Piezoelectric vibrator unit, ink jet recording head using the piezoelectric vibrator unit and method of manufacturing the same

0001The present invention relates to a piezoelectric vibrator unit, an ink jet recording head using the piezoelectric vibrator unit, a method of manufacturing a piezoelectric vibrator unit and a method of manufacturing an ink jet recording head. In particular, the present invention relates to a piezoelectric vibrator unit suitable for an ink jet recording head and having curved portions which correspond to deformable regions of the vibrator unit.

0002An actuator unit in which minute regions (arrayed at fixed pitches) are deflected is disclosed in <patcit id="pcit0001" dnum="JP58007364A"><text>Japanese Patent Laid-Open Publication No. Sho. 58-7364</text></patcit>. The actuator unit includes a lower electrode, formed on the surface of a thin plate, which is elastically deformable. A green sheet, which is shaped like a rectangular strip and made of piezoelectric material, is layered on the thin plate surface with the lower electrode by bonding or coating. The resultant structure is sintered to form a piezoelectric layer. In addition, upper electrodes are formed on the surface of the sintered structure.

0003However, the bonding or coating process, by which the rectangular green sheet made of piezoelectric material is layered on the thin plate's surface is an essential step in the manufacture of the above-mentioned actuator unit. Therefore, the manufacturing of the actuator unit is inefficient. Furthermore, the lower electrode is easily peeled away from the piezoelectric layer in the sintering process. In this respect, the actuator unit is poor in durability.

0004To cope with this, a unique actuator unit is proposed in <patcit id="pcit0002" dnum="JP62101455A"><text>Japanese Patent Laid-Open Publication No. Sho. 62-101455</text></patcit>. The actuator unit includes a thin elastic plate made of ceramic which has an electromechanical displacing property. A ceramic piece is inserted in a region of the elastic plate which is to be deflected. In addition, electrodes are attached to both sides of the region containing the ceramic piece.

0005The actuator unit described above eliminates the need for the bonding or coating process associated with the green sheet of piezoelectric material. In addition, the piezoelectric member has a single layer structure. Therefore, it rarely happens that the electrode is peeled away. However, the actuator unit has the following disadvantage. An elasticity and a rigidity of a vibrating region of the elastic plate are substantially equal to those in a non-vibrating region. Therefore, a displacement of the vibrated region by its deflection is small. Accordingly, when the actuator unit is applied to an ink jet recording head in which the volume of the pressure generating chamber is varied in order to discharge an ink droplet, a high voltage is required in order to drive the recording head.

0006<patcit id="pcit0003" dnum="US4588998A"><text>US 4, 588, 998</text></patcit> discloses a piezoelectric vibrator unit having an elastically deformable plate made of a piezoelectric material having a curved portion. The piezoelectric material is a single thin film of polyvinylidene fluoride (PVDF) or two PVDF films bonded together in a bimorph structure.

0007It is an object of the present invention to provide a piezoelectric vibrator which may be manufactured in a simplified manufacturing process, and it is also an object to provide a method for manufacturing such piezoelectric vibrator unit. Further it is an object of the present invention to provide an ink jet head which may be obtained by a simplified manufacturing process, and it is also an object to provide a method for manufacturing such ink jet head.

0008This object is solved by providing a piezoelectric vibrator unit, a method of manufacturing a piezoelectric vibrator unit, layered type ink jet recording head and a method for manufacturing a layered type ink jet recording head according to appended independent claims. Advantageous embodiments of the invention are defined in appended dependant claims.

0009According to an advantageous aspect of the invention, the piezoelectric vibrator unit may be manufactured without any bonding or coating process for forming a piezoelectric member.

0010According to a further aspect of the present invention, a method of manufacturing the piezoelectric vibrator unit shall be provided.

0011According to another aspect of the present invention an ink jet recording head using the piezoelectric vibrator unit shall be provided.

0012In order to carry out the above object of the invention, a piezoelectric vibrator unit is provided in accordance with a first embodiment of the present invention. The piezoelectric vibrator unit includes an elastically deformable plate made of piezoelectric material having curved portions lengthwise arrayed at fixed pitches. Preferably, a common electrode is formed on one side of the elastic plate, while discrete electrodes are formed on the curved portions of the elastic plate.

0013An extension and a contraction of the elastic plate are converted into deflection displacements that are made in conformity with a shape of each curved portion. Advantageously, the piezoelectric vibrator unit may be included in an ink jet recording head in which a pressure generating chamber is included. A rate of change of the volume of the pressure generating chamber per unit drive voltage is increased by employing the above mentioned elastically deformable plate having the curved portions instead of a vibrator unit including a flat plate.

0014These and other features, aspects and advantages of the present invention will become better understood with reference to the following description, appended claims, and accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figs. 1(a) and 1(b)</figref> are cross-sectional views showing a piezoelectric vibrator unit. <figref idref="f0001">Fig. 1(a)</figref> is a cross-sectional view showing the piezoelectric vibrator unit when a drive signal is not applied thereto. <figref idref="f0001">Fig. 1(b)</figref> is a cross-sectional view showing the piezoelectric vibrator unit when a drive signal is applied between one discrete electrode and a common electrode in the vibrator unit.</li><li><figref idref="f0002">Figs. 2(a) to 2(d)</figref> are sectional views showing a sequence of process steps of a method of manufacturing a piezoelectric vibrator unit according to another embodiment of the present invention.</li><li><figref idref="f0003">Figs. 3(a) to 3(e)</figref> are sectional views showing a sequence of process steps of a method of manufacturing a piezoelectric vibrator unit according to yet another embodiment of the present invention.</li><li><figref idref="f0004">Figs. 4(a) to 4(d)</figref> are sectional views showing a sequence of process steps of a method of manufacturing a piezoelectric vibrator unit according to still yet another embodiment the present invention.</li><li><figref idref="f0005">Figs. 5(a) and 5(b)</figref> are cross-sectional views showing a portion of an ink jet recording head utilizing a piezoelectric vibrator unit.</li><li><figref idref="f0006">Figs. 6(a) and 6(b)</figref> are cross-sectional views showing another ink jet recording head utilizing a piezoelectric vibrator unit.</li><li><figref idref="f0007">Figs. 7(a) and 7(b)</figref> are cross-sectional views showing still another ink jet recording head utilizing a piezoelectric vibrator unit constructed in accordance with the present invention.</li><li><figref idref="f0008">Figs. 8(a) and 8(b)</figref> are cross-sectional views showing yet another ink jet recording head utilizing a piezoelectric vibrator unit constructed in accordance with the present invention.</li><li><figref idref="f0009">Fig. 9</figref> is a cross-sectional view showing still yet another embodiment of a piezoelectric vibrator unit.</li><li><figref idref="f0009">Fig. 10</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0009">Fig. 9</figref>.</li><li><figref idref="f0010">Fig. 11</figref> is a cross-sectional view showing a piezoelectric vibrator unit.</li><li><figref idref="f0010">Fig. 12</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0010">Fig. 11</figref>.</li><li><figref idref="f0011">Fig. 13</figref> is a cross-sectional view showing a piezoelectric vibrator unit.</li><li><figref idref="f0011">Fig. 14</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0011">Fig. 13</figref>.</li><li><figref idref="f0012">Fig. 15</figref> is a cross-sectional view showing a piezoelectric vibrator unit.</li><li><figref idref="f0012">Fig. 16</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0012">Fig. 15</figref>.</li><li><figref idref="f0013">Fig. 17</figref> is a cross-sectional view showing a piezoelectric vibrator unit.</li><li><figref idref="f0013">Fig. 18</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0013">Fig. 17</figref>.</li><li><figref idref="f0014">Fig. 19</figref> is a graph showing variations of the quantities of deflection of the curved portions of the piezoelectric vibrator units of <figref idref="f0009">Figs. 9</figref>, <figref idref="f0010">11</figref> and <figref idref="f0011">13</figref> with respect to initial deflection quantities thereof.</li><li><figref idref="f0015">Figs. 20(a) to 20(d)</figref> are sectional views showing a sequence of process steps of an additional embodiment of a method of manufacturing a piezoelectric vibrator unit according to the present invention.</li><li><figref idref="f0016">Fig. 21</figref> is a diagram showing a structure for leading out an electrode formed on a piezoelectric vibrator unit in an ink jet recording head using the piezoelectric vibrator unit as an actuator.</li><li><figref idref="f0017">Fig. 22</figref> is a diagram showing the rear sides of the separated piezoelectric vibrator units in the electrode lead-out structure of <figref idref="f0016">Fig. 21</figref>.</li><li><figref idref="f0018">Fig. 23</figref> is a diagram showing a conductive layer formed on the spacer and common electrodes formed on the rear sides of the piezoelectric vibrator units in the electrode lead-out structure of <figref idref="f0016">Fig. 21</figref>.</li><li><figref idref="f0019">Fig. 24</figref> is a diagram showing another electrode lead-out structure in an ink jet recording head using the piezoelectric vibrator unit as an actuator.</li><li><figref idref="f0020">Figs. 25(a) to 25(c)</figref> are sectional views showing a sequence of process steps of a method of manufacturing a piezoelectric vibrator unit according to an embodiment of the present invention.</li><li><figref idref="f0021">Fig. 26</figref> is a perspective view showing a piezoelectric vibrator unit.</li><li><figref idref="f0022">Fig. 27(a)</figref> is a lengthwise cross sectional view of the recording head in <figref idref="f0021">Fig. 26</figref>. <figref idref="f0022">Fig. 27(b)</figref> is a widthwise cross sectional view of the recording head in <figref idref="f0021">Fig. 26</figref>.</li><li><figref idref="f0023">Fig. 28</figref> is a cross sectional view of a piezoelectric vibrator unit.</li></ul>

0015The preferred embodiments of the present invention, which are illustrated in detail in the accompanying drawings, will be described hereunder.

0016<figref idref="f0001">Fig. 1</figref> is a cross-sectional view showing a piezoelectric vibrator unit 5. The vibrator unit 5 includes an elastically deformable plate 1, made of piezoelectric material, e.g., PZT. By way of example, the plate 1 may be about 7µm thick. The elastic plate 1 has a surface including troughs or curved portions 2 which are laterally spaced at fixed pitches. A common electrode 3 is layered over one side of the elastic plate 1.

0017To form the common electrode 3, platinum is vapor deposited over one side of the elastic plate 1. Alternatively, one side of the elastic plate may be coated with a conductive material which forms the common electrode 3. Discrete electrodes 4 are layered on the other side of the elastic plate 1 over the curved portions 2 that serve as deformable regions.

0018The discrete electrodes 4 may be formed by vapor depositing platinum or the like over the surfaces of the curved portions 1. Alternatively, the surface of the curved portions 2 of the elastic plate 1 may be coated with conductive material which forms the discrete electrodes 4.

0019In the above-mentioned embodiment, a drive voltage is applied between the common electrodes 3 and at least one of the discrete electrodes 4. Thus, only the deformable region of the elastic plate 1, which is sandwiched between those electrodes 3 and 4, contracts, so that the corresponding curved portion 2 is displaced outwardly (upwardly in the drawing), as shown in <figref idref="f0001">Fig. 1(b)</figref>. Specifically, the length L of the deformable region of the elastic plate 1 is increased to the length L' when the side edges of the deformable region are held by the corresponding side edges of one of the discrete electrodes 4. As a result, a tension is generated in the deformable region. To balance the tension, the deformable region varies its curvature. Consequently, the curved portion 2 moves upwards and reduces its depth by ΔH.

0020In this state, an electric charge of the deformable region defined by the electrodes 3 and 4 is discharged so that the deformable region is restored to its original shape (i.e., the original shape of the curved portion 2), as shown in <figref idref="f0001">Fig. 1(a)</figref>. Thus, the deformable regions of the elastic plate 1 of the single layer structure, which are defined by the discrete electrodes, may be selectively deformed when a drive signal is applied between the common electrode 3 and at least one of the discrete electrodes 4 which defines that region.

0021In the above-mentioned piezoelectric vibrator unit, a magnitude of deflection of the elastic plate 1 is maximized when a magnitude of deflection ΔH of the deformable region of the elastic plate 1 is selected to be one to two times as large as the thickness of the elastic plate 1.

0022<figref idref="f0002">Figs. 2(a)-2(d)</figref> show a sequence of process steps of a method of manufacturing the piezoelectric vibrator unit according to the present invention. A common electrode 11 is formed on one side of a green sheet 10 and discrete electrodes 12 are formed on the other side thereof. The green sheet 10 is made of piezoelectric material, e.g., PZT. The common electrode 11 consists of a deformable layer, made of a conductive material, formed by coating, as shown in <figref idref="f0002">Fig. 2a</figref>.

0023The green sheet 10 is then placed between a lower mold 13 and an upper mold 14, as shown in <figref idref="f0002">Fig. 2(b)</figref>. In this case, the discrete electrodes 12 on the green sheet 10 are confronted with inwardly curved portions 13a of the lower mold 13, which are configured in conformity with the above-mentioned curved portions. The upper mold 14 having outwardly curved portions 14a is positioned so that the outwardly curved portions 14a thereof are confronted with the discrete electrodes 12 of the green sheet 10. The green sheet 10 is then pressed between the upper and lower molds 13 and 14 by applying a fixed pressure to the upper mold 14. As a result, the green sheet 10 and the electrodes 11 and 12 are configured as defined by the shapes of the upper and the lower molds 13 and 14, as shown in <figref idref="f0002">Fig. 2(c)</figref>.

0024After the green sheet 10 is taken out of the lower and upper molds 13 and 14, or while the green sheet 10 is kept to be placed between the molds 13 and 14 under a fixed pressure, the green sheet 10 is sintered at a temperature, e.g., 1200°C, which is sufficient to transform its nature into a ceramic. In this way, a piezoelectric vibrator unit is manufactured.

0025The resulting piezoelectric vibrator unit consists of an elastic plate 18 having curved portions 17 configured as defined by the inwardly and outwardly curved portions 13a and 14a of the molds 13 and 14, a common electrode 19 layered on one side of the elastic plate 18, and drive (i.e., discrete) electrodes 20 formed and discretely arrayed on the other side thereof, as shown in <figref idref="f0002">Fig. 2(d)</figref>.

0026In the manufacturing process mentioned above, the common electrode 19 and the discrete electrodes 20 are attached to the green sheet 18 before the green sheet 18 is subjected to the above process.

0027Another process for manufacturing a piezoelectric vibrator unit is also provided in accordance with the present invention, as shown in <figref idref="f0003">Figs. 3(a)-3(e)</figref>. According to the inventive manufacturing process, the green sheet 10 made of piezoelectric material is molded and sintered in the manner shown in <figref idref="f0003">Figs. 3(a)-3(c)</figref>. An elastic plate 18 is then formed which has curved portions 17 that are defined by the inwardly and outwardly curved portions 13a and 14a of the molds 13 and 14, as shown in <figref idref="f0003">Fig. 3(d)</figref>.

0028Subsequently, a common electrode 19 is formed on one side of the elastic plate 18, and drive (i.e., discrete) electrodes 20 are formed on the curved portions 17 of the other side of the elastic plate 18, as shown in <figref idref="f0003">Fig. 3(e)</figref>. A vapor deposition or sputtering process may be used to form the common and discrete electrodes 19 and 20 on the surfaces of the elastic plate 18.

0029<figref idref="f0004">Figs. 4(a)-4(d)</figref> show a method of manufacturing a piezoelectric vibrator unit in accordance with another embodiment the present invention. According to the inventive method, a common electrode 11 is formed on one side of a green sheet 10, and discrete electrodes 12 are formed on the other side thereof. The green sheet 10 is made of piezoelectric material, e.g., PZT. The common electrode 11 consists of a deformable layer made of conductive material, which maybe formed as a coating, as shown in <figref idref="f0004">Fig. 4(a)</figref>. Lumps 15 are then placed on the surfaces of the discrete electrodes 12 at the same pitches as the curved portions 17 (i.e., deformable regions) to be formed, as shown in <figref idref="f0004">Fig. 4(a)</figref>. Each of the lumps 15 has a proper shape for forming the curved portions 17 of an elastic plate when the lumps are pressed by an upper mold 14.

0030The green sheet 10 is sandwiched between a lower mold 13 and an upper mold 14, as shown in <figref idref="f0004">Fig. 4(b)</figref>. The lower mold 13 has inwardly curved portions 13a that are configured in conformity with the shape of the curved portions 17. The upper mold 14 has depressions 14b which are deep enough to allow the upper mold to press the lumps 15, as shown in <figref idref="f0004">Fig. 4(b)</figref>. The green sheet 10 is compressed by the molds 13 and 14 to which a fixed force is applied. The surface of the green sheet 10 on which the discrete electrodes 12 are formed (which corresponds to deformable regions of the green sheet 10) are inwardly deformed due to the presence of the lumps 15. In addition, portions of the other surface of the green sheet 10 on which the common electrode 11 is formed (which also correspond to the deformable regions of the green sheet 10) are outwardly deformed as defined by the configuration of the inwardly curved portions 13a of the lower mold 13.

0031After the green sheet 10 is taken out of the molds 13 and 14, or while the green sheet 10 is kept to be placed between the molds 13 and 14 to which a fixed pressure is applied, the green sheet 10 is sintered at a temperature, e.g., 1200°C, which is sufficient to transform the green sheet 10 into a ceramic. Through the sintering process, the lumps 15 are moltened away, as shown in <figref idref="f0004">Fig. 4(c)</figref>. In this manner, the inventive piezoelectric vibrator unit is manufactured.

0032The piezoelectric vibrator unit consists of an elastic plate 18 having curved portions 17 which are defined by the inwardly curved portions 13a of the lower mold 13 and the contour of the lumps 15, a common electrode 19 layered on one side of the elastic plate 18, and discrete (i.e., drive) electrodes 20 formed on the curved portions 17 of the other side of the elastic plate, as shown in <figref idref="f0004">Fig. 4(d)</figref>.

0033The manufacturing process described above may be modified in the same manner that the first embodiment was modified. According to the modified process, a green sheet 10 is first subjected to the shaping and sintering process using the lumps 15, and the molds 13 and 14. Then, a common electrode 11 and discrete electrodes 12 are disposed on the shaped and sintered green sheet 10.

0034<figref idref="f0005">Figs. 5(a) and 5(b)</figref> show a component ink jet recording head utilizing a piezoelectric vibrator unit 5. The ink jet recording head includes a spacer 22 formed from a ceramic plate made of zirconia, for example. The spacer 22 has a proper thickness for forming pressure generating chambers 23 (e.g., 150µm). Through-holes 27 and 28, which are configured so as to conform the pressure generating chambers 23, are formed at fixed pitches in the spacer 22. By way of example, the pressure generating chamber 23 may have a discharge orifice pitch which is 90 dpi, a width which is 190 to 210µm, and a length which is about 2mm.

0035The piezoelectric vibrator unit 5 serves as a first covering member which covers and seals one of the sides of the spacer 22. To this end, an initial deflection of each of the curved portions 17 of the piezoelectric vibrator unit is selected to be 5µ or larger, preferably about 30µm or larger at the deepest part thereof, and generally one to two times as large as the thickness of the elastic plate 18.

0036A second covering member 26 covers and seals the other side of the spacer 22. The second covering member 26 is made of zirconia, for example. The piezoelectric vibrator unit 5, the spacer 22, and the second covering member 26 define the pressure generating chamber 23. The second covering member includes a first through-hole 27 which communicates with one end of the pressure generating chamber 23, and a second through-hole 28 which communicates with the other end of the pressure generating chamber 23.

0037One side of an ink-supply-port forming plate 29, which may be made of zirconia, is fixed to the second covering member 26. An ink supply port 30, which communicates with the first through-hole 27 of the second covering member 26, is formed in the ink-supply-port forming plate 29. The ink-supply-port forming plate 29 further includes a through-hole 31 which is formed at a location corresponding to the second through-hole 28 of the second covering member 26.

0038An ink-chamber forming plate 32 is formed from a plate member having a proper thickness for forming a common ink chamber by way of example, the plate member may be 150µm thick and may be formed of zirconia. The ink supply port 30 has an opening at the top of the common ink chamber 33. A through-hole 34, which is formed in the ink-chamber forming plate 32, communicatively connects the pressure generating chamber 23 with a discharge orifice 36.

0039A nozzle plate 35 is also provided in the ink jet recording head. The nozzle plate 35 is a metal plate member, such as stainless steel. Advantageously, the metal plate member is corrosion resistant to ink. A discharge orifice 36 is formed in the nozzle plate at a location which corresponds to the pressure generating chamber 23 so that it is communicatively connected to the pressure generating chamber 23 via the through-holes 28, 31 and 34. The nozzle plate 35 is bonded to the ink-chamber forming plate 32 by means of a bonding layer 37, e.g., a thermally molten film, inserted therebetween. In addition, a bonding layer 38 is also provided for bonding the ink-supply-port forming plate 29 to the common ink-chamber forming plate 32.

0040In the above-described example, a drive voltage is applied between the common electrode 3 and a discrete (i.e, drive) electrode 4 which are associated with the pressure generating chamber 23 so that only the region sandwiched between the electrodes 3 and 4, (i.e., the deformable region) contracts. As a result, the curved portion 2 moves upwards and its bottom rises by an amount ΔH, as shown in <figref idref="f0001">Fig. 1(b)</figref>.

0041When the curved portion 2 moves upwards, the volume of the pressure generating chamber 23 increases and ink flows from the common ink chamber 33 into the pressure generating chamber 23 through the passage including the ink supply port 30 and the first through-hole 27.

0042In this state, an electric charge of the elastic plate 1 in the deformable region is discharged and the elastic plate 1 is restored to its original shape. In particular, the original shape of the curved portion 2 is restored and the volume of the pressure generating chamber 23 decreases. Consequently, the pressure generating chamber 23 compresses ink therein, so that the ink is discharged outside through the discharge orifice 36 in the form of an ink droplet.

0043It is noted that the elastic plate 1 includes curved portions 2 that are formed by curving the elastic plate per se. With this unique elastic plate, the expansion and/or contraction of the elastic plate 1 can easily vary the volume of the pressure generating chamber, as compared to the case in which a deflection deformation is caused by expanding and contracting a planar vibrating plate. Therefore, the volume of the pressure generating chamber 23 increases when it sucks ink into itself and decreases when it discharges the ink droplet at a faster rate when a curved vibrating plate is used in the ink jet recording head instead of a planar vibrating plate. As a result, ink droplets can be more efficiently discharged from the ink jet recording head under the application of the same drive signal.

0044In the above-mentioned example, the electrode 3 is used as a common electrode. In an ink jet recording head which embodies another example, at least one discrete electrode 39 is used in place of the common electrode as shown in <figref idref="f0006">Figs. 6(a) and 6(b)</figref>. The electrode 39 is formed on the lower side of the deformable region so that it is exposed to the pressure generating chamber 23.

0045<figref idref="f0007">Figs. 7(a) and 7(b)</figref> show an ink jet recording head incorporating a piezoelectric vibrator unit according to the present invention. As shown in <figref idref="f0007">Figs. 7(a) and 7(b)</figref>, a vibration inducing plate 40 is layered on the common electrode 3 on the inner side of each curved portion 2 of the elastic plate 1. In addition, the vibration inducing plate 40 extends in the longitudinal direction of the pressure generating chamber 23 and on a central line on the inner side of the curved portion 2. The vibration inducing plate 40 is made of a material having a larger rigidity than the piezoelectric material of the elastic plate 1. By way of example, the vibration inducing plate 40 may be made of metal or ceramic. In addition, a vibration inducing plate may be formed on the discrete electrode alone, or in addition to the vibration inducing plate which is formed on the common electrode.

0046Advantageously, the vibration inducing plate 40 cooperates with the elastic plate 1 to provide a bimetal effect. Therefore, the deformable region is more easily bendable, and its endurance against a pressure generated at the time of applying pressure to the ink is improved by an amount corresponding to the increase of the thickness of the deformable region structure. Accordingly, pressure can be efficiently applied to the ink.

0047In the embodiments mentioned above, the curved portions 2 of the elastic plate 1 are each curved toward the pressure generating chamber 23. However, those curved portions 2 may also be outwardly curved, as shown in <figref idref="f0008">Figs. 8(a) and 8(b)</figref>. In this case, if the vibration inducing plates 40 are required, they may be formed on the side of the elastic plate 1 that faces the pressure generating chambers 23.

0048In the embodiments mentioned above, the common electrodes 3 are exposed to ink in the pressure generating chambers 23. Therefore, the common electrodes 3 are preferably covered with layers (each having a thickness, e.g., 1µm) which will not interrupt a vibration of the deformable region structure. These layers may be made of piezoelectric material, such as silicon oxide, zirconia, or the like. Where the electrodes 3 are covered with the layers, the electrodes are separated from ink and prevented from being corroded.

0049As a further refinement, the spacer 22 and the covering member 26 may be formed from ceramic material other than zirconia, such as alumina. Further, if the spacer 22, the covering member 26 and the elastic plate 1 are made of the same material, those members may be formed in a one-piece construction.

0050<figref idref="f0009">Fig. 9</figref> shows a piezoelectric vibrator unit according to another example. The piezoelectric vibrator unit includes thin plates 43 and 44 made of piezoelectric material which are curved so as to form curved portions 45 that are lengthwise arrayed at fixed pitches. Individual electrodes 46 are buried in the curved portions 45, as shown in <figref idref="f0009">Fig. 9</figref>. In addition, common electrodes 47 and 48 are layered on the exposed surfaces of the thin plates 43 and 44 made of piezoelectric material.

0051In operation, a drive signal is applied to those electrodes 46, 47 and 48 in order to generate electric fields, which are in the same direction, so that a deformable region of the curved portion 45 is deformed. Since the plates 43 and 44 made of piezoelectric material are thin, a low voltage of the drive signal may be used for generating the required electric fields.

0052<figref idref="f0009">Fig. 10</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0009">Fig. 9</figref>. With the exception of the piezoelectric vibrator unit, the ink jet recording head is similar to the examples described above.

0053The piezoelectric vibrator unit is fixed to the spacer 22 so that the curved portion 45 is located in the corresponding pressure generating chamber 23 defined by the spacer 22. Advantageously, the ink droplet can be discharged by a relatively low drive voltage.

0054<figref idref="f0010">Fig. 11</figref> is a cross-sectional view showing a piezoelectric vibrator unit 51 according to yet another example. The piezoelectric vibrator unit 51 includes fillers 50 which are placed on and along the upper side of the curved portions 2 of the piezoelectric vibrator unit 51. The piezoelectric vibrator unit 51 is similar to the one shown in <figref idref="f0001">Fig. 1(a)</figref>.

0055<figref idref="f0010">Fig. 12</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit 51 of <figref idref="f0010">Fig. 11</figref>. With the exception of the piezoelectric vibrator unit 51, the ink jet recording head is similar to the examples described above. In the ink jet recording head, the piezoelectric vibrator unit 51 is fixed to a spacer 22 so that the lower side of a curved portion 2 thereof is located in a corresponding pressure generating chamber 23 defined by the spacer 22.

0056<figref idref="f0011">Fig. 13</figref> is a cross-sectional view showing a piezoelectric vibrator unit according to yet another example. In the piezoelectric vibrator unit 54, fillers 52 are disposed on the upper side of the curved portions 2 of the elastic plate 1. The width w2 of each filler 52 is slightly shorter than the width w1 of the filler 50 shown in the <figref idref="f0010">Fig. 11</figref>. In addition, second fillers 53 are placed on a lower side of the curved portions 2 of the elastic plate 1. Each of the second fillers 53 extends so that its left end reaches a position corresponding to the right end of an adjacent filler 52 located to the left of that filler 53. Similarly, the right end of each filler 53 reaches to a position corresponding to the left end of an adjacent filler 52 located on the right side of that filler 53.

0057<figref idref="f0011">Fig. 14</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit of <figref idref="f0011">Fig. 13</figref>. With the exception of the piezoelectric vibrator unit 54, the ink jet recording head is similar to the examples described above. In the ink jet recording head, the piezoelectric vibrator unit 54 is fixed to a spacer 22 so that the lower side of a curved portion 2 is located in a corresponding pressure generating chamber 23 defined by the spacer 22. Portions of the second fillers 53 are put on corresponding surfaces of walls of the pressure generating chamber 23, the walls being defined by the spacer 22.

0058<figref idref="f0012">Fig. 15</figref> is a cross-sectional view showing a piezoelectric vibrator unit according to yet another example. The piezoelectric vibrator unit 56 includes a filler 55 which is placed on the upper side of each curved portion <i>2</i> of an elastic plate 1. The filler 55 may be configured independently of the shape of the curved portion 2.

0059<figref idref="f0012">Fig. 16</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit 56 of <figref idref="f0012">Fig. 15</figref>. With the exception of the piezoelectric vibrator unit 56, the ink jet recording head is similar to the examples described above. In the ink jet recording head, the piezoelectric vibrator unit 56 is fixed to the spacer 22 so that the lower side of a curved portion 2 is located in a corresponding pressure generating chamber 23 defined by the spacer 22.

0060<figref idref="f0013">Fig. 17</figref> is a cross-sectional view showing a piezoelectric vibrator unit according to still yet another example. In the piezoelectric vibrator unit 63 of this example, an elastic plate is formed from a couple of layered thin plates 58 and 59. However, discrete electrodes 57 are sandwiched between the thin plates 58 and 59 at the locations of corresponding curved portions 2. Common electrodes 60 and 61 are layered on the upper and lower sides (when viewed in the drawing) of the elastic plate. In addition, fillers 62, which are upwardly curved, are placed on the upper side of the curved portions 2.

0061<figref idref="f0013">Fig. 18</figref> is a partial cross-sectional view showing an ink jet recording head incorporating the piezoelectric vibrator unit 63 of <figref idref="f0013">Fig. 17</figref>. With the exception of the piezoelectric vibrator unit 63, the ink jet recording head is similar to the examples described above. In the ink jet recording head, the piezoelectric vibrator unit 63 is fixed to a spacer 22 so that a lower side of a curved portion 2 is located in a corresponding pressure generating chamber 23 defined by the spacer 22.

0062<figref idref="f0014">Fig. 19</figref> is a graph showing variations A, B and C of the magnitude of deflection of the curved portions of the piezoelectric vibrator units shown in <figref idref="f0009">Figs. 9</figref>, <figref idref="f0010">11</figref> and <figref idref="f0011">13</figref>, respectively, with respect to an initial deflection magnitude thereof. To plot the graph, the magnitude of deflection of each of the curved portions was measured under a fixed voltage of a drive signal that is applied to the curved portion of the piezoelectric vibrator unit. The thickness of the elastic plate used was 10µm. The curved portions of the elastic plate were arrayed at pitches of 150 µm along the piezoelectric vibrator unit.

0063As seen from the graph, in the piezoelectric vibrator unit of <figref idref="f0010">Fig. 11</figref> where fillers 50 are respectively placed on and along (after the shape of) the upper side of the curved portions 2, a great displacement of the curved portion is caused with its initial deflection being small.

0064<figref idref="f0015">Figs. 20(a)-20(d)</figref> shows an embodiment of a method of manufacturing a piezoelectric vibrator unit which is similar to the one shown in <figref idref="f0002">Fig. 2(d)</figref>. Initially, discrete electrodes 12 are formed on one side of a green sheet 10 in the regions thereof which will define the inwardly curved side of the curved portions of the piezoelectric vibrator unit, as shown in <figref idref="f0015">Fig. 20(a)</figref>. The discrete electrodes 12 are deformable and are made of conductive material. By way of example, the electrodes 12 may be formed as a conductive coating. The green sheet 10 is made of piezoelectric material, such as PZT. If necessary, a common electrode 11 can be provided which is also deformable and made of conductive material. The common electrode 11 is formed on the other side of the green sheet 10, as shown in <figref idref="f0015">Fig. 20(b)</figref>. In addition, green sheets 70, which are used as fillers, are formed on the discrete electrodes 12. The green sheets 70 are made of heat resistant material, e.g., ceramic, which is deformable when it is under pressure.

0065The green sheet 10 having the electrodes 11 and 12 and the green sheets 70 is inserted between a lower mold 13 and an upper mold 14, as shown in <figref idref="f0015">Fig. 20(c)</figref>. The lower mold 13 has inwardly curved portions 13a which are each configured in conformity with a curved portion of the piezoelectric vibrator unit. The upper mold 14 has outwardly curved portions 14a. Subsequently, the green sheet 10 is compressed with the upper and lower molds 14 and 13 so that the green sheet 10, having the electrodes and the green sheets 70, is molded into a shape defined by the combined molds 13 and 14, as shown in <figref idref="f0015">Fig. 20(d)</figref>.

0066After the green sheet 10 is taken out of the molds 13 and 14, or while the green sheet 10 is kept to be placed between the molds 13 and 14 under a fixed pressure, the green sheet 10 is sintered at a temperature, e.g., 1200°C, which is sufficient to transform it into a ceramic. As a result, the green sheet 10, made of piezoelectric material, and the green sheets 70, which will be used as fillers, are transformed into a ceramic so that a piezoelectric vibrator unit is manufactured.

0067In the just described embodiment, the green sheet 10 is sintered after the common electrode 11 is formed thereon. However, the common electrode may be formed on the green sheet 10 by vapor deposition, sputtering, or the like after the green sheet is sintered.

0068Although the fillers are formed by a sintering process, they also may be formed so that the curved portions 2 of the piezoelectric vibrator unit 5 are coated with a high polymer.

0069In the piezoelectric vibrator unit 5, the electrodes are provided on both sides of the elastic plate. When the piezoelectric vibrator unit is incorporated into the recording head, the common electrode formed on the reverse side of the elastic plate is covered with the spacer of the recording head. Therefore, it is difficult to connect the electrode to an external drive circuit.

0070An example of a spacer which can solve the above-mentioned problem is shown in <figref idref="f0016">Fig. 21</figref>. According to the present invention, a conductive layer 72 is formed on the surface of the spacer 22 to which piezoelectric vibrator units will be fixed. The conductive layer 72 extends through a region of the spacer surface which contacts the common electrodes 75 of the piezoelectric vibrator unit 74 and a region of the spacer surface, which is free from a vibration of the piezoelectric vibrator units 74 (the central region of the spacer surface where two series of pressure generating chambers 23 are confronted with each other in this embodiment).

0071When the piezoelectric vibrator units 74 are set on the spacer 22 with the conductive layer 72 such that the curved portions 2 of the piezoelectric vibrator units 74 are positioned within the pressure generating chambers 23, as shown in <figref idref="f0018">Fig. 23</figref>, the piezoelectric vibrator units 74 are formed having corresponding widths, W3 and W3'. These dimensions ensure that a gap 73 is produced between the vibrator units 74. In addition, the common electrode 75 is formed to reach the conductive layer 72 of the spacer 22 so that the later has an exposed portion 72a, as shown in <figref idref="f0018">Fig. 23</figref>. To connect the common electrodes of the piezoelectric vibrator units, the exposed portion 72a of the conductive layer 72 is connected to an external drive circuit by a flexible cable, for example.

0072In the embodiment described above, to expose the conductive layer of the spacer, two piezoelectric vibrator units are separately arranged. However, a single piezoelectric vibrator unit may be applied to the two series of pressure generating chambers of the spacer, as a matter of course. In this case, which is shown in <figref idref="f0019">Fig. 24</figref>, a piezoelectric vibrator unit 76 is cut out to form a cutout portion 78 which faces a conductive layer 77 of the spacer 22. By including the cutout portion 78, the conductive layer 77 formed on the spacer may be exposed through the cutout portion 78 even when the piezoelectric vibrator unit is layered over the spacer.

0073The piezoelectric vibrator unit is sintered, and then fixed to the spacer 22 in the above-mentioned embodiments depicted in <figref idref="f0016 f0017 f0018 f0019">Figs. 21-24</figref>. Advantageously, the spacer 22 may be used for a molding member in order to form the deflecting member of the piezoelectric vibrator unit of the present invention. The use of the spacer in this fashion is shown in <figref idref="f0020">Figs. 25(a)-(c)</figref>.

0074In particular, a common electrode 11 may be formed on one side of a green sheet 10 and discrete electrodes 12 formed on the other side thereof, as shown in <figref idref="f0020">Fig. 25(a)</figref>. The green sheet 10 is made of piezoelectric material, for example, PZT. The common electrode 11 is deformable and made of conductive material, such as a conductive coating.

0075The green sheet 10 having the electrodes 11 and 12 is positioned so that the discrete electrodes 12 on the green sheet 10 lie above the pressure generating chambers 23 of the spacer 22, respectively. An upper mold 14 is provided which has outwardly curved portions 14a arrayed at the same pitches as the pressure generating chambers 23, as shown in <figref idref="f0020">Fig. 25(b)</figref>. The spacer 22 is used as a lower mold.

0076The upper mold 14 is pressed against the green sheet 10 and the lower mold 22 by applying a fixed pressure to the upper mold 14, as shown in <figref idref="f0020">Fig. 25(c)</figref>. As a result, the green sheet 10 and the electrodes 11 and 12 are configured as defined by the shape of the outward curved portions 14a of the upper mold 14.

0077After the upper mold 14 is detached from the green sheet 10, or while the upper mold 14 is kept to be pressed, the green sheet 10 is then sintered at a temperature, e.g., 1200°C, which is sufficient to transform it into a ceramic. Advantageously, the piezoelectric vibrator unit is bonded to the spacer 22 by the process of sintering, without using adhesive.

0078A displacement of the vibrating plate, which ensues from the expansion and contraction of the vibrating plate, is easily converted into a deflection displacement which is made in conformity with a shape of the curved portion. Therefore, even if the piezoelectric vibrator unit is applied to an ink jet recording head of high density type in which it is required to reduce the volume of each pressure generating chamber, the vibrating plate can be deflected to such an extent as to discharge an ink droplet whose ink amount is required for the printing, by using a high drive voltage.

0079<figref idref="f0021">Figs. 26</figref>, <figref idref="f0022">27(a) and 27(b)</figref> show an ink jet recording head in which another piezolectric vibrator unit is used. In this example, no curved portions are formed in the elastically deformable plate. Further, not only one vibration inducing plate as shown in <figref idref="f0007 f0008">Figs. 7(a)-8(b)</figref>, but also first and second vibration inducing plates 40a and 40b are layered on the electrode 3 and 4. The first vibration inducing plates 40a are formed on the surface of the discrete electrodes 4 and the second vibration inducing plates 40b are formed on the surface of the common electrode 3. A lead-out electrode 40a', which is continuous to the first vibration inducing plates 40a, is extended to beyond the pressure generating chamber 23.

0080In the recording head thus constructed, a common electrode 4 is formed, by sputtering or vapor deposition, in a region of one of the major surfaces of a green sheet made of piezoelectric material, e.g., PZT, which will be formed into a vibrating plate by sintering, the region facing the pressure generating chambers 23. Then, second vibration inducing plates 40b are formed on the surface of the common electrode 4 such that a gap is created in a region facing the pressure generating chambers 23, and the second vibration inducing plates 40b are respectively centered at the partitioning walls 22a of the spacer 22 partitioning the pressure generating chamber 23. In this case, thick-film plating, sputtering, a thick-film printing method, or the like may be used for forming the second vibration inducing plates 40b.

0081The structure formed in the above-mentioned process is bonded to one of the major surfaces of the spacer 22, and the covering member 26 is bonded to the other major surface of the spacer 22. In this state, the discrete electrodes 4 and the first vibration inducing plates 40a are not yet formed on the surface of the elastic plate 1. Therefore, it never happens that the elastic plate 1 subsides into the pressure generating chambers 23 and is deflected. Accordingly, pressure is applied to the elastic plate 1 uniformly over its entire surface, and the respective layers are reliably bonded together.

0082The structure is sintered to complete a semi-product of a piezolectric vibrator unit not having the discrete electrodes 4 and the first vibration inducing plates 40a which will be formed on the upper surface of the elastic plate 1. Then, discrete electrodes 4 are formed on the surface of the semi-product so as to face the pressure generating chambers 23 by sputtering or vapor depositing conductive material. Metal is vapor deposited over the surface of the structure, and first vibration inducing plates 40a of ceramic are formed thereon by a thick-film printing method.

0083<figref idref="f0023">Figs. 28</figref> shows an ink jet recording head in which a piezolectric vibrator unit similar to the embodiment in <figref idref="f0022">Figs. 27(a) and 27(b)</figref> is used. In the embodiment in <figref idref="f0022">Figs. 27(a) and 27(b)</figref>, the second vibration inducing plate 40b is formed of a continuous body put on the related partitioning wall 22a of the spacer 22. However, in <figref idref="f0023">Fig. 28</figref>, the second vibration inducing plate 40b has two separate bodies 40b' and 40b'.