Piezoelectric actuator

Abstract

This piezoelectric actuator comprises: a piezoelectric element that comprises a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in the stated order on a substrate; and a drive unit that applies a drive voltage to the piezoelectric element. The drive unit is either: a first drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the second electrode, and a DC voltage generation circuit that applies a DC voltage having a predetermined value other than 0 V to the first electrode and / or the third electrode; or a second drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the first electrode and the third electrode, and a DC voltage generation circuit that applies a DC voltage having a predetermined value other than 0 V to the second electrode.

Description

Piezoelectric actuator

[0001] This disclosure relates to a piezoelectric actuator.

[0002] To obtain high piezoelectric properties, a multilayer piezoelectric element has been proposed in which multiple piezoelectric films are stacked with an electrode layer in between.

[0003] For example, Japanese Patent Publication No. 2024-052272 proposes a multilayer piezoelectric element in which a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode are sequentially stacked on a substrate. An actuator equipped with such a multilayer piezoelectric element having two layers of piezoelectric films can achieve approximately twice the displacement compared to an actuator equipped with a piezoelectric element having only one layer of piezoelectric film.

[0004] Japanese Patent Publication No. 2024-052272 describes a method for driving a multilayer piezoelectric element, which involves grounding the first and third electrodes and applying a driving voltage to the second electrode, or grounding the second electrode and applying a driving voltage to both the first and third electrodes. In the former case, the second electrode functions as the driving electrode, while in the latter case, the first and third electrodes function as the driving electrodes.

[0005] The drive waveform used to apply voltage to the drive electrode is set according to the purpose of the actuator. This can be a drive waveform in which the voltage changes periodically within a range where the relationship between displacement and voltage is linear, or a drive waveform in which the voltage changes periodically within a range where the displacement is maximized. A drive waveform generation circuit that generates a drive waveform with periodically changing voltage has an upper limit on the maximum output voltage fixed by the power supply voltage. Therefore, in order to obtain a large displacement, a drive waveform generation circuit equipped with a power supply with a large maximum voltage may be required. However, if a drive waveform generation circuit with a large maximum voltage is prepared, the size of the power supply will increase, leading to higher costs.

[0006] In view of the above circumstances, this disclosure aims to provide a piezoelectric actuator equipped with a stacked piezoelectric element that can apply a drive waveform according to the intended use while suppressing the high cost of the drive waveform generation circuit.

[0007] The piezoelectric actuator of this disclosure comprises a piezoelectric element having a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in that order on a substrate, and a drive unit that applies a drive voltage to the piezoelectric element, wherein the drive unit is either a first drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the second electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to at least one of the first electrode and the third electrode, or a second drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the first electrode and the third electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to the second electrode.

[0008] The first piezoelectric film and the second piezoelectric film may each have asymmetric bipolar polarization-voltage hysteresis characteristics, each having two countervoltages with different absolute values.

[0009] Preferably, the drive unit is a first drive unit, and the DC voltage generation circuit includes a first DC voltage generation circuit that applies a first DC voltage to a first electrode and a second DC voltage generation circuit that applies a second DC voltage to a third electrode.

[0010] In a case where the drive unit is a first drive unit, and the DC voltage generation circuit includes a first DC voltage generation circuit that applies a first DC voltage to a first electrode and a second DC voltage generation circuit that applies a second DC voltage to a third electrode, the drive waveform generation circuit may be a circuit that generates a negative polarity voltage waveform, and the first DC voltage generation circuit and the second DC voltage generation circuit generate the first DC voltage V ｄｃ１ Let the second DC voltage be V ｄｃ２ In that case, V ｄｃ１ > (-1) × Vc1 ＋ V ｄｃ２ >Vc2 － Satisfying the condition, where Vc1 ＋ Vc2 is the positive resistance voltage among the two resistance voltages in the first hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the first piezoelectric film, measured by grounding the first electrode and changing the potential applied to the second electrode. －preferably represents a negative-side coercive voltage among two coercive voltages in a second hysteresis curve measured by grounding the second electrode and changing the potential applied to the third electrode, which indicates the bipolar polarization-voltage hysteresis characteristic of the second piezoelectric film.

[0011] In the case where the drive unit is a first drive unit, and the direct-current voltage generation circuit includes a first direct-current voltage generation circuit that applies a first direct-current voltage to the first electrode and a second direct-current voltage generation circuit that applies a second direct-current voltage to the third electrode, the drive waveform generation circuit may be a circuit that generates a positive polarity voltage waveform, and the first direct-current voltage generation circuit and the second direct-current voltage generation circuit set the first direct-current voltage as V ｄｃ１ and set the second direct-current voltage as V ｄｃ２ In this case, ｄｃ１ < (-1)×Vc1 － V ｄｃ２ <Vc2 ＋ is satisfied, wherein Vc1 － is a negative-side coercive voltage among two coercive voltages in a first hysteresis curve measured by grounding the first electrode and changing the potential applied to the second electrode, which indicates the bipolar polarization-voltage hysteresis characteristic of the first piezoelectric film, and Vc2 ＋ preferably is a positive-side coercive voltage among two coercive voltages in a second hysteresis curve measured by grounding the second electrode and changing the potential applied to the third electrode, which indicates the bipolar polarization-voltage hysteresis characteristic of the second piezoelectric film.

[0012] It is preferable that both the first piezoelectric film and the second piezoelectric film contain a perovskite-type oxide represented by the general formula Pb{(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ}O ３ where M is a metal element selected from the group consisting of V, Nb, Ta, Sb, Mo and W, and 0 < x < 1, 0 < y < 1.

[0013] It is preferable that the metal element M is Nb and y is greater than 0.1.

[0014] According to the technology disclosed herein, a piezoelectric actuator equipped with a stacked piezoelectric element can be obtained that can apply a drive waveform according to the intended use while suppressing the high cost of the drive waveform generation circuit.

[0015] This figure shows the schematic configuration of the piezoelectric actuator of the first embodiment. This figure illustrates the drive voltage applied to the piezoelectric actuator of the first embodiment. This figure shows the schematic configuration of the piezoelectric actuator of the second embodiment. This figure illustrates the drive voltage applied to the piezoelectric actuator of the second embodiment. This figure shows the schematic configuration of the piezoelectric actuator of the third embodiment. This figure illustrates the drive voltage applied to the piezoelectric actuator of the third embodiment. This is a schematic diagram showing the schematic configuration of the piezoelectric actuator for evaluation. This figure shows the P-V hysteresis characteristics of the first piezoelectric film of the piezoelectric element used in the embodiment. This figure shows the P-V hysteresis characteristics of the second piezoelectric film of the piezoelectric element used in the embodiment.

[0016] Embodiments of the piezoelectric actuator of this disclosure will be described below with reference to the drawings. Note that, for ease of viewing, the layer thicknesses and their ratios in the following drawings have been modified as appropriate and do not necessarily reflect the actual layer thicknesses and ratios. In each figure, the same components are denoted by the same reference numerals.

[0017] <First Embodiment> Figure 1 is a diagram showing the schematic configuration of the piezoelectric actuator 1 of the first embodiment. The piezoelectric actuator 1 comprises a piezoelectric element 2 and a drive unit 30. In Figure 1, the piezoelectric element 2 is shown in a schematic cross-sectional view showing its layered structure.

[0018] As shown in Figure 1, the piezoelectric element 2 is formed by sequentially stacking a first electrode 12, a first piezoelectric film 14, a second electrode 16, a second piezoelectric film 18, and a third electrode 20 on a substrate 10. Details of each layer will be described later.

[0019] The drive unit 30 supplies a drive voltage to the first piezoelectric film 14 and the second piezoelectric film 18. The drive unit 30 includes a drive waveform generation circuit 31 and a DC voltage generation circuit 32. In the piezoelectric actuator 1, the drive waveform generation circuit 31 applies a unipolar voltage waveform as a drive waveform to the second electrode 16. Here, the drive waveform generation circuit 31 is a circuit that generates a negative polarity voltage waveform, and applies a negative polarity pulse waveform as a unipolar voltage waveform to the second electrode 16.

[0020] The DC voltage generation circuit 32 outputs a predetermined DC voltage V (not 0V) to the first electrode 12 and the third electrode 20. ｄｃ１ , V ｄｃ２ Apply the first DC voltage V to the first electrode 12. In this example, the DC voltage generation circuit 32 applies the first DC voltage V to the first electrode 12. ｄｃ１ A first DC voltage generating circuit 32a applies a second DC voltage V to the third electrode 20. ｄｃ２ It includes a second DC voltage generation circuit 32b that applies a first DC voltage V. The drive unit 30 is an example of the "first drive unit" of this disclosure. In Figure 1, the first DC voltage V is applied to the first electrode 12. ｄｃ１ = Bias voltage of V1, second DC voltage V applied to the third electrode 20 ｄｃ２ = V ３ A bias voltage is applied, and the absolute maximum value V is used as the drive waveform. ２ This shows an example of applying a negative pulse waveform.

[0021] As shown in Figure 2, +V is applied to the first electrode 12. １ A bias voltage of the magnitude V is applied to the second electrode 16. ２ When a pulse waveform of the above is input, the first piezoelectric film 14 substantially emits -V １ Shifted amplitude V ２ A negative pulse voltage of the magnitude V will be applied. In addition, an amplitude V will be applied to the second electrode 16. ２ A negative pulse waveform is input, and +V is applied to the third electrode 20. ３ When the bias voltage is applied, the second piezoelectric film 18 has substantially +V ３ Shifted amplitude V ２ A positive pulse voltage will be applied.

[0022] The rightmost figure in Figure 2 schematically shows the polarization P-voltage V hysteresis curves of the first piezoelectric film 14 and the second piezoelectric film 18. The hysteresis curve of the first piezoelectric film 14 was obtained by grounding the first electrode 12 and applying a sweep voltage to the second electrode 16. The hysteresis curve of the second piezoelectric film 18 was obtained by grounding the second electrode 16 and applying a sweep voltage to the third electrode 20. In this specification, the hysteresis curves of the first piezoelectric film 14 and the second piezoelectric film 18 are assumed to have been obtained as described above.

[0023] "The first piezoelectric film 14 has substantially -V １ Shifted amplitude V ２ "A negative pulse voltage will be applied" means that in the hysteresis curve of the first piezoelectric film 14, the dashed line between -V, indicated by the double arrow, is applied. １ ~-V ２ -V １ This means that a driving voltage in the range of is applied to the first piezoelectric film 14. Similarly, the second piezoelectric film 18 is substantially +V ３ Shifted amplitude V ２ "A positive pulse voltage of +V will be applied" means that in the hysteresis curve of the second piezoelectric film 18, the dashed line indicated by the double arrow is +V. ３ ~V ２ +V ３ This means that a driving voltage within this range is applied to the second piezoelectric film 18.

[0024] In this specification, the negative resistance voltage shown in the hysteresis curve for the first piezoelectric film 14 is Vc1 － The positive side resistance voltage is Vc1 ＋ The negative resistance voltage shown in the hysteresis curve for the second piezoelectric film 18 is Vc2 － The positive side resistance voltage is Vc2 ＋ As in this embodiment, a negative voltage waveform is applied to the second electrode 16, and the first DC voltage V is applied to the first electrode 12. ｄｃ１ Apply the second DC voltage V to the third electrode 20. ｄｃ２ When applying the following, it is preferable that the following conditions be met: V ｄｃ１ > (-1) × Vc1 ＋ V ｄｃ２ >Vc2－

[0025] As described above, the piezoelectric actuator 1 of this embodiment includes, in addition to a drive waveform generation circuit 31 for inputting a drive waveform to the drive electrode (the second electrode in the above description), a DC voltage generation circuit 32 for applying a DC voltage as a bias voltage to at least one of the first electrode and the third electrode in the drive unit 30. With this configuration, the piezoelectric element 2 can be driven with a drive waveform shifted by the bias voltage according to the purpose of use, while keeping the cost of the drive unit 30 low. When shifting the drive waveform to the negative or positive side according to the purpose of use, it is also conceivable to superimpose an offset voltage on the drive waveform. However, since the maximum voltage is limited by the maximum voltage output of the drive waveform generation circuit, if the shift amount is increased, it may be necessary to prepare a drive waveform generation circuit equipped with a power supply with a large maximum voltage output. It is relatively less costly to prepare a DC voltage generation circuit for applying the bias voltage than to prepare such a power supply with a large maximum voltage output. In addition, it may be unnecessary to prepare a new power supply for the DC voltage generation circuit by drawing the power supply voltage for the DC voltage generation circuit from the power supply for driving other electronic components attached to the device to which the piezoelectric actuator is applied.

[0026] The P-V hysteresis curves of the first piezoelectric film 14 and the second piezoelectric film 18 shown in Figure 2 exhibit asymmetric bipolar polarization-voltage hysteresis characteristics, where the absolute values ​​of the negative and positive resistance voltages are different. The technology of this disclosure is also applicable when the first piezoelectric film 14 and the second piezoelectric film 18 have symmetric hysteresis characteristics. However, it is particularly effective when the piezoelectric element 2 is equipped with piezoelectric films having asymmetric hysteresis characteristics stacked on top of each other.

[0027] Furthermore, when a negative voltage waveform is applied to the second electrode 16, the first DC voltage V applied to the first electrode 12 ｄｃ１ (-1) × Vc1 ＋ The value should be greater than V ｄｃ１ > (-1) × Vc1 ＋By satisfying this condition, the first piezoelectric film 14 can be driven using a region in which the relationship between voltage and displacement exhibits relatively high linearity. In addition, the second DC voltage V applied to the third electrode 20 ｄｃ２ The negative side resistance voltage Vc2 of the second piezoelectric film 18 － The value should be greater than V ｄｃ２ >Vc2 － By satisfying this condition, the second piezoelectric film 18 can be driven using a region in which the relationship between voltage and displacement exhibits relatively high linearity.

[0028] <Second Embodiment> Figure 3 is a diagram showing the schematic configuration of the piezoelectric actuator 3 of the second embodiment. The piezoelectric actuator 3 comprises a piezoelectric element 2 and a drive unit 33. The piezoelectric element 2 is the same as in the first embodiment.

[0029] The drive unit 33 supplies a drive voltage to the first piezoelectric film 14 and the second piezoelectric film 18. The drive unit 33 includes a drive waveform generation circuit 34 and a DC voltage generation circuit 35. In the piezoelectric actuator 3, the drive waveform generation circuit 34 applies a unipolar voltage waveform as a drive waveform to the second electrode 16. Here, the drive waveform generation circuit 34 is a circuit that generates a positive polarity voltage waveform, and applies a positive polarity pulse waveform as a unipolar voltage waveform to the second electrode 16.

[0030] The DC voltage generation circuit 35 outputs a predetermined DC voltage V (not 0V) to the first electrode 12 and the third electrode 20. ｄｃ１ , V ｄｃ２ Apply the first DC voltage V to the first electrode 12. In this example, the DC voltage generation circuit 35 applies the first DC voltage V to the first electrode 12. ｄｃ１ A first DC voltage generating circuit 35a applies a second DC voltage V to the third electrode 20. ｄｃ２ It includes a second DC voltage generating circuit 35b that applies the first DC voltage V. The drive unit 33 is an example of the "first drive unit" of this disclosure. In Figure 3, the first DC voltage V is applied to the first electrode 12. ｄｃ１ = -V1 bias voltage, second DC voltage V applied to third electrode 20 ｄｃ２ = -V ３ A bias voltage is applied, and the absolute maximum value V is used as the drive waveform. ２ This shows an example of applying a negative pulse waveform.

[0031] As shown in FIG. 4, -V is applied to the first electrode 12 １ bias voltage is applied, and the amplitude V is applied to the second electrode 16 ２ is input as a positive pulse waveform, the first piezoelectric film 14 is substantially applied with +V １ shifted amplitude V ２ positive pulse voltage is applied. Further, when the amplitude V is applied to the second electrode 16 ２ positive pulse waveform is input, and -V is applied to the third electrode 20 ３ bias voltage is applied, the second piezoelectric film 18 is substantially applied with -V ３ shifted amplitude V ２ negative pulse voltage is applied. That is, in the hysteresis curve of the first piezoelectric film 14, a drive voltage within the range between the broken lines indicated by the double-headed arrow V １ to V ２ +V １ is applied to the first piezoelectric film 14. Then, in the hysteresis curve of the second piezoelectric film 18, a drive voltage within the range between the broken lines indicated by the double-headed arrow -V ３ to -V ２ -V ３ is applied to the second piezoelectric film 18.

[0032] As in the present embodiment, when a positive voltage waveform is applied to the second electrode 16, a first DC voltage V is applied to the first electrode 12 ｄｃ１ is applied, and a second DC voltage V is applied to the third electrode 20 ｄｃ２ is applied, it is preferable that the following conditions are satisfied. V ｄｃ１ < (-1)×Vc1 － V ｄｃ２ <Vc2 ＋

[0033] Also in the piezoelectric actuator 3 of the present embodiment, similarly to the piezoelectric actuator 1 of the first embodiment, the piezoelectric element 2 can be driven with a drive waveform shifted by the bias voltage amount according to the purpose of use while suppressing an increase in cost of the drive unit 33. Further, the present invention is particularly effective in a case where the piezoelectric element 2 is provided with laminated piezoelectric films having asymmetric hysteresis characteristics. In the present embodiment, the drive waveform generation circuit 34 generates a positive polarity voltage waveform, and is less expensive than the drive waveform generation circuit 31 that generates a negative polarity voltage waveform used in the first embodiment, so cost reduction can be achieved as a whole.

[0034] In the case where a positive polarity voltage waveform is applied to the second electrode 16, the first DC voltage V applied to the first electrode 12 ｄｃ１ is set to (-1)×Vc1 － that is, V ｄｃ１ < (-1)×Vc1 － By satisfying this requirement, the first piezoelectric film 14 can be driven using a region where the relationship between voltage and displacement exhibits relatively high linearity. Further, the second DC voltage V applied to the third electrode 20 ｄｃ２ is set to be smaller than the coercive voltage Vc2 on the positive side of the second piezoelectric film 18 ＋ that is, V ｄｃ２ < Vc2 ＋ By satisfying this requirement, the second piezoelectric film 18 can be driven using a region where the relationship between voltage and displacement exhibits relatively high linearity.

[0035] In the first embodiment and the second embodiment, the DC voltage generation circuits 32 and 35 respectively include a first DC voltage V applied to the first electrode 12 ｄｃ１ first DC voltage generation circuits 32a and 35a that apply, and a second DC voltage V applied to the third electrode 20 ｄｃ２The device includes second DC voltage generating circuits 32b and 35b that apply a DC voltage. However, the DC voltage generating circuit may consist of only one DC voltage generating circuit, and may be configured to short-circuit the first electrode 12 and the third electrode 20 and apply the same DC voltage to the first electrode 12 and the third electrode 20. In this case, the number of wires can be reduced and miniaturization is possible compared to the case in which voltage is applied to the first electrode 12 and the third electrode 20 individually. Alternatively, the DC voltage generating circuit may be configured to apply a DC voltage other than 0V to only one of the first electrode 12 and the third electrode 20, and to ground the other.

[0036] In the piezoelectric actuators 1 and 3 of the first and second embodiments, the drive waveform is input to the second electrode 16. However, as in the third embodiment described later, it is also possible to configure the actuators so that a unipolar voltage waveform is applied to the first and third electrodes as the drive waveform, and a DC voltage is applied to the second electrode as the bias voltage.

[0037] <Third Embodiment> Figure 5 shows a schematic configuration of the piezoelectric actuator 5 of the third embodiment. The piezoelectric actuator 5 comprises a piezoelectric element 2 and a drive unit 37. The piezoelectric element 2 is the same as that of the first and second embodiments.

[0038] The drive unit 37 includes a drive waveform generation circuit 38 and a DC voltage generation circuit 39. In the piezoelectric actuator 5, the drive waveform generation circuit 38 applies a unipolar voltage waveform as a drive waveform to the first electrode 12 and the third electrode 20. In this example, the drive waveform generation circuit 38 is a circuit that generates a positive polarity voltage waveform, and applies a positive polarity pulse waveform as a unipolar voltage waveform to the first electrode 12 and the third electrode 20. The DC voltage generation circuit 39 applies a DC voltage V of a predetermined value other than 0V to the second electrode 16. ｄｃ The following is applied. The drive unit 37 is an example of the "second drive unit" of this disclosure.

[0039] In Figure 5, a DC voltage V is applied to the second electrode 16. ｄｃ Apply a bias voltage of =V, and the absolute maximum value V is used as the drive waveform. １３ This shows an example of applying a positive pulse waveform.

[0040] As shown in Figure 6, the amplitude V of the first electrode 12 １３ When a positive pulse waveform is input and a bias voltage of -V is applied to the second electrode 16, the first piezoelectric film 14 receives an amplitude V that is substantially shifted by +V. １３ A positive pulse voltage of is applied. Additionally, a bias voltage of -V is applied to the second electrode 16, and an amplitude V is applied to the third electrode 20. １３ When a positive pulse waveform is input, the second piezoelectric film 18 receives a substantially -V shifted amplitude V １３ A negative pulse voltage is applied to the first piezoelectric film 14. In other words, in the hysteresis curve of the first piezoelectric film 14, between the dashed line V to V indicated by the double arrow １３ A driving voltage in the range of +V is applied to the second piezoelectric film 18. １３ A drive voltage in the range of -V is applied.

[0041] In this embodiment, the piezoelectric actuator 5, like the piezoelectric actuator 1 of the first embodiment or the piezoelectric actuator 3 of the second embodiment, can drive the piezoelectric element 2 with a drive waveform shifted by the bias voltage according to the intended use, while suppressing the high cost of the drive unit 37. This is particularly effective when the piezoelectric element 2 is made up of a piezoelectric film laminated with asymmetric hysteresis characteristics. In this embodiment, the drive waveform generation circuit 38 generates a positive voltage waveform, and is less expensive than the drive waveform generation circuit 31 that generates a negative voltage waveform used in the first embodiment, thus reducing overall costs.

[0042] In this example, the first electrode 12 and the third electrode 20 are short-circuited, and the drive waveform generation circuit 38 is configured to input the same drive waveform to both the first electrode 12 and the third electrode 20. However, the drive waveform generation circuit 38 may also include a first drive waveform generation circuit that inputs a first drive waveform to the first electrode 12 and a second drive waveform generation circuit that inputs a second drive waveform to the third electrode 20. Alternatively, the drive waveform generation circuit 38 may be replaced with a drive waveform generation circuit that generates a negative unipolar voltage waveform.

[0043] An example of the configuration of the piezoelectric element 2 is described below. The substrate 10 is not particularly limited and can be a substrate such as silicon, glass, stainless steel, yttrium-stabilized zirconia, alumina, sapphire, or silicon carbide. The substrate 10 is a silicon substrate with SiO on the surface. ２ A laminated substrate such as a silicon substrate with a thermal oxide film formed thereon may be used. Alternatively, the substrate 10 may be a resin substrate such as PET (polyethylene terephthalate), PEN (polyethylene naphthalate), or polyimide.

[0044] The first electrode 12 is formed on the substrate 10. The main component of the first electrode 12 is not particularly limited and includes metals or metal oxides such as Au (gold), Pt (platinum), Ir (iridium), Ru (ruthenium), Ti (titanium), Mo (molybdenum), Ta (tantalum), Al (aluminum), and combinations thereof. Also, ITO (Indium Tin Oxide) and LaNiO are also possible. ３ , and SRO(SrRuO ３ You may also use things like ) etc.

[0045] The second electrode 16 is laminated on the first piezoelectric film 14, and the third electrode 20 is laminated on the second piezoelectric film 18. The first electrode 12 and the second electrode 16 work together to apply an electric field to the first piezoelectric film 14. The second electrode 16 and the third electrode 20 work together to apply an electric field to the second piezoelectric film 18.

[0046] The main components of the second electrode 16 and the third electrode 20 are not particularly limited, and include the materials exemplified for the first electrode 12, as well as electrode materials commonly used in semiconductor processes such as Cr, and combinations thereof. However, it is preferable to use an oxide conductor for the layer in contact with the first piezoelectric film 14 or the second piezoelectric film 18. Specifically, the oxide conductor layer can be ITO (Indium Tin Oxide), Ir oxide, SRO (SrRuO ３ In addition to ), LaNiO ３ Examples include doped ZnO.

[0047] The thickness of the first electrode 12, the second electrode 16, and the third electrode 20 is not particularly limited, but is preferably about 50 nm to 300 nm, and more preferably 100 nm to 300 nm.

[0048] The first piezoelectric film 14 and the second piezoelectric film 18 are not particularly limited, but it is preferable that they are films in which the direction of spontaneous polarization is aligned in the film thickness direction immediately after film formation, as shown in Figure 1, etc. It is preferable that the first piezoelectric film 14 and the second piezoelectric film 18 are mainly composed of perovskite-type oxides. Here, the main component refers to the component that accounts for 80 mol% or more. It is preferable that the first piezoelectric film 14 and the second piezoelectric film 18 each account for 90 mol% or more of perovskite-type oxides, and it is more preferable that the first piezoelectric film 14 and the second piezoelectric film 18 consist of perovskite-type oxides (however, they include unavoidable impurities).

[0049] The perovskite-type oxide is preferably a lead zirconate titanate (PZT) system containing Pb (lead), Zr (zirconium), Ti (titanium), and O (oxygen).

[0050] In particular, it is preferable that the perovskite-type oxide is a compound represented by the following general formula (1), which contains a metal element M as an additive at the B site of PZT. Pb{(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ}O ３ (1) Here, the metallic element M is preferably one or more elements selected from V (vanadium), Nb (niobium), Ta (tantalum), Sb (antimony), Mo (molybdenum), and W (tungsten). Here, 0 < x < 1 and 0 < y < 1. Note that in general formula (2), Pb: {(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ}:O is based on a 1:1:3 ratio, but may deviate within the range that allows for a perovskite structure. Below, Pba{(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ}O ３This is called M-doped PZT. For example, if the metal element M is Nb, it is called Nb-doped PZT.

[0051] The metal element M may be a single element such as V only or Nb only, or it may be a combination of two or more elements such as a mixture of V and Nb, or a mixture of V, Nb, and Ta. When the metal element M is one of these elements, a very high piezoelectric constant can be achieved when combined with the A-site element Pb.

[0052] In particular, Pb{(Zr ｘ Ti １－ｘ ) １－ｙ Nb ｙ}O ３ This is optimal. In this case, a higher piezoelectric constant can be obtained when y > 0.1. When a piezoelectric film is formed by vapor phase growth method such as sputtering using Nb-doped PZT where M is Nb, a piezoelectric film with a very high piezoelectric constant can be obtained in which the spontaneous polarization is more aligned upward from the substrate in the film thickness direction.

[0053] It is preferable that the perovskite-type oxide of the first piezoelectric film 14 and the perovskite-type oxide of the second piezoelectric film 18 have the same composition. Here, assuming that each element symbol represents its respective molar ratio, the Pb composition ratio in the perovskite-type oxide is Pb / (Zr+Ti+M), the Zr composition ratio in the B site is Zr / (Zr+Ti), the Ti composition ratio is Ti / (Zr+Ti), and the M composition ratio is M / (Zr+Ti+M), which is the composition ratio of the metal element M. The perovskite-type oxide of the first piezoelectric film 14 and the perovskite-type oxide of the second piezoelectric film 18 have the same composition, which means that the Pb composition ratios, Zr composition ratios, Ti composition ratios, and M composition ratios are equal within the range of measurement error.

[0054] The film thickness of the first piezoelectric film 14 and the second piezoelectric film 18 is preferably 0.2 μm or more and 5 μm or less, and more preferably 1 μm or more.

[0055] The following describes specific examples and comparative examples of the piezoelectric elements of this disclosure. First, the manufacturing method of each example piezoelectric element will be described. In describing the manufacturing method, the reference numerals of each layer of the piezoelectric element 2 shown in Figure 1 will be used for the explanation.

[0056] (First Electrode Film Formation) A silicon on insulator (SOI) substrate with a thermal oxide film was used as the substrate 10. The first electrode 12 was formed on the substrate 10 by RF (radio-frequency) sputtering. Specifically, the substrate temperature was set to 350°C, and a 50 nm TiW layer and a 200 nm Ir layer were stacked on the substrate 10 in that order to form the first electrode 12.

[0057] (First Piezoelectric Film) A first piezoelectric film 14 was deposited on the first electrode 12 by RF sputtering. The substrate temperature was set to 700°C, and an Nb-doped PZT film with an Nb addition amount of 12 at% to the B site was deposited as the first piezoelectric film 14. Nb-doped PZT was used as the target, and the amount of Pb in the target was set to be greater than the stoichiometric composition. In addition, the Ti / Zr molar ratio in the target was set to the MPB composition (Ti / Zr = 52 / 48).

[0058] (Second electrode) A second electrode 16 was deposited on the first piezoelectric film 14 by RF sputtering. The substrate temperature was set to 350°C, and a 50 nm IrO ｚ (Z≦2) and 200 nm Ir were stacked in this order to form the second electrode 16.

[0059] (Second piezoelectric film) An Nb-doped PZT film was deposited as the second piezoelectric film 18 under the same deposition conditions as the first piezoelectric film 14.

[0060] (Third electrode) A third electrode 20 was deposited on the second piezoelectric film 18 by RF sputtering. At room temperature, 50 nm IrO ｚ The 100 nm Ir layers were stacked in this order to form the third electrode 20.

[0061] (Fabrication of a piezoelectric actuator for evaluation) A piezoelectric actuator 101 equipped with an evaluation piezoelectric element 102 was fabricated using a piezoelectric laminate formed by laminating electrodes and a piezoelectric film on a substrate as described above. Figure 7 is a schematic diagram showing the cross-sectional structure of the evaluation piezoelectric element 102. In Figure 7, layers equivalent to those shown in Figure 1 are denoted by the same reference numerals.

[0062] To connect the first electrode 12, the second electrode 16, and the third electrode 20 to the electrode pad for voltage application, the third electrode 20, the second piezoelectric film 18, the second electrode 16, and the first piezoelectric film 14 were sequentially patterned by photolithography and dry etching. Subsequently, an insulating film 105 was deposited and patterned by photolithography and dry etching to provide insulation for each layer. The insulating film was fabricated by the CVD (Chemical vapor deposition) method. Here, SiO was used as the insulating film. ２ Al was used as the insulating film. ２ O ３ Alternatively, an organic insulating film such as photosensitive polyimide may be used. Then, a wiring 106 for applying a drive signal to the second electrode 16 and a first DC voltage V to the first electrode 12 are applied. ｄｃ１ Wiring 107 for applying the second DC voltage V to the third electrode 20 ｄｃ２ Wiring 108 for applying the current was formed. Finally, the silicon of the back handle layer was removed by vertical etching, leaving only the SOI device layer (10 μm in this case) that forms the diaphragm in the actuator displacement portion, to create a diaphragm shape.

[0063] <Measurement of P-V Hysteresis Characteristics> For each piezoelectric film described above, the lower side (substrate side) in the film thickness direction is grounded, and a bipolar voltage is applied to the upper side to measure the polarization (charge density) P [μC / cm²]. ２ The relationship between the voltage V[V] and the hysteresis characteristics of the first piezoelectric film 14 was measured by grounding the first electrode 12 and applying a bipolar voltage to the second electrode 16, and the P-V hysteresis characteristics of the second piezoelectric film 18 were measured by grounding the second electrode 16 and applying a bipolar voltage to the third electrode 20.

[0064] Figure 8 shows the P-V hysteresis of the first piezoelectric film 14, and Figure 9 shows the P-V hysteresis of the second piezoelectric film 18. The two resistance voltages Vc1 of the first piezoelectric film 14 obtained from Figures 8 and 9 are shown. － , Vc1 ＋ , the two resistance voltages Vc2 of the second piezoelectric film 18 － , Vc2 ＋ The P-V characteristics of these components were as shown in Tables 1 and 2 below.

[0065] As shown in Figures 8 and 9, the hysteresis curves of both piezoelectric films 14 and 18 are biased towards the positive side in the voltage direction and are asymmetrical. This means that the spontaneous polarization in both cases is aligned in the direction from the substrate side to the film deposition surface side in the film thickness direction. Furthermore, when the spontaneous polarization is aligned in this manner immediately after film deposition, polarization treatment becomes unnecessary, which reduces manufacturing costs and is therefore preferable.

[0066] The first electrode 12, second electrode 16, and third electrode 20 of the piezoelectric element 102 shown in Figure 7 are electrically insulated from each other. A drive voltage waveform is input to the second electrode 16 of the piezoelectric element 102 via wiring 106, and a bias voltage V is input to the first electrode 12 via wiring 107. ｄｃ１ The following is input, and the third electrode 20 receives a bias voltage via the wiring 108. Ｖｄｃ２ A drive circuit (drive unit), not shown in the diagram, is connected so that the input is received.

[0067] <Measurement of Displacement During Driving> A pulse waveform (see Figure 1, etc.) was used as the driving waveform, and the peak value of the current and the displacement during driving were measured. Here, the maximum value of the absolute voltage value in one period of the pulse waveform is defined as V2, and the minimum value as V0.

[0068] The maximum and minimum values ​​of the drive waveform (pulse waveform) input to the second electrode 16, and the bias voltage V input to the first electrode 12. ｄｃ１ and the bias voltage V input to the third electrode 20 ｄｃ２ For the examples and comparative examples in which at least one of the above was changed, the peak value of the current during operation and the displacement were measured. Examples 1 to 7 and Comparative Example 1 used a power supply with a maximum output voltage of 48V, while Comparative Example 2 used a power supply with a maximum output voltage of 60V. The respective voltage values ​​are summarized in Table 3 below.

[0069] The drive circuit that outputs the drive waveform comprises a function generator and a voltage amplification amplifier. The drive voltage waveform is output from the function generator, amplified to the desired voltage value via the voltage amplification amplifier, and applied to the sample. The time evolution of the current during driving was measured using a current probe, and the maximum current within one pulse period was recorded as the peak value of the current.

[0070] The displacement was measured using a laser Doppler vibrometer, capturing the time waveform of the displacement velocity at the actuator's maximum displacement point (the center point of the diaphragm). Table 3 shows the maximum displacement values.

[0071] Table 3 shows the peak current values ​​(mA) and displacement amounts (nm) measured in each example and comparative example. Note that the "percentages" of current and displacement are normalized values ​​based on the values ​​of Comparative Example 1, and represent the ratio to the values ​​of Comparative Example 1.

[0072] As shown in Table 1, in Examples 1 to 5, the displacement amount decreased to 87% to 91% compared to the case without bias voltage (Comparative Example 1), but the current peak value was significantly suppressed to 44% to 60%. Example 6 achieved a displacement amount equivalent to Comparative Example 1 with a current peak value of approximately 73%. By applying the drive voltage waveform and bias voltage to separate electrodes, it is possible to freely select a drive voltage range that can suppress power consumption and maintain the displacement amount in the hysteresis shown in Figures 8 and 9. Furthermore, in Example 7, although the current amount increased, a larger displacement amount was obtained compared to the case without bias voltage. Example 7 uses the same drive waveform generation circuit with a maximum output voltage of 48V as Comparative Example 1, and it was possible to obtain a large displacement without changing the maximum output voltage of the drive waveform generation circuit.

[0073] In Comparative Example 2, the first electrode and the third electrode are grounded (i.e., V ｄｃ１ = V ｄｃ２(Assuming = 0), an offset voltage of -10V is superimposed on the drive waveform. Superimposing an offset voltage of -10V on the drive waveform, as in Comparative Example 2, is equivalent to applying a DC voltage of 10V to the first and third electrodes, as in Example 2. In other words, the voltage applied to the first and second piezoelectric films is substantially the same in Comparative Example 2 and Example 2. Therefore, the amount of current and displacement were the same in both cases. However, the required power supply voltage differs between Comparative Example 2 and Example 2. In Example 2, a 48V power supply can be used, but in Comparative Example 2, since the absolute maximum voltage of the pulse waveform is 50V, a 48V power supply cannot be used, and a 60V power supply had to be used. A 60V power supply is more expensive and larger than a 48V power supply. Here, it is assumed that a power supply with a standardized specification for industrial use is used, and either a 48V power supply or a 60V power supply was used. This is because power supplies with non-standardized voltages are not generally available and tend to be more expensive than standardized ones.

[0074] The disclosure of Japanese Patent Application No. 2025-047163, filed on 21 March 2025, is incorporated herein by reference in its entirety. All documents, patent applications and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application and technical standard were specifically and individually noted to be incorporated by reference.

[0075] The following additional information is disclosed regarding the above embodiment.

[0076] <Note 1> A piezoelectric actuator comprising a piezoelectric element having a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in this order on a substrate, and a drive unit that applies a drive voltage to the piezoelectric element, wherein the drive unit is either a first drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the second electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to at least one of the first electrode and the third electrode, or a second drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the first electrode and the third electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to the second electrode. <Note 2> The piezoelectric actuator according to Note 1, wherein the first piezoelectric film and the second piezoelectric film each have asymmetric bipolar polarization-voltage hysteresis characteristics having two countervoltages with different absolute values ​​from each other. <Note 3> The drive unit is a first drive unit, and the DC voltage generation circuit includes a first DC voltage generation circuit that applies a first DC voltage to a first electrode and a second DC voltage generation circuit that applies a second DC voltage to a third electrode, as described in Note 1 or Note 2, for the piezoelectric actuator. <Note 4> The drive waveform generation circuit is a circuit that generates a negative polarity voltage waveform, and the first DC voltage generation circuit and the second DC voltage generation circuit generate the first DC voltage V ｄｃ１ Let the second DC voltage be V ｄｃ２ In that case, V ｄｃ１ > (-1) × Vc1 ＋ V ｄｃ２ >Vc2 － Satisfying the condition, where Vc1 ＋ Vc2 is the positive resistance voltage among the two resistance voltages in the first hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the first piezoelectric film, measured by grounding the first electrode and changing the potential applied to the second electrode. －The piezoelectric actuator described in Appendix 3, wherein the second hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the second piezoelectric film, is the negative resistance voltage of the two resistance voltages in the second hysteresis curve measured by grounding the second electrode and changing the potential applied to the third electrode. <Appendix 5> The drive waveform generation circuit is a circuit that generates a positive polarity voltage waveform, and the first DC voltage generation circuit and the second DC voltage generation circuit generate the first DC voltage V ｄｃ１ Let the second DC voltage be V ｄｃ２ In that case, V ｄｃ１ < (-1) × VC1 － V ｄｃ２ <Vc2 ＋ Satisfying the condition, where Vc1 － Vc2 is the negative resistance voltage among the two resistance voltages in the first hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the first piezoelectric film, measured by grounding the first electrode and changing the potential applied to the second electrode. ＋ This is the positive resistance voltage of the two resistance voltages in the second hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the second piezoelectric film, measured by grounding the second electrode and changing the potential applied to the third electrode, as described in Appendix 3 of the piezoelectric actuator. <Appendix 6> Both the first piezoelectric film and the second piezoelectric film are based on the general formula Pb{(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ}O ３ A piezoelectric actuator according to any one of the appendices 1 to 5, wherein M is a metallic element selected from the group consisting of V, Nb, Ta, Sb, Mo, and W, and includes a perovskite-type oxide represented by 0 < x < 1 and 0 < y < 1. <Appendix 7> A piezoelectric actuator according to appendix 6, wherein the metallic element M is Nb and y is greater than 0.1.

Claims

1. A piezoelectric actuator comprising: a piezoelectric element having a first electrode, a first piezoelectric film, a second electrode, a second piezoelectric film, and a third electrode in this order on a substrate; and a drive unit that applies a drive voltage to the piezoelectric element, wherein the drive unit is either a first drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the second electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to at least one of the first electrode and the third electrode, or a second drive unit comprising a drive waveform generation circuit that applies a unipolar voltage waveform to the first electrode and the third electrode and a DC voltage generation circuit that applies a DC voltage of a predetermined value other than 0V to the second electrode.

2. The piezoelectric actuator according to claim 1, wherein the first piezoelectric film and the second piezoelectric film each have asymmetric bipolar polarization-voltage hysteresis characteristics having two countervoltages with different absolute values ​​from each other.

3. The piezoelectric actuator according to claim 1 or 2, wherein the drive unit is the first drive unit, and the DC voltage generation circuit includes a first DC voltage generation circuit for applying a first DC voltage to the first electrode and a second DC voltage generation circuit for applying a second DC voltage to the third electrode.

4. The drive waveform generation circuit is a circuit that generates a negative polarity voltage waveform, and the first DC voltage generation circuit and the second DC voltage generation circuit generate the first DC voltage V ｄｃ１ Let the second DC voltage be V ｄｃ２ In that case, V ｄｃ１ > (-1) × Vc1 ＋ V ｄｃ２ >Vc2 － Satisfying the condition, where Vc1 ＋ Vc2 is the positive resistance voltage among the two resistance voltages in the first hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the first piezoelectric film, measured by grounding the first electrode and changing the potential applied to the second electrode. － The piezoelectric actuator according to claim 3, wherein is the negative resistance voltage of the two resistance voltages in the second hysteresis curve, which shows the bipolar polarization-voltage hysteresis characteristics of the second piezoelectric film, measured by grounding the second electrode and changing the potential applied to the third electrode.

5. The drive waveform generating circuit is a circuit that generates a positive polarity voltage waveform, and the first DC voltage generating circuit and the second DC voltage generating circuit set the first DC voltage as V ｄｃ１ , and when the second DC voltage is set as V ｄｃ２ , V ｄｃ１ <(-1)×Vc1 － V ｄｃ２ <Vc2 ＋ is satisfied, wherein Vc1 － is the negative-side coercive voltage among two coercive voltages in a first hysteresis curve that indicates the bipolar polarization-voltage hysteresis characteristic of the first piezoelectric film and is measured by grounding the first electrode and changing the potential applied to the second electrode, and Vc2 ＋ is the positive-side coercive voltage among two coercive voltages in a second hysteresis curve that indicates the bipolar polarization-voltage hysteresis characteristic of the second piezoelectric film and is measured by grounding the second electrode and changing the potential applied to the third electrode. The piezoelectric actuator according to claim 3.

6. Both the first piezoelectric film and the second piezoelectric film are of the general formula Pb{(Zr ｘ Ti １－ｘ ) １－ｙ M ｙ }O ３ The piezoelectric actuator according to claim 1 or 2, wherein M is a metallic element selected from the group consisting of V, Nb, Ta, Sb, Mo, and W, and comprises a perovskite-type oxide represented by 0 < x < 1 and 0 < y < 1.

7. The piezoelectric actuator according to claim 6, wherein the metal element M is Nb and y is greater than 0.1.

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