JP6325280B2 - Piezoelectric MEMS device and manufacturing method thereof - Google Patents

Description

  The present invention relates to a micro electro mechanical systems (MEMS) device including a piezoelectric element and a manufacturing method thereof.

A thin film (piezoelectric thin film) made of a piezoelectric material typified by lead zirconate titanate (PZT) is widely used for an actuator of an inkjet head, various sensors for pressure and temperature, and the like (for example, Patent Document 1).
This piezoelectric thin film is expected to further expand the application field by being incorporated in MEMS using advanced semiconductor microfabrication technology.
Examples of means for improving the piezoelectric properties of the piezoelectric thin film include improvement of crystal orientation, use of additives, poling to apply a DC voltage, and various attempts have been made in consideration of production efficiency and reliability. Has been made.

Here, regarding the improvement of crystal orientation, ferroelectric hysteresis is saturated in two stages by applying an alternating voltage to a ferroelectric formed with (100) and (001) oriented PZT thin films while gradually increasing it. Has been reported (Non-Patent Document 1). Accordingly, it has been found that the piezoelectric constant d33 increases from a value of 50 pm / V or less to 200 pm / V or more.
In this Non-Patent Document 1, (100) and (001) oriented PZT thin films having a thickness of 2 μm are formed on a Pt / Ti / SiO ₂ / Si substrate by chemical vapor deposition (CVD), and the PZT thin film is formed on the PZT thin film. A ferroelectric obtained by forming an upper electrode (platinum) having a diameter of 200 μm is used.

Japanese Patent Laid-Open No. 11-214763

Nakajima et al., Applied Physics Letters, vol. 97, 181907 (2010)

Microscopically, the increase in the piezoelectric constant due to the application of AC voltage is due to the microscopic change of the (100) orientation component of the PZT thin film to the (001) orientation component. In order to improve the crystal orientation of the piezoelectric thin film, it is important to improve the (001) orientation (c-axis orientation).
However, when the crystal orientation is changed by applying an alternating voltage, the piezoelectric thin film is restrained by the support substrate, and therefore a stress corresponding to the restraining force acts. There is a risk that micro cracks (micro cracking) may occur due to the stress.
Therefore, the present invention relates to a piezoelectric device, and an object thereof is to ensure reliability without causing cracks in a piezoelectric thin film while improving piezoelectric characteristics based on crystal orientation.

If the piezoelectric thin film is supported on the substrate, it is inevitable that stress acts due to the restraining force of the substrate when the crystal orientation changes. However, the substrate is necessary to ensure rigidity as a device.
By the way, in the MEMS, a structure in which mechanical elements are formed is laminated on a support substrate. A piezoelectric thin film is provided on the structure. The MEMS structure is, for example, a micro cantilever of a probe of a scanning probe microscope (SPM), and has a thickness equivalent to that of a piezoelectric thin film to about 10 times the thickness. If the piezoelectric thin film is supported on the structure having such a thickness, the structure follows the distortion of the piezoelectric thin film accompanying the change in crystal orientation, so that the stress can be released.

The first piezoelectric MEMS device of the present invention made there is provided with a structure including a mechanical element manufactured by a semiconductor processing process, a support substrate that supports the structure, and a piezoelectric thin film supported by the structure. ing.
In the present invention, the structure includes a supported portion supported on the support surface of the support substrate and a functional portion extending beyond the support surface, and the piezoelectric thin film functions at least in the structure. C-axis orientation by an alternating voltage application process performed after forming the support substrate or a one-side voltage application process that applies a voltage that changes only on one of the positive and negative sides performed after the support substrate molding. sex has increased, the piezoelectric thin film includes a tetragonal, made of lead zirconate titanate is tetra composition, the voltage applied by the AC voltage applying process or one-sided voltage application process, the thickness of the piezoelectric thin film It is characterized by being 20 V or more per 1 μm .
In the first piezoelectric MEMS device of the present invention, it is preferable that the voltage applied in the one-side voltage application process is 20 to 40 V per 1 μm film thickness of the piezoelectric thin film.

In addition, a second piezoelectric MEMS device of the present invention includes a structure including a mechanical element manufactured by a semiconductor processing process, a support substrate that supports the structure, and a piezoelectric thin film supported by the structure. Yes.
In the present invention, the structure integrally includes a supported portion supported on the support surface of the support substrate and a functional portion extending beyond the support surface. The AC voltage application process that is provided at least in the functional unit and that is performed after the support substrate is molded, or the one-side voltage application process that is performed after the support substrate is molded and that applies a voltage that changes only on one of the positive and negative sides. The axial orientation is enhanced, and the piezoelectric thin film is composed of lead zirconate titanate containing tetragonal crystal and having a morphotropic phase boundary composition, and the voltage applied in the one-side voltage application process is the film of the piezoelectric thin film. It is characterized by being 30 V or more per 1 μm thickness .

In both the first and second inventions, the support for the piezoelectric thin film is left to the structure while using the support substrate to maintain the rigidity of the entire piezoelectric MEMS device, thereby reducing the binding force on the piezoelectric thin film. Yes.
Since the stress of the piezoelectric thin film during the AC voltage application process is relieved by the bending of the functional part of the structure, the piezoelectric characteristics can be improved without causing cracks in the piezoelectric thin film.
The functional part of the structure of the present invention refers to a part that extends beyond the support surface of the support substrate on which the supported part of the structure is supported. The form of a supported part and a function part is not ask | required. Examples of the functional part include a beam-like one having one end continuous to the supported part and extending to the other end, and a diaphragm-like one extending inside the frame-like supported part.

In the piezoelectric MEMS device of the present invention, it is preferable that the piezoelectric thin film has a c-axis orientation enhanced by an AC voltage application process or a one-side voltage application process without performing a process of applying a DC voltage.
In the piezoelectric MEMS device of the present invention, the AC voltage or voltage applied to the piezoelectric thin film is preferably higher than the coercive electric field.
When AC voltage application processing or one-side voltage application processing is performed at a voltage higher than the coercive electric field, the piezoelectric characteristics are more reliably obtained in a shorter time than when AC voltage application processing or one-side voltage application processing is performed at a voltage lower than the coercive electric field. Can be improved.

In the first piezoelectric MEMS device of the present invention, the piezoelectric thin film is composed of lead zirconate titanate containing tetragonal crystal and having a tetra composition, and the voltage applied in the alternating voltage application process or the one-side voltage application process is piezoelectric. It is set to 20 V or more per 1 μm thickness of the thin film .
Since the voltage is equal to or higher than the voltage at which the residual polarization value is saturated in two stages in the ferroelectric hysteresis, the c-axis orientation of the piezoelectric thin film can be more reliably increased.

In the second piezoelectric MEMS device of the present invention, the piezoelectric thin film is composed of lead zirconate titanate containing tetragonal crystals and having a morphotropic phase boundary composition (MPB (Morphotropic Phase Boundary) composition), and one-side voltage application The voltage applied in the treatment is set to 30 V or more per 1 μm film thickness of the piezoelectric thin film .

In the first and second piezoelectric MEMS devices of the present invention, the supported portion includes a facing portion that faces the supporting surface, and a float portion that continues to the facing portion and extends beyond the supporting surface, It is preferable that the piezoelectric thin film is also provided in the float portion.
In the structure, the float portion is formed by removing a part of the support substrate. By providing a piezoelectric thin film in the float part, the restraint by the support substrate can be eliminated and the restraining force on the piezoelectric thin film can be minimized. Thereby, it can prevent more reliably that a crack arises in a piezoelectric thin film.

The manufacturing method of the present invention for manufacturing the first and second piezoelectric MEMS devices is characterized in that an AC voltage application process or a one-side voltage application process is performed on the piezoelectric thin film after forming the support substrate.
If an AC voltage application process is performed after the support substrate is molded, the piezoelectric property is improved by the AC voltage application process without deteriorating the piezoelectric properties due to the freezing of polarization resulting from the pinning of the polarization due to heating during the molding and plasma damage. Characteristics can be maintained.

  ADVANTAGE OF THE INVENTION According to this invention, reliability can be ensured, improving a piezoelectric characteristic based on crystal orientation, by applying an alternating voltage application process to the MEMS device which has a thin film structure.

1 is a perspective view showing a piezoelectric MEMS device according to a first embodiment of the present invention. It is a figure which shows the manufacture procedure of a piezoelectric MEMS device. It is a figure which shows the result of the ferroelectric hysteresis measurement performed prior to manufacture of a piezoelectric MEMS device. It is a figure which shows the X-ray-diffraction result and ferroelectric hysteresis of a piezoelectric thin film in each after the etching of a support substrate, after an etching, and after an alternating voltage application process. It is a figure which shows the comparative example with 1st Embodiment. It is a figure which shows the displacement amount of the front-end | tip of a micro cantilever with respect to a drive voltage. It is a perspective view which shows the piezoelectric MEMS device used for optimization of an alternating voltage. It is a figure which shows the ratio and lattice constant of the (001) orientation component with respect to alternating voltage. (A) is a figure which shows the displacement amount of the front-end | tip of a micro cantilever with respect to alternating voltage. (B) is a figure which shows the sensor output voltage with respect to alternating voltage. Both the tip displacement amount and the output voltage are peak-to-peak values. It is a figure which shows the dielectric loss with respect to alternating voltage. It is a perspective view which shows the piezoelectric MEMS device which concerns on the example of improvement of embodiment. It is a figure for demonstrating the positive / negative sign of the voltage applied to a PZT thin film. It is a figure for demonstrating each of (a) bipolar polling, (b) unipolar polling, and (c) DC polling. It is a figure which shows the direction of the polarization by each polling shown in FIG. The dependence of the piezoelectric constant d31 on the poling voltage is shown for each of the poling shown in FIG. 13 for (a) a PZT thin film having a tetra composition and (b) a PZT thin film having an MPB composition. FIG. It is a figure which shows each piezoelectric constant d33 at the time of performing bipolar polling (a) 1 time and (b) 10 times.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
[First Embodiment]
A piezoelectric MEMS device 1 according to the first embodiment shown in FIG. 1 includes a device body 2 and a rectangular support substrate 10 that supports the device body 2.
In the following description, the upper and lower sides in FIG. 1 are defined as “upper” and “lower”.

  The support substrate 10 is made of Si, stainless steel, titanium, glass, polymer, or the like. The thickness of the support substrate 10 is about 100 to 1000 μm.

The device body 2 provided on one surface of the support substrate 10 includes a MEMS structure 20 including mechanical elements manufactured by a semiconductor microfabrication process, and a PZT thin film 21 provided on the MEMS structure 20 (shown by cross-hatching in FIG. 1). ).
The MEMS structure 20 includes a micro cantilever 22 and a probe (not shown) provided at the tip of the micro cantilever 22. The MEMS structure 20 is made of Si, stainless steel, titanium, glass, polymer, or the like. The thickness of the MEMS structure 20 is 0.5 to 50 times the thickness of the PZT thin film 21 described later, and is, for example, about 1 to 50 μm.

The micro cantilever 22 includes a rectangular lever base end (supported portion) 22A supported on the support surface 10S of the support substrate 10 and a lever front end that protrudes vertically from the lever base end 22A beyond the support surface 10S. Part (functional part) 22 </ b> B and cantilevered by the support substrate 10. The dimensions of the micro cantilever 22 are, for example, a length of 1.1 mm, a width of 0.3 mm, and a thickness of 0.01 mm. Although the MEMS structure 20 including the micro cantilever 22 is illustrated in a simplified manner, it has a structure in which a plurality of films are stacked.
An oxide film 11 is interposed between the lever base end portion 22 </ b> A and the support substrate 10.
A lower electrode 13 is provided on the entire upper surface of the lever base end portion 22A and the lever tip end portion 22B with the oxide film 12 interposed therebetween.
The oxide films 11 and 12 are a silicon oxide film, a titanium oxide film, or the like.

The PZT thin film 21 is provided on the MEMS structure 20 so as to overlap the entire lever distal end portion 22B and to overlap a part of the lever proximal end portion 22A. The conductive surface of the lower electrode 13 is exposed beside the PZT thin film 21.
PZT (lead zirconate titanate) is used for the PZT thin film 21. As a film forming method, a sputtering method, a sol-gel method, a MOD (Metal Organic Chemical Vapor Deposition) method, a MOCVD (Metal Organic Chemical Vapor Deposition) method, or the like can be arbitrarily employed.
The thickness of the PZT thin film 21 is about 0.5 to 20 μm and can be arbitrarily determined, but in the present embodiment, it is 1.7 μm.
As the composition of the PZT thin film 21, for example, an MPB (Morphotropic Phase Boundary) composition (Zr / Ti = 52/48) or a tetra composition (Zr / Ti = 30/70) can be employed. Their compositions are shown here in atomic weight ratio (molar ratio).

  The PZT thin film 21 is supported by a micro cantilever 22 that is cantilevered by the support substrate 10. The PZT thin film 21 is not supported by the support substrate 10 at the lever tip 22B protruding beyond the support surface 10S of the support substrate 10. Since the micro cantilever 22 is thinner than the support substrate 10, the micro cantilever 22 is less rigid than the support substrate 10. In the present embodiment, the support substrate 10 is used to maintain the rigidity of the entire piezoelectric MEMS device 1, and the support of the PZT thin film 21 is left to the microcantilever 22.

An upper electrode 14 is provided on the entire top surface of the PZT thin film 21. A voltage is applied to the PZT thin film 21 by the upper electrode 14 and the lower electrode 13.
The upper electrode 14 and the lower electrode 13 are made of a metal material such as gold, platinum, iridium and the like that does not chemically react (including a case where the material does not substantially react), and iridium oxide, LaNiO ₃ , SrRuO. ₃ and an oxide such as LaSrCoO ₃ . The upper electrode 14 and the lower electrode 13 are formed by covering the base electrode formed of the metal material with an oxide.

Next, a manufacturing procedure of the piezoelectric MEMS device 1 will be described.
As shown in FIG. 2A, the oxide film 11, the base material 220 of the structure 20, the oxide film 12, the lower electrode 13, the PZT thin film 21, and the upper electrode 14 are sequentially formed on the support substrate 10 (stacking step). ).
Next, as shown in FIG. 2B, the upper electrode 14, the PZT thin film 21, the lower electrode 13, and the oxide film 12 are partially removed by etching (piezoelectric thin film forming step).

Subsequently, the base material 220 of the structure 20 is etched to form the microcantilever 22 as shown in FIG. 2C (structure forming step).
Further, when the support substrate 10 is also etched, the portion of the support substrate 10 that faces the lever tip 22B is removed as shown in FIG. 2D, and the support substrate 10 is formed (support substrate forming). Step).

Thereafter, in order to improve the crystal orientation of the PZT thin film 21, an AC voltage application process for applying an AC voltage to the PZT thin film 21 is performed (AC voltage application process step).
In this embodiment, as an AC voltage application process, an AC voltage of 1 kHz at 80 V that is equal to or higher than the coercive electric field is applied to the PZT thin film 21 for 10 cycles. For example, as shown in FIG. 13A, an alternating voltage can be applied intermittently after a predetermined time (here, 0.1 second).
The waveform of the AC voltage is a triangular wave here, but may be a sine wave, a rectangular wave, or the like.
The voltage during the AC voltage application process can be determined based on a ferroelectric hysteresis measurement performed in advance on a sample having the same configuration (material, composition, and film thickness) as the PZT thin film 21. At this time, it is preferable to examine the voltage at which the remanent polarization value is saturated in two stages and perform the AC voltage application process at a voltage higher than that voltage.
In the case of the material (PZT), composition (tetra composition), and film thickness (1.7 μm) of the PZT thin film 21 of this embodiment, as shown in FIG. 3, the applied AC voltage is gradually increased to measure the ferroelectric hysteresis. Then, after the remanent polarization value (2Pr) rises, the AC voltage that once flattens, rises again, and becomes flat again (that is, the AC voltage that is saturated in two steps) becomes about 80V.
Therefore, the applied voltage during the AC voltage application process is 80V.

The piezoelectric MEMS device 1 is manufactured through the above manufacturing steps.
Next, the piezoelectric characteristics of the piezoelectric MEMS device 1 will be described.
4 to 6 described below show the characteristic values of the PZT thin film 21 having the tetra composition described above, the characteristic values of the PZT thin film 21 having the MPB composition show the same tendency. The same applies to FIGS. 8 to 10 described later.
FIG. 4 shows how the X-ray diffraction result and the ferroelectric hysteresis change depending on the manufacturing steps of the piezoelectric MEMS device 1. The left column in FIG. 4 corresponds to the piezoelectric MEMS device intermediate body before etching the support substrate 10 (FIG. 2C), and the middle column shows the piezoelectric MEMS device 1 after etching the support substrate 10 (FIG. 2D). )), The right column corresponds to the piezoelectric MEMS device 1 after the AC voltage application process at 80V.

The X-ray diffraction diagram shown in the upper part of FIG. 4 shows the X-ray intensity distribution according to the diffraction angle. In the distribution, peaks of orientation components (200) and (002) appear. Note that (n _a n _b n _c ) in this specification (n _a , n _b , and n _c are all integers) indicates a Miller index that specifies a crystal lattice plane. A-axis of the unit cell, the b-axis and _c-axis, n a, _{n b,} and _{n c} correspond.
The middle part of FIG. 4 shows (100) and (001) converted from the diffraction angle of the (200) and (002) orientation components and the area ratio of the peaks of the (200) and (002) orientation components in the X-ray diffraction diagram. The table | surface of the ratio of the orientation component of is shown. The sum of the orientation components (100) and (001) is 100%.

As shown in the left column, the middle column, and the right column in FIG. 4, the piezoelectric characteristics of the piezoelectric MEMS device 1 change every time before and after the support substrate 10 is etched, after the support substrate 10 is etched, and after the AC voltage application process. To do.
Here, when the AC voltage application process is performed, the ratio of the (001) orientation component increases from 34% to 44%. This is presumably because the (100) orientation component changes to the (001) orientation component by application of an alternating voltage.
With the improvement of the crystal orientation, the degree of polarization (2Pr) based on the remanent polarization values Pr and -Pr in the ferroelectric hysteresis loop (lower stage in FIG. 4) showing the polarization with respect to the electric field is 20.3 to 57.5. Greatly increased. That is, the piezoelectric characteristics are improved by the AC voltage application process.

  The (100) / (001) -oriented PZT thin film described above is a state in which a (100) -oriented structure and a (001) -oriented structure are mixed. Of these, the (100) -oriented structure does not show a piezoelectric effect even when a voltage of about 2 V is applied to a film thickness of about 2 μm. On the other hand, a (001) -oriented structure (c-axis orientation) shows a piezoelectric effect. If the proportion of the (001) -oriented tissue is increased by the AC voltage application process, the proportion of the tissue exhibiting the piezoelectric effect is increased, and thus the piezoelectric constant d31 is increased.

For comparison with the present embodiment, FIG. 5 shows ferroelectric hysteresis when the alternating voltage application process is performed after the MEMS structure 20 is etched (FIG. 2C) and then the support substrate 10 is etched. Indicates a loop. As shown in this comparative example, when the alternating voltage application process is performed at 80 V after the etching process of the MEMS structure 20 (FIG. 5A), as shown in FIG. Although it increases (similar to the right column in FIG. 4), it can be seen that the remanent polarization value Pr significantly decreases as shown in FIG. 5C after the support substrate 10 is etched. Thereafter, even if the AC voltage application process is performed again, as shown in FIG. 5D, the remanent polarization value Pr does not recover to the state after the first AC voltage application process (FIG. 5B). Symmetry is also lost.
As described above, the remanent polarization value is lowered (FIG. 5C) due to heating and plasma damage in forming the support substrate 10. Piezoelectric phenomena appear when the direction of polarization changes following voltage, or when the direction of polarization changes with applied force. Piezoelectric properties are not only improved in c-axis orientation but also in polarization. The direction (direction of ion shift) must be aligned.
Therefore, if the charge is stuck in the crystal of the PZT thin film 21 due to heat or plasma at the time of forming the support substrate 10 and the ion shift cannot be performed (polarization pinning), the polarization is frozen, so that the piezoelectric characteristics are lowered. End up.
From the above, in order to avoid the deterioration of the piezoelectric characteristics due to the freezing of polarization due to the heating and the plasma damage due to the formation of the support substrate 10, the alternating voltage application process is performed by etching the support substrate 10 and the piezoelectric MEMS device 1. It can be said that it is better to carry out in a chip state in which molding is completed.

Then, operation | movement of the piezoelectric MEMS device 1 of this embodiment is confirmed. FIG. 6 shows the amount of displacement of the tip (free end) of the microcantilever 22 when an AC drive voltage of several V (Peak-to-peak value) is applied to the PZT thin film 21. The frequency of the driving voltage is 1 kHz.
The data of the piezoelectric MEMS device 1 of the present embodiment subjected to the AC voltage application process at 80 V is plotted with white triangles (Δ), and the data when the AC voltage application process is performed at 30 V is plotted with black circles (●). In addition, the data when the AC voltage application process is not performed is plotted with white circles (◯).

  As shown in FIG. 6, the amount of displacement of the tip of the micro cantilever 22 increases in proportion to the increase in drive voltage. Here, the rate of increase of the displacement with respect to the drive voltage is greater when the AC voltage application process is performed (● and Δ) than when the AC voltage application process is not performed (O). The rate of increase of the displacement amount is larger when AC voltage application processing is performed at 80 V (Δ) than when AC voltage application processing is performed at 30 V (●).

The operation results shown in FIG. 6 are consistent with the orientation characteristics shown in FIG. If cracks (microcracks) are generated in the PZT thin film 21 by the AC voltage application process, the displacement shown in FIG. 6 should be much smaller due to the cracks even if the orientation characteristics are improved. Based on the fact that the amount of tip displacement increases in proportion to the increase in applied voltage, it is assumed that no crack has occurred.
The crack does not occur because the PZT thin film 21 is provided at the lever tip 22B of the micro cantilever 22 so that the restraining force on the PZT thin film 21 is significantly larger than that in the case where the PZT thin film 21 is supported by the support substrate 10. This is because it is reduced. The thickness of the micro-cantilever 22 is only about 6 times the thickness of the PZT thin film 21, and due to its flexibility, the lever tip 22B mainly has the PZT thin film 21 when the crystal orientation is changed by the AC voltage application process. It can be deformed following the distortion. Therefore, the PZT thin film 21 is not cracked.

The value of the lateral piezoelectric constant d31 obtained from the displacement with respect to the drive voltage shown in FIG. 6 is also -13 pm / V when the AC voltage application process is not performed (O), but when the AC voltage application process is performed at 30 V (●) is −24 pm / V, and when AC voltage is applied at 80 V, (Δ) is −42 pm / V, and its absolute value increases. The piezoelectric constant d31 is proportional to the amount of displacement of the microcantilever 22.
As described above, the drive performance and drive accuracy of the microcantilever 22 can be increased by increasing the displacement rate increase rate with respect to the drive voltage and increasing the piezoelectric constant d31.

  From the above, it was confirmed that the piezoelectric characteristics were improved by the AC voltage application process also from the operation side of the piezoelectric MEMS device 1.

According to the present embodiment, the PZT thin film 21 is supported by the MEMS structure 20 having a thickness that is not so different from the thickness of the PZT thin film 21, thereby relieving the stress of the PZT thin film 21 during the AC voltage application process. It can be avoided that the PZT thin film 21 is cracked. Therefore, the piezoelectric characteristics can be improved while ensuring reliability.
Note that the MEMS structure 20 may have various forms depending on the function thereof, and the support form on the support substrate 10 may also be supported at both ends or in other support forms. Regardless of the form and support form of the MEMS structure 20, since the PZT thin film 21 is provided at least in the functional part in the MEMS structure 20, the binding force on the PZT thin film 21 is reduced as described above. Piezoelectric properties can be improved without causing cracks in the PZT thin film 21.
Further, since the film thickness of the tetra-composition PZT thin film 21 of this embodiment is 1.7 μm and the applied voltage at the time of the alternating voltage application process is 80 V, in the category of the tetra-composition PZT thin film, at the time of the alternating voltage application process When the applied voltage is set to ± 50 V or more per 1 μm of film thickness, the c-axis orientation of the piezoelectric thin film can be improved more reliably.

Next, the optimization of the voltage of the AC voltage application process will be examined.
In the following, the sensor / actuator integrated micro cantilever 3 as the piezoelectric MEMS device shown in FIG. 7 is used.
In addition, the same code | symbol is attached | subjected to the structure similar to the structure already demonstrated.
The sensor / actuator integrated micro cantilever 3 includes a sensor body 3A and a support substrate 3B that supports the sensor body 3A.
The support substrate 3B is formed in a rectangular frame with the same material and the same thickness as the support substrate 10 described above.

The sensor body 3A includes a micro cantilever 30 as a MEMS structure including mechanical elements manufactured by a semiconductor microfabrication process, and a detection PZT thin film 31 and a driving PZT thin film 32 provided on the micro cantilever 30. . The detection PZT thin film 31 and the driving PZT thin film 32 are formed at intervals so as not to contact each other.
Each of the detection PZT thin film 31 and the drive PZT thin film 32 is provided with an upper electrode 141 and a lower electrode 131, respectively, thereby constituting a piezoelectric element structure in which a piezoelectric body is sandwiched between two electrodes.
The micro cantilever 30 is cantilevered by the support substrate 3B, and extends along the side of the support substrate 3B on the support surface 3S, and extends beyond the support surface 3S from the terminal portion 30B. And an elongated displacement detector 30C disposed in a rectangular opening 3C on the inner periphery of the support substrate 3B.
The thickness of the micro cantilever 30 is 0.5 to 50 times the thickness of the detection PZT thin film 31 and the drive PZT thin film 32, and is, for example, about 1 to 50 μm.
A detection terminal 301 for taking out a voltage from the upper electrode 141 and the lower electrode 131 of the detection PZT thin film 31 is provided in the center of the terminal portion 30B.
Driving terminals 302 for applying a voltage to the upper electrode 142 and the lower electrode 132 of the driving PZT thin film 32 are provided at both ends of the terminal portion 30B.

The detection PZT thin film 31 and the drive PZT thin film 32 are formed in the same manner as the PZT thin film 21 described above.
The driving PZT thin film 32 is formed in a U shape along the length direction of the displacement detector 30C.
The detection PZT thin film 31 is disposed between both arms of the drive PZT thin film 32.

The sensor / actuator integrated micro cantilever 3 detects the displacement generated in the micro cantilever 30 as a voltage by the detection PZT thin film 31.
Here, similarly to the piezoelectric MEMS device 1 described above, the displacement amount of the microcantilever 30 is proportional to the piezoelectric constant d31 of the driving PZT thin film 32. Further, if the displacement amount of the microcantilever 30 is the same, a higher voltage is generated when the piezoelectric constant d31 of the detection PZT thin film 31 is higher, so that sensitivity (detection accuracy) to the displacement amount is higher.
In order to confirm the piezoelectric characteristics of the sensor / actuator integrated micro cantilever 3, a voltage is applied to the driving PZT thin film 32 to vibrate the entire micro cantilever 30, and the vibration displacement at that time is detected from the detecting PZT thin film 31. Monitoring based on the output voltage of

The sensor / actuator integrated micro cantilever 3 is manufactured through etching of the support substrate 3B, etching of the base material of the micro cantilever 30, and AC voltage application processing, in the same manner as the manufacturing procedure of the piezoelectric MEMS device 1 described above.
Here, in order to derive the voltage of the AC voltage application process, the applied voltage during the AC voltage application process is changed in the range of 20 V to 90 V to obtain a plurality of samples.
Based on the X-ray diffraction of these samples, FIG. 8 shows the ratio (Vc) of the (001) orientation component (c-axis orientation component) of the detection PZT thin film 31 and the drive PZT thin film 32, and the a-axis and c-axis. The lattice constant of the axis is shown.
The (001) orientation component ratio Vc does not change much until the AC voltage reaches 50V, but increases at 50V or higher. Vc increases rapidly above 50V.
Also, the c-axis lattice constant increases at 50 V or higher.

On the other hand, based on FIG. 9, the operation of the sensor / actuator integrated micro cantilever 3 is confirmed.
In FIG. 9, when a sinusoidal driving voltage of 5 V and a resonance frequency (here 2.2 kHz) is applied, the sample (sensor / actuator integrated micro cantilever) A, sample B, and sample C are vibrated. The state in which the tip end displacement of the cantilever 30 and the output voltage of the detection PZT thin film 31 change according to the AC voltage is shown. Samples A, B, and C and samples D and E in FIG. 10 are all extracted from the same wafer.
The tip displacement amount and output voltage shown in FIG. 9 reflect the polarization state in the crystal lattice of the PZT thin films 31 and 32, and the tip displacement amount is proportional to the piezoelectric constant d31 of the driving PZT thin film 32, and the output voltage Is proportional to the product of the piezoelectric constant d31 of the driving PZT thin film 32 and the piezoelectric constant d31 of the detecting PZT thin film 31. That is, since both the tip displacement amount and the output voltage are proportional to the piezoelectric constant d31, measuring the tip displacement amount and the output voltage leads to optimization of the AC voltage application process.
Both the tip displacement amount and the output voltage increase rapidly between 20V and 30V and become maximum at about 60V, but decrease at higher AC voltages. When the output voltage of the detection PZT thin film 31 exceeds 60 V, it rapidly decreases.

As shown in FIG. 8, as the AC voltage is increased, the (001) orientation component ratio Vc continues to increase. However, as shown in FIG. 9, both the tip displacement amount and the output voltage are about 60 V. And turn to decrease.
The reason is considered to be caused by an increase in dielectric loss shown in FIG.
The dielectric loss obtained based on Sample D and Sample E is about 0.02 at an AC voltage of 60 V or less, and is a standard value for a PZT thin film, but the AC voltage suddenly varies between 60 V and 80 V. To increase. The dielectric loss at 70 V takes a positive value outside the margin of FIG.

As shown in FIG. 10, the dielectric loss increases because the terminal portion 30B of the microcantilever 30 is supported by the support substrate 10, and the support substrate 10 in that portion is used for the detection PZT thin film 31 and the drive PZT thin film 32. This is probably because the detection PZT thin film 31 and the driving PZT thin film 32 are cracked during the alternating voltage application process due to the restraining force applied to.
If the applied voltage during the AC voltage application process is small, the change in crystal orientation and the stress in the detection PZT thin film 31 and the driving PZT thin film 32 are also small, but the change in crystal orientation increases due to the increase in applied voltage, and detection When the stress of the PZT thin film 31 for driving and the PZT thin film 32 for driving becomes large, the restraining force on the piezoelectric thin film increases and cracks occur.

  From the above examination, according to the sample used in the present embodiment, the applied voltage during the AC voltage application process is preferably about 40V to about 60V. That is, in the AC voltage application process, it is preferable to apply as much AC voltage as possible to the piezoelectric thin film as long as the piezoelectric thin film is not cracked. Accordingly, the piezoelectric characteristics can be greatly improved while ensuring reliability.

Next, a structure is shown in which the restraining force of the support substrate 10 on the detection PZT thin film 31 and the driving PZT thin film 32 can be eliminated as much as possible.
The piezoelectric MEMS device 4 shown in FIG. 11A includes a device body 4A and a support substrate 4B that supports the device body 4A.
The device body 4 </ b> A includes a MEMS structure 40 and a PZT thin film 21. In addition, the same code | symbol is attached | subjected to the structure similar to the structure already demonstrated.

The MEMS structure 40 includes a rectangular terminal portion 41 that is supported on the support surface 4S of the support substrate 4B, and a structure body 42 that extends perpendicularly from the terminal portion 41 beyond the support surface 4S. Yes. The PZT thin film 21 is provided on the MEMS structure 40 so as to overlap the entire structure body 42 and the central portion 41 </ b> A of the terminal portion 41.
The terminal portion 41 includes a central portion 41A and opposing portions 41B and 41C that are continuous with both sides of the central portion 41A and face the support surface 4S of the support substrate 4B.
Here, in the support substrate 4B, a portion corresponding to the central portion 41A is removed by etching over the entire thickness. The terminal portion 41 is bridged over the portions P1 and P2 facing each other across the space S of the support substrate 4B above the space S formed by removing the support substrate 4B.

  According to the above structure, even if the PZT thin film 21 extends to the central portion 41A of the terminal portion 41 for voltage application or extraction, the support surface 4S of the support substrate 4B exists below the central portion 41A. Instead, the entire PZT thin film 21 is supported by the MEMS structure 40. Then, the restraining force by the support substrate 4B can be eliminated and the restraining force on the PZT thin film 21 can be minimized, so that the PZT thin film 21 can be more reliably prevented from cracking.

As long as the MEMS structure 40 can be supported by the support substrate 4B, the range and shape in which the support substrate 4B is removed are arbitrary.
In the example shown in FIG. 11B, the support substrate 4B is removed from the support surface 4S by a predetermined depth so that the lower side of the central portion 41A of the terminal portion 41 does not contact the support substrate 4B. This configuration is also included in the present invention because the restraining force on the PZT thin film 21 can be reduced.

[Second Embodiment]
Next, a piezoelectric MEMS device and a manufacturing method thereof according to a second embodiment of the present invention will be described.
In the first embodiment described above, the c-axis orientation of the PZT thin film is improved by the process of applying an alternating voltage whose magnitude changes while being positively or negatively reversed with respect to 0 V that is the reference potential (alternating voltage application process). In the second embodiment, the c-axis orientation of the PZT thin film is improved by applying a voltage that changes in magnitude on either the positive or negative side with respect to the reference potential.
Hereinafter, the process of applying a voltage whose magnitude changes within a positive or negative single pole (unipolar) range to the PZT thin film is referred to as unipolar poling, and is performed in the first embodiment. As in the AC voltage application process (AC voltage application process), applying a voltage whose sign is inverted to both positive and negative polarities is called bipolar polling.
The process of applying a DC voltage to the PZT thin film is called DC poling.
Poling refers to a process of applying residual electric field to provide residual polarization that remains after the electric field is removed.

The piezoelectric MEMS device of the second embodiment is configured in the same manner as the piezoelectric MEMS device 1 (FIG. 1) of the first embodiment except that unipolar poling is performed instead of the AC voltage application process (AC voltage application process). ing.
That is, the piezoelectric MEMS device according to the second embodiment also includes the device body 2 having the MEMS structure 20 and the PZT thin film 21 and the support substrate 10 (see FIG. 1).
As the composition of the PZT thin film 21, for example, an MPB (Morphotropic Phase Boundary) composition (Zr / Ti = 52/48) and a tetra composition (Zr / Ti = 30/70) can be adopted as in the first embodiment. .

The piezoelectric MEMS device according to the second embodiment includes the manufacturing steps ((a) stacking step, (b) piezoelectric thin film forming step, (c) laminate forming step, (d) supporting substrate described with reference to FIG. By the molding step), the molding is performed in the same manner as the piezoelectric MEMS device 1 of the first embodiment.
Thereafter, a process of applying a voltage whose magnitude changes within a range in which the sign is not inverted with respect to the reference potential (0 V) is performed on the PZT thin film 21 (unipolar polling step), whereby the piezoelectric MEMS device of the present embodiment. Can be manufactured.

Hereinafter, the effect of improving the piezoelectric characteristics by unipolar poling will be described in comparison with the case where bipolar poling and direct current poling are performed.
Here, as indicated by the downward arrow Ef1 in FIG. 12A, a voltage that generates an electric field from the PZT thin film 21 toward the support substrate 10 is defined as a positive voltage. At this time, the ground of a voltage applying device connected as a power source to the PZT thin film 21 is connected to the lower electrode 13. On the other hand, as shown by an upward arrow Ef2 in FIG. 12B, a voltage that generates an electric field from the support substrate 10 toward the PZT thin film 21 is defined as a negative voltage. At this time, the ground of the voltage application device is connected to the upper electrode 14.

FIGS. 13A and 13B show examples of voltage waveforms in bipolar polling and unipolar polling, respectively. FIG. 13C shows a voltage in DC polling.
FIG. 13A shows a waveform of a voltage that can be applied in the bipolar polling (AC voltage application process) of the first embodiment. The applied voltage is an alternating voltage whose magnitude changes while being reversed positively and negatively with respect to 0V.
Here, the AC voltage of 1 kHz in which one cycle of the voltage value takes a positive value and a negative value is 0.001 second, and is repeated one cycle at a predetermined time (0.1 second) 10 times. Apply. When intermittently applied in this manner, the waveform becomes a pulse shape that changes rapidly in a short time.
The required time from the start of application of the first pulse to the end of application of the last pulse is 1 second.
The waveform of the applied voltage is not limited to the illustrated triangular wave, and may be a sine wave, a rectangular wave, a sawtooth wave, or the like.
The applied voltage can be determined in consideration of the film thickness of the PZT thin film 21.

FIG. 13B shows voltage waveforms that can be applied in the unipolar polling of this embodiment. The applied voltage is only on one side with respect to 0 V, and the magnitude gradually changes as time (t) elapses.
Here, by applying a voltage with the polarity shown in FIG. 12A, the voltage value changes only on the positive side. In addition, after the voltage value gradually increases from 0V, it gradually decreases and then returns to 0V. The 1 kHz voltage at which one cycle is 0.001 second is repeated 10 times at predetermined intervals (0.1 seconds). Apply. When intermittently applied in this manner, the waveform becomes a pulse shape that changes rapidly in a short time.
The required time from the start of application of the first pulse to the end of application of the last pulse is 1 second.
The waveform of the applied voltage is not limited to the illustrated triangular wave, and may be a sine wave, a rectangular wave, a sawtooth wave, or the like.
The applied voltage is set such that the peak value reaches a coercive electric field that is the magnitude of the electric field (electric field) when the polarization direction of the PZT thin film 21 is reversed.

FIG. 13C shows DC poling for applying a DC voltage. Although the applied voltage varies slightly, it is maintained at a predetermined set value, and the sign does not change.
Here, a positive DC voltage is applied continuously for a predetermined time (5 minutes) by applying a voltage with the polarity shown in FIG.
The applied voltage is set to a maximum voltage value that does not cause the PZT thin film 21 to be mechanically broken by the dielectric breakdown between the electrodes. Here, it is 20V.

The direction of polarization remaining in the PZT thin film 21 by each poling shown in FIGS. 13A to 13C is schematically shown by arrows PVa to PVc in FIG.
The direction of polarization is determined by the voltage direction defined above.
According to the bipolar polling in which the voltage is switched from positive to negative, the residual polarization PVa in the direction from the support substrate 10 toward the PZT thin film 21 is given to the PZT thin film 21 because the last voltage of the cycle is negative. . According to bipolar polling in which the voltage is switched from negative to positive, the direction of polarization is reversed. Further, according to unipolar poling that applies a pulse that changes in a positive range, a remanent polarization PVb directed from the PZT thin film 21 toward the support substrate 10 is given to the PZT thin film 21.
Then, according to DC poling in which a positive DC voltage is applied, residual polarization PVc in a direction from the PZT thin film 21 toward the support substrate 10 is given to the PZT thin film 21.

The piezoelectric MEMS device of this embodiment is completed by performing unipolar poling shown in FIG. 13B after the support substrate 10 is formed.
Here, bipolar poling and direct current are performed for the case where the PZT thin film 21 of the piezoelectric MEMS device of the present embodiment has a tetra composition (FIG. 15A) and the case where it has an MPB composition (FIG. 15B). The performance of the piezoelectric MEMS device is verified while comparing with the case where polling is performed.
15A and 15B show the relationship between the drive voltage and the amount of displacement of the tip (free end) of the microcantilever 22 when an AC drive voltage is applied to the PZT thin film 21 of the piezoelectric MEMS device for which poling has been completed. The dependence of the obtained piezoelectric constant d31 on the poling voltage is shown. The driving voltage is 2V (Peak-to-peak value) and the driving frequency is 800 Hz. The driving frequency is extremely low with respect to the resonance frequency (for example, 10 kHz) of the piezoelectric MEM device.
As described above, the piezoelectric constant d31 is proportional to the amount of displacement of the microcantilever 22, and the performance of the microcantilever 22 can be increased by increasing the value of the piezoelectric constant d31.

The symbols in FIGS. 15A and 15B will be described.
Data (BP-P) of the device subjected to bipolar polling is plotted with white circles (◯).
The data (DC-P ↓) of the device in which the DC polling is performed with a positive voltage corresponding to Ef1 (downward ↓) in FIG. 12A is plotted with a broken line.
Data (DC-P ↑) of a device in which DC polling is performed with a negative voltage corresponding to Ef2 (upward ↑) in FIG. 12B is plotted with a one-dot chain line.
Device data (UP-P ↓) obtained by performing unipolar polling with a positive voltage corresponding to Ef1 (downward ↓) in FIG. 12A is plotted with white triangles (▽).
Device data (UP-P ↑) obtained by performing unipolar polling with a negative voltage corresponding to Ef2 (upward ↑) in FIG. 12B is plotted with black triangles (▲).

First, the case of the tetra composition shown in FIG.
The d31 obtained by direct current poling is about 40 pm / V when a positive voltage is applied (DC-P ↓) and about 30 pm / V when a negative voltage is applied (DC-P ↑). Here, in direct current poling, the larger the applied voltage, the higher the effect of improving the piezoelectric characteristics. Therefore, as described above, the maximum voltage (20 V) that does not cause discharge due to dielectric breakdown is applied. The same applies to the MPB composition shown in FIG.
The maximum value of d31 obtained by bipolar polling (BP-P) is about 40 pm / V when the applied voltage at the time of polling is in the range of 50 to 60 V, which is higher than the value at the time of DC polling.
Furthermore, d31 obtained by unipolar polling (UP-P) exceeds the value in the case of bipolar polling in the case of applying a positive voltage (UP-P ↓) and in the case of applying a negative voltage (UP-P ↑). 50 pm / V. Similar to bipolar polling, d31 shows the maximum value when the applied voltage during polling is in the range of 50 to 60V.
From the above, in the case of the tetra composition, it can be seen that high performance can be obtained by unipolar poling as compared with DC poling and bipolar poling, and that the proper unipolar poling voltage is 50 to 60 V in the experimental category.
In the present embodiment, the film thickness of the PZT thin film 21 having a tetra composition is 1.7 μm, and in the case of the tetra composition, the applied voltage during unipolar poling is set to a range of 20 to 40 V per 1 μm of film thickness. The c-axis orientation can be more reliably increased without forming cracks in the thin film.

Next, the case of MPB composition will be described.
D31 obtained by direct current poling is about 80 pm / V when a positive voltage is applied (DC-P ↓), and is about 65 pm / V when a negative voltage is applied (DC-P ↑).
On the other hand, d31 obtained by bipolar polling (BP-P) tends to increase as the applied voltage at the time of polling increases, but remains at about 50 pm / V at the maximum.
On the other hand, d31 obtained by unipolar polling (UP-P) is about 110 pm / V at maximum when positive voltage is applied (UP-P ↓), and about 90 pm / V at maximum when negative voltage is applied (UP-P ↑). Reach up to. In both cases of applying a positive voltage and a negative voltage, d31 tends to increase as the applied voltage at the time of polling increases. And d31 by unipolar polling exceeds d31 by bipolar polling over the entire polling voltage, and d31 by DC polling also exceeds in a wide voltage range.
From the above, even in the case of MPB composition, high performance can be obtained by unipolar polling compared with DC polling and bipolar polling, and in the category of experiments, an appropriate unipolar polling voltage is 80 to 100V. Recognize.
In the present embodiment, the film thickness of the PZT thin film 21 having the MPB composition is 1.9 μm, and in the case of the MPB composition, the applied voltage during unipolar poling is set to 30 V or more per 1 μm film thickness, so that c The axial orientation can be more reliably increased. Unlike the case of the tetra composition, the MPB composition has a small volume change due to the improvement of the c-axis orientation, so that it is difficult to form a crack even when the applied voltage is increased. For this reason, it is desirable to increase the applied voltage as much as possible without causing dielectric breakdown.

  Here, when bipolar polling (BP-P) was performed at 100 V and DC polling was performed at a positive voltage, d31 increased to less than 100 pm / V. However, in addition to 1 second required for bipolar polling, a processing time of 5 minutes required for DC polling is required.

  Therefore, by performing unipolar polling as in this embodiment, the time required for the polarization process is significantly reduced from the time of the minute order required for DC polling to 1 second or less, but the piezoelectric characteristics that exceed DC polling are improved. Can be achieved.

  Moreover, the piezoelectric MEMS device of this embodiment supports the PZT thin film 21 by the MEMS structure 20 similarly to the piezoelectric MEMS device 1 of the first embodiment, so that the stress of the PZT thin film 21 during unipolar poling is reduced. Since it is relaxed, it is possible to avoid the occurrence of cracks in the PZT thin film 21. Therefore, the piezoelectric characteristics can be improved while ensuring reliability.

  Further, as in the first embodiment, after the support substrate 10 is formed, the PZT thin film 21 is poled, so that the piezoelectric characteristics are improved by heating at the time of forming the support substrate 10 and freezing of polarization caused by plasma damage. The piezoelectric characteristics enhanced by unipolar poling can be maintained without deteriorating.

  The unipolar polling according to the second embodiment can also be applied to the sensor / actuator integrated micro cantilever 3 described with reference to FIG. 9 and the piezoelectric MEMS device 4 illustrated in FIGS. .

The magnitude, polarity (positive / negative), frequency, and voltage of the applied voltage are applied in the AC voltage application process (same as bipolar polling) described in the first embodiment and the bipolar polling and unipolar polling described in the second embodiment. The time (number of cycles), when applying voltage intermittently, the time during which no voltage is applied between adjacent pulses (voltage non-application time), the number of repetitions of the pulse, etc. are arbitrarily determined. be able to.
The frequency of the applied voltage is preferably 100 Hz or more. The upper limit of the frequency can be determined with a frequency (for example, 10 MHz) that the PZT thin film 21 can follow.
Moreover, it is preferable that the number of periods which apply a voltage is about 1-100.
For example, if a voltage of 100 Hz is applied for 10 cycles with a time of 0.05 seconds between cycles, a polling time of 1.45 seconds can be realized.
Here, in bipolar polling and unipolar polling, the periodicity of the applied voltage is not necessarily required.
Further, the voltage is not applied intermittently (intermittently) as shown in FIGS. 13 (a) and 13 (b), but with any continuous waveform (sine wave, triangular wave, rectangular wave, sawtooth wave, etc.) without interruption. A voltage can also be applied.
For example, when a voltage of 100 Hz is continuously applied for 10 cycles, a required polling time of 1 second can be realized. Even if the voltage is continuously applied in this way, the same effect as that when the voltage is applied with a time interval of 0.1 seconds can be obtained.
When the voltage is applied intermittently, the voltage may be applied at irregular time intervals instead of being applied at a constant time interval as described above.

As the piezoelectric thin film of the present invention, in addition to PZT exemplified in the first and second embodiments, for example, barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), potassium niobate (KNbO ₃ ), niobium Lithium oxide (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), sodium tungstate (Na _x WO ₃ ), zinc oxide (ZnO, Zn ₂ O ₃ ), sodium potassium niobate ((K, Na) NbO ₃ ), Bismuth ferrite (BiFeO ₃ ) or the like can also be used.
Here, bipolar poling and unipolar poling can be easily applied to piezoelectric thin films which are difficult to perform DC poling because of a large leakage current, such as bismuth ferrite, and thus can be expected to have a wide range of applications.

The voltage application process performed in the present invention is based on the fact that if a pulse or an AC voltage is applied, dielectric breakdown does not occur even when a voltage higher than the polling for applying the DC voltage is applied.
If it is a pulse or an alternating voltage, it is possible to apply a voltage higher than the coercive electric field without causing dielectric breakdown, so that the piezoelectric thin film can be polled more reliably and in a short time.
In the case of applying a voltage higher than the coercive electric field, in the alternating voltage application process described in the first embodiment, the bipolar polling and the unipolar polling described in the second embodiment, even if it is applied only once (one cycle), It can change the crystal structure and improve the piezoelectric characteristics. Of course, the effect becomes more certain by repeating the number of times several times or about ten times.
In the case of applying a voltage less than the coercive electric field, it is preferable to repeat the number of times, for example, about 10 to 500 times in order to ensure the effect.

Data when polling only once (cycle) is shown in FIG.
Here, the piezoelectric constant d33 of the PZT thin film 21 having a dot-like tetra composition having a diameter of 300 μm was measured. The piezoelectric constant d33 and the piezoelectric constant d31 are basically in a proportional relationship.
The left graph of FIG. 16A shows the displacement amount of the piezoelectric MEMS device when an AC drive voltage of 30 V is applied to the PZT thin film 21 that is bipolar-polled with an AC pulse of 40 V. The piezoelectric constant d33 + corresponding to the displacement when the drive voltage is positive is 92.7 (unit: [pm / V], the same applies hereinafter), and the piezoelectric constant corresponding to the displacement when the drive voltage is negative. d33− is −95.4.
The graph on the right side of FIG. 16A is different from the graph on the left only in that the pulse voltage during bipolar polling is 60V. The piezoelectric constant d33 + is 166.2, and the piezoelectric constant d33− is −185.9.
In addition, d33 + and d33− shown in the table of FIG. 16A were obtained when bipolar polling was performed with 50 V and 70 V pulses.

FIG. 16B shows data when 10 pulses are polled with respect to the PZT thin film 21 similar to FIG.
As shown in the left graph of FIG. 16B, the piezoelectric constant d33 + obtained when a 30 V AC driving voltage is applied to the PZT thin film 21 bipolar-polled with a 40 V AC pulse is 89.4. Yes, and the piezoelectric constant d33- is -109.3.
The graph on the right side of FIG. 16B is different from the graph on the left only in that the pulse voltage during bipolar polling is 60V. The piezoelectric constant d33 + is 168.7, and the piezoelectric constant d33− is −218.0.
In addition, d33 + and d33− shown in the table of FIG. 16B were obtained when bipolar polling was performed with 50 V and 70 V pulses.
From the above, it can be seen that even when a one-time pulse is applied (FIG. 16A), almost the same result as that obtained when 10 pulses are applied (FIG. 16B) can be obtained. .
In the case of polling the unipolar pulse, the same tendency as in FIGS. 16A and 16B is shown.

  In addition to the above, as long as the gist of the present invention is not deviated, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

The piezoelectric MEMS device of the present invention is used in gyroscopes, inkjet heads, RF-MEMS switches, relay switches, wireless sensor terminal activation switches, vibration power generation elements, etc. in various industrial fields such as the sensor industry, printing industry, and wireless sensor industry. Widely available.
In addition, a cantilever that applies a voltage to a minute region of a recording layer of a ferroelectric memory included in a write / read head of a data storage device can be exemplified as an application destination of the present invention.

DESCRIPTION OF SYMBOLS 1 Piezoelectric MEMS device 2 Device main body 3 Sensor / actuator integrated micro cantilever 3A Sensor main body 3B Support substrate 3C Opening 3S Support surface 4 Piezoelectric MEMS device 4A Device main body 4B Support substrate 4S Support surface 10 Support substrate 10S Support surfaces 11, 12 Oxide film 13 Lower electrode 14 Upper electrode 20 MEMS structure 21 PZT thin film (piezoelectric thin film)
22 Micro cantilever 22A Lever base end (supported part)
22B Lever tip (functional part)
30 Micro cantilever 30B Terminal part (supported part)
30C Displacement detection unit (function unit)
31 PZT thin film for detection 32 PZT thin film for driving 40 MEMS structure 41 Terminal portion (supported portion)
41A Center (Float)
41B, 41C Opposing part 42 Structure body (functional part)
131, 132 Lower electrode 141, 142 Upper electrode 220 Base material 301 Detection terminal 302 Drive terminal P1, P2 Partial S Space

Claims (7)

A structure including mechanical elements produced by a semiconductor processing process;
A support substrate for supporting the structure;
A piezoelectric thin film supported by the structure,
The structure is
A supported portion supported on a support surface of the support substrate;
And a functional part extending beyond the support surface,
The piezoelectric thin film is
While being provided at least in the functional part in the structure,
The AC voltage application processing is performed after the molding of the supporting substrate, or, are c-axis orientation is improved by only one side voltage application process of applying a voltage that changes in either one of positive and negative which is performed after the molding of the support substrate ,
The piezoelectric thin film is composed of lead zirconate titanate containing tetragonal crystals and having a tetra composition,
The voltage applied in the AC voltage application process or the one-side voltage application process is 20 V or more per 1 μm of film thickness of the piezoelectric thin film.
A piezoelectric MEMS device characterized by the above. The voltage applied in the one-side voltage application process is 20 to 40 V per 1 μm film thickness of the piezoelectric thin film,
The piezoelectric MEMS device according to claim 1. A structure including mechanical elements produced by a semiconductor processing process;
A support substrate for supporting the structure;
A piezoelectric thin film supported by the structure,
The structure is
A supported portion supported on a support surface of the support substrate;
And a functional part extending beyond the support surface,
The piezoelectric thin film is
While being provided at least in the functional part in the structure,
The AC voltage application processing is performed after the molding of the supporting substrate, or, are c-axis orientation is improved by only one side voltage application process of applying a voltage that changes in either one of positive and negative which is performed after the molding of the support substrate ,
The piezoelectric thin film is composed of lead zirconate titanate containing tetragonal crystal and having a morphotropic phase boundary composition,
The voltage applied in the one-side voltage application process is 30 V or more per 1 μm thickness of the piezoelectric thin film,
A piezoelectric MEMS device characterized by the above. The piezoelectric thin film is
  Without performing the process of applying a DC voltage, the c-axis orientation is enhanced by the AC voltage application process or the one-side voltage application process,
The piezoelectric MEMS device according to any one of claims 1 to 3. The AC voltage or the voltage applied to the piezoelectric thin film is:
More than coercive electric field,
The piezoelectric MEMS device according to any one of claims 1 to 4 . The supported portion is
A facing portion facing the support surface;
A float portion that is continuous with the facing portion and extends beyond the support surface;
The piezoelectric thin film is also provided in the float part,
The piezoelectric MEMS device according to any one of claims 1 to 5. A method for manufacturing a piezoelectric MEMS device according to any one of claims 1 to 6 , comprising:
After forming the support substrate,
Performing the AC voltage application process or the one-sided voltage application processing on the piezoelectric thin film,
A method for manufacturing a piezoelectric MEMS device.

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