JP2007331199A - Inkjet head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head having a structure that a piezoelectric body can be adequately driven. <P>SOLUTION: This inkjet head comprises an ejection nozzle 111 for ejecting a liquid, a discrete liquid chamber 106 communicating with the ejection nozzle 111, a diaphragm 107 contacting the discrete liquid chamber 106, and a piezoelectric element provided on the diaphragm 107. The piezoelectric element includes a lower electrode 102 provided on the diaphragm 107, a piezoelectric thin film 103 provided on the lower electrode 102 to have a shape extended in the longitudinal direction, and an upper electrode 104 provided on the piezoelectric thin film 103 in the longitudinal direction. The upper electrode 104 has a shape that the thickness in the width direction intersecting the longitudinal direction is varied stepwise. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention has an ejection port for ejecting droplets, an individual liquid chamber communicating with the ejection port, and a diaphragm provided in contact with the individual liquid chamber, and ejects droplets from the ejection port on the diaphragm. The present invention relates to an ink jet head provided with a piezoelectric element that deforms a vibration plate in order to make the diaphragm.

  A conventionally known inkjet head includes a flow path substrate provided with a liquid flow path, an individual liquid chamber provided on the first surface of the flow path substrate, and a second flow path substrate from the individual liquid chamber. And a through passage penetrating the surface. The ink jet head further includes an orifice plate having a discharge port that is bonded to the second surface of the flow path substrate and communicates with the through path.

  In order to discharge ink droplets, it is necessary to pressurize the individual liquid chambers. The pressure generating means is a bubble type that discharges liquid droplets by firing liquid with a heating element installed in the individual liquid chamber, and the diaphragm that forms a part of the individual liquid chamber is deformed by a piezoelectric element. In general, a piezo-type device that forms a droplet by forming a droplet is generally used. Alternatively, an electrostatic type that discharges droplets by deforming a diaphragm with electrostatic force is also known.

  In such an ink jet head, with the recent demand for higher definition of image formation, higher integration is performed in which a large number of pressure source sources such as individual liquid chambers of a flow path substrate and piezoelectric elements are arranged. ing. In order to meet these demands, in a piezo-type ink jet head, for example, an electrode and a piezoelectric body are formed on the entire surface of the diaphragm by a film formation technique, and an upper electrode and a piezoelectric body corresponding to an individual liquid chamber using a photolithography technique. The one which processes is proposed. A high-density ink jet head is realized by using a film forming technique and a photolithography technique. Further, by using a Si substrate or a metal member for the flow path substrate or the orifice plate, it is possible to form a highly accurate flow path or discharge port.

  Generally, the upper electrode and the piezoelectric body are processed corresponding to each individual liquid chamber. As the material of the upper electrode, Pt, Cr, or the like is often used from the viewpoints of conductivity and corrosion, film adhesion, and the like.

The background art described above is disclosed in Patent Document 1.
Japanese Patent Application Laid-Open No. 2000-141643

  Power supply to the upper electrode is generally performed via a flexible cable or the like from a region corresponding to a location away from the upper portion of the individual liquid chamber, that is, a lead electrode that is one end in the longitudinal direction of the upper electrode. However, in the longitudinal direction of the upper electrode, when a driving voltage is supplied, a delay in voltage application occurs according to the distance from the connection portion such as a flexible cable, and the displacement behavior in the longitudinal direction of the piezoelectric body is shifted. End up.

  Further, with respect to the displacement of the piezoelectric body, the upper electrode on the upper part can hinder the displacement of the piezoelectric body, and therefore it is desirable that the upper electrode has a configuration that does not hinder the displacement as much as possible. Furthermore, the upper electrode is required to have a configuration that can withstand long-time driving.

  SUMMARY An advantage of some aspects of the invention is that it provides an inkjet head having a configuration capable of driving a piezoelectric body better.

  In order to achieve the above object, an inkjet head of the present invention is provided with a discharge port for discharging a liquid, an individual liquid chamber communicating with the discharge port, a diaphragm in contact with the individual liquid chamber, and the diaphragm. A piezoelectric element that imparts energy for discharging the liquid from the discharge port to the liquid in the individual liquid chamber, wherein the piezoelectric element includes a lower electrode provided on a diaphragm; A piezoelectric thin film having a shape extending on the lower electrode and extending in the longitudinal direction; and an upper electrode provided on the piezoelectric thin film along the longitudinal direction. It has a shape in which the thickness in the width direction intersecting with the direction changes stepwise.

  According to the present invention, it is possible to provide an ink jet head having a configuration capable of driving the piezoelectric body more satisfactorily.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a perspective view schematically showing an ink jet head according to the first embodiment of the present invention.

  As shown in FIG. 1, the ink jet head of this embodiment has an SOI (Silicon On Insulator) wafer 101 in which a plurality of individual liquid chambers 106 are formed. On the surface of the SOI wafer 101 where the silicon oxide film 105 and the silicon single crystal film 107 (see FIG. 2) are formed, the lower electrode 102 is formed over almost the entire surface. Further, a piezoelectric thin film 103 having a shape extending in the longitudinal direction along the individual liquid chamber 106 is provided at a position facing each individual liquid chamber 106 on the lower electrode 102. On each piezoelectric thin film 103, an upper electrode 104 including an upper electrode lower layer portion 104a and an upper electrode upper layer portion 104b is provided. The lower electrode 102, the piezoelectric thin film 103, and the upper electrode 104 constitute a piezoelectric element. On the other surface of the SOI wafer 101, an orifice plate 110 in which a discharge port 111 is formed is provided.

  According to the ink jet head of this embodiment configured as described above, when a voltage is applied between the lower electrode 102 and the upper electrode 104, the piezoelectric thin film 103 is deformed, and along with the deformation, the silicon single crystal film 107 is deformed. The diaphragm made of is deformed. Then, a liquid such as ink stored in the individual liquid chamber 106 in contact with the vibration plate is pressurized and discharged as a droplet from the discharge port 111 of the orifice plate 110.

  Next, a method for manufacturing the ink jet head of the present embodiment will be described with reference to FIGS.

  As shown in FIG. 2A, an adhesion layer functioning as the lower electrode 102 is formed on an SOI wafer 101 having a thickness of 200 μm formed by forming a silicon oxide film 105 and a silicon single crystal film 107 on a silicon substrate. . This adhesion layer is formed by forming a Ti film with a thickness of 10 nm and forming a Pt film thereon with a thickness of 200 nm.

Subsequently, as shown in FIG. 2B, a piezoelectric thin film 103 is formed on the lower electrode 102. In forming the piezoelectric thin film 103, first, the SOI wafer 101 is put in a sputtering apparatus, and Pb (Zr, Ti) O ₃ perovskite oxide (hereinafter referred to as “PZT”) composed of lead, titanium, and zirconium is used. .) Is formed on the lower electrode 102 to a thickness of 3 μm by sputtering. Thereafter, the SOI wafer 101 is taken out from the sputtering apparatus and baked at 700 ° C. in an oxygen atmosphere to crystallize the PZT film. Thereby, the piezoelectric thin film 103 is formed. In order to improve the piezoelectricity of the piezoelectric thin film 103, the composition of the PZT thin film is made to be Pb (Zr _0.52 Ti _0.48 ) O ₃ . The composition of the PZT film is not necessarily limited to the above composition, and may be another composition. Further, the PZT film thickness is not limited to 3 μm.

  Next, as illustrated in FIG. 2C, the upper electrode 104 is formed on the piezoelectric thin film 103. First, a Pt film having a thickness of 30 nm, which is a part of the upper electrode 104 and serves as the upper electrode lower layer portion 104a, is formed on the piezoelectric thin film 103. A Ti layer may be provided on the piezoelectric thin film 103 as an adhesion layer. Further, an Au film that becomes the upper electrode upper layer portion 104b that is also a part of the upper electrode 104 is formed on the Pt film. Note that Au is one of noble metals having higher conductivity than Pt and having higher conductivity among metals. Au, like Pt, is excellent in voltage resistance and is a material that is not easily corroded. In the present embodiment, the thickness of the Au film is 400 nm.

  Thereafter, the upper electrode 104 and the piezoelectric thin film 103 are processed by etching. Details thereof will be described with reference to FIG.

First, after applying a photoresist on the upper electrode upper layer portion 104b, this is patterned, and the Au film is wet-etched with an iodine potassium iodide (KI + I ₂ ) solution or the like. As a result, as shown in FIG. 3A, the upper electrode upper layer portion 104b having a width of 10 μm and a length of 6 mm in the longitudinal direction shown in FIG. 1 was formed. The etching of the Au film is not limited to wet etching, and may be performed by dry etching by RIE.

  Next, after applying a resist again so as to cover the upper electrode upper layer portion 104b, the patterning is performed and the Pt film is etched. As a result, as shown in FIG. 3B, an upper electrode lower layer portion 104a having a width of 70 μm was formed.

  The upper electrode 104 including the upper electrode upper layer portion 104b made of Au having a thickness of 400 nm and a width of 10 μm and the upper electrode lower layer portion 104a made of Pt having a thickness of 30 nm and a width of 70 μm was formed by the above-described two etching steps.

  Note that the thickness, width and length of the Pt film and Au film are not limited to the above dimensions. The materials of the upper electrode lower layer portion 104a and the upper electrode upper layer portion 104b are not limited to the above materials. For example, as the material of the upper electrode lower layer portion 104a, Cr, Zr, or the like that has voltage resistance and excellent film adhesion may be used. Further, as the material of the upper electrode upper layer portion 104b, Cu, Ag, Al, or the like having good conductivity like Au may be used.

Thereafter, patterning is again performed with a resist, and the piezoelectric thin film 103 is etched (FIG. 3C). In this embodiment, dry etching is performed using a mixed gas of Cl ₂ and CF ₄ . The mask for etching the piezoelectric thin film 103 is not limited to the resist described above, and the upper electrode lower layer 104b and the piezoelectric thin film 103 are collectively etched using the pattern used for etching the upper electrode lower layer 104b as it is. It doesn't matter.

  Thereafter, as shown in FIG. 3D, etching is performed from the back surface of the SOI wafer 101 using the silicon oxide film 105 of the SOI wafer 101 as an etching stop layer, thereby forming an individual liquid chamber 106 in the SOI wafer 101. For the etching, an ICP (Inductively Coupled Plasma) etching apparatus known as an apparatus for deepening Si is used. Note that the Si single crystal film 107 of the SOI wafer 101 functions as a vibration plate that applies a pressure for discharging droplets to the liquid filled in the individual liquid chamber 106.

  Finally, when the orifice plate 110 in which the Si substrate is processed by ICP and the discharge port 111 is formed is bonded to the back surface of the SOI wafer 101, the ink jet head shown in FIG. 1 is completed.

  In this embodiment, an SOI wafer is used as a member for forming the individual liquid chamber 106 and the vibration plate (Si single crystal film) 107, and an Si substrate is used as the orifice plate 110. However, the present invention is not limited to this, and other wafers are used. Alternatively, the substrate may be used for other manufacturing methods.

  In general, application of voltage to each piezoelectric thin film is often performed from one end in the longitudinal direction of the upper electrode through a flexible cable or a probe. When the individual liquid chamber is long in the longitudinal direction and the upper electrode is long in the longitudinal direction, a delay in voltage application to the piezoelectric thin film occurs depending on the distance from the connection portion of the flexible cable and the probe contact, and the length of the piezoelectric thin film Differences occur in the displacement behavior in the direction. It may be possible to eliminate such inconvenience by increasing the conductivity by forming the upper electrode thick, but if the entire upper electrode is formed thick, it will hinder the displacement of the piezoelectric thin film, and further, when driving the piezoelectric thin film There is a possibility that the upper electrode peels off from the piezoelectric thin film.

  On the other hand, in this embodiment, the upper electrode 104 is configured to have the upper electrode upper layer portion 104b at the center in the width direction. Thereby, the upper electrode 104 has a shape whose thickness changes stepwise in the width direction. More specifically, the upper electrode 104 in this embodiment has a thickness of 430 nm at the central portion of the total width of 70 μm and a thickness of 430 nm at both sides thereof. Therefore, the upper electrode 104 of this embodiment has a configuration in which only the central portion in the width direction is thick and most of the other portions are thin.

  As described above, since the upper electrode 104 of the present embodiment is formed with a thick central portion, the conductivity is improved as compared with the case where the upper electrode is formed thin overall. Therefore, it is possible to suppress a delay in voltage application to the piezoelectric thin film 103 according to the distance from the connection portion of the flexible cable in the longitudinal direction. Further, since the upper electrode upper layer portion 104b that forms the center portion of the upper electrode 104 is formed of an Au film having high conductivity, the delay of voltage application to the piezoelectric thin film in the longitudinal direction of the upper electrode 104 is further reduced. ing.

  In addition, since the upper electrode 104 is mostly thin, it is difficult to hinder the displacement of the piezoelectric thin film 103. Further, since the upper electrode 104 is thin in most parts, it is easily deformed along with the deformation of the piezoelectric thin film 103, and the possibility of peeling when the piezoelectric thin film 103 is driven is low.

(Second Embodiment)
FIG. 4 is a perspective view schematically showing an ink jet head according to the second embodiment of the present invention.

  As shown in FIG. 4, the ink jet head of this embodiment has a Si substrate 201 on which a plurality of individual liquid chambers 202 are formed. A vibration plate 205 is provided on the Si substrate 201 so as to be in contact with the individual liquid chamber 202. A lower electrode 206 is formed on the diaphragm 205 over almost the entire surface. Furthermore, a piezoelectric thin film 207 having a shape extending in the longitudinal direction along the individual liquid chamber 202 is provided at a position facing each individual liquid chamber 202 on the lower electrode 206. On each piezoelectric thin film 207, there is provided an upper electrode 208 composed of a thin upper electrode both ends 208a and a thick upper electrode central portion 208b. On the other surface of the Si substrate 201, an orifice plate 210 in which a discharge port 211 is formed is provided.

  Next, a method for manufacturing the ink jet head of this embodiment will be described with reference to FIGS.

  First, as shown in FIG. 5, a flow path such as an individual liquid chamber 202 is formed on a Si substrate 201 having a thickness of 300 μm. First, an oxide film having a thickness of 1 μm is formed on the surface of the Si substrate 201 as an etching mask for forming the individual liquid chamber 202. Thereafter, the individual liquid chamber 202 having a depth of 100 μm is formed by ICP etching using an ICP (Inductively Coupled Plasma) etching apparatus. The length of the individual liquid chamber 202 in the longitudinal direction is 4 mm.

  Next, after forming a pattern etching mask for forming the nozzle communication port 203 and the common liquid chamber 204 on the back surface of the Si substrate 201, the nozzle communication port 203 and the common liquid chamber having a depth of 100 μm are formed using an ICP etching apparatus. 204 is formed.

  After processing the Si substrate 201 in this way, a diaphragm 205 is formed on the surface of the Si substrate 201 so as to cover the individual liquid chamber 202. In this embodiment, SD2 glass (registered trademark of HOYA) is anodically bonded as the diaphragm 205 and then polished to form a diaphragm 205 having a thickness of 5 μm.

Next, Pt having a thickness of 300 nm is formed as a lower electrode 206 on the vibration plate 205 by a film forming method, and a piezoelectric thin film 207 is further formed thereon. In forming the piezoelectric thin film 207, first, the Si substrate 201 is placed in a sputtering apparatus, and Pb (Zr, Ti) O ₃ perovskite oxide (PZT) composed of lead, titanium, and zirconium is sputtered. A thickness of 3 μm is formed on the lower electrode 206. Thereafter, the Si substrate 201 is taken out from the sputtering apparatus and baked at 700 ° C. in an oxygen atmosphere to crystallize the PZT film. Thereby, the piezoelectric thin film 207 is formed. In order to improve the piezoelectricity of the piezoelectric thin film 207, the composition of the PZT thin film is made to be Pb (Zr _0.52 Ti _0.48 ) O ₃ . The composition of the PZT film is not necessarily limited to the above composition, and may be another composition. Further, the PZT film thickness is not limited to 3 μm.

  Next, a 300 nm-thick Pt film to be the upper electrode 208 is formed on the piezoelectric thin film 207. Thereafter, the piezoelectric thin film 207 and the upper electrode 208 are processed by etching so as to correspond to the individual liquid chambers 202. The details will be described with reference to FIG. 6 in which the individual liquid chamber 202 is viewed from the cross-sectional direction.

First, after applying a photoresist on the Pt film 208, this is patterned, and a region other than the part corresponding to the individual liquid chamber 202 of the Pt film 208 is etched with a gas such as BCl ₃ (FIG. 6). (A)). At that time, not all the film thickness of the Pt film 208 is etched, but so-called half-etching is performed so as to leave a certain film thickness. The etching rate of the Pt film 208 is relatively stable, and the etching amount can be controlled by managing the etching time. In this embodiment, about 300 nm of the 300 nm thick Pt film 208 is etched, and about 50 nm is left on the piezoelectric thin film 207.

In addition to dry etching using BCl ₃ , the Pt film 208 can be processed by Ar milling.

Next, as shown in FIG. 6B, the resist is patterned again so as to cover the region including the portion corresponding to the individual liquid chamber 202 of the Pt film 208, and the other region of the Pt film 208 and its region The lower piezoelectric thin film 207 is etched and removed at once. In this embodiment, dry etching is performed using a mixed gas of Cl ₂ and CF ₄ . According to this dry etching, first, the Pt film 208 left to a thickness of 50 nm is etched, and then the PZT film as the piezoelectric thin film 107 is etched.

  Thereafter, the resist is removed to form an upper electrode 208 having a relatively thin upper electrode end portion 208a having a thickness of 50 nm and a relatively thick upper electrode central portion 208b having a thickness of 300 nm (FIG. 6C). )).

  In this embodiment, the width of the upper electrode end portion 208a is 100 μm, and the width of the upper electrode central portion 208b is 70 μm.

  Finally, the orifice plate 210 in which the discharge port 211 is formed by processing the Si wafer by ICP on the back surface of the Si substrate 201, or the orifice plate 210 in which the discharge port 211 is formed by punching on a stainless steel sheet plate or the like is attached. Match. Thereby, the inkjet head shown in FIG. 4 is completed.

  In this embodiment, a Pt film is used as the upper electrode 208, but it is not necessarily Pt, and an Au film, a Cr film, or the like may be used.

  Also in this embodiment, as in the first embodiment, since the upper electrode 208 is formed thick at the center, the conductivity is improved as compared with the case where the upper electrode is formed thin overall. Yes. Therefore, it is possible to suppress a delay in voltage application to the piezoelectric thin film 207 in accordance with the distance from the connection portion of the flexible cable in the longitudinal direction. Further, the upper electrode both ends 208a of the upper electrode 208 are thinner than the upper electrode central portion 208b. Therefore, when the piezoelectric thin film 107 is driven, particularly when it is necessary to continuously drive for a long time, the upper electrode 208 is damaged, or both end portions in the width direction of the upper electrode 208 are peeled off from the piezoelectric thin film 207. Can be prevented.

1 is a perspective view schematically showing an ink jet head according to a first embodiment of the present invention. It is a figure which shows the manufacturing method of the inkjet head shown in FIG. It is a figure which shows the manufacturing method of the inkjet head shown in FIG. It is a perspective view which shows typically the inkjet head which concerns on the 2nd Embodiment of this invention. It is a figure which shows the manufacturing method of the inkjet head shown in FIG. It is a figure which shows the manufacturing method of the inkjet head shown in FIG.

Explanation of symbols

102, 206 Lower electrode 103, 207 Piezoelectric thin film 104, 208 Upper electrode 106, 202 Individual liquid chamber 107, 205 Diaphragm 111, 211 Discharge port

Claims (6)

An ejection port for ejecting liquid, an individual liquid chamber communicating with the ejection port, a diaphragm in contact with the individual liquid chamber, and an energy for ejecting the liquid from the ejection port are provided on the diaphragm. In an inkjet head having a piezoelectric element applied to the liquid in the individual liquid chamber,
The piezoelectric element includes a lower electrode provided on the diaphragm, a piezoelectric thin film provided on the lower electrode and having a shape extending in a longitudinal direction, and the piezoelectric thin film along the longitudinal direction. An upper electrode provided,
The ink jet head according to claim 1, wherein the upper electrode has a shape whose thickness in the width direction intersecting with the longitudinal direction changes stepwise.   The inkjet head according to claim 1, wherein the upper electrode has a thickness at both ends in the width direction smaller than a thickness at a center in the width direction.   The inkjet head according to claim 1, wherein the upper electrode is composed of a plurality of layers made of different materials. The upper electrode is composed of two layers of an upper electrode lower layer portion formed on the piezoelectric thin film and an upper electrode upper layer portion formed on the upper electrode lower layer portion,
The inkjet head according to claim 3, wherein the conductivity of the material constituting the upper electrode upper layer portion is higher than the conductivity of the material constituting the upper electrode lower layer portion.   The inkjet head according to claim 2, wherein a part of the upper electrode is processed by dry etching. The diaphragm is deformed by deformation of the piezoelectric thin film that occurs when a voltage is applied between the lower electrode and the upper electrode, thereby applying the energy to the liquid in the individual liquid chamber. The ink jet head according to claim 1, wherein the liquid in the liquid chamber is caused to fly from the discharge port.

Images