Transducer

Abstract

A transducer (10A) is provided with: a substrate (20) that contains silicon; and a piezoelectric element (30) that is disposed on the substrate (20). The substrate (20) has: a film body (21) having a first surface (21a) and a second surface (21b) that face one another from opposite directions in a thickness direction; and a frame body (22) that surrounds the film body (21) when viewing the film body (21) from the thickness direction. The piezoelectric element (30) is disposed on the first surface (21a) of the film body (21). A portion of an outer edge (21c) of the film body (21) when viewed from the thickness direction forms a connected part (21d) that is connected to the frame body (22), and the remainder of the outer edge (21c) aside from the connected part (21d) is separated from the frame body (22). The substrate (20) has a projecting part (24) that projects in the thickness direction from a region, of the second surface (21b), that includes at least a portion of the remainder of the outer edge (21c).

Description

[Technical Field]

[0001] The present embodiment relates to a transducer. [Background technology]

[0002] A transducer is known as one of various MEMS (Micro Electro Mechanical Systems) manufactured using semiconductor manufacturing processes. A MEMS transducer includes a piezoelectric element and a membrane body driven by the piezoelectric element, and is housed in, for example, a portable electronic device case as a speaker or microphone (see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2018 / 061805 Summary of the Invention [Problem to be solved by the invention]

[0004] The membrane that constitutes the transducer may be formed as a cantilever. That is, one end (i.e., the base end) of the membrane is supported by a support member as a fixed end, and the other end (i.e., the tip) of the membrane is formed as a free end. The outer edge of the membrane other than the part supported by the support member is slightly spaced from the support member. Gas flows from the gap between the outer edge of the membrane and the member facing the outer edge, such as the support member, due to the vibration of the membrane. The pressure change caused by this gas flow has an opposite phase to the change in sound pressure generated by the membrane and acts to cancel out this sound pressure. Therefore, if the above-mentioned gas flow is excessively large, the sound pressure that should be obtained will not be obtained, and sound reproducibility may be reduced.

[0005] Furthermore, a film formed as a cantilever is prone to warping due to the stress of the piezoelectric element and its protective film on its surface. If this warping is excessive, it limits the amplitude of vibration of the film (piezoelectric element). Therefore, in this case too, the sound pressure that should be obtained cannot be obtained, and sound reproducibility may be reduced.

[0006] The present embodiment aims to provide a transducer that can improve the reproducibility of sound. [Means for solving the problem]

[0007] One aspect of this embodiment is a transducer comprising a substrate containing silicon and a piezoelectric element disposed on the substrate. The substrate has a film body portion having a first surface and a second surface facing in opposite directions in the thickness direction, and a frame body portion surrounding the film body portion when viewed from the thickness direction. The piezoelectric element is disposed on the first surface of the film body portion, and a portion of the outer edge of the film body portion when viewed from the thickness direction forms a connection portion connected to the frame body portion, and the remainder of the outer edge other than the connection portion is separated from the frame body portion. The substrate has a protrusion protruding in the thickness direction from a region of the second surface that includes at least a portion of the remainder of the outer edge. The protrusion is disposed opposite the inner surface of the frame across the slit separating the membrane and frame, and extends the slit in the thickness direction to suppress gas flow through the slit when the membrane vibrates.

[0008] The substrate may have a semiconductor layer and an oxide layer stacked on top of each other in the thickness direction. The transducer may further include a lid attached to the frame and covering the first surface of the film body at a distance from the first surface of the film body. The lid may have an opening that overlaps at least a portion of the piezoelectric element when viewed in the thickness direction.

[0009] The protrusion may be disposed on a portion of the remaining outer edge facing the connecting portion. The substrate may have a reinforcing portion protruding from the second surface in the thickness direction and connected to the protrusion. The protrusion may be disposed over the entire remaining outer edge. The protrusion may have a plurality of protruding cells divided along the outer edge. The planar shape of the protrusion viewed from the thickness direction may be symmetrical with a line connecting the center of the connecting portion and the center of the portion of the outer edge facing the connecting portion as the axis of symmetry. The height of the protrusion in the thickness direction may be 3 μm or more. The maximum length of the protrusion in a direction parallel to the second surface of the film body may be 10 μm to 100 μm. The piezoelectric element may be disposed on the frame body and the film body so as to straddle the connecting portion. When the film body is viewed from the thickness direction, a portion of the oxide layer may overlap the protrusion. A portion of the oxide layer may be included in the protrusion. The lid may be attached to the frame body via a protective film formed on the substrate. The protective film may include a first protective film that covers the piezoelectric element and the surface of the surrounding frame body, and a second protective film that covers the surface of the frame body except for the area including the film body and the piezoelectric element. The first protective film may contain alumina as a component. The second protective film may contain tetraethoxysilane as a component. [Effects of the Invention]

[0010] According to this embodiment, it is possible to provide a transducer that can improve the reproducibility of sound. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A is a top view of a transducer according to a first embodiment. [Figure 1B] FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A. [Figure 1C] FIG. 1C is an exploded view showing the configuration of FIG. 1B in a simplified manner. [Figure 1D] FIG. 1D is a cross-sectional view taken along line ID-ID in FIG. 1B. [Figure 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. 1A. [Figure 3A]FIG. 3A is a rear view of the substrate according to the first embodiment. [Figure 3B] FIG. 3B is a rear view of the substrate according to the first embodiment. [Figure 3C] FIG. 3C is a rear view of the substrate according to the first embodiment. [Figure 4A] FIG. 4A is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4B] FIG. 4B is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4C] FIG. 4C is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4D] FIG. 4D is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4E] FIG. 4E is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4F] FIG. 4F is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4G] FIG. 4G is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4H] FIG. 4H is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4I] FIG. 4I is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 4J] FIG. 4J is a diagram showing a manufacturing process of the transducer according to the first embodiment. [Figure 5] FIG. 5 is a diagram for explaining the tendency of warping of the film body portion due to the oxide film. [Figure 6] Figure 6 is a diagram for explaining the change in the amount of warping of the film body portion due to the piezoelectric element and the protective film, where Figure 6(a) is a diagram showing the change in the neutral position of the opposing portion depending on the area of ​​the piezoelectric element, and Figure 6(b) is a diagram showing the change in the neutral position of the opposing portion depending on the film thickness of the protective film. [Figure 7] FIG. 7 is a diagram showing the amount of warping of the membrane portion and the neutral position of the opposing portions of the membrane according to the second embodiment. [Figure 8A] FIG. 8A is a top view of a substrate according to a first example of the second embodiment. [Figure 8B] FIG. 8B is a cross-sectional view taken along line VIIIB-VIIIB in FIG. 8A. [Figure 9A] FIG. 9A is a top view of a substrate according to a second example of the second embodiment. [Figure 9B] FIG. 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A. [Figure 9C] FIG. 9C is a partially enlarged view of the cross section of the film body and the protective film shown in FIG. 9B. DETAILED DESCRIPTION OF THE INVENTION

[0012] The embodiments will be described with reference to the drawings. Note that the same reference numerals will be used in the drawings to designate structurally or functionally identical parts in the respective embodiments, and redundant description of these parts will be omitted.

[0013] Each embodiment is a MEMS (Micro Electro Mechanical Systems) having a membrane body configured to be displaceable (flexible, distortable), and can be applied to transducers such as speakers and microphones that use piezoelectric elements to control or detect the displacement (flexure, distortion, vibration) of the membrane body.

[0014] (First embodiment) The configuration of the transducer 10A according to the first embodiment will be described. Fig. 1A is a top view of the transducer 10A, Fig. 1B is a cross-sectional view taken along line IB-IB in Fig. 1A, Fig. 1C is an exploded view showing a simplified configuration of Fig. 1B, and Fig. 1D is a cross-sectional view taken along line ID-ID in Fig. 1B.

[0015] 1A to 1D, the transducer 10A includes a substrate 20 containing silicon, a piezoelectric element 30 disposed on the substrate 20, and a cover 40. The substrate 20 also includes a membrane portion 21 having a front surface (first surface) 21a and a back surface (second surface) 21b facing in opposite directions in the thickness direction, and a frame portion (support portion) 22 provided around the membrane portion 21 and connected to a part of the outer edge 21c of the membrane portion 21. The frame portion 22 surrounds the membrane portion 21 when the membrane portion 21 is viewed from the thickness direction of the membrane portion 21.

[0016] The piezoelectric element 30 is disposed on a first surface of the membrane part 21 and controls or detects the displacement of the membrane part 21 in the Z direction. That is, when the transducer 10A is used as a speaker, the piezoelectric element 30 vibrates the membrane part 21 in the Z direction. On the other hand, when the transducer 10A is used as a microphone, the piezoelectric element 30 detects the displacement of the membrane part 21.

[0017] The substrate 20 is an SOI (Silicon on Insulator) substrate including an active layer 51, which is a semiconductor layer, a support layer 52, which is also a semiconductor layer, and an interlayer insulating layer (BOX layer, oxide layer) 53 disposed between the active layer 51 and the support layer 52. The active layer 51, the interlayer insulating layer 53, and the support layer 52 are stacked in this order in the Z direction. That is, the semiconductor layer and the oxide layer are stacked one on top of the other in the Z direction. The film body 21 is formed, for example, from the active layer 51, and the frame body 22 is formed, for example, from the active layer 51, the interlayer insulating layer 53, and the support layer 52. However, the substrate 20 is not limited to an SOI substrate as long as it contains silicon. That is, the substrate 20 may be a silicon substrate without an interlayer insulating layer. An oxide film 54 is formed on the front surface 20a of the substrate 20, which is the outer surface of the active layer 51, and an oxide film 55 is formed on the back surface 20b of the substrate 20, which is the outer surface of the support layer 52 (see FIG. 4A).

[0018] For ease of explanation, the stacking direction of the active layer 51, the support layer 52, and the interlayer insulating layer 53 will be referred to as the Z direction, and two directions that are perpendicular to the Z direction and perpendicular to each other will be referred to as the X direction and the Y direction. The Z direction is also the thickness direction of the substrate 20, the piezoelectric element 30, and the film body portion 21, and is also the direction in which the substrate 20 and the lid body 40 are stacked.

[0019] The membrane portion 21, the frame portion 22, and the protrusion portion 24 described below are integrally formed from the substrate 20, which is a single member.

[0020] The membrane 21 is a thin film that expands in the X and Y directions and has a thickness (e.g., 2 to 3 μm) that allows it to be displaced (flexible, deformable) in the Z direction. The membrane 21 also has a front surface (first surface) 21a and a back surface (second surface) 21b that face in opposite directions in the Z direction. The front surface 21a faces the lid 40, and the back surface 21b faces the space 23. If the substrate 20 is an SOI substrate, the back surface 21b of the membrane 21 may remain covered with an interlayer insulating layer 53 (see FIG. 1B).

[0021] When viewed from the Z direction, a portion of the outer edge 21c of the membrane portion 21 forms a connection portion 21d connected to the frame portion 22. Meanwhile, the remainder of the outer edge 21c other than the connection portion 21d is separated from the frame portion 22. A slit 25 is interposed between the remainder of the outer edge 21c and the frame portion. The remainder of the outer edge 21c also includes a facing portion 21e facing the connection portion 21d. In other words, the membrane portion 21 includes the connection portion 21d as a fixed end and the facing portion 21e as a free end, and functions as a cantilever that displaces (vibrates) in the Z direction. The membrane portion 21 is formed together with the space 23, for example, by etching the back surface 22b of the frame portion 22 (substrate 20).

[0022] The frame portion 22 has a frame-like shape that surrounds the membrane portion 21 when the substrate 20 is viewed from the Z direction. The frame portion 22 has an inner surface 22c that faces the outer edge 21c of the membrane portion 21 across the slit 25. The inner surface 22c faces the outer edge 21c of the membrane portion 21 across the slit 25. Meanwhile, the substrate 20 has a space 23 that is surrounded by the back surface 21b of the membrane portion 21 and the inner surface 22c of the frame portion 22. That is, the substrate 20 has a recess with the back surface 21b of the membrane portion 21 as its bottom surface and the inner surface 22c of the frame portion 22 as its side surface.

[0023] 1B and 1C, the slit 25 penetrates the substrate 20 in the Z direction via the space 23. The width of the slit 25 is, for example, 10 μm. The slit 25 is formed by etching one surface of the substrate 20, including the front surface (first surface) 21a of the membrane body portion 21. Therefore, the width of the slit 25 can be set with high precision.

[0024] Furthermore, the front surface 21a of the membrane portion 21 and the front surface 22a of the frame portion 22 are also formed from one surface of the substrate 20 in conjunction with the formation of the slits 25. If the bending of the membrane portion 21 is not taken into consideration, the heights of the two in the Z direction are the same.

[0025] The lid 40 is attached to the frame 22 by adhesive and covers the front surface 21a of the membrane 21 with a space (gap) 41 (described later) between them. The lid 40 is made of a semiconductor material containing, for example, silicon (Si). The lid 40 has a front surface 40a and a back surface 40b facing opposite directions in the Z direction. An opening 43 is formed in the back surface 40b of the lid 40. An inner surface (recess) 44 of the opening 43 forms a space 41 within the lid 40. The space 41 also communicates with the external space of the transducer 10A via a through-hole 42 formed in the front surface 40a. The through-hole 42 overlaps at least a portion of the piezoelectric element 30 when viewed from the Z direction. The opening area of ​​the through-hole 42 is smaller than the area of ​​the membrane 21, and the opening areas of the opening 43 and the space 41 are larger than the area of ​​the membrane 21.

[0026] The inner surface 44 of the opening 43 comes into contact with the membrane portion 21 when the membrane portion 21 is deformed. This prevents excessive bending of the membrane portion 21. It also prevents gas from leaking from the slits 25, which will be described later. However, the lid 40 may be omitted depending on the specifications of the transducer.

[0027] 1B, the piezoelectric element 30 is disposed on the front surface 21a of the membrane body part 21 so as to face the opening 43 of the lid body 40. The piezoelectric element 30 may be disposed on the front surface 22a of the frame body part 22 and the front surface 21a of the membrane body part 21 so as to straddle the outer edge 21c of the membrane body part 21.

[0028] The piezoelectric element 30 includes a pair of electrodes 31, 33, and a piezoelectric film 32 sandwiched between the pair of electrodes 31, 33. The pair of electrodes 31, 33 and the piezoelectric film 32 have shapes corresponding to the shape of the film body portion 21.

[0029] An electrode 31, a piezoelectric film 32, and an electrode 33 are laminated in this order along the Z direction on the front surface 21a of the membrane body part 21. The piezoelectric element 30 is formed on the membrane body part 21 before the lid body 40 is attached to the frame body part 22.

[0030] For example, when the transducer 10A is used as a speaker, when a drive voltage is applied between the pair of electrodes 31 and 33, the membrane portion 21 is displaced due to expansion and contraction of the piezoelectric film 32. Specifically, the tip side of the membrane portion 21 is displaced so as to warp along the Z direction.

[0031] By repeatedly applying a drive voltage to the pair of electrodes 31, 33, the membrane portion 21 alternately repeats displacement toward the space 23 side and toward the space 41 side. That is, the membrane portion 21 vibrates in the Z direction. This vibration of the membrane portion 21 vibrates the air around the membrane portion 21, generating sound waves. These sound waves propagate through the through-hole 42 in the lid 40 to the space outside the transducer 10A.

[0032] The electrodes 31 and 33 are formed of a thin conductive metal film such as platinum, molybdenum, iridium, or titanium. The electrode 31 is located on the upper surface of the piezoelectric film 32, and the electrode 33 is located on the lower surface of the piezoelectric film 32.

[0033] The piezoelectric film 32 is made of, for example, lead zirconate titanate (PZT), but may also be made of aluminum nitride (AlN), zinc oxide (ZnO), lead titanate (PbTIO3), or the like.

[0034] The piezoelectric element 30 and the surrounding front surface 22a of the frame body 22 are covered with a protective film 56 (first protective film) 57 containing, for example, alumina as a component. Furthermore, on the front surface 22a of the frame body 22, the area other than the area including the membrane body 21 and the piezoelectric element 30 is covered with a protective film 56 (second protective film) 58 containing, for example, tetraethoxysilane (TEOS) as a component. The protective film 58 is formed, for example, to provide insulation between the wiring of the electrodes 31, 33.

[0035] The protrusion 24 according to this embodiment will be described. 2 is a cross-sectional view taken along line II-II in FIG. 1A, and is an enlarged view of the periphery of the facing portion 21e of the membrane portion 21. FIGS. 3A to 3C are rear views of the substrate 20. FIG.

[0036] As shown in Figure 2, the substrate 20 has a protrusion 24. The protrusion 24 protrudes in the thickness direction of the membrane body 21 from a region of the back surface 21b of the membrane body 21 that includes at least a portion of the remainder of the outer edge 21c. The protrusion 24 is formed integrally with the membrane body 21 and protrudes from the outer edge 21c of the membrane body 21 toward the space 23 within the frame body 22. The gap between the protrusion 24 and the inner surface 22c of the frame body 22 is continuous with a slit 25.

[0037] 3A, the protrusion 24 is disposed in the opposing portion 21e of the remaining portion of the outer edge 21c of the film body 21 other than the connecting portion 21d, the opposing portion 21e being opposed to the connecting portion 21d. The protrusion 24 may also extend along the outer edge 21c. Furthermore, when the film body 21 is viewed from the Z direction, a portion of the interlayer insulating layer 53 overlaps with the protrusion 24. When the thickness of the film body 21 is smaller than the original thickness of the active layer 51, this portion of the interlayer insulating layer 53 is included in the protrusion 24.

[0038] The height of the protrusion 24 in the Z direction is set in consideration of the maximum amplitude of the membrane 21 and the width w1 of the slit 25. The height is, for example, 3 μm to several hundred μm. The thickness of the protrusion 24 is set in consideration of the mechanical strength of the protrusion 24 and the weight of the membrane 21. The thickness is, for example, 10 μm to 100 μm. The thickness here refers to the maximum length of the protrusion 24 in the direction parallel to the back surface 21b of the membrane 21.

[0039] When the membrane 21 vibrates to generate sound waves, gas flows between the space 23 and the space 41 through the slit 25. The change in pressure due to this gas flow (leakage) has an opposite phase to the change in sound pressure generated by the membrane 21, and acts to cancel out this sound pressure. Therefore, if the gas flow is excessively large, the sound pressure that should be obtained may not be obtained, and sound reproducibility may be reduced. For example, the amplitude of the membrane vibration in the low-frequency range tends to be larger than that in the high-frequency range, and in this case, the sound pressure is likely to be canceled out by the gas flow.

[0040] However, according to this embodiment, the protrusion 24 extends the gap of width w1 defined by the slit 25 in the Z direction. Therefore, compared to when the protrusion 24 is not provided, the change in the width of the slit 25 during vibration is suppressed, and the flow of gas between the space 23 and the space 41 is suppressed. As a result, the cancellation of the sound pressures described above is suppressed. For example, it is possible to increase the sound pressure in the low frequency range where sound pressures tend to cancel each other out. In other words, it is possible to improve the reproducibility of the sound that should be obtained.

[0041] As shown in FIG. 3A, when the protrusion 24 is provided on the facing portion 21e, the substrate 20 may have at least one reinforcing portion 26. The reinforcing portion 26 protrudes from the back surface 21b of the membrane portion 21 in the Z direction (i.e., toward the space 23) and connects to the protrusion 24. The reinforcing portion 26 also extends from the protrusion 24 toward the connecting portion 21d of the membrane portion 21. For example, the reinforcing portion 26 is provided on a straight line 12 of the membrane portion 21 that extends from the connecting portion 21d of the membrane portion 21 to the facing portion 21e of the membrane portion 21. The straight line 12 connects the center of the connecting portion 21d and the center of the facing portion 21e of the outer edge 21c that faces the connecting portion 21d. When multiple reinforcing portions 26 are provided, they are arranged parallel to the straight line 12.

[0042] The length of the reinforcing portion 26 may be equal to or less than the length from the opposing portion 21e to the connecting portion 21d. The reinforcing portion 26 functions as a rib that prevents damage due to excessive deformation of the protruding portion 24. The reinforcing portion 26 also prevents the membrane portion 21 from bending, which generates unnecessary harmonics. This allows the amplitude of the membrane portion 21 to be increased.

[0043] As shown in FIG. 3B, the protruding portion 24 may be provided on the entire remaining portion of the outer edge 21c of the membrane portion 21 except for the connecting portion 21d. In this case, the above-mentioned gas leakage is further suppressed. Also, as shown in FIG. 3C, the protruding portion 24 may have a plurality of protruding cells 24a divided along the outer edge 21c of the membrane portion 21. In this case, compared to the example in which the protruding portion 24 is provided on the entire remaining portion of the outer edge 21c, the membrane portion 21 is made lighter and has improved elasticity.

[0044] 3A to 3C, the planar shape of protrusion 24 as viewed in the Z direction may be symmetrical about a line 12 connecting the center of connection portion 21d and the center of opposing portion 21e of outer edge 21c opposing connection portion 21d. In this case, asymmetric bending of membrane portion 21 and the associated generation of unnecessary harmonics can be suppressed.

[0045] Next, a method for manufacturing the transducer 10A will be described. Figures 4A to 4J are diagrams showing the manufacturing process of the transducer 10A.

[0046] 4A shows the substrate 20 before the piezoelectric element 30 is formed. The substrate 20 is placed on a support table (not shown) of a manufacturing apparatus with the back surface 20b in contact with the support table (not shown). Next, as shown in FIG. 4B, a conductive layer that will become the electrode 33, a piezoelectric material that will become the piezoelectric film 32, and a conductive layer that will become the electrode 31 are laminated in this order while performing etching or the like as appropriate in a set area 38 of the piezoelectric element 30 defined on the front surface 20a of the substrate 20, to form the piezoelectric element 30.

[0047] 4C, a protective film 57 is formed on the piezoelectric element 30 and the surrounding front surface 20a. The protective film 57 is a film containing, for example, alumina (Al2O3), and has a thickness of, for example, 80 nm.

[0048] Next, a protective film 58 and the wiring 34 are formed on the protective film 57. The protective film 58 is, for example, a film (TEOS film) containing tetraethoxysilane (TEOS). The protective film 58 is formed before and after the formation of the wiring 34, and has a thickness of, for example, 1.5 μm. The TEOS film can be manufactured by chemical vapor deposition, such as thermal CVD or plasma CVD. The wiring 34 and the electrode 33 are electrically connected by forming a contact between them.

[0049] Next, as shown in FIG. 4D, the area of ​​the protective film 58 that includes the positions where the piezoelectric element 30 and the slit 25 are formed is removed by etching. This makes the vibrating portion, including the membrane portion 21, thinner and lighter. The protective film 58 can be etched using a resist patterned using a typical photolithography method as a mask. The resist is removed with oxygen plasma, sulfuric acid, or the like. The protective film 58 can be etched by wet etching using hydrofluoric acid or dry etching such as reactive ion etching.

[0050] Next, as shown in FIG. 4E, the active layer 51 is etched at the position where the slit 25 is to be formed, thereby forming the slit 25. This etching is performed until the slit 25 reaches a predetermined depth (for example, a depth that reaches the interlayer insulating layer 53). A silicon oxide film is deposited on the active layer 51 as a mask material. Thermal CVD or plasma CVD can be used as the deposition method. Next, a resist is patterned on the mask material. A general photolithography method can be used as the patterning method. The mask material is etched using the patterned resist as a mask. The mask material has an opening in the portion where the slit 25 is to be formed. Dry etching such as reactive ion etching can be used as the etching method.

[0051] 4F, the lid 40 is attached to the substrate 20 by adhesive or the like. During this attachment, the protective film 56 is positioned between the lid 40 and the substrate 20. Furthermore, by manipulating a support substrate (not shown) temporarily adhered to the front surface 20a of the lid 40, the lid 40 is positioned relative to the substrate 20 so that the opening 43 faces the area including the piezoelectric element 30 and the slit 25.

[0052] Next, the support (not shown) is removed from the rear surface 20b of the substrate 20. Thereafter, as shown in Fig. 4G, the oxide film 55 formed on the rear surface 20b is removed by etching.

[0053] 4H, a resist 61 is applied to the rear surface 20b, and then the resist 61 is removed from the areas 70 corresponding to the membrane body portion 21 and the slits 25 using a general photolithography method.

[0054] Next, as shown in FIG. 4I, the support layer 52 of the substrate 20 is etched (removed) using a patterned resist 61 until a thickness approximately equal to the height of the protrusion 24 is obtained. Furthermore, the resist 61 is again applied to the surface 20c of the substrate 20 formed by this etching, and the resist 61 is patterned so that the resist 61 remains only in positions corresponding to the protrusion 24. Then, the surface 20c is etched using the patterned resist 61 to remove the support layer 52 and the interlayer insulating layer 53, thereby forming the protrusion 24 (see FIG. 4J). Note that this etching may remove a portion of the active layer 51 depending on the thickness of the film body 21. Alternatively, the interlayer insulating layer 53 may remain.

[0055] 4J, all of the remaining resist 61 is removed. Thereafter, the support substrate (not shown) that supports the lid 40 is appropriately removed from the front surface 40a.

[0056] (Second embodiment) A second embodiment will be described. The configuration of the transducer 10B according to the second embodiment is the same as the configuration of the transducer 10A according to the first embodiment. Therefore, in the following description, differences from the first embodiment will be described, and the same reference numerals will be used to designate components common to both embodiments, and their description will be omitted. Note that the transducer 10B according to the second embodiment may or may not have a protrusion 24 (see FIG. 1B). For ease of explanation, the protrusion 24 and wiring 34 are omitted from the drawings according to the second embodiment.

[0057] As will be described later, in this embodiment, the warpage of the membrane portion 21 is adjusted. First, this warpage will be explained using the example of a cantilever 80 having the same thickness as the membrane portion 21. Figure 5 is a diagram for explaining the tendency of warpage of the cantilever 80. For ease of explanation, the Z direction in the figure is defined as the vertical direction, the X direction as the horizontal direction, the upper side of the figure as the top, and the lower side of the figure as the bottom. Gravity and internal stress of the cantilever 80 will not be taken into consideration.

[0058] Cantilever 80 has the same thickness as membrane portion 21, and has an upper surface 80a and a lower surface 80b facing in opposite directions in the Z direction. Cantilever 80 extends in the X direction, with only one end connected to support portion 82, and the rest of the cantilever 80 is separated from all members such as support portion 82. In other words, cantilever 80 has a fixed end 80c connected to support portion 82 and a free end 80d that is freely displaceable in the Z direction.

[0059] The support part 82 surrounds the cantilever 80, similar to the frame part 22. The cantilever 80 and the support part 82 are integrally formed from a single substrate containing silicon. When no external force is applied to the cantilever 80, the top surface 80a of the cantilever 80 and the top surface 80a of the support part 82 are located within the same reference plane 86.

[0060] Here, suppose that an oxide film 84 is formed as a protective film on the top surface 80a of the cantilever 80. The oxide film 84 is formed when the cantilever 80 is manufactured. When the oxide film 84 is formed, the cantilever 80 is heated, and therefore, when the temperature of the cantilever 80 drops to room temperature, membrane stress (internal stress) is generated in the oxide film 84, and this force acts in a direction that causes contraction in the surface direction, causing the cantilever 80 to warp with the top surface 80a facing inward.

[0061] 5, the free end 80d of the cantilever 80 is displaced upward from its position when there is no membrane stress (i.e., the position of the reference surface 86). When an object 88 having an inner surface 88a facing the cantilever 80, such as the lid 40 (see FIG. 1B), is placed on the support 82, if the distance between the inner surface 88a and the free end 80d in the Z direction is smaller than the sum of the maximum amplitude of the cantilever 80 (free end 80d) and the movement distance of the free end 80d in the Z direction caused by warping, the free end 80d is more likely to come into contact with the inner surface, and the maximum amplitude of the cantilever 80 (free end 80d) is limited by the warping of the cantilever 80.

[0062] The amount of warping (degree of warping) of cantilever 80 varies depending on the magnitude of the film stress of the film formed on its surface. For example, a significant difference was observed in the amount of warping of cantilever 80 when oxide film 84 was formed by thermal oxidation and when it was formed by CVD. This suggests that it is possible to adjust the amount of warping of cantilever 80 by controlling the film stress of the formed film.

[0063] When this is applied to the transducer according to this embodiment, it is found that the amount of warpage of the membrane body part 21 can be adjusted by controlling the film stress of the material formed on the front surface (first surface) 21a of the membrane body part 21. In this embodiment, this material is the piezoelectric element 30 and the protective film 56.

[0064] 4C, the protective film 56 is formed on the piezoelectric element 30 and the surrounding front surface 20a of the substrate 20, and includes a protective film 57 containing alumina (Al2O3), or a protective film 58 containing the protective film 57 and tetraethoxysilane (TEOS). In the first embodiment, the protective film 58 on the piezoelectric element 30 is removed. However, as described below, it may remain in the second embodiment. Furthermore, the material of the protective film 56 is not limited to the above, and the protective film 56 may include three or more layers.

[0065] We will now explain the change in the amount of warping of the membrane portion 21 due to the piezoelectric element 30 and the protective film 56. Figures 6(a) and 6(b) are diagrams showing the change in the neutral position of the facing portion 21e of the membrane portion 21 accompanying the change in warping of the membrane portion 21. The neutral position of the facing portion 21e is the position (height) of the facing portion 21e in the Z direction when the membrane portion 21 is not receiving an external force from the piezoelectric element 30 (neutral state).

[0066] First, a description will be given with reference to FIG. 6(a). FIG. 6(a) is a diagram showing the change in the neutral position of the facing portion 21e according to the area of ​​the piezoelectric element 30. The vertical axis indicates the neutral position of the facing portion 21e along the Z direction, and the horizontal axis indicates the area of ​​the piezoelectric element 30. The area of ​​the piezoelectric element 30 is changed by changing the position of the edge portion 30b (see FIG. 8A) of the piezoelectric element 30 near the facing portion 21e along the X direction, while keeping the position of the edge portion 30a (see FIG. 8A) of the piezoelectric element 30 near the connecting portion 21d fixed. However, in any area, the width of the piezoelectric element 30 along the connecting portion 21d is constant, and the thickness of the piezoelectric element 30 is also constant.

[0067] As shown in FIG. 6(a), when the thickness of the protective film 56 is constant, the neutral position of the facing portion 21e of the film body portion 21 rises as the area of ​​the piezoelectric element 30 increases.

[0068] For ease of explanation, the degree of uneven distribution is defined below. The degree of uneven distribution is an index indicating how close the piezoelectric element 30 is disposed to the connection portion 21d, and is defined, for example, by the ratio of the distance g2 to the distance g1 along the X direction (see FIG. 8A). The distance g1 is the distance from the center 38c of the setting region 38 of the piezoelectric element 30 set on the substrate 20, including the front surface 21a, to the edge 30a of the piezoelectric element 30. The distance g2 is the distance from the center 38c of the setting region 38 to the center 30c of the piezoelectric element 30. For example, when the degree of uneven distribution is zero, the piezoelectric element 30 is formed over the entire setting region 38. Furthermore, when the degree of uneven distribution is a value other than zero, the center 30c of the piezoelectric element 30 is located closer to the connection portion 21d than the center 38c of the setting region 38. The neutral position of the facing portion 21e rises as the degree of uneven distribution decreases.

[0069] Next, a description will be given with reference to Fig. 6(b). Fig. 6(b) is a diagram showing changes in the neutral position of the facing portion 21e depending on the film thickness of the protective film 56 (see Figs. 8B, 9B, etc.) covering the piezoelectric element 30. Note that the above-mentioned film thickness is a spatially averaged value of the film thickness of the protective film 56 on the film body portion 21. As shown in this figure, when the area of ​​the piezoelectric element 30 formed on the film body portion 21 is constant, the neutral position of the facing portion 21e decreases as the film thickness of the protective film 56 increases.

[0070] As described above, as the area of ​​the piezoelectric element 30 (degree of uneven distribution of the piezoelectric element 30) increases, the neutral position of the facing portion 21e rises, and as the thickness of the protective film 56 increases, the neutral position of the facing portion 21e falls. In other words, the piezoelectric element 30 has a film stress that warps the film body portion 21 with the back surface 21b facing inward, while the protective film 56 has a film stress that warps the film body portion 21 with the front surface 21a facing inward. In other words, these film stresses act on the film body portion 21 to warp in opposite directions. Therefore, by changing the combination of the area (degree of uneven distribution) of the piezoelectric element 30 and the thickness of the protective film 56, the amount and direction of warping of the film body portion 21 in the neutral state can be controlled.

[0071] For example, first, the degree of uneven distribution of the piezoelectric elements 30 is set, and then the film thickness of the protective film 56 is set taking this degree of uneven distribution into consideration. Alternatively, the film thickness of the protective film 56 may be set, and then the degree of uneven distribution of the piezoelectric elements 30 may be set taking this film thickness into consideration. In either case, the film thickness of the protective film 56 is set to a value that causes the protective film 56 to extend linearly from the connecting portion 21d toward the opposing portion 21e or to warp toward the back surface 21b (with the back surface 21b facing inward) due to the resultant force of the film stress of the protective film 56 and the film stress of the piezoelectric elements 30.

[0072] As a result, as shown in FIGS. 7(a) and 7(b), the membrane portion 21 is flush with the front surface 22a of the frame portion 22, or the membrane portion 21 is warped with the back surface 22b facing inward (warped into the space 23 within the frame portion 22). Because the neutral position of the facing portion 21e is located in the space 23 within the frame portion 22, the distance between the neutral position of the facing portion 21e and the inner surface 44 of the lid 40 is wider than when the membrane portion 21 is warped with the front surface 21a facing inward. This improves the range of motion of the membrane portion 21. For example, when the transducer 10B is used as a speaker, the maximum amplitude of the membrane portion 21 in response to the voltage applied to the piezoelectric element 30 can be increased, improving the dynamic range and sound reproducibility. When the transducer 10B is used as a microphone, the maximum amplitude of the membrane portion 21 can be increased, improving the dynamic range of the detected sound pressure.

[0073] Furthermore, because the membrane portion 21 in the neutral state is located in the space 23 within the frame portion 22, the portion of the piezoelectric element 30 that protrudes (is exposed) toward the lid 40 from the front surface 22a of the frame portion 22 is reduced. Therefore, contact of the lid 40 with the piezoelectric element 30, etc., when bonding the lid 40 to the frame portion 22 can be avoided or the probability of contact can be reduced. Furthermore, because there is a margin in the depth of the space 41 within the lid 40, the height of the lid 40 in the Z direction can be reduced. In other words, the transducer 10B can be made smaller.

[0074] FIG. 8A is a top view of the substrate 20 according to a first example of this embodiment. FIG. 8B is a cross-sectional view taken along line VIIIB-VIIIB in FIG. 8A. As shown in FIG. 8A, the piezoelectric elements 30 are unevenly distributed in a region 39 close to the connection portion 21d on the front surface 21a of the membrane portion 21. Also, as shown in FIG. 8B, the protective film 56 covers the unevenly distributed piezoelectric elements 30 and the surrounding front surface 21a of the membrane portion 21 (in other words, the portion of the front surface 21a where the piezoelectric elements 30 are not disposed). The piezoelectric elements 30 are formed on the front surface 20a of the substrate 20 at a position that achieves a desired degree of uneven distribution in the process shown in FIG. 4B.

[0075] Compared to when the formation area of ​​the piezoelectric element 30 is set to the maximum (when the degree of uneven distribution is zero), the increase in the degree of uneven distribution suppresses the rise of the facing portion 21e, and the thickness of the protective film 56 required to achieve a state in which the film body portion 21 extends linearly or warps with the back surface 21b facing inward is reduced. This makes it possible to reduce the weight of the film body portion 21, the piezoelectric element 30, and the protective film 56 as a whole. In the example shown in FIG. 8B, only the protective film 57 is formed as the protective film 56 in the set region 38. However, the protective film 58 of a desired thickness may be formed (left) on the protective film 57 depending on the set film stress.

[0076] 9A is a top view of the substrate 20 according to a second example of this embodiment. FIG. 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A. FIG. 9C is a partially enlarged cross-sectional view of the film body portion 21 and the protective film 56 shown in FIG. 9B. As shown in FIG. 9A, the piezoelectric element 30 is formed over the entire surface of the setting region 38. Meanwhile, the protective film 56 on the piezoelectric element 30 includes a plurality of recesses 59.

[0077] The recesses 59 are spaced apart in a direction (e.g., the X direction) from the connecting portion 21d of the outer edge 21c of the film body portion 21 toward the opposing portion 21e of the outer edge 21c, and extend in a direction (e.g., the Y direction) intersecting the direction from the connecting portion 21d of the outer edge 21c toward the opposing portion 21e of the outer edge 21c. That is, as shown in FIG. 9A, the recesses 59 are formed in a striped pattern on the piezoelectric element 30. The recesses 59 are formed by forming a patterned resist on the protective film 56 and etching it. For example, when removing the protective film 58 shown in FIG. 4D, a patterned resist is formed on the protective film 58, and the protective film 58 is etched at the locations that will become the recesses 59.

[0078] According to this example, the formation of the recesses 59 reduces the average film thickness of the protective film 56. In other words, simply forming the recesses 59 can change the film stress of the protective film 56. The reduction in the average film thickness can be appropriately adjusted by setting the depth dz, width w2, or pitch p ( FIG. 9C ) of the recesses 59. For example, if the protective film 56 includes multiple protective films made of materials with different etching rates, such as the protective films 57 and 58, the recesses 59 are formed so that the underlying protective film (protective film 57 in this example) is exposed relative to the outermost protective film (protective film 58 in this example). In this case, the depth dz of the recesses 59 is equal to the film thickness of the outermost protective film, making it easier to control the etching of the outermost protective film.

[0079] In this example, the piezoelectric element 30 may also be unevenly distributed as in Example 1. The uneven distribution of the piezoelectric element 30 and the formation of the recess 59 increase the variable range of the resultant force of the film stresses of the piezoelectric element 30 and the protective film 56, making it easier to set the resultant force according to the dimensions of the film body part, such as the film thickness.

[0080] When viewed from the Z direction, the piezoelectric element 30 and the protective film 56 may be positioned in line symmetry with the line 12 as the axis of symmetry. In this case, the resultant force of the film stresses of the piezoelectric element 30 and the protective film 56 can be easily applied to the film body part 21 in line symmetry with the line 12 as the axis of symmetry, making it easier to obtain line-symmetric warping of the film body part 21.

[0081] Similarly, the multiple recesses 59 may be positioned in line symmetry with the straight line 12 as the axis of symmetry. In this case as well, it becomes easier to apply the resultant force of the film stresses of the piezoelectric element 30 and the protective film 56 to the film body portion 21 in line symmetry with the straight line 12 as the axis of symmetry, making it easier to obtain line-symmetric warping of the film body portion 21.

[0082] The shape of the recesses 59 is not limited to a shape extending in one direction with a constant width. That is, as long as the desired warpage of the membrane body portion 21 is obtained, each recess 59 may have a shape such as a circle, an ellipse, a rectangle, or another polygon when viewed from the Z direction.

[0083] As described above, the transducer 10B according to the second embodiment includes a substrate 20 containing silicon and a piezoelectric element 30 disposed on the substrate 20. The substrate 20 includes a membrane portion 21 having a first surface (front surface) 21a and a second surface (rear surface) 21b facing in opposite directions in the thickness direction (Z direction), and a frame portion 22 surrounding the membrane portion 21 when viewed from the thickness direction. The piezoelectric element 30 is disposed on at least a portion of the first surface 21a of the membrane portion 21. The piezoelectric element 30 and the first surface 21a around it are covered with a protective film 56. A portion of the outer edge 21c of the membrane portion 21 when viewed from the thickness direction forms a connection portion 21d connected to the support portion 82, and the remaining portion of the outer edge 21c other than the connection portion 21d includes a facing portion 21e that is spaced apart from the frame portion 22 and faces the connection portion 21d. The thickness of the protective film 56 is set to a value that causes the protective film 56 to extend linearly from the connecting portion 21d to the opposing portion 21e or to warp with the second surface 21b facing inward due to the combined force of the film stress of the protective film 56 and the film stress of the piezoelectric element 30.

[0084] The substrate 20 may have a semiconductor layer and an oxide layer stacked on top of each other in the Z direction. As described above, in this embodiment, the semiconductor layer forms the active layer 51 and the support layer 52, and the oxide layer forms the interlayer insulating layer 53.

[0085] The piezoelectric element 30 may be unevenly distributed in a region on the first surface 21a close to the connection portion 21d.

[0086] The protective film 56 may include a plurality of recesses 59 .

[0087] The multiple recesses 59 may be spaced apart in a direction from the connecting portion 21d of the outer edge 21c toward the opposing portion 21e of the outer edge 21c, and may extend in a direction intersecting the direction from the connecting portion 21d of the outer edge 21c toward the opposing portion 21e of the outer edge 21c.

[0088] When viewed in the thickness direction, the piezoelectric element 30 and the protective film 56 may be positioned symmetrically with respect to a straight line 12 connecting the center of the connecting portion 21d and the center of the opposing portion 21e of the outer edge 21c opposing the connecting portion 21d.

[0089] The transducer 10B may further include a lid 40 that is bonded to the frame portion 22 and covers the first surface 21a of the membrane portion 21 with a space 41 therebetween. The lid 40 may have an opening that overlaps with at least a portion of the piezoelectric element 30 when viewed in the thickness direction.

[0090] The protective film 56 may include a protective film (first protective film) 57 that covers the piezoelectric element 30 and the surface of the frame body part 22 around it, and a protective film (second protective film) 58 that covers the protective film 57.

[0091] The protective film 58 may cover the area covered by the protective film 57 other than the area including the film body portion 21 and the piezoelectric element 30 (for example, the area facing the setting area 38 or the opening 34).

[0092] The protective film 57 may contain alumina as a component, and the protective film 58 may contain tetraethoxysilane as a component.

[0093] When the protective film 56 includes the protective film 57 and the protective film 58 and a plurality of recesses 59 , each recess 59 may have a depth equal to the thickness of the protective film 58 .

[0094] The piezoelectric element 30 may be placed on the frame portion 22 and the film portion 21 so as to straddle the connection portion 21d of the film portion 21.

[0095] Furthermore, when viewed from the Z direction, a part of outer edge 21c of membrane body 21 forms connecting portion 21d connected to frame body 22, and the remainder of outer edge 21c other than connecting portion 21d is separated from frame body 22. In this case, substrate 20 may have protruding portion 24 that protrudes in the Z direction from a region including at least a part of the remainder of outer edge 21c described above. [Explanation of symbols]

[0096] 10A, 10B transducers 12 Straight line (center line) 20 PCB 21 Membrane body part 21a Front (first side) 21b Back (second side) 21c outer edge 21d Connection 21e Opposite section 22 Frame part (support part) 23 Space 24 Protrusion 24a Protruding cell 25 slit 26 Reinforcement 30 Piezoelectric element 40 Lid 42 Through hole 51 Active layer (semiconductor layer) 52 Support layer (semiconductor layer) 53 Interlayer insulation layer (BOX layer, oxide layer)

Claims

1. a substrate comprising silicon; a piezoelectric element disposed on the substrate, The substrate is a membrane body portion having a first surface and a second surface facing in opposite directions in a thickness direction; a frame portion surrounding the membrane portion when viewed from the thickness direction, the piezoelectric element is disposed on the first surface of the membrane body portion; a part of an outer edge of the film body portion when viewed from the thickness direction forms a connection portion connected to the frame body portion, and the remaining part of the outer edge other than the connection portion is separated from the frame body portion, the substrate has a protrusion that protrudes in the thickness direction from a region of the second surface that includes at least a portion of the remainder of the outer edge, The protrusion is disposed so as to face the inner surface of the frame body across the slit separating the membrane body and the frame body, thereby extending the slit in the thickness direction and suppressing gas flowing through the slit when the membrane body vibrates. Transducer.

2. The substrate has a semiconductor layer and an oxide layer stacked on top of each other in the thickness direction. The transducer of claim 1 .

3. a cover attached to the frame body and spaced apart from the first surface of the membrane body to cover the first surface of the membrane body; 3. A transducer according to claim 1 or 2.

4. The lid has an opening that overlaps at least a part of the piezoelectric element when viewed in the thickness direction. The transducer of claim 3 .

5. 5. The transducer according to claim 1, wherein the protrusion is disposed at a portion of the remaining portion of the outer edge that faces the connecting portion.

6. The transducer according to claim 5 , wherein the substrate has a reinforcing portion that protrudes from the second surface in the thickness direction and is connected to the protruding portion.

7. The transducer according to any one of claims 1 to 4, wherein the protrusion is disposed over the remainder of the outer edge.

8. 8. The transducer according to claim 1, wherein the protrusion has a plurality of protruding cells divided along the outer edge.

9. A transducer described in any one of claims 1 to 8, wherein the planar shape of the protrusion when viewed from the thickness direction is an axisymmetric shape with a straight line connecting the center of the connection portion and the center of the opposing portion of the outer edge facing the connection portion as the axis of symmetry.

10. The height of the protrusion in the thickness direction is 3 μm or more. A transducer according to any one of claims 1 to 8.

11. The maximum length of the protrusion in a direction parallel to the second surface of the membrane body is 10 μm to 100 μm. A transducer according to any one of claims 1 to 8.

12. The piezoelectric element is installed on the frame body part and the film body part so as to straddle the connection part. A transducer according to any one of claims 1 to 11.

13. When the film body is viewed from the thickness direction, a part of the oxide layer overlaps with the protrusion. The transducer of claim 2 .

14. A portion of the oxide layer is included in the protrusion.

14. The transducer of claim 13.

15. The cover is attached to the frame via a protective film formed on the substrate.

5. A transducer according to claim 3 or 4.

16. The protective film includes a first protective film that covers the piezoelectric element and the surface of the frame body portion around it, and a second protective film that covers an area on the surface of the frame body portion other than an area including the film body portion and the piezoelectric element.

16. The transducer of claim 15.

17. The first protective film contains alumina as a component.

17. The transducer of claim 16.

18. The second protective film contains tetraethoxysilane as a component.

18. A transducer according to claim 16 or 17.

Images