a higher singlet excited state, which is energetically unfavorable for fluorescence. Therefore, this energy will be lost by the non-emissive decay process, which only tends to heat the device.

After all, since the discovery that phosphorescent materials can be used as luminescent materials in highly efficient OLEDs, there has been great interest in finding even more efficient electrophosphorescent materials and OLED structures containing such materials to date. Has been held.

Phosphorescent dopant, factris (2-phenylpyridine) iridium [Ir (ppy)₃] High-efficiency organic light emitting devices (OLEDs) have been demonstrated using several different conductive host materials. MA Baldo et al., Nature, vol. 395, 151 (1998); DF O'Brien et al., Appl. Phys. Lett., Vol. 74, 442 (1999); MA Baldo et al., Appl. Phys Lett., vol. 75, 4 (1999); T. Tsutsui and others, Japanese. J. Appl. Phys., Part 2, vol. 38, L1502 (1999); C. Adachi and others, Appl. Phys. Lett., Vol. 77, 904 (2000); MJ Young (Yang) and others, Japanese. J. Appl.Phys., Part 2, vol. 39, L828 (2000); and CL Lee (Lee) In addition, Appl. Phys. Lett., Vol. 77, 2280 (2000). Green emitting Ir (ppy)₃Since the triplet level of the metal / ligand charge transfer state of is between 2.5eV and 3.0eV, a deep blue fluorescein having a peak wavelength at about 400 nm, for example, 4,4'-N, N'- Dicarbazole-biphenyl (CBP) appears to be a candidate as a triplet energy transfer and exciton confinement medium. 6% -10% Ir (ppy) during CBP₃Efficient Ir (ppy)₃It will give a phosphor. In addition to the energy resonance between the dopant and the host, control of charge carrier injection and transport in the host layer is believed to be necessary to achieve efficient formation of luminescent excitons. Ir (ppy) doped into CBP with 2,9-dimethyl-4,7-diphenyl-phenanthroline (BCP) electron transport and exciton block layer₃A large electrophosphorescence efficiency has been achieved using. MA Baldo et al., Appl. Phys. Lett., Vol. 75, 4 (1999). In that device, the doped CBP layer has been found to easily transport holes.

<p><patcit num="1"><text>U.S. Pat. No. 5,707,745</text></patcit><patcit num="2"><text>U.S. Pat. No. 5,703,436</text></patcit><patcit num="3"><text>U.S. Pat. No. 6,013,538</text></patcit></p>

<p><nplcit num="1"><text>MA Baldo et al., Nature, vol. 395, 151 (1998)</text></nplcit><nplcit num="2"><text>DF O'Brien et al., Appl. Phys. Lett., Vol. 74, 442 (1999)</text></nplcit><nplcit num="3"><text>MA Baldo et al., Appl. Phys. Lett., Vol. 75, 4 (1999)</text></nplcit><nplcit num="4"><text>T. Tsutsui et al., Japanese. J. Appl. Phys., Part 2, vol. 38, L1502 (1999)</text></nplcit><nplcit num="5"><text>C. Adachi et al., Appl. Phys. Lett., Vol. 77, 904 (2000)</text></nplcit><nplcit num="6"><text>MJ Young et al., Japanese. J. Appl. Phys., Part 2, vol. 39, L828 (2000)</text></nplcit><nplcit num="7"><text>CL Lee et al., Appl. Phys. Lett., Vol. 77, 2280 (2000)</text></nplcit><nplcit num="8"><text>MA Baldo et al., Appl. Phys. Lett., Vol. 75, 4 (1999)</text></nplcit></p>

<p> The materials currently used for phosphorescent OLEDs can be used to form devices with internal quantum efficiencies close to 100%. However, the materials used to transport holes, recombine, and form block layers in these conventional devices tend to have triplet energies that correspond to the emission of the green part of the spectrum. Inserting a dopant capable of producing blue phosphorescence into such a device utilizing existing materials and structures results in inefficiency, if not at all, emission only from the matrix material and phosphorescence. It is no longer from the dopant material. Therefore, it is very important to find an efficient OLED structure that can emit light in the blue region of the visible electromagnetic spectrum.</p>

<p>(Outline of the present invention) The present invention relates to a phosphorescent OLED having a double-doped layer structure. The OLED of the present invention comprises an anode, a first hole transporting layer (HTL) above the anode, a phosphorescent material-doped second HTL on the first HTL, and phosphorescence on the second HTL. It typically has a material-doped first electron transporting layer (ETL), a second ETL above the first ETL, and a cathode above the second ETL. In each aspect of the invention, the OLED has an HTL doped with a phosphorescent material and an ETL doped with the same phosphorescent material.</p><p> The present invention preferably relates to a phosphorescent OLED having a double-doped layer structure that emits light in the blue range of the visible spectrum. Preferably, the phosphorescent OLEDs of the present invention include blue phosphorescent OLEDs with high efficiency levels.</p>

<figref num="1">Figure 1 shows (1) ITO / R854 (450Å) / TAZ: 6% -Ir (4,6-F)₂ppy) (pico) (250Å) / Alq₃OLED with (450Å) / MgAg layer structure (host # 1); and (2) ITO / R854 (400Å) / R854: 6% -Ir (4,6-F)₂ppy) (pico) (200Å) / TAZ: 6% -Ir (4,6-F)₂ppy) (pico) (200Å) / Alq₃FIG. 5 is a graph showing electroluminescence (EL) intensity as a function of wavelength for OLEDs with (400 Å) / MgAg layered structure (host # 2).</figref><figref num="2">Figure 2 shows ITO / R854 (400Å) / R854: 6% -Ir (4,6-F)₂ppy) (pico) (200Å) / TAZ: 6% -Ir (4,6-F)₂ppy) (pico) (200Å) / Alq₃For each OLED with a (400 Å) / MgAg layer structure, (1) external quantum efficiency (η) as a function of current density_ext) And (2) Power efficiency (η) as a function of current density_p) Is shown in the graph.</figref>

(Detailed explanation) The present invention will be described in the following description in the context of exemplary embodiments. These embodiments are considered merely as illustration examples and are not intended to limit the invention to them.

The present invention relates to a phosphorescent organic light emitting device (OLED) having a double-doped layer structure. That is, in each aspect of the present invention, the OLED has a hole transport layer (HTL) doped with a phosphorescent material and an electron transport layer (ETL) doped with the same phosphorescent material. For example, the OLED of the present invention can be composed of an anode, a first HTL, a second HTL doped with a phosphorescent material, a first ETL and a second ETL doped with a phosphorescent material, and a cathode. According to the present invention, the phosphorescent dopant in the hole transport layer is the same material as the phosphorescent dopant in the electron transport layer. The material that makes up the first HTL need not be the same as the material that makes up the second HTL, and the material that makes up the first ETL need not be the same as the material that makes up the second ETL. It is to those skilled in the art that the hole transport layer material is a material in which charge carrier transport is mainly carried out by transporting holes, and the electron transport material is a material in which charge carrier transport is mainly carried out by electron transport. You will understand.

In one aspect of the invention, the OLED structure is a substrate, an anode on the substrate, a first HTL on the anode, a second HTL doped with a phosphorescent material on the first HTL. Has a phosphorescent material-doped first ETL on the second HTL, a second ETL above the first ETL, and a cathode above the second ETL.

In another aspect of the invention, the OLED structure has an inverted OLED on a substrate. In this embodiment, the cathode is placed on the substrate, the second ETL on the cathode, the first ETL on the second ETL, the second HTL on the first ETL, the first on the second HTL. It has a cathode above the HTL, and the first HTL. The second HTL and the first ETL are doped with a phosphorescent material. Alternatively, in yet another embodiment, the inverted OLED may have a phosphorescent material-doped HTL and a phosphorescent material-doped ETL.

For example, the first hole transport layer may substantially function as a hole injection layer (HIL). The hole injection material of the present invention can be characterized as a material that flattens or wets the anode surface so as to provide efficient hole injection from the anode to the hole injection material. The hole injection material of the present invention is further defined by the relative IP energies described herein, which is convenient with the adjacent anode layer on one side of the HIL layer and the phosphorescent dope hole transport layer on the other side of the HIL. It is characterized as having a well-matched HOMO (highest occupied molecular orbital) energy level.

A preferred property of HIL materials is that holes can be efficiently injected from the anode into the HIL material. In particular, the HIL material preferably has an IP that is about 0.7 eV or less greater than the IP of the anode material. More preferably, the HIL material has an IP greater than or equal to about 0.5 eV than the anode material.

The HIL material is also the conventional hole transport material typically used in the OLED hole transport layer, in which the hole mobility of such a HIL material is substantially smaller than the hole mobility of the conventional hole transport material. It is distinguished in that it has mobility. For example, m-MTDATA is, for example, 4,4'-bis [N- (naphthyl) -N-phenyl-amino] biphenyl (α-NPD), or N, N'-bis (3-methylphenyl) -N. , Probably reduced HTL HONO level / ITO offset energy, to facilitate hole injection from ITO into HTL consisting of N'-diphenyl- [1,1'-biphenyl] 4,4'-diamine (TPD), Alternatively, it has been confirmed to be effective due to the wetting of the ITO surface. About 5 × 10^-4cm²/ V seconds and 9x10^-4cm²Compared to conventional hole transport materials such as α-NPD or TPD, which each have hole mobilities of / V seconds, the HIL material m-MTDATA is about 3 × 10^-5cm²It is believed to have a hole mobility of / V seconds. Therefore, the m-MTDATA material has hole mobility that is an order of magnitude higher than the commonly used HIL materials α-NPD and TPD.

In those aspects of the invention containing two HTLs, the first HTL may contain any suitable material that acts as a transporter of good charge (ie, holes). Suitable hole transport materials are known in the art and examples of materials suitable for the first hole transport layer can be found in US Pat. No. 5,707,745, which is hereby incorporated by reference in its entirety. Can be done. Other materials suitable for use as the first hole transport layer include, for example, 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (α-NPD); N, N. '-Diphenyl-N, N'-Bis (3-Methylphenyl) 1-1'Biphenyl-4,4'-Diamine (TPD); 4,4'-Bis [N, N'-(3-Trill) Amino ] -3,3'-Dimethylbiphenyl (M14); 4,4', 4''-Tris (30 Methylphenylphenylamino) Triphenylamine (MTDATA); and 4,4'-Bis [N, N'- (3-Trill) Amino] -3,3'-Dimethylbiphenyl (HMTPD) is included. In a preferred embodiment, the first hole transport layer has the following chemical formula, 3,3'-dimethyl-N.⁴, N⁴, N^4’, N^4’-Tetra-p-trill-biphenyl-4,4'-diamine (R854):

<chemistry num="1"><img file="JP5117428B2_D0001.tif" /></chemistry>

The second HTL, which is a phosphorescent-doped light emitting layer (EML), acts as a transporter of good charges (ie, holes), whatever is suitable for effectively transferring energy to highly luminescent guests. It may contain material. Suitable hole transport materials are known in the art and examples of materials suitable for the second hole transport layer are described in US Pat. No. 5,707,745 (which, as shown above, by reference in its entirety. Incorporated in this application). Other materials suitable for use as the second hole transport layer include, for example, 4,4'-bis [N- (1-naphthyl) -N-phenyl-amino] biphenyl (α-NPD); N, N. '-Diphenyl-N, N'-Bis (3-Methylphenyl) 1-1'Biphenyl-4,4'-Diamine (TPD); 4,4'-Bis [N, N'-(3-Trill) Amino ] -3,3'-Dimethylbiphenyl (M14); 4,4', 4''-Tris (30 Methylphenylphenylamino) Triphenylamine (MTDATA); and 4,4'-Bis [N, N'- (3-Trill) Amino] -3,3'-Dimethyldiphenyl (HMTPD) is included. In one preferred embodiment, the second hole transport layer has the following chemical formula of 3,3'-dimethyl-N.⁴, N⁴, N^4’, N^4’-Tetra-p-trill-biphenyl-4,4'-diamine (R854):

<chemistry num="2"><img file="JP5117428B2_D0002.tif" /></chemistry>

The first ETL, which is a phosphorescent-doped light emitting layer (EML), acts as a transporter of good charges (ie, electrons), whatever is suitable for effectively transferring energy to highly luminescent guests. It may contain host material. Suitable electron transport materials are known in the art, and examples of materials suitable for the first electron transport layer are US Patent Application No. 09 / 629,335 filed on August 5, 2000 in the joint application. (This is incorporated herein by reference in its entirety). Examples of materials suitable for use as the first electron transport layer include, for example, 1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole (OXD-7). Oxadiazole, oxadiazole derivative, phenanthroline such as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (vasocuproin or BCP), BCP derivative, or substituted or unsubstituted benzoxazole or benzthiazole Contains compounds. In a preferred embodiment, the first electron transport layer is a host material for 3-phenyl-4- (1'-naphthyl) -5-phenyl-1,2,4-triazole (TAZ) having the following chemical formula:

<chemistry num="3"><img file="JP5117428B2_D0003.tif" /></chemistry>

In those aspects of the invention with two ETLs, the second ETL acts as a good charge (ie, electron) mobile and also acts as an effective electron inject layer (EIL) of any suitable. It may contain material. Suitable electron transfer materials are known in the art, and examples of materials suitable for the second ETL are incorporated herein by reference in their entirety, US Pat. No. 5,707,745. Can be found in). In a preferred embodiment, the second ETL is an electron transport material, tris- (8-hydroxyquinoline) aluminum (Alq).₃), Which is used to transport electrons to the first electron transport layer and has the following chemical formula:

<chemistry num="4"><img file="JP5117428B2_D0004.tif" /></chemistry>

An effective electron injection layer may consist of a phthalocyanine compound, for example copper phthalocyanine (CuPc).

In addition to acting as an electron injection layer, the second ETL also functions as a hole block layer and / or an exciton block layer. The hole block layer and / or exciton block layer in the OLED device substantially blocks the diffusion of holes and / or excitons, respectively, thereby effectively placing the holes and / or excitons within the light emitting region of the device, respectively. And increase device efficiency.

Any phosphorescent light emitter can be used as the phosphorescent dopant of the present invention. Preferred phosphorescent dopants are organometallic compounds disclosed in Co-pending U.S. Patent Application No. 09 / 637,766, filed August 11, 2000, which is hereby incorporated by reference in its entirety. Examples of such preferred phosphorescent dopants are platinum (II) (2-phenylpyridinato-N, C).^2’) (Acetylacetone) [Pt (ppy) (acac)], Platinum (II) (2- (p-tryl) pyridinato-N, C^2’) (Acetylacetone) [Pt (tpy) (acac)], Shirokane (II) (7,8-Benzoquinolinato-N, C^3’) (Acetylacetoneate) [Pt (bzq) (acac)], Platinum (II) (2- (2'-(4', 5'-benzothienyl) pyridinate-N, C^3’) (Acetylacetone) [Pt (btp) (acac)], Platinum (II) (2- (4', 6'-difluorophenyl) pyridinato-N, C^2’) (Acetylacetone) [Pt (4,6-F)₂ppy) (acac)], platinum (II) (2- (4', 5'-difluorophenyl) pyridinato-N, C^2’) (Acetylacetone) [Pt (4,5-F₂ppy) (acac)], and platinum (II) (2- (4', 5'-difluorophenyl) pyridinato-N, C^2’) (2-Picorinato) [Pt (4,5-F₂ppy) (pico)] are included, and their corresponding chemical structures can be seen below:

<chemistry num="5A"><img file="JP5117428B2_D0005.tif" /></chemistry><chemistry num="5B"><img file="JP5117428B2_D0006.tif" /></chemistry>

Another preferred phosphorescent dopant is iridium (2- (4', 6'-difluorophenyl) pyridinato-N, C.^2’) (2-Picorinato) [Ir (4,6-F)₂ppy) (pico)], which is used as a phosphorescent dopant in the examples of the present invention, which will be discussed later in the present specification.

In the OLED structure of the present invention, light is emitted from the base material side of the device, or, otherwise, from the side opposite to the base material of the device, that is, as a top emitting device. A top light emitting device is a device having an opaque and / or reflective substrate so that light is emitted only from the top surface of the device and not through the substrate. The substrate is typically referred to as being at the bottom of the device.

The substrate according to the invention may be rigid or flexible, opaque or substantially transparent, and / or plastic, metal, or glass. The substrate is not limited to the thickness range described herein, but may be as thin as 10 mm if present as a flexible plastic or metal leaf substrate, or hard, transparent or opaque. If present as a substrate for, or if the substrate is made of silicon, it may be substantially thicker.

Suitable electrode (ie, anode and cathode) materials include metals, metal alloys, or conductive materials such as ITO that form metal contacts. Deposition of electrical contacts can be achieved by vapor deposition or other suitable metal deposition methods. These electrical contacts can be made from, for example, indium, magnesium, platinum, gold, silver, or a combination such as Ti / Pt / Au, Cr / Au, or Mg / Ag.

Damage to the organic layer should be avoided when depositing electrodes on the top electrode layer (ie, the cathode or anode, typically the cathode), the side farthest from the substrate of the OLED. For example, organic layers should not be heated above their glass transition temperature. The top electrode is preferably deposited from a direction substantially perpendicular to the substrate.

In a preferred embodiment, the cathode is a low work function electron injecting material, such as a metal layer. The cathode preferably has a work function smaller than about 4 eV. The cathode is preferably a metal layer having a thickness of about 100 Å or less, and may have a thickness of about 50 Å or less. The contacts are preferably made of magnesium silver or an alloy of magnesium and silver. The metal cathode layer may be substantially thicker if it makes the cathode layer opaque.

For top emitting devices, transparent cathodes as described in US Pat. No. 5,703,436, or co-pending US Pat. Nos. No. 08 / 964,863 and 09 / 054,707 may be used. The transparent cathode has light transmission characteristics such that the OLED has an optical transmission of at least about 50%. The transparent cathode preferably has light transmission properties that allow the OLED to have at least 70%, more preferably at least about 85% optical transmission.

The anode is preferably a hole-injected metal anode layer having a large work function, such as an indium tin oxide (ITO) layer. ITO is a transparent conductor and acts as an anode. ITO is a degenerate semiconductor formed by doping a broadband semiconductor. The carrier concentration of ITO is 10¹⁹/cm³Is over. The ITO anode layer may have a thickness of about 500 Å to about 4000 Å or more. For top light emitting devices with opaque or reflective anodes, high work function metals such as Au may be used.

The OLEDs of the present invention are manufactured using materials that provide electroluminescence emission in a relatively narrow band with a center near the selected spectral range corresponding to one of the three primary colors, red, green, and blue. It is desirable to be able to use as a colored layer in the OLED. It is also desirable that such compounds can be easily vapor-deposited as thin layers using vacuum-deposited methods so that they can be easily incorporated into OLEDs that are entirely produced from vacuum-deposited organic materials.

The OLEDs and OLED structures of the present invention can optionally be from protective layers (to protect certain materials during the manufacturing process), insulating layers, reflective layers to direct waves in certain directions, and the environment. It contains additional materials or layers with the desired effect, such as electrodes and protective caps that cover the organic layers to protect the layers. A description of the insulating layer and protective cap is contained, for example, in US Pat. No. 6,013,538, which is hereby incorporated by reference in its entirety.

The type of layer present, depending on whether an OLED layer in reverse order is present, whether the OLED is considered to emit light in a preferred spectral range, or whether yet another design change is used. , Number, thickness, and order will vary substantially.

The present invention will be described in detail below in connection with showing how a particular representative embodiment thereof can be made, but the materials, devices, and processing steps are merely for illustration purposes. It should be understood as an example. In particular, the present invention is not limited to the methods, materials, conditions, process parameters, devices, etc. specifically described herein.

<p> [Example 1] The first HTL was first deposited on an ITO (indium tin oxide) coated glass substrate. The first HTL consists of R854 of about 400 Å. The second HTL consists of R854 of about 200 Å and is deposited on the first HTL. The second HTL is Ir (4,6-F)₂It is about 6% doped with ppy) (pico). The first ETL consists of a TAZ of about 200 Å and is deposited on the second HTL. The first ETL is Ir (4,6-F)₂It is about 6% doped with ppy) (pico). Alq with a thickness of about 400 Å₃The second ETL of the above is deposited on the first ETL. The device was completed by depositing Mg / Ag electrodes on the second ETL. This Mg / Ag electrode had a thickness of about 100 nm. All deposits are 5x10^-5The vacuum was lower than that of Thor. The device was tested in air without packaging.</p><p> Figure 1 shows a graph depicting EL intensity as a function of wavelength for two different OLEDs. The first OLED (host # 1) is ITO / R854 (450Å) / TAZ: 6% -Ir (4,6-F)₂ppy) (pico) (250Å) / Alq₃It has a (450 Å) / MgAg layer structure and the second OLED (host # 2) has the structure according to Example 1 above. That is, the first OLED and the second OLED are similar in structure, except that the first OLED lacks the phosphorescent material-doped second hole transport layer present in the second OLED, which is representative of Example 1. There is. As can be seen from Figure 1, both OLEDs show peak EL intensities at about 472 nm, while the first OLED (which lacks the second HTL doped with phosphorescent material) is separate at about 400 nm. Has a peak intensity of. Eliminating this other peak helps increase overall device efficiency. In addition, the use of adjacent phosphorescent doped layers may also help increase device efficiency by eliminating the formation of exciplexes.</p><p> Figure 2 shows 6% -Ir (4,6-F)₂ppy) (pico) Doping R854 / 6% -Ir (4,6-F)₂external quantum efficiency (η) of ppy) (pico) doped TAZ device_ext) Is shown. Maximum η of about 2%_extHowever, about 0.1 ~ 1.0mA / cm² It is obtained with the current density of, and the values of CIE are X = 0.14 and Y = 0.32.</p><p> This is considered to be the first report to prove the presence of electrophosphorescence in the blue region of the spectrum. Furthermore, an external quantum efficiency of 2% indicates that even greater quantum efficiencies could eventually be achieved using the materials and device structures described here as producing blue electrophosphorescence.</p><p> Figure 2 shows 6% -Ir (4,6-F)₂ppy) (pico) Doping R854 / 6% -Ir (4,6-F)₂ppy) (pico) Doped TAZ device power efficiency (η)_p) Is shown. Maximum η of about 2.5lm / W_pBut about 0.1mA / cm² It is obtained with the current density of.</p><p> The structures of the present invention can be used, for example, in virtually any type of device, such as bulletin boards and signs containing one or more OLEDs, computer monitors, vehicles, telecommunications devices, telephones, printing. Includes machines, televisions, large screen wall screens, theater screens and stadium screens.</p><p> Although the present invention has been described in relation to specific examples and preferred embodiments, it will be appreciated that the invention is not limited to these examples and embodiments. In particular, the present invention can be applied to an extremely wide variety of electrical devices. Therefore, it will be apparent to those skilled in the art that the claimed invention includes the specific examples described herein and modifications of preferred embodiments.</p>