Piezoelectric actuator and its manufacturing method, droplet dispensing head, ultrasonic device

Abstract

To provide a piezoelectric actuator including a piezoelectric material having excellent crystallinity.SOLUTION: A piezoelectric actuator includes a substrate, and a first piezoelectric element and a second piezoelectric element formed on the substrate. The first piezoelectric element includes a first lower electrode, a first piezoelectric material, and a first upper electrode. The second piezoelectric element includes a second lower electrode, a second piezoelectric material, and a second upper electrode. The side face of the first lower electrode is not covered with the first piezoelectric material, and the side face of the second lower electrode is not covered with the second piezoelectric material. The piezoelectric actuator includes a common electrode formed on the substrate and connected to the first upper electrode and the second upper electrode, and insulation layers positioned between the common electrode and the first lower electrode, and between the common electrode and the second lower electrode.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a piezoelectric actuator, a method for manufacturing the same, a droplet discharge head, and an ultrasonic device.

Background Art

[0002] Conventionally, as described in, for example, Patent Document 1, a droplet discharge head having a piezoelectric layer covering a first conductor layer (lower electrode) individually patterned thereon and a second conductor layer covering the piezoelectric layer is known.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, after forming a metal film on a diaphragm and then etching, individually patterned lower electrodes were formed, and then a piezoelectric layer covering the lower electrodes was formed. In such a manufacturing method, if etching solution or resist components remain on the lower electrodes in the process of patterning the lower electrodes, defects may occur in the piezoelectric layer formed on the lower electrodes, leading to a reduction in yield. Also, the orientation may differ between the piezoelectric body that grows from the surface of the diaphragm and the piezoelectric body that grows from the surface of the lower electrode, resulting in cracks in the piezoelectric layer around the edge of the lower electrode or the formation of regions where the crystal orientation is disturbed.

Means for Solving the Problems

[0005] According to one aspect of the present invention, a piezoelectric actuator is provided comprising a substrate, a first piezoelectric element and a second piezoelectric element formed on the substrate. The first piezoelectric element has a first lower electrode formed on the substrate, a first piezoelectric body formed on the first lower electrode, and a first upper electrode formed on the first piezoelectric body. The second piezoelectric element has a second lower electrode formed in a region different from the first lower electrode on the substrate, a second piezoelectric body formed on the second lower electrode, and a second upper electrode formed on the second piezoelectric body. The sides of the first lower electrode are not covered by the first piezoelectric body, and the sides of the second lower electrode are not covered by the second piezoelectric body. The piezoelectric actuator has a common electrode formed on the substrate and connected to the first upper electrode and the second upper electrode, and an insulating layer located between the common electrode and the first lower electrode, and between the common electrode and the second lower electrode.

[0006] According to one aspect of the present invention, a method for manufacturing a piezoelectric actuator is provided, comprising the steps of: preparing a substrate; forming a lower electrode film on the substrate; forming a piezoelectric film on the lower electrode; etching the lower electrode and the piezoelectric film to form a laminated film of a first lower electrode and a first piezoelectric film, and a laminated film of a second lower electrode and a second piezoelectric film, at different positions on the substrate; forming an insulating layer covering at least a portion of the side surface of the first lower electrode and at least a portion of the side surface of the second lower electrode; and forming a common electrode on the first piezoelectric film, the second piezoelectric film and the insulating layer. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is an exploded perspective view schematically showing the droplet dispensing head of the embodiment. [Figure 2] Figure 2 is a schematic partial plan view showing a piezoelectric actuator provided in the droplet dispensing head of the embodiment. [Figure 3] Figure 3 is a cross-sectional view taken along line III-III in Figure 2. [Figure 4]Figure 4 is a cross-sectional view taken along line IV-IV in Figure 2. [Figure 5] Figure 5 shows another example of a common electrode configuration. [Figure 6] Figure 6 shows other configuration examples for the lower electrode and lead electrodes. [Figure 7] Figure 7 is a cross-sectional view showing a method for manufacturing a droplet dispensing head according to an embodiment. [Figure 8] Figure 8 is a cross-sectional view showing a method for manufacturing a droplet dispensing head according to an embodiment. [Figure 9] Figure 9 is a cross-sectional view showing a method for manufacturing a droplet dispensing head according to an embodiment. [Figure 10] Figure 10 is a cross-sectional view showing a method for manufacturing a droplet dispensing head according to an embodiment. [Figure 11] Figure 11 is a cross-sectional view showing a method for manufacturing a droplet dispensing head according to an embodiment. [Figure 12] Figure 12 is a schematic perspective view showing a printer according to this embodiment. [Figure 13] Figure 13 is a plan view of an ultrasonic device in which the piezoelectric element of the above embodiment is mounted as an ultrasonic transducer. [Figure 14] Figure 14 is a partial cross-sectional view along the line XIV-XIV in Figure 13. [Modes for carrying out the invention]

[0008] Embodiments of the present invention will be described below with reference to the drawings. However, the following description represents one aspect of the present invention and can be arbitrarily modified within the scope of the invention. Members denoted by the same reference numerals in each figure represent the same member, and their descriptions are omitted as appropriate. In each figure, X, Y, and Z represent three mutually orthogonal spatial axes. In this specification, the directions along these axes will be described as the X-axis direction, Y-axis direction, and Z-axis direction, respectively. The Z-axis direction represents the thickness direction or lamination direction of plates, layers, and films. The X-axis direction and Y-axis direction represent the in-plane direction of plates, layers, and films.

[0009] (Droplet dispensing head) The liquid discharge head according to this embodiment will be described with reference to the drawings. Figure 1 is a schematic exploded perspective view showing the droplet dispensing head of this embodiment. Figure 2 is a schematic partial plan view showing the piezoelectric actuator provided in the droplet dispensing head of this embodiment. Figure 3 is a cross-sectional view taken along line III-III of Figure 2. Figure 4 is a cross-sectional view taken along line IV-IV of Figure 2.

[0010] As shown in Figures 1 to 4, the droplet dispensing head 1 includes a plurality of piezoelectric elements 300, a flow channel substrate 10, a nozzle plate 20, a diaphragm 50, a protective substrate 30, a circuit board 120, and a compliance substrate 40. Figure 2 shows the upper surface of the diaphragm 50. In this embodiment, the plurality of piezoelectric elements 300 are arranged along the X-axis. As will be described in detail later, the diaphragm 50 and the plurality of piezoelectric elements 300 constitute the piezoelectric actuator 2 of this embodiment.

[0011] The flow channel substrate 10 is, for example, a silicon substrate. The flow channel substrate 10 is provided with a plurality of pressure chambers 12. The plurality of pressure chambers 12 are arranged along the X-axis direction. The pressure chambers 12 are partitioned by a plurality of partition walls 11. The volume of the pressure chambers 12 changes due to the movement of the piezoelectric element 300.

[0012] In the flow path substrate 10, a first communication passage 13 and a second communication passage 14 are provided at the +Y axis end of the pressure chamber 12. The first communication passage 13 is configured to reduce its opening area by narrowing the +Y axis end of the pressure chamber 12 from the X axis direction. The width of the second communication passage 14 in the X axis direction is, for example, the same as the width of the pressure chamber 12 in the X axis direction. In the +Y direction of the second communication passage 14, a third communication passage 15 is provided that communicates with multiple second communication passages 14. The third communication passage 15 constitutes part of the manifold 100. The manifold 100 is a common liquid chamber for each pressure chamber 12. Thus, the flow path substrate 10 is provided with a supply flow path 17 consisting of the first communication passage 13, the second communication passage 14, and the third communication passage 15, and the pressure chamber 12. The supply flow path 17 communicates with the pressure chamber 12 and supplies liquid to the pressure chamber 12.

[0013] The nozzle plate 20 is attached to one side surface of the flow path substrate 10. The material of the nozzle plate 20 is, for example, SUS (Steel Use Stainless). The nozzle plate 20 is joined to the flow path substrate 10 by, for example, an adhesive or a heat welding film. A plurality of nozzles 21 arranged along the X-axis direction are provided on the nozzle plate 20. The nozzles 21 communicate with the inside of the pressure chamber 12 and discharge liquid.

[0014] The diaphragm 50 is provided on the other side surface of the flow path substrate 10. The diaphragm 50 is composed of, for example, a silicon oxide layer 51 provided on the flow path substrate 10 and a zirconium oxide layer 52 provided on the silicon oxide layer 51. The diaphragm 50 may be a single-layer silicon oxide layer or a single-layer zirconium oxide layer. The thickness of the diaphragm 50 is, for example, 0.5 μm or more and 3 μm or less.

[0015] The piezoelectric elements 300 are provided on the diaphragm 50. A plurality of piezoelectric elements 300 are provided. The number of the piezoelectric elements 300 is not particularly limited. As shown in FIG. 3, the piezoelectric element 300 includes a lower electrode 60, a piezoelectric body 70, and an upper electrode 80.

[0016] The lower electrode 60 is provided on the diaphragm 50. The lower electrode 60 is provided between the diaphragm 50 and the piezoelectric body 70. The thickness of the lower electrode 60 is, for example, 3 nm or more and 300 nm or less. The lower electrode 60 is, for example, a metal layer such as a platinum layer, an iridium layer, a titanium layer, a ruthenium layer, their conductive oxide layers, a lanthanum nickel oxide (LaNiO3: LNO) layer, a strontium ruthenium oxide (SrRuO3: SRO) layer, etc. The lower electrode 60 may have a structure in which a plurality of the layers exemplified above are laminated.

[0017] In the droplet dispensing head 1, the lower electrode 60 is configured as an independent individual electrode for each pressure chamber 12. As shown in Figure 4, the width of the lower electrode 60 in the X-axis direction is narrower than the width of the pressure chamber 12 in the X-axis direction. As shown in Figure 3, the length of the lower electrode 60 in the Y-axis direction is longer than the length of the pressure chamber 12 in the Y-axis direction. In the Y-axis direction, both ends of the lower electrode 60 are positioned on either side of the ends of the pressure chamber 12. A lead electrode 55 is connected to the -Y end of the lower electrode 60.

[0018] The piezoelectric element 70 is provided on the lower electrode 60. The piezoelectric element 70 is provided between the lower electrode 60 and the upper electrode 80. In this embodiment, the piezoelectric element 70 is provided on the lower electrode 60 and on the diaphragm 50. The thickness of the piezoelectric element 70 is, for example, 100 nm or more and 3 μm or less. The piezoelectric element 70 can be deformed by applying a voltage between the lower electrode 60 and the upper electrode 80.

[0019] The width of the piezoelectric element 70 in the X-axis direction is narrower than the width of the lower electrode 60 in the X-axis direction. The length of the piezoelectric element 70 in the Y-axis direction is longer than the length of the pressure chamber 12 in the Y-axis direction and shorter than the length of the lower electrode 60 in the Y-axis direction. The piezoelectric element 70 is formed only on the upper surface of the lower electrode 60. That is, the piezoelectric element 70 does not cover the sides of the lower electrode 60.

[0020] The piezoelectric body 70 is constructed using a piezoelectric material consisting of a composite oxide with a perovskite structure represented by the general formula ABO3. In this embodiment, lead zirconate titanate (PZT; Pb(Zr,Ti)O3) is used as the piezoelectric material. By using PZT as the piezoelectric material, a piezoelectric body 70 with a relatively large piezoelectric constant d31 can be obtained.

[0021] In the perovskite composite oxide represented by the general formula ABO3, oxygen atoms are 12-coordinate at the A site and 6-coordinate at the B site, forming an octahedron. In this embodiment, lead (Pb) is located at the A site, and zirconium (Zr) and titanium (Ti) are located at the B site.

[0022] Piezoelectric materials are not limited to the above-mentioned PZT. Other elements may be present at the A and B sites. For example, the piezoelectric material may be a perovskite material such as barium zirconate titanate (Ba(Zr,Ti)O3), lead lanthanum zirconate titanate ((Pb,La)(Zr,Ti)O3), lead zirconium magnesium niobate titanate (Pb(Zr,Ti)(Mg,Nb)O3), or lead zirconate titanate niobate titanate containing silicon (Pb(Zr,Ti,Nb)O3).

[0023] In addition, piezoelectric materials may be materials with reduced lead content, so-called low-lead materials, or materials that do not use lead, so-called lead-free materials. Using low-lead materials as piezoelectric materials can reduce the amount of lead used. Furthermore, using lead-free materials as piezoelectric materials eliminates the need for lead. Therefore, using low-lead or lead-free materials as piezoelectric materials can reduce the environmental burden.

[0024] Examples of lead-free piezoelectric materials include BFO-based materials containing bismuth ironate (BFO; BiFeO3). In BFO, Bi is located at the A site and iron (Fe) is located at the B site. Other elements may be added to BFO. For example, KNN may be added with at least one element selected from manganese ironate (Mn), aluminum (Al), lanthanum (La), barium (Ba), titanium (Ti), cobalt (Co), cerium (Ce), samarium (Sm), chromium (Cr), potassium (K), lithium (Li), calcium (Ca), strontium (Sr), vanadium (V), niobium (Nb), tantalum (Ta), molybdenum (Mo), tungsten (W), nickel (Ni), zinc (Zn), praseodymium (Pr), neodymium (Nd), and europium (Eu).

[0025] Another example of lead-free piezoelectric materials is KNN-based materials containing potassium sodium niobate (KNN; KNaNbO3). Other elements may be added to KNN. For example, KNN may be supplemented with at least one element selected from manganese (Mn), lithium (Li), barium (Ba), calcium (Ca), strontium (Sr), zirconium (Zr), titanium (Ti), bismuth (Bi), tantalum (Ta), antimony (Sb), iron (Fe), cobalt (Co), silver (Ag), magnesium (Mg), zinc (Zn), copper (Cu), vanadium (V), chromium (Cr), molybdenum (Mo), tungsten (W), nickel (Ni), aluminum (Al), silicon (Si), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), and europium (Eu).

[0026] Piezoelectric materials include materials with compositions that are partially deficient in elements, materials with compositions that are partially deficient in elements, and materials with compositions in which partially deficient in elements are replaced by other elements. As long as the basic properties of the piezoelectric body 70 remain unchanged, materials that deviate from the stoichiometric composition due to deficiencies or excesses, and materials in which partially deficient in elements are replaced by other elements, are also included as piezoelectric materials according to this embodiment. Of course, the piezoelectric materials that can be used in this embodiment are not limited to materials containing Pb, Bi, Na, K, etc. as described above.

[0027] The upper electrode 80 is provided on the piezoelectric body 70. In this embodiment, the upper electrode 80 is formed only on the upper surface of the piezoelectric body 70. That is, the upper electrode 80 does not cover the sides of the piezoelectric body 70 or the sides of the lower electrode 60. The upper electrode 80 is provided as an independent individual electrode for each piezoelectric element 300. The thickness of the upper electrode 80 is, for example, 3 nm to 300 nm. The upper electrode 80 is, for example, a metal layer such as an iridium layer, a platinum layer, a titanium layer, or a ruthenium layer, a conductive oxide layer thereof, a lanthanum nickel oxide layer, or a strontium ruthenium oxide layer. The upper electrode 80 may have a structure in which multiple layers as exemplified above are stacked.

[0028] The piezoelectric element 300 may also be configured without an upper electrode 80. That is, the piezoelectric body 70 and the common electrode 90, which will be described later, may be directly connected. In this case, it is preferable to select a conductive material that has excellent adhesion to the piezoelectric body 70 as the constituent material of the common electrode 90. As in this embodiment, by providing an upper electrode 80, the upper electrode 80 can also function as an adhesion layer between the piezoelectric element 70 and the common electrode 90. This reduces the restrictions on the constituent material of the common electrode 90, making it easier to use low-resistance conductive materials.

[0029] As shown in Figures 3 and 4, an insulating layer 150 is formed on the diaphragm 50, partially covering the laminate of the lower electrode 60, piezoelectric element 70, and upper electrode 80. The insulating layer 150 is made of, for example, aluminum oxide, silicon oxide, silicon nitride, zirconium oxide, etc. The insulating layer 150 may also have a structure in which multiple layers as exemplified above are laminated.

[0030] In this embodiment, the insulating layer 150 covers the sides of the lower electrode 60, the piezoelectric element 70, and the upper electrode 80. The insulating layer 150 has openings at multiple locations on the piezoelectric element 300 that penetrate the insulating layer 150 in the thickness direction. Specifically, the insulating layer 150 has a contact hole 151, a contact hole 152, and an opening 153.

[0031] Contact hole 151 opens in the insulating layer 150 on the lower electrode 60 that protrudes in the -Y axis direction from the lower end of the piezoelectric element 70. Contact hole 152 opens in the insulating layer 150 located on the +Y axis end of the upper electrode 80. Opening 153 opens in the insulating layer 150 located in the region where the upper electrode 80 and the pressure chamber 12 overlap in a plan view (view in the Z axis direction).

[0032] A lead electrode 55 is formed at the -Y end of each piezoelectric element 300, partially overlapping with the lower electrode 60 in a plan view. The lead electrode 55 and the lower electrode 60 are electrically connected via a contact hole 151.

[0033] A common electrode 90 is formed at the +Y direction ends of the multiple piezoelectric elements 300, extending in the X direction across the multiple piezoelectric elements 300. In a plan view, the common electrode 90 overlaps with the region containing the contact hole 152 of each piezoelectric element 300. The common electrode 90 is electrically connected to the upper electrode 80 via the contact hole 152.

[0034] The opening 153 is provided in the insulating layer 150 in the portion located above the pressure chamber 12. By partially removing the insulating layer 150, which is harder than the constituent layers of the piezoelectric element 300, the deformability of the piezoelectric element 300 can be increased. The insulating layer 150 can also be configured without the opening 153.

[0035] In this embodiment, the opening 153 is located within the planar region of the upper electrode 80, and the peripheral edge of the upper electrode 80 is covered by the insulating layer 150. The insulating layer 150 is formed continuously from the peripheral edge of the upper electrode 80 to the side surface of the piezoelectric element 300. With this configuration, since the surface of the piezoelectric body 70 is not exposed to the outside air, the intrusion of moisture and the like into the piezoelectric body 70 can be suppressed, and deterioration of the piezoelectric element 300 due to moisture and the like can be suppressed.

[0036] In the piezoelectric element 300, applying a voltage between the lower electrode 60 and the upper electrode 80 allows a voltage to be applied to the piezoelectric body 70, causing it to deform. In this embodiment, the piezoelectric element 300 and the diaphragm 50 constitute a piezoelectric actuator 2 that changes the volume of the pressure chamber 12. The diaphragm 50 constitutes the substrate in the piezoelectric actuator 2.

[0037] In the droplet ejection head 1, the diaphragm 50 and the lower electrode 60 are displaced by the deformation of the piezoelectric element 70, which has electromechanical conversion characteristics. In other words, in the droplet ejection head 1, the diaphragm 50 and the lower electrode 60 substantially function as a diaphragm.

[0038] In the piezoelectric actuator 2 of this embodiment, as shown in Figures 2 to 4, the multiple piezoelectric elements 300 are formed on the diaphragm 50 as separate, independent elements. The following will be a detailed explanation using the first piezoelectric element 300A and the second piezoelectric element 300B shown in the figures. First piezoelectric element 300A and the second piezoelectric element 300B are two piezoelectric elements 300 having a common configuration, and are shown separately for the sake of clarity.

[0039] The first piezoelectric element 300A includes a first lower electrode 60A formed on the diaphragm 50 (substrate), a first piezoelectric body 70A formed on the first lower electrode 60A, and a first upper electrode 80A formed on the first piezoelectric body 70A. The second piezoelectric element 300B includes a second lower electrode 60B formed in a region different from the first lower electrode 60A on the diaphragm 50 (substrate), a second piezoelectric body 70B formed on the second lower electrode 60B, and a second upper electrode 80B formed on the second piezoelectric body 70B.

[0040] The side surface of the first lower electrode 60A of the first piezoelectric element 300A is not covered by the first piezoelectric body 70A. The side surface of the second lower electrode 60B of the second piezoelectric element 300B is not covered by the second piezoelectric body 70B. The piezoelectric actuator 2 has a common electrode 90 formed on the diaphragm 50 and connected to the first upper electrode 80A and the second upper electrode 80B. The piezoelectric actuator 2 has an insulating layer 150 located between the common electrode 90 and the first lower electrode 60A, and between the common electrode 90 and the second lower electrode 60B.

[0041] In this configuration, the first piezoelectric element 70A is formed only on the first lower electrode 60A, and the second piezoelectric element 70B is formed only on the second lower electrode 60B. Therefore, it is possible to suppress the inclusion of cracks and orientation disturbances that tend to occur on the edges of the first lower electrode 60A and the second lower electrode 60B in the first piezoelectric element 70A and the second piezoelectric element 70B. In this configuration, the side surface of the first lower electrode 60A is exposed between the first piezoelectric element 70A and the diaphragm 50, and the side surface of the second lower electrode 60B is exposed between the second piezoelectric element 70B and the diaphragm 50. Therefore, by forming an insulating layer 150 that covers the side surfaces of the first lower electrode 60A and the second lower electrode 60B, the common electrode 90 formed on the diaphragm 50 can be electrically connected to the first upper electrode 80A and the second upper electrode 80B without short-circuiting the first lower electrode 60A and the second lower electrode 60B.

[0042] In this embodiment, the insulating layer 150 covers the entire side surface of the piezoelectric element 70, but the embodiment is not limited to this configuration. The insulating layer 150 can prevent short circuits between the common electrode 90 and the lower electrode 60 as long as it is formed at least between the side surface of the lower electrode 60 and the common electrode 90. Therefore, the insulating layer 150 may be formed only on a portion of the side surface of the lower electrode 60. The insulating layer 150 may also cover the side surface of the lower electrode 60 but not the side surface of the piezoelectric element 70.

[0043] If the insulating layer 150 does not cover the sides of the piezoelectric element 70, the piezoelectric actuator 2 may have a protective film that covers the sides of the piezoelectric element 70 (first piezoelectric element 70A, second piezoelectric element 70B). As the protective film, for example, nitrides such as titanium nitride, silicon nitride, aluminum nitride, and TiAlN; oxides such as aluminum oxide, titanium oxide, tantalum oxide, chromium oxide, iridium oxide, and hafnium oxide; resin-based materials such as parylene, adhesives, and photosensitive resists; and carbon-based materials such as diamond-like carbon can be used. By providing a protective film that covers the piezoelectric element 70, the intrusion of moisture into the piezoelectric element 70 can be effectively suppressed.

[0044] The protective substrate 30 is bonded to the diaphragm 50 by an adhesive (not shown). The protective substrate 30 has a through hole 32 that penetrates the protective substrate 30 in the thickness direction (Z-axis direction). The through hole 32 communicates with the third communication passage 15 through a through hole provided in the diaphragm 50. The through hole 32 and the third communication passage 15 constitute a manifold 100 which is a common liquid chamber for each pressure chamber 12. The protective substrate 30 has another through hole 33 that penetrates the protective substrate 30 in the Z-axis direction. The ends of the lead electrodes 55 are placed in the through hole 33. The protective substrate 30 has an opening 31 that opens toward the diaphragm 50. The opening 31 is a space that does not obstruct the driving of the piezoelectric element 300. The opening 31 may or may not be sealed. The circuit board 120 is provided on the protective substrate 30. The circuit board 120 includes a semiconductor integrated circuit (IC) for driving the piezoelectric element 300. The circuit board 120 and the lead electrodes 55 are electrically connected via connecting wiring (not shown). The compliance board 40 is provided on the protective board 30. The compliance board 40 has a sealing layer 41 provided on the protective board 30 and a fixing plate 42 provided on the sealing layer 41. The sealing layer 41 seals the upper opening of the through hole 32. The sealing layer 41 seals the manifold 100. The sealing layer 41 is, for example, flexible. The fixing plate 42 has a through hole 43 that penetrates the fixing plate 42 in the Z-axis direction. The through hole 43 overlaps with the manifold 100 when viewed from the Z-axis direction.

[0045] In this embodiment, the droplet ejection head 1 takes in ink from an ink inlet connected to an external ink supply means (not shown), fills the inside with ink from the manifold 100 to the nozzle 21, and then applies a voltage between the lower electrode 60 and the upper electrode 80 corresponding to the pressure chamber 12 according to a recording signal from the drive circuit. As a result, the diaphragm 50 flexes and deforms together with the piezoelectric element 300, increasing the pressure in each pressure chamber 12, and ink droplets are ejected from each nozzle 21.

[0046] In this embodiment, the common electrode 90 is positioned so as to overlap only the end of the piezoelectric element 300. That is, the common electrode 90 is positioned in a region that does not overlap with the pressure chamber 12 in a plan view. With this configuration, the common electrode 90 is not positioned in the region where the piezoelectric element 300 displaces the diaphragm 50, so the deformation of the piezoelectric element 300 is not hindered by the common electrode 90, and a large amount of displacement can be obtained.

[0047] The configuration of the common electrode 90 is not limited to that of this embodiment. As shown in Figure 5, the common electrode 90 may be configured to cover the piezoelectric body 70. In the configuration shown in Figure 5, the common electrode 90 is also formed on the opening 153 of the insulating layer 150. In this example, the common electrode 90 and the upper electrode 80 are electrically connected at two locations: the contact hole 152 and the opening 153. It is also possible to have a configuration that does not include either the contact hole 152 or the opening 153.

[0048] As shown in Figure 5, by configuring the common electrode 90 to cover the piezoelectric element 70, the intrusion of moisture and other substances into the piezoelectric element 70 can be further suppressed. In particular, in a configuration where the sides of the piezoelectric element 70 are not covered by the insulating layer 150, the common electrode 90 can also function as a protective film, thereby improving the reliability of the piezoelectric actuator 2.

[0049] The configuration shown in Figure 5 is suitable when the piezoelectric element 300 does not have an upper electrode 80. In the configuration without an upper electrode 80, a common electrode 90 is formed to cover the piezoelectric body 70, so that the common electrode 90 functions as the upper electrode of each piezoelectric element 300.

[0050] Furthermore, the lead electrodes 55 and the common electrode 90 need to be insulated from each other. For this reason, in the vicinity of the lead electrodes 55, the common electrode 90 may not cover the piezoelectric element 70. In the example shown in Figure 5, the side of the piezoelectric element 70 facing the lead electrodes 55 (-Y direction) is not covered by the common electrode 90. However, the end of the piezoelectric element 70 located near the lead electrodes 55 is a part that does not overlap with the pressure chamber 12 in a plan view, and therefore contributes almost nothing to the vibration operation of the diaphragm 50. Therefore, even if some moisture enters the piezoelectric element 70 near the lead electrodes 55, it will not affect the performance of the piezoelectric element 300. In other words, the common electrode 90 only needs to cover at least the part of the piezoelectric element 70 that overlaps with the pressure chamber 12 in a plan view.

[0051] In this embodiment, the lead electrode 55 and the lower electrode 60 are connected via a contact hole 151, but the configuration is not limited to this. For example, the configuration shown in Figure 6 can also be used. In the example shown in Figure 6, the lower electrode 60 has a wiring portion 60a that protrudes significantly in the -Y direction relative to the piezoelectric body 70. The wiring portion 60a of the lower electrode 60 is not covered by the insulating layer 150. The lead electrode 55 is formed in contact with the upper surface of the wiring portion 60a of the lower electrode 60. With this configuration, the contact area between the lower electrode 60 and the lead electrode 55 can be increased. This improves the reliability of the electrical connection between the lead electrode 55 and the lower electrode 60, and also reduces the electrical resistance of the wiring connected to the piezoelectric element 300.

[0052] (Manufacturing method) Figures 7 to 11 are cross-sectional views showing the manufacturing method of the droplet dispensing head of the above embodiment. The cross-sections shown in each figure are located along the line XI-XI shown in Figure 2.

[0053] First, prepare the silicon substrate W1 shown in Figure 7. Next, a diaphragm 50 is formed on the surface of the silicon substrate W1. In the process of forming the diaphragm 50, first, a silicon oxide layer 51 made of silicon dioxide is formed by thermal oxidation of the silicon substrate W1.

[0054] Next, a zirconium oxide layer 52 made of zirconium oxide (ZrOx) is formed on the silicon oxide layer 51 by a liquid-phase method. To form the zirconium oxide layer 52, first, a metal alkoxide or metal carboxylate salt and a thickener are added to a carboxylic acid, then water (H2O) is added, and the mixture is heated and stirred at approximately 70°C for approximately 2 hours to obtain a homogeneous and transparent precursor solution. This precursor solution is applied to the silicon substrate W1 by a spin-coating method (coating step). Next, the solution applied to the silicon substrate W1 is heated to 160°C to 200°C and dried for approximately 5 minutes to obtain a dried film (drying step). Then, this dried film is degreased by heating it to 375°C to 415°C and holding it for approximately 5 minutes (degreasing step). If a thicker zirconium oxide layer 52 is desired, the process may be repeated after the degreasing step, returning to the initial coating step, followed by the drying step and the degreasing step. After this degreasing step, the dried film is heated to 750°C to 850°C and held for approximately 10 seconds to 3 minutes to crystallize (pre-calcination step). If a thicker zirconium oxide layer 52 is desired, the process may be repeated after this pre-calcination step, returning to the initial coating step, followed by the drying step, degreasing step, and pre-calcination step. After the pre-calcination step, the zirconium oxide layer 52 is formed by heating to 800°C to 950°C and holding for approximately 1 hour (final calcination step). Examples of heating devices used in the drying step, degreasing step, pre-calcination step, and final calcination step include RTA (Rapid Thermal Annealing) devices that heat by irradiation with infrared lamps and hot plates.

[0055] Next, as shown in Figure 8, a lower electrode 60 is formed on the entire surface of the diaphragm 50. The material of the lower electrode 60 is not particularly limited, but it is essential that it is a material that does not lose its conductivity due to oxidation during heat treatment (generally 500°C or higher) when forming the piezoelectric body 70 or due to diffusion of materials contained in the piezoelectric body 70. For this reason, metals such as platinum and iridium that do not lose conductivity even at high temperatures, conductive oxides such as iridium oxide and lanthanum nickel oxide, and laminated materials of these materials are preferably used as the material of the lower electrode 60. The lower electrode 60 can be formed by vapor phase deposition such as sputtering, PVD (physical vapor deposition), or laser ablation, or by liquid phase deposition such as spin coating. In addition, an adhesion layer may be used between the conductive material and the diaphragm 50 to ensure adhesion. In this embodiment, although not specifically shown, titanium is used as the adhesion layer. Zirconium, titanium, titanium oxide, etc., can be used as the adhesion layer. The method for forming the adhesion layer is the same as for the electrode material. Furthermore, a control layer may be formed on the electrode surface (the film-forming side of the piezoelectric element 70) to control the crystal growth of the piezoelectric element 70. In this embodiment, titanium is used as the crystal control layer for the piezoelectric element 70 (PZT). Since titanium is incorporated into the piezoelectric element 70 during film formation, it does not exist as a film after the piezoelectric element 70 is formed. As the crystal control layer, a conductive oxide with a perovskite-type crystal structure, such as lanthanum nickel oxide, may be used. The method for forming the crystal control layer is the same as for the electrode material. It is desirable that the insulating crystal control layer does not exist between the piezoelectric element 70 and the lower electrode 60 after the piezoelectric element 70 is formed. This is because the crystal control layer and the piezoelectric element 70 form a series capacitor, which reduces the electric field applied to the piezoelectric element 70. As in this embodiment, by using titanium as the orientation control layer, it undergoes heat treatment that would normally result in an oxide (insulator), but it is incorporated into the piezoelectric element 70 and therefore does not exist as a film.

[0056] Next, in this embodiment, a piezoelectric body 70 made of lead zirconate titanate (PZT) is formed. In this embodiment, the piezoelectric body 70 is formed using a so-called sol-gel method, in which a so-called sol, obtained by dissolving and dispersing a metal complex in a solvent, is coated and dried to gel, and then fired at a high temperature to obtain a piezoelectric body 70 made of a metal oxide. However, the method for manufacturing the piezoelectric body 70 is not limited to the sol-gel method, and for example, PVD (Physical Vapor Deposition) methods such as MOD (Metal-Organic Decomposition), sputtering, or laser ablation may be used. In other words, the piezoelectric body 70 may be formed by either a liquid-phase method or a gas-phase method. Alternatively, the piezoelectric body 70 may be formed by laminating multiple thin piezoelectric films.

[0057] The piezoelectric element 70 is formed on the unpatterned lower electrode 60. If the lower electrode 60 were patterned before forming the piezoelectric element 70, the lower electrode 60 would be patterned using a photoprocess, ion milling, and ashing, which would alter the surface of the lower electrode 60 and any crystalline species layers (such as titanium, not shown) on the surface. In that case, even if the piezoelectric element 70 is formed on the altered surface, it would be difficult to obtain a piezoelectric element 70 with good crystallinity. In contrast, if the piezoelectric element 70 is formed without patterning the lower electrode 60, the surface of the lower electrode 60 remains unaltered, allowing for the formation of a piezoelectric element 70 with good crystallinity throughout its entire surface. Furthermore, since the piezoelectric element 70 and the diaphragm 50 do not come into contact, the diffusion of components contained in the piezoelectric element 70, such as lead (Pb) and bismuth (Bi), into the diaphragm 50 is suppressed.

[0058] Next, the upper electrode 80 is formed on the piezoelectric body 70. Suitable materials for the upper electrode 80 include metals that do not lose conductivity even at high temperatures, such as platinum and iridium, conductive oxides such as iridium oxide and lanthanum nickel oxide, and laminated materials of these materials. The same film formation method as for the lower electrode 60 can be used for forming the upper electrode 80.

[0059] The upper electrode 80 is formed on the unpatterned piezoelectric material 70. Since no alteration of the surface of the piezoelectric material 70 occurs due to the patterning process, the upper electrode 80 having good crystallinity throughout can be formed on the piezoelectric material 70. Through the above process, a laminated film LF is formed on the diaphragm 50, in which the lower electrode 60, the piezoelectric element 70, and the upper electrode 80 are stacked in that order.

[0060] Next, as shown in Figure 9, the multilayer film LF, consisting of the lower electrode 60, the piezoelectric element 70, and the upper electrode 80, is patterned collectively. The patterning of the multilayer film LF can be performed by dry etching, such as reactive ion etching (RIE) or ion milling. If possible, the patterning of the multilayer film LF may be performed using photolithography or wet etching using an etching solution. For the portion of the lower electrode 60 that protrudes in the -Y direction from the piezoelectric element 70, as shown in Figures 2 and 3, the piezoelectric element 70 and the upper electrode 80 on the lower electrode 60 are selectively removed by etching or ion milling. This patterning process forms a plurality of piezoelectric elements 300 spaced apart from each other on the diaphragm 50.

[0061] The piezoelectric element 300 formed by the manufacturing method of this embodiment is manufactured by patterning the multilayer film LF in a single piece. Therefore, the sides of the lower electrode 60, the piezoelectric body 70, and the upper electrode 80 are exposed to the sides of the piezoelectric element 300. That is, the side of the lower electrode 60 is not covered by the piezoelectric body 70. Also, the side of the piezoelectric body 70 is not covered by the upper electrode 80.

[0062] Next, as shown in Figure 10, an insulating layer 150 is formed across one side of the silicon substrate W1 (the side on which the laminated film LF is formed). The insulating layer 150 covers the surfaces of the multiple piezoelectric elements 300 and the surface of the diaphragm 50 on which the piezoelectric elements 300 are not formed. The insulating layer 150 can be formed using PVD methods such as sputtering or laser ablation, vapor phase deposition methods such as CVD, or liquid phase deposition methods such as sol-gel.

[0063] Next, as shown in Figure 11, the insulating layer 150 is partially removed to form the contact holes 151, 152, and opening 153 shown in Figure 2. The patterning of the insulating layer 150 can be performed by photolithography. Next, a common electrode 90 connected to the upper electrode 80 via a contact hole 152, and a lead electrode 55 (see Figure 2) connected to the lower electrode 60 via a contact hole 151 are patterned on the diaphragm 50.

[0064] Next, as shown in Figure 11, the silicon substrate W1 is patterned. Specifically, a mask film (not shown) is formed on the side of the silicon substrate W1 opposite to the diaphragm 50, and then anisotropic etching (wet etching) using an alkaline solution such as KOH is performed through the mask film to form a pressure chamber 12 corresponding to the piezoelectric element 300, thus forming the flow channel substrate 10. Through these steps, the piezoelectric actuator 2 of this embodiment is manufactured.

[0065] Subsequently, a nozzle plate 20 having a nozzle 21 is bonded to the side of the flow channel substrate 10 opposite to the diaphragm 50. Furthermore, by bonding a separately manufactured protective substrate 30 and compliance substrate 40, the droplet ejection head of this embodiment is completed.

[0066] According to the manufacturing method of this embodiment described above, since the piezoelectric material 70 is formed on the unpatterned lower electrode 60, the surface of the lower electrode 60 is not altered during the patterning process, and a piezoelectric material 70 with good crystallinity can be formed over its entire surface. Furthermore, by patterning the lower electrode 60, the piezoelectric material 70, and the upper electrode 80 together, the piezoelectric material 70 of the multiple piezoelectric elements 300 all become piezoelectric materials with good crystallinity. A piezoelectric actuator 2 having piezoelectric elements 300 with excellent displacement characteristics can be manufactured.

[0067] Furthermore, when a piezoelectric body 70 is formed on a patterned lower electrode 60, the crystallinity of the piezoelectric body 70 formed on the lower electrode 60 and the diaphragm 50 may differ, which can lead to cracks occurring in the piezoelectric body 70 on the edge of the lower electrode 60 or the formation of regions with disordered crystallinity. According to the manufacturing method of this embodiment, these cracks and disordered crystallinity of the piezoelectric body 70 can also be suppressed.

[0068] If the droplet dispensing head 1 of this embodiment is configured without an upper electrode 80, the film deposition step for the upper electrode 80 is omitted in the manufacturing method described above. In the patterning step, the laminated film LF consisting of the lower electrode 60 and the piezoelectric body 70 is patterned, and then a common electrode 90 is deposited on the piezoelectric body 70. In the configuration without an upper electrode 80, it is preferable to form a common electrode 90 that covers the piezoelectric body 70, as shown in Figure 5.

[0069] (printer) Next, the printer according to this embodiment will be described with reference to the drawings. Figure 12 is a schematic perspective view showing the printer 200 according to this embodiment. The printer 200 is an inkjet printer. The printer 200 includes a head unit 210, as shown in Figure 12. The head unit 210 has, for example, a droplet ejection head 1. The number of droplet ejection heads 1 is not particularly limited. The head unit 210 is equipped with removable cartridges 212 and 214 that constitute the supply means. The carriage 216 on which the head unit 210 is mounted is axially movable on a carriage shaft 222 attached to the device body 220 and ejects liquid supplied from the liquid supply means.

[0070] Here, a liquid refers to any material in a liquid phase, including sols, gels, and other liquid materials. Furthermore, liquids include not only liquids as a state of matter, but also compositions in which particles of functional materials, such as pigments and metal particles, are dissolved, dispersed, or mixed in a solvent. Typical examples of liquids include inks and liquid crystal emulsifiers. Ink encompasses various liquid compositions, including common water-based and oil-based inks, as well as gel inks and hot-melt inks.

[0071] In the printer 200, the driving force of the drive motor 230 is transmitted to the carriage 216 via a plurality of gears (not shown) and a timing belt 232, causing the carriage 216, on which the head unit 210 is mounted, to move along the carriage axis 222. Meanwhile, the main body of the device 220 is provided with transport rollers 240 as a transport mechanism for moving a sheet S, which is a recording medium such as paper, relative to the droplet ejection head 1. The transport mechanism for transporting the sheet S is not limited to transport rollers, but may also be a belt or a drum.

[0072] The printer 200 includes a printer controller 250 as a control unit that controls the droplet ejection head 1 and the transport rollers 240. The printer controller 250 is electrically connected to the circuit board 120 of the droplet ejection head 1. The printer controller 250 includes, for example, a RAM (Random Access Memory) for temporarily storing various data, a ROM (Read Only Memory) for storing control programs, a CPU (Central Processing Unit), and a drive signal generation circuit that generates drive signals to be supplied to the droplet ejection head 1.

[0073] (Ultrasonic device) Figure 13 is a plan view of an ultrasonic device in which the piezoelectric element of the above embodiment is mounted as an ultrasonic transducer. Figure 14 is a partial cross-sectional view along the line XIV-XIV in Figure 13. In this embodiment, the transmission and reception of ultrasonic waves are performed using an electroacoustic transducer that utilizes the piezoelectric effect. This electroacoustic transducer is a piezoelectric element 300, and when ultrasonic waves are transmitted, electrical energy is converted into mechanical energy (inverse piezoelectric effect). Changes due to the contraction and expansion of the piezoelectric layer excite the diaphragm to vibrate, thereby transmitting ultrasonic waves. In this case, the piezoelectric element 300 is an ultrasonic transducer 301 for transmission. Furthermore, to receive ultrasonic waves reflected from the object to be detected, mechanical energy is converted into electrical energy (positive piezoelectric effect), and electrical energy is generated by the deformation of the piezoelectric element, and the electrical energy signal is detected. In this case, the piezoelectric element 300 is a receiving ultrasonic transducer 302.

[0074] As shown in Figures 13 and 14, multiple transmitting ultrasonic transducers 301 and receiving ultrasonic transducers 302 are arranged in an array on an aperture substrate 410 having multiple apertures 412, constituting an ultrasonic device 400 (array sensor). Multiple transmitting ultrasonic transducers 301 and multiple receiving ultrasonic transducers 302 are arranged alternately in columns, and the power supply is switched for each column of transducers. Line scanning and sector scanning are realized according to these power supply switches. In addition, the levels of ultrasonic output and input are determined according to the number of transducers and the number of columns to be powered. In the figures, a 6x6 array is depicted for brevity. The number of rows and columns in the array is determined according to the extent of the scan range.

[0075] It is also possible to alternate the transmitting ultrasonic transducer 301 and the receiving ultrasonic transducer 302 for each transducer. In this case, by aligning the central axes of the transmitting and receiving ultrasonic sources, it becomes easier to match the directivity angles of the transmitting and receiving signals.

[0076] In Figure 14, a diaphragm 50 is formed on the upper surface (piezoelectric element 70 side) of the aperture substrate 410. Multiple apertures 412 are formed in the aperture substrate 410. The apertures 412 can be formed using processing methods such as etching, polishing, and laser processing, depending on the substrate material. The lower electrode 60, piezoelectric element 70, and upper electrode 80 are the same as in the embodiment described above, so their configuration will not be explained. Although not shown in the figure, a common electrode 90 is connected to the upper electrode 80, as in the embodiment described above. It is preferable that the common electrode 90 is placed in a region that does not overlap with the apertures 412 in a plan view. With this configuration, the deformation of the piezoelectric element 300 is not hindered, resulting in an ultrasonic device equipped with an ultrasonic transducer with excellent deformation characteristics. In addition, compared to the previous embodiment, the ultrasonic device needs to be driven in a higher frequency range than the droplet ejection head 1, so the configuration, thickness, and physical properties such as Young's modulus of the piezoelectric element 70, the diaphragm 50, each electrode material, and the aperture substrate 410 may be adjusted.

[0077] Furthermore, wiring (not shown) is connected to the transmitting ultrasonic transducer 301 and the receiving ultrasonic transducer 302, and each wire is connected to a terminal section (not shown) of the control board (not shown) via a flexible printed circuit board (not shown). The control board is equipped with a control unit (not shown) consisting of a calculation unit, a memory unit, etc. The control unit is configured to control the input signal input to the transmitting ultrasonic transducer 301 and to process the output signal output from the receiving ultrasonic transducer 302.

[0078] Thus, in the ultrasonic device 400 of this embodiment, compared to sensors using bulk piezoelectric ceramics, the piezoelectric elements 300 fabricated using MEMS technology can be arranged at a narrow pitch (high resolution), and the driving voltage is low, which is effective in miniaturizing, thinning, and saving energy for the device and the equipment on which it is mounted. In addition, because there is little manufacturing variation between the piezoelectric elements 300, the recognition accuracy is also improved. Furthermore, by thinning the film thickness of the piezoelectric material 70, the displacement characteristics are improved, and the efficiency of ultrasonic wave transmission and reception can be improved. [Explanation of symbols]

[0079] 1…Droplet dispensing head, 2…Piezoelectric actuator, 10…Flow channel substrate, 12…Pressure chamber, 20…Nozzle plate, 21…Nozzle, 60…Lower electrode, 60A…First lower electrode, 60B…Second lower electrode, 70…Piezoelectric element, 70A…First piezoelectric element, 70B…Second piezoelectric element, 80…Upper electrode, 80A…First upper electrode, 80B…Second upper electrode, 90…Common electrode, 150…Insulating layer, 300…Piezoelectric element, 300A…First piezoelectric element, 300B…Second piezoelectric element, 400…Ultrasonic device, 410…Aperture substrate, 412…Aperture, LF…Laminated film

Claims

1. A piezoelectric actuator comprising a substrate, a first piezoelectric element and a second piezoelectric element formed on the substrate, The first piezoelectric element is A first lower electrode formed on the substrate, A first piezoelectric body formed on the first lower electrode, A first upper electrode formed on the first piezoelectric element, It has, The second piezoelectric element is A second lower electrode is formed in a region different from the first lower electrode on the substrate, A second piezoelectric element formed on the second lower electrode, A second upper electrode formed on the second piezoelectric element, It has, The side surface of the first lower electrode is not covered by the first piezoelectric material. The side surface of the second lower electrode is not covered by the second piezoelectric material. A common electrode formed on the substrate and connected to the first upper electrode and the second upper electrode, An insulating layer located between the common electrode and the first lower electrode, and between the common electrode and the second lower electrode, It has, The common electrode covers at least a portion of the upper part of the first piezoelectric body and at least a portion of the upper part of the second piezoelectric body. Piezoelectric actuator.

2. The first piezoelectric element and the second piezoelectric element each have a protective film covering them. The piezoelectric actuator according to claim 1.

3. The process of preparing the circuit board, A step of forming a lower electrode film on the substrate, A step of forming a piezoelectric film on the lower electrode, Etching step to form a laminated film of the first lower electrode and the first piezoelectric material, and a laminated film of the second lower electrode and the second piezoelectric material, at different positions on the substrate by etching the lower electrode and the piezoelectric material, A step of forming an insulating layer that covers at least a portion of the side surface of the first lower electrode and at least a portion of the side surface of the second lower electrode, A step of forming a common electrode on the first piezoelectric element, the second piezoelectric element, and the insulating layer, such that it covers at least a portion of the upper part of the first piezoelectric element and at least a portion of the upper part of the second piezoelectric element. Having, A method for manufacturing a piezoelectric actuator.

4. The process further includes a step of forming an upper electrode on the piezoelectric material between the step of forming the piezoelectric material and the etching step, In the etching process, the lower electrode, the piezoelectric element, and the upper electrode are etched to form a first piezoelectric element on the substrate, which consists of a laminated film of the first lower electrode, the first piezoelectric element, and the first upper electrode, and a second piezoelectric element, which consists of a laminated film of the second lower electrode, the second piezoelectric element, and the second upper electrode. In the step of forming the common electrode, the common electrode connected to the first upper electrode and the second upper electrode is formed. A method for manufacturing a piezoelectric actuator according to claim 3.

5. A nozzle plate having a nozzle for dispensing liquid, A flow path substrate provided on the nozzle plate and having a pressure chamber connected to the nozzle, A piezoelectric actuator according to claim 1 is provided on the flow channel substrate, A droplet dispensing head equipped with a liquid droplet head.

6. A substrate with an opening, A piezoelectric actuator according to claim 1 is provided on the aperture substrate, An ultrasonic device equipped with [specific features / features].

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