JP7718201B2 - Piezoelectric element - Google Patents

Description

The present invention relates to a piezoelectric element having a vibrating portion.

Piezoelectric elements with a vibrating portion have been proposed in the past (see, for example, Patent Document 1). Specifically, this piezoelectric element is configured by stacking a vibrating portion, which includes a piezoelectric film and an electrode film electrically connected to the piezoelectric film, on a support. The piezoelectric element has a recess formed in the support, and a portion of the vibrating portion forms a floating region that is floating above the support. In addition, in this piezoelectric element, slits are formed in the floating region, dividing the floating region into multiple regions to form the vibration regions. Note that this piezoelectric element has slits formed in it that completely divide the floating region into four regions.

When pressure such as sound pressure is applied to the vibration area of such a piezoelectric element, the vibration area vibrates, and the electric charge generated in the piezoelectric film is output as a detection signal.

Patent No. 5936154

However, with the above-mentioned piezoelectric element, pressure escapes through the slit, which may narrow the detection band.

In view of the above, the present invention aims to provide a piezoelectric element that can prevent the detection band from narrowing.

In order to achieve the above object, claims 1 and 2 provide a piezoelectric element having a vibration section (20) disposed on a support (10), the vibration section including a piezoelectric film (40) and an electrode film (50) connected to the piezoelectric film, the vibration section having a support region (21a) supported by the support and a floating region (21b) connected to the support region and floating above the support, the floating region having a plurality of vibration regions (22a-22d) partitioned by slits (30), adjacent vibration regions being connected at their support region side. In claims 1 and 2, the slits are formed so as to extend from the floating region to the support region, adjacent vibration regions are connected at their support region side by an additional thin film (81) covering the support region side of the slit, and adjacent vibration regions are connected at their support region side by an additional thin film (82) covering the support region side of the slit.
Furthermore, in claim 1, the additional thin film arranged on the side opposite the support region side is thicker and has a larger Young's modulus than the additional thin film arranged on the support region side. In claim 2, the additional thin film arranged on the side opposite the support region side is thinner and has a smaller Young's modulus than the additional thin film arranged on the support region side.

This means that adjacent vibration regions are connected at the support region side. Therefore, the opening area of the slit can be made smaller compared to when adjacent vibration regions are completely separated. This means that the detection band can be prevented from narrowing by reducing the low-frequency roll-off frequency. Furthermore, compared to when adjacent vibration regions are connected at the region opposite the support region side, connecting the vibration regions tends to have less of an effect on the vibration of each vibration region, preventing a decrease in detection sensitivity.

Note that the reference symbols in parentheses attached to each component indicate an example of the correspondence between that component and the specific components described in the embodiments described below.

FIG. 2 is a plan view of the piezoelectric element according to the first embodiment. FIG. 2 is a cross-sectional view taken along line II-II in FIG. FIG. 2 is a cross-sectional view taken along line III-III in FIG. FIG. 10 is a diagram showing the relationship between the coverage of the slit with the additional thin film and the roll-off frequency and the decrease in sensitivity. FIG. 10 is a plan view of a piezoelectric element according to a second embodiment. 6 is a cross-sectional schematic diagram of the vibration part and the additional thin film taken along line VI-VI in FIG. 5. 7 is a cross-sectional schematic diagram of the vibration part and the additional thin film taken along line VII-VII in FIG. 5. FIG. 10 is a plan view of a piezoelectric element according to a third embodiment. FIG. 11 is a plan view of a piezoelectric element according to a modified example of the third embodiment. FIG. 10 is a plan view of a piezoelectric element according to a fourth embodiment. FIG. 11 is a plan view of a piezoelectric element according to a fifth embodiment.

Embodiments of the present invention will be described below with reference to the accompanying drawings. Note that in the following embodiments, identical or equivalent parts will be denoted by the same reference numerals.

(First embodiment)
The piezoelectric element of the first embodiment will be described with reference to Figures 1 to 3. The piezoelectric element of this embodiment is suitable for use in piezoelectric microphones mounted on smartphones, AI (artificial intelligence) speakers, etc. The piezoelectric element of this embodiment is also suitable for use in ultrasonic sensors, etc.

As shown in Figures 1 to 3, the piezoelectric element comprises a support 10 and a vibrating part 20 disposed on the support 10, and has a rectangular planar shape. The support 10 has a support substrate 11 with one surface 11a and an insulating film 12 formed on the one surface 11a of the support substrate 11. The support substrate 11 is made of, for example, a silicon substrate, and the insulating film 12 is made of, for example, an oxide film.

A recess 10a is formed in the support 10 to allow the inner edge of the vibrating section 20 to float. Therefore, the vibrating section 20 has a support area 21a arranged on the support 10, and a floating area 21b that is connected to the support area 21a and floats above the recess 10a. In this embodiment, the open end of the recess 10a facing the vibrating section 20 has a planar rectangular shape. Therefore, the entire floating area 21b has a planar rectangular shape.

In addition, in this embodiment, the vibrating section 20 has an opening 20a formed on its outer edge that exposes the outer edge of the insulating film 12. The insulating film 12 has an opening 12a formed on its outer edge that exposes the outer edge of the support substrate 11. As a result, the outer edge of the support substrate 11 is exposed from the insulating film 12 and the vibrating section 20. Note that the opening 12a formed in the insulating film 12 and the opening 20a formed in the vibrating section 20 facilitate the dicing process when manufacturing the piezoelectric element, and are not necessarily required to be formed.

Slits 30 are formed in the floating region 21b, penetrating the floating region 21b in the thickness direction. In this embodiment, the slits 30 are formed so as to divide the floating region 21b into four parts. Specifically, two slits 30 are formed, passing through the center C of the floating region 21b and extending toward opposite corners of the floating region 21b. In other words, the slits 30 extend from each corner of the floating region 21b, which has a rectangular shape in plan view, toward the center C, and are formed so that each slit 30 intersects at the center C. This separates the floating region 21b into first to fourth vibration regions 22a to 22d, each of which has an approximately triangular shape in plan view. Although not particularly limited, in this embodiment, the spacing between each vibration region 22a to 22d (i.e., the width of the slits 30) is approximately 1 μm. In addition, in this embodiment, the slits 30 extend to the support region 21a, but they may also be formed so that they terminate at the boundary between the floating region 21b and the support region 21a.

The first to fourth vibration regions 22a to 22d are configured as cantilevers with the end on the support region 21a side as a fixed end and the tip end on the opposite side to the support region 21a (hereinafter simply referred to as the tip end) as a free end.

The vibrating section 20 is configured to include a piezoelectric film 40 and an electrode film 50 connected to the piezoelectric film 40. Specifically, the piezoelectric film 40 includes a lower-layer piezoelectric film 41 and an upper-layer piezoelectric film 42 laminated on the lower-layer piezoelectric film 41. The lower-layer piezoelectric film 41 and the upper-layer piezoelectric film 42 are made of lead-free piezoelectric ceramics such as scandium aluminum nitride (ScAlN) and aluminum nitride (AlN). The lower-layer piezoelectric film 41 and the upper-layer piezoelectric film 42 are made of lead zirconate titanate (PZT) or the like.

The electrode film 50 is formed on each vibration region 22a-22d so as to connect to the piezoelectric film 40, and is made of molybdenum (Mo). However, the electrode film 50 may also be made of metal materials other than molybdenum, such as titanium (Ti), platinum (Pt), aluminum (Al), or ruthenium (Ru).

In this embodiment, the electrode films 50 include a lower electrode film 51 formed below the lower piezoelectric film 41, an intermediate electrode film 52 formed between the lower piezoelectric film 41 and the upper piezoelectric film 42, and an upper electrode film 53 formed above the upper piezoelectric film 42. The lower electrode film 51 and the intermediate electrode film 52 are arranged to face each other with the lower piezoelectric film 41 in between. The intermediate electrode film 52 and the upper electrode film 53 are arranged to face each other with the upper piezoelectric film 42 in between.

As described below, the piezoelectric element of this embodiment outputs, as a detection signal, the charge that changes as each of the vibration regions 22a to 22d vibrates. The piezoelectric element of this embodiment is configured to output the change in charge in the first to fourth vibration regions 22a to 22d as a single pressure detection signal. Specifically, the electrode films 50 of the first to fourth vibration regions 22a to 22d are electrically connected in series via wiring (not shown). More specifically, the first vibration region 22a to 22d has a so-called bimorph structure, in which the lower electrode films 51, intermediate electrode films 52, and upper electrode films 53 formed in each of the vibration regions 22a to 22d are connected in parallel, while the vibration regions 22a to 22d are connected in series.

The piezoelectric element is formed with a first electrode portion 61 and a second electrode portion 62 so as to connect to the ends of the series-connected electrode films 50 of the first to fourth vibration regions 22a to 22d. Specifically, the first electrode portion 61 has a first through electrode 61b and a first pad portion 61c, and is formed to connect to the lower electrode film 51 and upper electrode film 53 formed in the first vibration region 22a in the support region 21a. The second electrode portion 62 has a second through electrode 62b and a second pad portion 62c, and is formed to be electrically connected to the intermediate electrode film 52 formed in the fourth vibration region 22d in the support region 21a.

More specifically, as shown in FIG. 2, the lower electrode film 51 and upper electrode film 53 formed in the first vibration region 22a extend to the support region 21a. A first hole 61a is formed so as to penetrate the upper piezoelectric film 42 and the lower piezoelectric film 41 and expose the lower electrode film 51, and a first through electrode 61b is disposed in the first hole 61a so as to be electrically connected to the lower electrode film 51. A first pad 61c is disposed on the upper piezoelectric film 42 so as to be electrically connected to the first through electrode 61b and the upper electrode film 53.

As shown in FIG. 3, the intermediate electrode film 52 formed in the fourth vibration region 22d extends to the support region 21a. A second hole 62a is formed so as to penetrate the upper piezoelectric film 42 and expose the intermediate electrode film 52, and a second through electrode 62b is disposed in the second hole 62a so as to be electrically connected to the intermediate electrode film 52. A second pad 62c is disposed on the upper piezoelectric film 42 so as to be electrically connected to the second through electrode 62b.

Furthermore, the vibration section 20 of this embodiment has a buffer layer 70 on the support 10 side, on which the lower piezoelectric film 41 and lower electrode film 51 are disposed. The buffer layer 70 is made of, for example, aluminum nitride (AlN) or the like.

The piezoelectric element of this embodiment is provided with an additional thin film 81 that covers part of the slit 30 formed in the floating region 21b. Specifically, the additional thin film 81 is disposed in the portion of the slit 30 that is located on the support region 21a side. The additional thin film 81 is also formed to connect adjacent vibration regions 22a to 22d via the slit 30. As a result, the vibration regions 22a to 22d are connected at the portion on the support region 21a side.

In this embodiment, the additional thin film 81 is formed from the support region 21a side to the floating region 21b. However, the additional thin film 81 may be formed only in the floating region 21b, or may be arranged so that the end of the slit 30 on the support region 21a side is exposed from the additional thin film 81.

The additional thin film 81 is intended to prevent pressure from escaping through the slit 30. For this reason, the additional thin film 81 may be placed within the slit 30, or may not be placed within the slit 30. The additional thin film 81 is preferably made of a material with a low Young's modulus so that it does not affect the vibration of each of the vibration regions 22a to 22d, and is made of an organic material containing urethane, for example.

The above is the structure of the piezoelectric element in this embodiment. When pressure such as sound pressure is applied to each of the vibration regions 22a to 22d of this piezoelectric element, the vibration regions 22a to 22d vibrate. For example, if the tip end side (i.e., the free end side) of each of the vibration regions 22a to 22d is displaced upward, tensile stress is generated in the lower piezoelectric film 41, and compressive stress is generated in the upper piezoelectric film 42. Therefore, pressure such as sound pressure can be detected by extracting the charge from the first electrode portion 61 and the second electrode portion 62.

In this embodiment, the slit area is reduced by the additional thin film 81. This makes it difficult for pressure to escape through the slit 30, and as shown in Figure 4, the detection band can be broadened by reducing the roll-off frequency. Note that the sensitivity reduction in Figure 4 shows the simulation results when the sound pressure is set to 1 kHz. Furthermore, the slit area here refers to the area of the slit 30 when viewed from the stacking direction of the support body 10 and the vibration part 20, and is the opening area of the slit 30.

In this case, the larger the slit 30 covered by the additional thin film 81, the lower the roll-off frequency can be; however, the larger the slit 30 covered by the additional thin film 81, the more the vibration of each vibration region 22a to 22d is inhibited, resulting in a decrease in sensitivity. Therefore, it is preferable to adjust the area of the slit 30 covered by the additional thin film 81 according to the required performance.

For example, as shown in Figure 1, the length of the slit 30 along its longitudinal direction is defined as length L1, and the length of the additional thin film 81 along its longitudinal direction is defined as length L2. In this case, according to studies by the inventors, when the length L1 of the slit 30 is set to 477 μm, it has been confirmed that the roll-off frequency can be set to approximately 20 Hz by setting the length L2 of the additional thin film 81 to 250 μm. Setting the roll-off frequency to 20 Hz means matching the roll-off frequency to a frequency on the low frequency side of the audible range.

Furthermore, as shown in FIG. 1, if the length of the additional thin film 81 in the direction intersecting the longitudinal direction of the slit 30 is defined as width d, the narrower the width d, the less it will affect the vibration of each vibration region 22a to 22d. Here, the additional thin film 81 of this embodiment is made using an organic material as described above. This additional thin film 81 is made, for example, by applying and patterning an organic material. For this reason, taking into account manufacturing limitations and simplification of the manufacturing process, it is preferable that the additional thin film 81 be formed so that width d is less than the sum of the width of the slit 30 and 15 μm.

In the embodiment described above, an additional thin film 81 is provided to cover the portion of the slit 30 facing the support region 21a, and adjacent vibration regions 22a to 22d are connected at the portion facing the support region 21a. This allows the opening area of the slit 30 to be reduced, and the low-frequency roll-off frequency can be reduced to prevent the detection band from becoming narrower.

Furthermore, the additional thin film 81 is provided to cover the portion of the slit 30 on the support region 21a side. Therefore, compared to when the additional thin film 81 is provided on the portion of the slit 30 opposite the support region 21a, the additional thin film 81 is less likely to affect the vibration of each vibration region 22a to 22d, and a decrease in detection sensitivity can be suppressed.

(1) In this embodiment, an additional thin film 81 is provided to cover the portion of the slit 30 on the support region 21a side. This makes it easy to adjust the opening area of the slit 30.

Second Embodiment
A second embodiment will be described. This embodiment is the same as the first embodiment except that an additional thin film is added. As the other features are the same as the first embodiment, a description thereof will be omitted here.

As shown in Figures 5 to 7, the piezoelectric element of this embodiment has an additional thin film 82 arranged to cover the portion of the slit 30 formed in the floating region 21b on the side opposite the support region 21a. In other words, the piezoelectric element also has an additional thin film 82 arranged in the portion of the slit 30 that defines the free end sides of the first to fourth vibration regions 22a to 22d. Therefore, the free end sides of each vibration region 22a to 22d are also connected. Hereinafter, in this embodiment, the additional thin film 81 that covers the support region 21a side of the slit 30 will be referred to as the fixed end side additional thin film 81, and the additional thin film 82 that covers the portion of the slit 30 on the side opposite the support region 21a will be referred to as the free end side additional thin film 82.

Note that Figures 6 and 7 show a simplified shape of the vibration section 20, but in reality, the vibration section 20 is formed as shown in Figures 2 and 3. Also, Figure 6 shows a diagram in which the free-end side additional thin film 82 is arranged so as to fill the slit 30, but the free-end side additional thin film 82 does not have to be arranged so as to fill the slit 30. Similarly, Figure 7 shows a diagram in which the fixed-end side additional thin film 81 is arranged so as to fill the slit 30, but the fixed-end side additional thin film 81 does not have to be arranged so as to fill the slit 30.

The free-end side additional thin film 82 is thicker than the fixed-end side additional thin film 81. The free-end side additional thin film 82 also has a larger Young's modulus than the fixed-end side additional thin film 81. For example, the free-end side additional thin film 82 is made of polyimide or the like with a Young's modulus of about 4 GPa, and is about 3 μm thick. On the other hand, the fixed-end side additional thin film 81 is made of urethane or the like with a Young's modulus of about 0.1 GPa, and is about 1 μm thick.

In the present embodiment described above, an additional thin film 81 is provided to cover the portion of the slit 30 on the support region 21a side, thereby achieving the same effects as in the first embodiment.

(1) In this embodiment, a free end side additional thin film 82 is disposed on the portion of the slit 30 opposite the support region 21a. This prevents the free end side of the vibration regions 22a to 22d from warping due to residual stress in each vibration region 22a to 22d that occurs when manufacturing the piezoelectric element. This prevents the slit area from increasing and the detection band from decreasing.

(2) In this embodiment, the free-end-side additional thin film 82 is thicker and has a larger Young's modulus than the fixed-end-side additional thin film 81. Therefore, warping due to residual stress can be further reduced compared to when the free-end-side additional thin film 82 is thinner and has a smaller Young's modulus than the fixed-end-side additional thin film 81.

(Modification of the second embodiment)
A modification of the second embodiment will now be described. In the second embodiment, the free-end-side additional thin film 82 may be thinner and have a smaller Young's modulus than the fixed-end-side additional thin film 81. This makes it possible to suppress the free-end-side additional thin film 82 from affecting the vibration of each of the vibration regions 22 a to 22 d, and to suppress a decrease in detection sensitivity, compared to when the free-end-side additional thin film 82 is thicker and has a larger Young's modulus than the fixed-end-side additional thin film 81.

(Third embodiment)
The third embodiment will be described. This embodiment is different from the second embodiment in that the shape of the tip end side of each of the vibration regions 22a to 22d is changed. As the rest is the same as the second embodiment, the description will be omitted here.

As shown in Figure 8, in the piezoelectric element of this embodiment, each of the vibration regions 22a to 22d has a rounded tip shape so that the portion that overlaps with the free-end-side additional thin film 82 in the stacking direction is minimized. In other words, each of the vibration regions 22a to 22d has a chamfered tip.

In the present embodiment described above, an additional thin film 81 is provided to cover the portion of the slit 30 on the support region 21a side, thereby achieving the same effects as in the first embodiment.

(1) In this embodiment, each of the vibration regions 22a to 22d has a rounded tip shape so that the portion that overlaps with the free-end-side additional thin film 82 in the stacking direction is minimized. This makes it even less likely that the free-end-side additional thin film 82 will affect the vibration of each of the vibration regions 22a to 22d, further preventing a decrease in detection sensitivity.

(Modification of the third embodiment)
A modification of the third embodiment will now be described. In the third embodiment, each of the vibration regions 22a to 22d may have a flat trapezoidal shape with a chamfered tip. Even with such a piezoelectric element, the free-end-side additional thin film 82 is less likely to affect the vibration of each of the vibration regions 22a to 22d, so that the same effect as in the third embodiment can be obtained.

(Fourth embodiment)
A fourth embodiment will be described. This embodiment is different from the first embodiment in that the shape of the additional thin film 81 is changed. As the rest of the configuration is the same as the first embodiment, a description thereof will be omitted here.

In the piezoelectric element of this embodiment, as shown in Figure 10, the additional thin film 81 has a planar elliptical shape in the stacking direction. In other words, the additional thin film 81 has a planar shape with chamfered corners.

In the present embodiment described above, an additional thin film 81 is provided to cover the portion of the slit 30 on the support region 21a side, thereby achieving the same effects as in the first embodiment.

(1) In this embodiment, the additional thin film 81 has a planar shape with chamfered corners in the stacking direction. This prevents stress from concentrating at specific locations on the additional thin film 81, and prevents the additional thin film 81 from peeling off. Although not specifically shown, the free-end-side additional thin film 82 of the second and third embodiments also has a planar shape with chamfered corners, which prevents the free-end-side additional thin film 82 from peeling off.

Fifth Embodiment
A fifth embodiment will be described. This embodiment is different from the first embodiment in that the shape of the slit 30 is changed. As the rest of the configuration is the same as the first embodiment, a description thereof will be omitted here.

In the piezoelectric element of this embodiment, as shown in FIG. 11, the slits 30 are not formed to reach the corners of the floating region 21b, which has a rectangular planar shape, but are shaped to terminate within the floating region 21b. As a result, the vibration regions 22a to 22d are connected at the portion on the support region 21a side.

In the present embodiment described above, the slits 30 are formed so that the vibration regions 22a to 22d are connected at the support region 21a side, which reduces the opening area of the slits 30. Therefore, the same effects as in the first embodiment can be achieved.

(Other embodiments)
Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and modifications within the scope of equivalents. In addition, various combinations and forms, as well as other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

For example, in each of the above embodiments, the floating region 21b may have a polygonal planar shape, such as a pentagonal, hexagonal, or octagonal shape, rather than a rectangular shape. The number of vibration regions 22a to 22d formed in the floating region 21b can be changed as appropriate. Furthermore, the piezoelectric element may have a polygonal planar shape, such as a pentagonal or hexagonal shape, rather than a rectangular shape.

Furthermore, in each of the above embodiments, the vibration section 20 may be configured to have at least one layer of piezoelectric film 40 and one layer of electrode film 50.

In each of the above embodiments, the piezoelectric element does not necessarily have to have an opening 20a formed in the vibrating portion 20 or an opening 12a formed in the insulating film 12.

Furthermore, in each of the above embodiments, each vibration region 22a-22d may output its own charge as a detection signal. In this case, a first electrode portion 61 is connected to the lower electrode film 51 and upper electrode film 53 of each vibration region 22a-22d, and a second electrode portion 62 is connected to the intermediate electrode film 52 of each vibration region 22a-22d.

The above embodiments can also be combined. For example, the second and third embodiments can be combined with the fourth embodiment, so that the planar shape of the free-end-side additional thin film 82 has chamfered corners.

10 Support 20 Vibration part 21a Support region 21b Floating region 22a to 22d Vibration region 30 Slit 40 Piezoelectric film 50 Electrode film

Claims (3)

A piezoelectric element in which a vibration part (20) is disposed on a support (10),
The support;
The vibration unit is disposed on the support, includes a piezoelectric film (40) and an electrode film (50) connected to the piezoelectric film, and has a support region (21a) supported by the support, and a floating region (21b) connected to the support and floating above the support,
The floating region has a plurality of vibration regions (22a to 22d) divided by slits (30),
The adjacent vibration regions are connected at the support region side ,
the slit is formed so as to reach the support region from the floating region,
The adjacent vibration regions are connected to each other by disposing an additional thin film (81) that covers the support region side portion of the slit, and
The adjacent vibration regions are connected to each other by disposing an additional thin film (82) that covers the portion of the slit opposite to the support region side, and
The additional thin film disposed on the side opposite to the support region has a greater thickness and a greater Young's modulus than the additional thin film disposed on the support region side . A piezoelectric element in which a vibration part (20) is disposed on a support (10),
The support;
The vibration unit is disposed on the support, includes a piezoelectric film (40) and an electrode film (50) connected to the piezoelectric film, and has a support region (21a) supported by the support, and a floating region (21b) connected to the support and floating above the support,
The floating region has a plurality of vibration regions (22a to 22d) divided by slits (30),
The adjacent vibration regions are connected at the support region side ,
the slit is formed so as to reach the support region from the floating region,
The adjacent vibration regions are connected to each other by disposing an additional thin film (81) that covers the support region side portion of the slit, and
The adjacent vibration regions are connected to each other by disposing an additional thin film (82) that covers the portion of the slit opposite to the support region side, and
The additional thin film disposed on the side opposite to the support region has a smaller thickness and a smaller Young's modulus than the additional thin film disposed on the support region side . 3. The piezoelectric element according to claim 1 , wherein the additional thin film has a flat shape with chamfered corners.