Piezoelectric element, manufacturing method for the same, liquid discharge head, and liquid discharge device

Abstract

To provide a piezoelectric element having excellent coating properties of an insulating film covering the piezoelectric element.SOLUTION: A piezoelectric element has a lower electrode, a piezoelectric film, and an upper electrode on a first surface of a substrate in this order, and a dielectric film covering at least the side of the piezoelectric film. The side of the piezoelectric film has multiple steps composed of two surfaces with different angles of inclination relative to the first surface. The angle formed by the two surfaces in the steps is 90° or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a piezoelectric element, a method for manufacturing a piezoelectric element, a liquid ejection head, and a liquid ejection apparatus. [Background technology]

[0002] Piezoelectric bodies, whose shape changes when an electric field is applied, are used in various industrial products as a means for moving or vibrating objects minutely and accurately. For example, they are used in small speakers, hard disk drives, printers (liquid ejection devices), etc. Among them, some printers use piezoelectric elements as elements that generate energy for ejecting droplets from a liquid ejection head. In such liquid ejection heads, a piezoelectric element is formed by electrodes (upper electrode, lower electrode) formed so as to sandwich a piezoelectric film from above and below. The piezoelectric element is driven by applying an electric field to the electrodes of this piezoelectric element to eject droplets. At this time, the voltage required to sufficiently displace the piezoelectric element is several tens of volts, and a relatively high voltage must be applied as a semiconductor device. For this reason, piezoelectric elements generally used in liquid ejection heads are covered almost entirely with an insulating film with good dielectric strength. However, such an insulating film may peel off during the manufacturing process after the process of forming the insulating film or during driving of the piezoelectric layer. Therefore, Patent Document 1 proposes a method of patterning the piezoelectric layer by wet etching to make the side surfaces of the piezoelectric layer uneven, thereby increasing the contact area between the piezoelectric layer and the organic insulating layer and thereby suppressing peeling of the insulating film. In the method described in Patent Document 1, a piezoelectric film is formed by stacking a plurality of precursor layers by repeating the formation of a precursor layer and the crystallization of the precursor layer by a sol-gel method a plurality of times. When this piezoelectric film is wet-etched, unevenness is formed on the side surface of the piezoelectric layer due to the difference in etching rate caused by the difference in composition ratio in each precursor layer. In the method described in Patent Document 1, the recessed portion on the side surface is a groove portion formed perpendicular to the film thickness direction of the piezoelectric layer and parallel to the stacking interface of the precursor layers. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-174022 A Summary of the Invention [Problem to be solved by the invention]

[0004] As in the piezoelectric film shape described in Patent Document 1, multiple grooves formed on the side wall of the piezoelectric layer can increase the surface area, but on the other hand, this can cause a decrease in the coverage of the insulating film in the subsequent insulating film formation process. During the inventors' studies, it was found that voids where no insulating film was formed were formed at the bottom of the grooves on the side wall of the piezoelectric layer, which could cause insulation peeling or cracks.

[0005] An object of the present invention is to provide a piezoelectric element having an excellent covering property of an insulating film that covers the piezoelectric element. [Means for solving the problem]

[0006] The present invention relates to A lower electrode, a piezoelectric film, and an upper electrode are provided on a first surface of a substrate in this order; Furthermore, the piezoelectric element has an insulating film covering at least a side surface of the piezoelectric film, the side surface of the piezoelectric film has a plurality of step portions each having two surfaces with different inclination angles relative to the first surface; The angle between the two surfaces at the step is 90° or more. Effect of the Invention

[0007] According to the present invention, it is possible to provide a piezoelectric element having excellent coverage by an insulating film that covers the piezoelectric element. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a schematic diagram for explaining a structure of an example of a piezoelectric element according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram for explaining a structure of an example of a piezoelectric element according to an embodiment of the present invention. [Diagram 3] 5A and 5B are schematic diagrams illustrating a structure of an example of a piezoelectric element of a comparative example. [Figure 4(a)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(b)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(c)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(d)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(e)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(f)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(g)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(h)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 4(i)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present invention. [Figure 5(a)] 2A to 2C are schematic diagrams illustrating a method for manufacturing the piezoelectric element of Example 1. [Figure 5(b)] 2A to 2C are schematic diagrams illustrating a method for manufacturing the piezoelectric element of Example 1. [Figure 5(c)] 2A to 2C are schematic diagrams illustrating a method for manufacturing the piezoelectric element of Example 1. [Figure 6] 5 is a schematic diagram for explaining the structure of a piezoelectric element according to Example 2. FIG. [Figure 7(a)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to a second embodiment. [Figure 7(b)] 5A to 5C are schematic diagrams illustrating a method for manufacturing a piezoelectric element according to a second embodiment. [Figure 8] 1A and 1B are diagrams illustrating a liquid ejection device and a liquid ejection head according to an embodiment of the present invention. [Figure 9] FIG. 2 is a diagram showing an element substrate according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Examples of the present invention will be described below with reference to the drawings. The examples described below are intended to show examples of the embodiments of the present invention, and are not intended to limit the scope of the present invention. The dimensions, shapes, numbers, materials, etc. of various members in the following examples can be appropriately changed within the scope of the present invention unless otherwise specified.

[0010] The present invention suppresses peeling and destruction of the piezoelectric element, particularly the insulating film covering the sidewall, by forming the sidewall of the piezoelectric element in a stepped shape. Here, the piezoelectric element includes the piezoelectric film and the lower electrode and upper electrode formed in the direction perpendicular to the film surface. For simplicity, a piezoelectric element is also called a piezoelectric element when an insulating film and an upper electrode pad, a sealing film, and a sealing film recess are provided on the piezoelectric element. In the following description, the long side direction (longitudinal direction) of the piezoelectric element is the X direction, the short side direction (short side direction) is the Y direction, and the thickness direction (film thickness direction) is the Z direction. The X direction, Y direction, and Z direction are mutually perpendicular.

[0011] FIG. 1(a) shows a top view of a piezoelectric element 108 in the embodiment, and FIG. 1(b) shows a cross-sectional view taken along line A-A' in FIG. 1(a). The piezoelectric element 108 has, on a first surface of a substrate 106, a lower electrode 202, a piezoelectric film 110 formed on the upper surface of the lower electrode 202, and an upper electrode 111 formed on the upper surface of the piezoelectric film 110, in this order. The piezoelectric element 108 also has an insulating film 210 that covers a portion of the upper surface of the lower electrode 202 where the piezoelectric film 110 is not formed, a portion of the upper surface of the piezoelectric film 110 where the upper electrode 111 is not formed, the upper surface of the upper electrode 111, and the side surface of the piezoelectric film 110. The piezoelectric element 108 is provided with a signal wiring 200 for supplying an operating signal, and a common wiring 201 for applying a common potential. The piezoelectric element 10 An upper electrode pad 114 is disposed at the X-direction end of the piezoelectric element 108, and is electrically connected to the signal wiring 200 and the upper electrode 111 of the piezoelectric element 108. An extension region of the lower electrode 202 is located near the end of the piezoelectric element 108 on the opposite side in the X-direction to the upper electrode pad 114, and a lower electrode pad 115 is disposed on the upper layer thereof. The lower electrode pad 115 is electrically connected to the common wiring 201 and the lower electrode 202.

[0012] The substrate 106 is selected from silicon nitride film, silicon, metal, heat-resistant glass, etc., depending on the required mechanical properties, reliability, etc. In this embodiment, a silicon wafer is used as the substrate 106, and a silicon oxide film is formed as an insulating film 209 on the surface of the substrate 106 on which the lower electrode 202 is formed.

[0013] The lower electrode 202 may be exposed to high temperatures of several hundred degrees Celsius in the process after its formation, and in such a case, it is preferable to use a material with a high melting temperature. Examples include copper, platinum, gold, chromium, cobalt, titanium, and alloys thereof. In addition, when the piezoelectric film 110 is formed in contact with the upper surface of the lower electrode 202, the lower electrode 202 may also serve as a film that controls the crystal orientation of the piezoelectric film. In that case, a material having an appropriate crystal structure is appropriately selected. For example, when the material of the piezoelectric film 110 is lead zirconate titanate, it is preferable to use platinum for the lower electrode 202 as a crystal orientation control film.

[0014] In this embodiment, lead zirconate titanate was used as the piezoelectric film 110 because it is easy to obtain a large amount of displacement. However, other piezoelectric materials such as barium titanate, lead titanate, lead metaniobate, bismuth titanate, zinc oxide, aluminum nitride, potassium sodium niobate, etc. may also be used. In this embodiment, the piezoelectric film 110 is formed by stacking a plurality of piezoelectric layers 100.

[0015] 1(b), the width of the piezoelectric film 110 in a direction (X direction) perpendicular to the film thickness direction (Z direction) increases monotonically from the upper electrode 111 toward the lower electrode 202 (in the -Z direction). As shown in FIG. 2, the side surface of the piezoelectric film 110 has a stepped shape having a plurality of step portions 116, 117 each made of two surfaces (first side surface 102, second side surface 103) having different inclination angles with respect to a surface (first surface (upper surface) of the substrate 106) parallel to the extension direction (XY direction) of the piezoelectric layer 100. In the step portions 116, 117, the angle θ formed by the first side surface 102 and the second side surface 103 is 90° or more.

[0016] The inclination angle of the second side surface 103 with respect to the first surface (upper surface) of the base material 106 is smaller than the inclination angle of the first side surface 102 with respect to the first surface (upper surface) of the base material 106 .

[0017] The step 116 is a concave step formed by the second side surface 103 and the first side surface 102 connected to the upper end of the second side surface 103. The step 117 is a convex step formed by the first side surface 102 and the second side surface 103 connected to the upper end of the first side surface 102. The step-like shape of the side surface of the piezoelectric film 110 is formed by alternating concave step portions 116 and convex step portions 117. The angle of the concave step portion 116 and the angle of the convex step portion 117 are both 90° or more, and as a result, the width of the piezoelectric film 110 in the X direction continues to increase from the upper electrode 111 toward the lower electrode 202. Each of the multiple steps 101 constituting the step-like side wall corresponds to each of the multiple piezoelectric layers 100 constituting the piezoelectric film 110. The side wall of one step 101 is composed of the first side surface 102 and the second side surface 103.

[0018] The upper electrode 111 may be any material as long as it is conductive, and may be made of any material generally used as an electrode, such as aluminum, copper, tungsten, titanium, chromium, gold, platinum, etc. However, if the internal stress of the lower electrode 202, etc. is large and the piezoelectric film 110 is bent, the upper electrode 111 should be given the opposite internal stress to prevent the entire element from bending. The material can also have the effect of offsetting the stress of the metal. An example of such a material is an alloy of titanium and tungsten.

[0019] For the insulating film 210, general insulating materials such as silica, silicon nitride, oxynitride, alumina, etc. may be used. Furthermore, a laminated film made of two or more materials selected from these may be used. Note that, since a high voltage of 30 V or more is generally applied to drive the piezoelectric element 108, the material and thickness of the insulating film 210 are selected in consideration of the breakdown electric field strength.

[0020] The piezoelectric element 108 expands and contracts when a high voltage is applied. If the adhesion between the insulating film 210 and the piezoelectric film 110 is insufficient, peeling and destruction may occur during expansion and contraction. The sidewall of the piezoelectric film 110 in this embodiment is stepped. Therefore, the contact area between the piezoelectric film 110 and the insulating film 210 is large, and the adhesion between the insulating film 210 and the piezoelectric film 110 is good. Therefore, peeling and destruction are unlikely to occur.

[0021] Here, a piezoelectric element of a comparative example will be described with reference to FIG. 3. In the comparative example, the unevenness of the sidewall of the piezoelectric film 110X is formed by grooves 104X that are perpendicular to the thickness direction (Z direction) of the piezoelectric film 110X and parallel to the stacking interface of the precursor layer. Even in the comparative example, the contact area between the piezoelectric film 110X and the insulating film 210X is large due to the unevenness caused by the grooves 104X. However, since the grooves 104X are in the shadow when the insulating film 210 is formed, voids 105X are likely to be formed in the grooves 104X. The voids 105X at the boundary between the insulating film 210X and the piezoelectric film 110X can cause cracks in the subsequent manufacturing process or when the piezoelectric element is driven.

[0022] 2, the sidewall of the piezoelectric film 110 has a stepped shape, and the angle θ between the first side surface 102 and the second side surface 103 is 90° or more. By making it have such a stepped shape, there is no area that is shaded when the insulating film 210 is formed, and the insulating film 210 and the piezoelectric film 110 can be tightly attached to each other without any gaps.

[0023] An upper electrode contact portion 203 is opened at one end of the piezoelectric element 108 in the X direction, and an upper electrode pad 114 connected to the signal wiring 200 is formed on the upper layer. The upper electrode pad 114 and the upper electrode 111 are electrically connected via the upper electrode contact portion 203. A lower electrode contact portion 204 is opened in the insulating film 210 on the extension region of the lower electrode 202 near the end opposite to the upper electrode pad 114 in the X direction. A lower electrode pad 115 connected to the common wiring 201 is formed on the upper layer. The lower electrode pad 115 and the lower electrode 202 are electrically connected via the lower electrode contact portion 204. A sealing film 211 is further formed on the upper layer, covering at least each wiring and each electrode pad.

[0024] The signal wiring 200 and the common wiring 201 can be made of a material generally used for electrical wiring. For example, aluminum, copper, gold, or an alloy thereof can be used. A titanium or chromium film can be inserted to improve adhesion to the underlayer. The piezoelectric element 108 is generally driven by applying a high voltage of 30 V or more at a high frequency of several hundred to several thousand Hz. Therefore, the wiring is made to have a high slew rate by making the wiring film relatively thick.

[0025] The sealing film 211 covers the signal wiring 200, the common wiring 201, the upper electrode pad 114, and the lower electrode pad 115. The sealing film 211 is made of a material that has both high insulation and coverage. For example, silica, silicon nitride, alumina, etc., which have high insulation properties, are preferably used. This makes it possible to prevent current from flowing on the device surface in a high humidity environment, which would cause a breakdown. The electroconductive element 108 can prevent the insulating layer from peeling off and cracking.

[0026] Example 1 A method for producing the piezoelectric element in Example 1 will be described with reference to Fig. 4. As shown in Fig. 4(a), a silicon wafer base material 106 was prepared, and a silicon thermal oxide film of about 500 nm was formed on the upper surface (first surface) of the base material 106 by a wet oxidation method in which a silicon thermal oxide film is formed using oxygen and hydrogen gas, thereby forming an insulating film 209.

[0027] Next, as shown in FIG. 4(b), the lower electrode 202 and the piezoelectric film 110 were formed in this order on the upper surface of the substrate 106 on which the insulating film 209 was formed. As the lower electrode 202, a platinum film having a thickness of 90 to 110 nm was formed by sputtering. In order to obtain adhesion between the lower electrode 202 and the insulating film 209, a titanium film having a thickness of 5 to 15 nm was formed as an adhesion layer (not shown). On the lower electrode 202, a lead zirconate titanate layer to be the piezoelectric layer 100 was formed by a liquid phase method (sol-gel method) so as to have a (100) orientation. In addition, the piezoelectric layer 100 was formed multiple times to form the piezoelectric film 110 having a thickness of 1.9 to 2.1 μm.

[0028] Next, as shown in FIG. 4(c), a resist pattern (not shown) was formed by photolithography so that the piezoelectric film 110 would have a desired pattern, and then the piezoelectric film 110 was patterned by wet etching. Pure Etch PT204 manufactured by Hayashi Pure Chemical Industries was used as the etchant. When the piezoelectric film 110 of lead zirconate titanate laminated by the sol-gel method was wet etched, grooves 104 were formed on the side walls of the piezoelectric film 110, which are concave in a direction parallel to the laminated surface of the piezoelectric layer 100, as shown in FIG. 4(c). This is because each of the piezoelectric layers 100 formed by the sol-gel method tends to be rich in lead titanate on the side of the lower electrode 202 and rich in lead zirconate on the opposite side. Since the etching rate of lead titanate is lower than that of lead zirconate, grooves 104 are formed in a direction parallel to the laminated surface of the piezoelectric layer 100, as shown in FIG. 4(c).

[0029] 4(d), an upper electrode 111 was formed on the piezoelectric film 110 by sputtering. An alloy of titanium and tungsten was used as the material for the upper electrode 111, and the thickness of the electrode was set to 90 to 110 nm. After that, a resist pattern (not shown) was formed by photolithography so that the upper electrode 111 had a desired pattern, and then patterning was performed by dry etching.

[0030] This dry etching process will be described in detail with reference to FIG. 5. FIG. 5(a) is a diagram showing the sidewall of the piezoelectric film 110 immediately after the upper electrode 111 is formed. As shown in FIG. 5(a), first, a metal film that will become the upper electrode 111 is formed on the entire pattern-forming surface of the substrate 106. The entire pattern-forming surface of the substrate 106 refers to the entire surface that is exposed upward in a member located above the substrate 106 (in the +Z direction). In FIG. 5(a), it refers to the upper surface of a portion of each piezoelectric layer 100 of the piezoelectric film 110 that does not have another piezoelectric layer 100 above, and the upper surface of a portion of the lower electrode 202 on which the piezoelectric film 110 is not formed. A resist 109 is patterned on the piezoelectric film 110.

[0031] Next, dry etching was performed using SF6 gas to remove the upper electrode 111 formed on the sidewall of the piezoelectric film 110. As a result, the upper electrode 111 is formed on the upper surface of the piezoelectric film 110. A schematic diagram of the sidewall of the piezoelectric film 110 after dry etching is shown in Figure 5(b).

[0032] Next, dry etching was performed using C4F8 gas to process the sidewall of the piezoelectric film 110. Here, the processing is to shape the sidewall into the above-mentioned stepped shape. The processing conditions were a pressure of 0.3 Pa, antenna RF of 400 W, bias RF of 150 W, and a predetermined processing time of 50 seconds. A schematic diagram of the sidewall of the piezoelectric film 110 after processing is shown in FIG. 5(c). The sidewall of the piezoelectric film 110 was stepped, and the angle θ between the first side surface 102 and the second side surface 103 was 100° to 140°.

[0033] Subsequently, as shown in FIG. 4(e), a resist pattern (not shown) was formed again by photolithography so that the lower electrode 202 would have a desired pattern, and then the lower electrode 202 was patterned by etching.

[0034] 4(f), an insulating film 210 was formed on the entire pattern-forming surface of the substrate 106. Although not shown in the figure, the insulating film 210 in Example 1 has a laminated structure. First, an aluminum oxide film having a thickness of 20 to 30 nm was formed using the ALD method (atomic layer deposition method), and then a silicon oxide film having a thickness of 350 to 450 nm was formed using the CVD method (chemical vapor deposition method). The insulating film 210 may be formed by a combination of the ALD method and the CVD method, or may be formed only by the CVD method.

[0035] 4(g), a resist pattern (not shown) was formed in the insulating film 210 by photolithography to form through holes to the upper electrode 111 and the lower electrode 202. After that, the upper electrode contact portion 203 and the lower electrode contact portion 204 were formed by etching.

[0036] 4(h), a wiring material was formed on the insulating film 210 by sputtering. An alloy material of aluminum and copper was used as the wiring material, and the thickness was set to 500 to 700 nm. After forming a resist pattern (not shown) into a desired pattern by photolithography, the signal wiring 200 and the common wiring 201, as well as the upper electrode pad 114 and the lower electrode pad 115, were formed by etching.

[0037] 4(i), a sealing film 211 was formed so as to cover each wiring and each electrode pad. A highly moisture-proof silicon nitride film was used for the sealing film, and it was deposited to a thickness of 150 to 250 nm by a CVD method. Although not shown, after this, openings were formed in the sealing film 211 above the electrode terminal parts for applying a voltage for driving the actuators, which are present at the wiring ends of the signal wiring 200 and the common wiring 201, by patterning and etching a resist.

[0038] A high-temperature, high-pressure bias test was performed on the piezoelectric element 108 thus obtained in order to evaluate its durability. Specifically, it was held for 200 hours in an environment of a temperature of 85°C and a humidity of 85% with a DC voltage of 60 V applied. After that, the state of the piezoelectric element 108 was checked, and it was confirmed that no damage or peeling of the insulating film 210 of the piezoelectric element 108 was observed, and that the element was maintained in a normal state.

[0039] Example 2 Fig. 6 shows a cross-sectional view of a sidewall of a piezoelectric film 110 of Example 2. In Example 2, as shown in Fig. 6, the sidewall of the piezoelectric film 110 is stepped and has a plurality of steps 116, 117. The steps 116, 117 are made up of two surfaces (first side surface 102, second side surface 103) with different inclination angles relative to a surface (first surface (upper surface) of the substrate 106) parallel to the extension direction (XY direction) of the piezoelectric layer 100. In the steps 116, 117, the angle θ formed by the first side surface 102 and the second side surface 103 is 90° or more.

[0040] The first side surface 102 forms an inclined portion inclined with respect to the first surface (top surface) of the base material 106, and the second side surface 103 forms a flat portion that is approximately parallel to the first surface (top surface) of the base material 106. The second side surface 103 being parallel to the first surface (top surface) of the base material 106 does not have to be parallel in the strict mathematical sense, and may have an inclination angle within a range that can be considered approximately parallel.

[0041] The step 116 is a concave step formed by the second side surface 103 and the first side surface 102 connected to the upper end of the second side surface 103. The step 117 is a convex step formed by the first side surface 102 and the second side surface 103 connected to the upper end of the first side surface 102. The stepped shape of the side surface of the piezoelectric film 110 is formed by alternating concave step portions 116 and convex step portions 117. The angle of the concave step portion 116 and the angle of the convex step portion 117 are both 90° or more, and as a result, the width of the piezoelectric film 110 in the X direction continues to increase from the upper electrode 111 toward the lower electrode 202.

[0042] Each of the multiple steps 101 constituting the stepped side surface corresponds to each of the multiple piezoelectric layers 100 constituting the piezoelectric film 110. The side surface of one step 101 is made up of a first side surface 102 and a second side surface 103. A protrusion 107 protruding in the film thickness direction (Z direction) is formed on the convex step portion 117. Since the second side surface 103 is flat, the protrusion 107 protrudes in a direction substantially perpendicular to the second side surface 103.

[0043] The angle θ between the first side 102 and the second side 103 is defined as the angle between a line virtually extending the first side 102 excluding the protrusion 107 and a line virtually extending the second side 103 excluding the protrusion 107 in the cross section of Figure 6 (cross section perpendicular to the Y direction).

[0044] In the piezoelectric element 108 of Example 2, the contact area between the piezoelectric film 110 and the insulating film 210 is wider than that of Example 1 due to the protrusions 107. In addition, the protrusions 107 act as a stopper against the peeling direction of the insulating film 210 (the direction indicated by the arrow in FIG. 6, the X direction), so that the peeling resistance can be further improved. However, if the height h of the protrusions 107 in the Z direction is too high, it may cause disconnection of the upper electrode pad 114 and the signal wiring 200 (both not shown). Therefore, it is preferable that the height h of the protrusions 107 is 1 / 5 or less of the thickness of the upper electrode pad 114 and the signal wiring 200. The height h of the protrusions 107 of Example 2 was 10 to 140 nm.

[0045] The method of manufacturing the piezoelectric element 108 in Example 2 is the same as that in Example 1, except for the process of processing the side surface of the piezoelectric film 110. Therefore, only the processing process will be described. FIG. 7 shows a schematic diagram of the processing process of the side surface of the piezoelectric film 110 in Example 2. The processing conditions in Example 2 are a pressure of 0.3 Pa, an antenna RF of 400 W, and a bias RF of 150 W, and the processing time is set to 200 seconds, which is longer than that in Example 1. As the processing process proceeds, the first side surface 102 of the piezoelectric film 110 is covered with an etching deposit 113 as shown in FIG. 7(a). Since the etching deposit 113 acts as an etching mask, as the processing process proceeds further, a protrusion 107 is formed near the intersection of the second side surface 103 with the first side surface 102 as shown in FIG. 7(b).

[0046] A high-temperature, high-pressure bias test was performed on the piezoelectric element thus obtained in order to evaluate its durability. Specifically, the element was held for 200 hours in an environment of 85°C temperature and 85% humidity with a DC voltage of 60V applied. After that, the state of the piezoelectric element 108 was checked, and it was confirmed that no damage or peeling of the insulating film 210 of the piezoelectric element 108 was observed, and that the element was in a normal state.

[0047] In each of the above embodiments, examples have been shown in which all of the side surfaces of the multiple piezoelectric layers constituting the piezoelectric film are composed of two surfaces with different inclination angles, but a configuration in which at least one of the multiple piezoelectric layers has a side surface composed of two surfaces with different inclination angles is also possible. In addition, the stepped shape of the side surface of the piezoelectric film is not limited to the shape of the above embodiments, so long as it is a shape that does not decrease or monotonically increases in width in the direction in which the piezoelectric layers extend from the upper electrode to the lower electrode (X direction in Figure 1). For example, the second side surface 103 may be a flat shape perpendicular to the stacking direction (Z direction) of the piezoelectric layers. The structure of the piezoelectric film 110 in the above embodiments can also be understood as follows. That is, the side surface of the piezoelectric film has multiple steps, and each surface constituting the steps is projected in the film thickness direction (Z direction). In the comparative example shown in Fig. 3, the projection in the Z direction of the umbrella-shaped portion constituting the groove portion 104X overlaps with the projection of another surface, and therefore this condition is not met.

[0048] Fig. 8 is a schematic diagram showing the configuration of the main parts of an inkjet printer as a liquid ejection device to which the present invention can be applied. Fig. 8(A) is an overall view showing the overall configuration of a liquid ejection device 1000. Here, a serial type liquid ejection device is shown as an example, but the present invention is also applicable to a full line type. Fig. 8(B) is a perspective view showing a liquid ejection head 2, which is a component of the liquid ejection device 1000.

[0049] 8(B), the liquid ejection head 2 includes an element substrate 1 having a plurality of nozzle rows in which a plurality of nozzles are arranged. The liquid ejection device 1000 records an image on a medium 3 by ejecting ink droplets from ejection ports (not shown) corresponding to the nozzles of the liquid ejection head 2.

[0050] FIG. 9 is a diagram showing the configuration of the main part of the element substrate 1 of the liquid ejection head 2 of the embodiment. The element substrate 1 has the piezoelectric element 108 of the embodiment described above. The base material 106 described in the embodiment above has an insulating film 209, a vibration plate 301, a flow path forming substrate 302, and a nozzle plate 303, and a plurality of nozzle holes 304 are formed in the nozzle plate 303. Liquid ink is ejected from the nozzle holes 304. The flow path forming substrate 302 is provided on the nozzle plate 303, and the flow path forming substrate 302 divides the space between the nozzle plate 303 and the vibration plate 301 to form pressure chambers 305. Although not shown in FIG. 9 for simplification, in addition to the pressure chambers 305, various flow paths for distributing ink are formed in the flow path forming substrate 302. The ink is provided outside the liquid ejection head 2 and is supplied to the ink flow path through a tube from an ink tank provided inside the liquid ejection device 1000. The piezoelectric element 108 is electrically connected to a drive circuit (not shown) and operates based on a signal from the drive circuit. The vibration plate 301 is deformed by the operation of the piezoelectric film 110 , and changes the internal pressure of the pressure chamber 305 , causing ink to be ejected from the nozzle hole 304 .

[0051] The disclosure of this embodiment includes the following configuration. (Configuration 1) A lower electrode, a piezoelectric film, and an upper electrode are provided on a first surface of a substrate in this order; Furthermore, the piezoelectric element has an insulating film covering at least a side surface of the piezoelectric film, the side surface of the piezoelectric film has a plurality of step portions each having two surfaces with different inclination angles relative to the first surface; A piezoelectric element in which the angle between the two surfaces at the step is 90° or more. (Configuration 2) The piezoelectric element of configuration 1, wherein the two surfaces forming the step portion are a first side surface inclined with respect to the first surface of the base material, and a second side surface having an inclination angle with respect to the first surface of the base material smaller than that of the first side surface. (Configuration 3) The piezoelectric element of configuration 1, wherein the two surfaces forming the step portion are a first side surface inclined with respect to the first surface of the base material and a second side surface parallel to the first surface of the base material. (Configuration 4) 4. The piezoelectric element according to any one of configurations 1 to 3, wherein the width of the piezoelectric film in a direction perpendicular to the thickness direction thereof increases monotonically from the upper electrode to the lower electrode. (Configuration 5) The piezoelectric element according to any one of configurations 2 to 4, wherein the side of the piezoelectric film has a stepped shape including a convex step formed by the first side and the second side connected to an upper end of the first side, and a concave step formed by the second side and the first side connected to an upper end of the second side. (Configuration 6) 6. The piezoelectric element according to configuration 5, wherein the convex step portion has a protrusion protruding in a thickness direction of the piezoelectric film. (Configuration 7) The piezoelectric element of any one of configurations 1 to 6, wherein the insulating film further covers a portion of the upper surface of the lower electrode where the piezoelectric film is not formed, a portion of the upper surface of the piezoelectric film where the upper electrode is not formed, and an upper surface of the upper electrode. (Configuration 8) A liquid ejection head comprising the piezoelectric element according to any one of configurations 1 to 7, which ejects liquid by driving the piezoelectric element. (Configuration 9) A liquid ejection device having the liquid ejection head according to configuration 8. (Method 10) forming a bottom electrode on a first surface of the substrate; forming a piezoelectric film by forming a piezoelectric layer on the upper surface of the lower electrode multiple times by a liquid phase method; patterning the piezoelectric film by wet etching; forming a metal film on the entire pattern-forming surface of the substrate; forming an upper electrode on an upper surface of the piezoelectric film by patterning the metal film by dry etching; processing a side surface of the piezoelectric film by dry etching; forming an insulating film over the entire pattern-forming surface of the substrate; A method for manufacturing a piezoelectric element comprising the steps of: (Method 11) 11. The method for producing a piezoelectric element according to Method 10, wherein the insulating film is formed by a CVD method or a combination of an ALD method and a CVD method. (Method 12) In the step of processing the side surface of the piezoelectric film, dry etching is performed for a predetermined processing time, The side surface of the piezoelectric film has a plurality of step portions each having two surfaces with different inclination angles with respect to the first surface. 12. The method for manufacturing a piezoelectric element according to Method 10 or 11, wherein the side surface of the piezoelectric film is formed such that the angle between the two surfaces at the step portion is 90° or more. (Method 13) In the step of processing the side surface of the piezoelectric film, dry etching is performed for a time longer than the predetermined processing time, 13. The method for producing a piezoelectric element according to method 12, wherein a protrusion protruding in a thickness direction of the piezoelectric film is formed on a convex one of the step portions. [Explanation of symbols]

[0052] 101: step, 102: first side, 103: second side, 108: piezoelectric element, 110: piezoelectric film, 111: upper electrode, 116: step portion, 117: step portion, 202: lower electrode, 210: insulating film

Claims

1. A lower electrode, a piezoelectric film, and an upper electrode are provided on a first surface of a substrate in this order; Furthermore, the piezoelectric element has an insulating film covering at least a side surface of the piezoelectric film, the side surface of the piezoelectric film has a plurality of step portions each having two surfaces with different inclination angles with respect to the first surface, A piezoelectric element in which the angle between the two surfaces at the step is 90° or more.

2. 2. The piezoelectric element of claim 1, wherein the two surfaces forming the step portion are a first side surface inclined with respect to the first surface of the substrate, and a second side surface having an inclination angle with respect to the first surface of the substrate smaller than that of the first side surface.

3. 2. The piezoelectric element according to claim 1, wherein the two surfaces forming the step portion are a first side surface inclined with respect to the first surface of the substrate, and a second side surface parallel to the first surface of the substrate.

4. 2. The piezoelectric element according to claim 1, wherein the width of the piezoelectric film in a direction perpendicular to the thickness direction thereof increases monotonically from the upper electrode to the lower electrode.

5. 4. The piezoelectric element of claim 2 or 3, wherein the side of the piezoelectric film has a stepped shape including a convex step formed by the first side and the second side connected to an upper end of the first side, and a concave step formed by the second side and the first side connected to an upper end of the second side.

6. The piezoelectric element according to claim 5 , wherein the convex step portion has a protrusion that protrudes in a thickness direction of the piezoelectric film.

7. A piezoelectric element as described in any one of claims 1 to 4, wherein the insulating film further covers a portion of the upper surface of the lower electrode where the piezoelectric film is not formed, a portion of the upper surface of the piezoelectric film where the upper electrode is not formed, and an upper surface of the upper electrode.

8. 5. A liquid ejection head comprising the piezoelectric element according to claim 1, which ejects liquid by driving the piezoelectric element.

9. A liquid ejection apparatus comprising the liquid ejection head according to claim 8.

10. forming a bottom electrode on a first surface of the substrate; forming a piezoelectric film by forming a piezoelectric layer on the upper surface of the lower electrode multiple times by a liquid phase method; patterning the piezoelectric film by wet etching; forming a metal film on the entire pattern-forming surface of the substrate; forming an upper electrode on an upper surface of the piezoelectric film by patterning the metal film by dry etching; processing a side surface of the piezoelectric film by dry etching; forming an insulating film over the entire pattern-forming surface of the substrate; A method for manufacturing a piezoelectric element comprising the steps of:

11. The method for manufacturing a piezoelectric element according to claim 10, wherein the insulating film is formed by a CVD method or a combination of an ALD method and a CVD method.

12. In the step of processing the side surface of the piezoelectric film, dry etching is performed for a predetermined processing time. By doing this, The side surface of the piezoelectric film has a plurality of step portions each having two surfaces with different inclination angles with respect to the first surface. The method for manufacturing a piezoelectric element according to claim 10 or 11, wherein the side surface of the piezoelectric film is formed such that the angle between the two surfaces at the step portion is 90° or more.

13. In the step of processing the side surface of the piezoelectric film, dry etching is performed for a time longer than the predetermined processing time, The method for manufacturing a piezoelectric element according to claim 12 , wherein a protrusion protruding in a thickness direction of the piezoelectric film is formed on a convex one of the step portions.

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