Piezoelectric transducer and method for preparing piezoelectric transducer

Abstract

The present invention provides a piezoelectric transducer and a method for manufacturing the piezoelectric transducer. The piezoelectric transducer includes a first wafer and a second wafer. The first wafer has a central portion located in a middle region separated by an annular slit and an outer ring portion surrounding the central portion; the second wafer includes an inner ring film connected to the central portion through an inner ring wall, an outer ring film connected to the outer ring portion through an outer ring wall, and an annular vibration film connected between the inner ring film and the outer ring film; the piezoelectric transducer can be manufactured by preparing the first wafer, preparing the second wafer, and then bonding the first wafer and the second wafer. Since the piezoelectric transducer has a central portion and an outer ring portion, and an elastic annular vibration film is connected between the inner ring film and the outer ring film, both the central portion and the inner ring film can vibrate, which can improve the vibration frequency of the piezoelectric transducer and improve the sensitivity. In addition, connecting the inner ring film and the outer ring film together can also improve the structural stability.

Description

Technical Field

[0002] The present invention belongs to the technical field of acoustic transducers, and particularly relates to a piezoelectric transducer and a preparation method thereof.

Background Art

[0004] A piezoelectric transducer is a device that converts acoustic energy and electrical energy into each other. The piezoelectric material in the piezoelectric transducer can generate a voltage difference at both ends when it deforms, and the piezoelectric material can deform when there is a voltage difference at both ends. By using this property of the piezoelectric material, the mutual conversion between mechanical vibration and alternating current can be realized.

[0005] The traditional piezoelectric transducer relies on the movement of a single-sided structure to generate elastic movement on the diaphragm, but the structure of this method is easily inhibited by movement, with a low vibration frequency and poor structural stability.

Summary of the Invention

[0007] The purpose of the present invention is to provide a piezoelectric transducer and a preparation method thereof. The prepared piezoelectric transducer can obtain a higher vibration frequency, a higher sound pressure, and a more stable structure.

[0008] The technical solution of the present invention is as follows: Provide a piezoelectric transducer, including a first wafer and a second wafer fixedly connected to one side of the first wafer. The first wafer includes a connecting wall fixedly connected to the second wafer, a base layer fixedly connected to the side of the connecting wall away from the second wafer, and a piezoelectric layer stacked on the side of the base layer away from the second wafer. The piezoelectric layer and the base layer are jointly provided with an annular slit, and the annular slit divides the piezoelectric layer and the base layer into a central part located in the middle area and an outer ring part surrounding the outside of the central part. The connecting wall includes an inner ring wall fixedly connected to the central part and an outer ring wall fixedly connected to the outer ring part and surrounding the outside of the inner ring wall; the second wafer includes an inner ring membrane fixedly connected to one end of the inner ring wall and having an opening in the middle, an outer ring membrane fixedly connected to one end of the outer ring wall and surrounding the outside of the inner ring membrane, and an annular vibration membrane with its inner peripheral edge connected to the outside of the inner ring membrane and its outer peripheral edge connected to the inside of the outer ring membrane.

[0009] Further, provide a preparation method of a piezoelectric transducer, including the steps:

[0010] Prepare a first wafer: provide a first substrate, form a piezoelectric layer on one side of the first substrate to obtain a first substrate; remove part of the material on the piezoelectric layer side of the first substrate, and form a first annular groove on the piezoelectric layer side of the first substrate, wherein the first annular groove divides the first substrate into an initial central portion located in the middle area and an initial outer annular portion enclosed outside the initial central portion; form an inner annular wall located within the area defined by the first annular groove and an outer annular wall enclosed outside the inner annular wall and located outside the area defined by the first annular groove on the side of the first substrate away from the piezoelectric layer;

[0011] Prepare a second wafer: provide a second substrate, remove part of the material on one side of the second substrate, form an intermediate groove and a second annular groove surrounding the intermediate groove on one side of the second substrate; form an initial film layer on the side of the second substrate where the intermediate groove is formed, the initial film layer comprising an intermediate film covering the inner surface of the intermediate groove, an annular film covering the inner surface of the second annular groove, an inner annular film connecting the intermediate film and the annular film, and an outer annular film connected to the outer periphery of the annular film;

[0012] Join the first wafer and the second wafer: fix one end of the inner ring wall to the inner ring film, and fix one end of the outer ring wall to the outer ring film; remove the material of the second wafer away from the initial film layer side to leave the initial film layer; remove the material of the first wafer located at the bottom of the first annular groove to separate the initial central portion and the initial outer ring portion to form a central portion and an outer ring portion, remove the intermediate film, and form the initial film layer into an annular diaphragm connecting the inner ring wall and the outer ring wall.

[0013] Furthermore, the providing of a first substrate, forming a piezoelectric layer on one side of the first substrate, to obtain a first substrate, comprises:

[0014] Providing a silicon-based substrate, growing silicon dioxide on both sides of the silicon-based substrate, so that the silicon-based substrate forms a first outer layer and a second outer layer respectively located on both sides of the silicon-based substrate, forming the first substrate;

[0015] forming a bottom electrode layer on the first outer layer side of the first substrate;

[0016] forming a piezoelectric ceramic layer on a side of the bottom electrode layer away from the first substrate;

[0017] A top electrode layer is formed on a side of the piezoelectric ceramic layer away from the first substrate.

[0018] Further, forming a bottom electrode layer on the first outer layer side of the first substrate includes:

[0019] Depositing a metal material on the first outer layer side of the first substrate to form an initial bottom electrode layer;

[0020] A photoresist is coated on the side of the initial bottom electrode layer away from the first substrate to form a first photoresist layer, and a first etching pattern is formed on the first photoresist layer by photoresist development;

[0021] The initial bottom electrode layer is etched to remove the material of the initial bottom electrode layer corresponding to the first etching pattern;

[0022] The remaining first photoresist layer is removed to obtain the bottom electrode layer.

[0023] Further, forming the piezoelectric ceramic layer on the side of the bottom electrode layer away from the first substrate includes:

[0024] PZT is deposited on the side of the first substrate where the bottom electrode layer is formed to form an initial piezoelectric ceramic layer;

[0025] A photoresist is coated on the side of the initial piezoelectric ceramic layer away from the first substrate to form a second photoresist layer, and a second etching pattern is formed on the second photoresist layer by photoresist development;

[0026] The initial piezoelectric ceramic layer is etched to remove the material of the initial piezoelectric ceramic layer corresponding to the second etching pattern;

[0027] The remaining second photoresist layer is removed to obtain the piezoelectric ceramic layer.

[0028] Further, forming the top electrode layer on the side of the piezoelectric ceramic layer away from the first substrate includes:

[0029] A metal material is deposited on the side of the first substrate where the piezoelectric ceramic layer is formed to form a second initial electrode layer;

[0030] A photoresist is coated on the side of the second initial electrode layer away from the first substrate to form a third photoresist layer, and a third etching pattern is formed on the third photoresist layer by photoresist development;

[0031] The second initial electrode layer is etched to remove the material of the second initial electrode layer corresponding to the third etching pattern;

[0032] The remaining third photoresist layer is removed to obtain the top electrode layer.

[0033] Further, removing a part of the material on the piezoelectric layer side of the first substrate and forming a first annular groove on the piezoelectric layer side of the first substrate includes:

[0034] Coating a photoresist on the side of the first substrate where the piezoelectric layer is formed to form a fourth photoresist layer, and forming a fourth etching pattern on the fourth photoresist layer by developing the photoresist, wherein the fourth etching pattern corresponds to the first annular groove;

[0035] Etching the piezoelectric layer and the first substrate from the side of the first substrate where the piezoelectric layer is formed to form an initial first annular groove;

[0036] The remaining portion of the fourth photoresist layer is removed.

[0037] Further, etching the piezoelectric layer and the first substrate from the side of the first substrate where the piezoelectric layer is formed to form an initial first annular groove comprises:

[0038] Sequentially etching the top electrode layer, the piezoelectric ceramic layer, and the bottom electrode layer;

[0039] The first outer layer is subjected to oxide etching to remove silicon dioxide material in a portion of the first outer layer corresponding to the fourth etching pattern.

[0040] Further, the silicon-based substrate includes an intermediate layer; the removing of part of the material on the piezoelectric layer side of the first substrate to form a first annular groove on the piezoelectric layer side of the first substrate also includes:

[0041] After removing the remaining part of the fourth photoresist layer, coating the piezoelectric layer-forming side of the first substrate with photoresist to form a fifth photoresist layer, and forming a fifth etching pattern on the fifth photoresist layer by photoresist development, wherein the fifth etching pattern is located in the initial first annular groove;

[0042] The silicon material between the middle layer and the first outer layer is subjected to silicon etching to form the first annular groove.

[0043] Furthermore, the inner ring wall located within the area defined by the first annular groove and the outer ring wall enclosed outside the inner ring wall and located outside the area defined by the first annular groove are formed on the side of the first substrate facing away from the piezoelectric layer, including:

[0044] Coating a photoresist on the second outer layer side of the first substrate to form a sixth photoresist layer, and forming a sixth etching pattern on the sixth photoresist layer by developing the photoresist;

[0045] The second outer layer of the first substrate is subjected to oxide etching to remove the silicon dioxide material of the second outer layer corresponding to the sixth etching pattern, and the side of the first substrate close to the sixth photoresist layer is subjected to silicon etching to remove the silicon material between the middle layer and the second outer layer corresponding to the sixth etching pattern.

[0046] Further, removing the material of the first wafer at the bottom of the first annular groove to separate the initial central part and the initial outer ring part to form a central part and an outer ring part includes:

[0047] Processing the intermediate layer by means of VHF oxide release to remove the material of the intermediate layer corresponding to the first annular groove, so that the first annular groove forms an annular slit.

[0048] Further, providing a second substrate, removing a part of the material on one side of the second substrate, and forming an intermediate groove and a second annular groove surrounding the intermediate groove on one side of the second substrate includes:

[0049] Providing a silicon-based substrate as the second substrate, coating a photoresist on one side of the second substrate to form a seventh photoresist layer, and forming a seventh etching pattern on the seventh photoresist layer by means of photoresist development, the seventh etching pattern corresponding to the second annular groove;

[0050] Performing silicon etching on the side of the second substrate coated with the seventh photoresist layer to remove the silicon material in the area of the second substrate corresponding to the seventh etching pattern, and forming the second annular groove on the second substrate;

[0051] Removing the remaining part of the seventh photoresist layer.

[0052] Further, providing a second substrate, removing a part of the material on one side of the second substrate, and forming an intermediate groove and an intermediate groove surrounding the intermediate groove on one side of the second substrate further includes:

[0053] Coating a photoresist on one side of the second substrate to form an eighth photoresist layer, and forming an eighth etching pattern on the eighth photoresist layer by means of photoresist development, the eighth etching pattern corresponding to the intermediate groove;

[0054] Performing silicon etching on the side of the second substrate coated with the eighth photoresist layer to remove the silicon material in the area of the second substrate corresponding to the eighth etching pattern, and forming the intermediate groove on the second substrate;

[0055] Removing the remaining part of the eighth photoresist layer.

[0056] Further, forming an initial film layer on the side of the second substrate where the intermediate groove is opened includes:

[0057] Performing an oxidation treatment on one side of the second substrate to convert the silicon material on one side of the second substrate into a silicon dioxide material, and forming a first silicon dioxide layer;

[0058] Silicon deposition is performed on the side of the first silicon dioxide layer away from the second substrate to form a silicon deposition layer;

[0059] A ninth photoresist layer is coated on the side of the silicon deposition layer facing away from the first silicon dioxide layer, and the ninth photoresist layer is subjected to photoresist development to form a ninth etching pattern, and the ninth etching pattern corresponds to the intermediate groove;

[0060] The silicon deposition layer is subjected to silicon etching to remove the part of the silicon deposition layer located in the intermediate groove and the remaining part of the ninth photoresist layer;

[0061] Silicon dioxide deposition is performed on the side of the silicon deposition layer away from the second substrate to form a second silicon dioxide layer.

[0062] Further, the removing the intermediate film to form an annular diaphragm connecting the inner ring wall and the outer ring wall by the initial film layer includes:

[0063] The intermediate film is processed by means of VHF oxide release to remove the material of the second silicon dioxide layer and the material of the region of the first silicon dioxide layer corresponding to the intermediate groove, thereby forming the annular diaphragm.

[0064] Further, the preparation of the first wafer further includes: forming an inner ring metal connection end on the end face of the inner ring wall and forming an outer ring metal connection end on the end face of the outer ring wall;

[0065] The preparation of the second wafer includes: forming an inner side metal connection end on the side of the inner ring film facing away from the second substrate and forming an outer side metal connection end on the side of the outer ring film facing away from the second substrate;

[0066] The fixing one end of the inner ring wall to the inner ring film and fixing one end of the outer ring wall to the outer ring film includes:

[0067] Bonding the inner ring metal connection end to the inner side metal connection end and bonding the outer ring metal connection end to the outer side metal connection end.

[0068] Further, the forming an inner ring metal connection end on the end face of the inner ring wall and forming an outer ring metal connection end on the end face of the outer ring wall includes:

[0069] Depositing a metal material on the side of the first substrate facing away from the piezoelectric layer to form a first metal bonding layer;

[0070] Coating a photoresist on the side of the first metal bonding layer facing away from the first substrate to form a sixth photoresist layer, and forming a sixth etching pattern on the sixth photoresist layer by means of photoresist development;

[0071] Etch the first metal bonding layer to remove the metal material of the first metal bonding layer corresponding to the sixth etching pattern, thereby forming the inner-ring metal connection end and the outer-ring metal connection end.

[0072] Further, forming an inner-side metal connection end on the side of the inner-ring film away from the second substrate, and forming an outer-side metal connection end on the side of the outer-ring film away from the second substrate, includes:

[0073] Deposit a metal material on the side of the initial film layer away from the second substrate to form a second metal bonding layer;

[0074] Coat a photoresist on the side of the second metal bonding layer away from the second substrate to form a tenth photoresist layer, and form a tenth etching pattern on the tenth photoresist layer by photoresist development;

[0075] Etch the second metal bonding layer to remove the metal material of the second metal bonding layer corresponding to the tenth etching pattern, thereby forming the inner-side metal connection end and the outer-side metal connection end;

[0076] Remove the remaining part of the tenth photoresist layer.

[0077] Further, removing the material on the side of the second wafer away from the initial film layer and leaving the initial film layer, includes:

[0078] Grind the side of the second wafer away from the initial film layer to thin the second substrate;

[0079] Etch the second substrate to remove the material of the second substrate and leave the initial film layer.

[0080] The beneficial effects of the present invention are as follows: Since the piezoelectric layer and the base layer are provided with annular slits, and an elastic annular vibration film is connected between the inner-ring film and the outer-ring film, the annular vibration film can play a spring role, enabling the central part to vibrate in the thickness direction of the first wafer relative to the outer-ring part, and enabling the inner-ring film to vibrate in the thickness direction of the second wafer relative to the outer-ring film. It is equivalent to the transducer having two drivers, which can improve the vibration frequency of the piezoelectric transducer, improve the SPL (sensitivity), and connect the inner-ring film and the outer-ring film together to improve the structural stability.

Description of the Drawings

[0082] Figure 1 is a schematic cross-sectional structure diagram of the piezoelectric transducer of the present invention;

[0083] Figure 2 is a schematic main process diagram of the manufacturing method of the piezoelectric transducer of the present invention;

[0084] Figure 3 Schematic flow chart of forming the bottom electrode layer during the preparation of the first wafer in the method for preparing the piezoelectric transducer of the present invention;

[0085] Figure 4 is Figure 3 Schematic structural diagram after the corresponding steps in

[0086] Figure 5 Schematic flow chart of forming the piezoelectric ceramic layer during the preparation of the first wafer in the method for preparing the piezoelectric transducer of the present invention;

[0087] Figure 6 is Figure 5 Schematic structural diagram after the corresponding steps in

[0088] Figure 7 Schematic flow chart of forming the top electrode layer during the preparation of the first wafer in the method for preparing the piezoelectric transducer of the present invention;

[0089] Figure 8 is Figure 7 Schematic structural diagram after the corresponding steps in

[0090] Figure 9 Schematic flow chart of forming the first annular groove during the preparation of the first wafer in the method for preparing the piezoelectric transducer of the present invention;

[0091] Figure 10 is Figure 9 Schematic structural diagram after the corresponding steps in

[0092] Figure 11 Schematic flow chart of forming the inner ring wall, outer ring wall, inner ring metal connection end and outer ring metal connection end during the preparation of the first wafer in the method for preparing the piezoelectric transducer of the present invention;

[0093] Figure 12 is Figure 11 Schematic structural diagram after the corresponding steps in

[0094] Figure 13 Schematic flow chart of forming the middle groove and the second annular groove during the preparation of the second wafer in the method for preparing the piezoelectric transducer of the present invention;

[0095] Figure 14 is Figure 13 Schematic structural diagram after the corresponding steps in

[0096] Figure 15 Schematic flow chart of forming the initial film layer during the preparation of the second wafer in the method for preparing the piezoelectric transducer of the present invention;

[0097] Figure 16 is Figure 15 Schematic structural diagram after the corresponding steps in

[0098] Figure 17 This is a schematic process diagram for forming the inner metal connection end and the outer metal connection end during the preparation of the second wafer in the method for preparing the piezoelectric transducer of the present invention;

[0099] Figure 18 is Figure 17 a schematic structural diagram after the corresponding steps in

[0100] Figure 19 This is a schematic process diagram for bonding the first wafer and the second wafer in the method for preparing the piezoelectric transducer of the present invention;

[0101] Figure 20 is Figure 19 a schematic structural diagram after the corresponding steps in

Detailed Embodiment

[0103] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0104] In this embodiment, as Figure 1 shown, a piezoelectric transducer is provided, including a first wafer 10 and a second wafer 20 fixedly connected to one side of the first wafer 10. Among them, the first wafer 10 includes a connection wall 103 fixedly connected to the second wafer 20, a base layer 102 fixedly connected to the side of the connection wall 103 away from the second wafer 20, and a piezoelectric layer 101 stacked on the side of the base layer 102 away from the second wafer 20. The piezoelectric layer 101 and the base layer 102 are jointly provided with an annular slit 110. The annular slit 110 divides the piezoelectric layer 101 and the base layer 102 into a central part 120 located in the middle area and an outer ring part 130 surrounding the outside of the central part 120. The connection wall 103 includes an inner ring wall 1031 fixedly connected to the central part 120 and an outer ring wall 1032 fixedly connected to the outer ring part 130 and surrounding the outside of the inner ring wall 1031; the second wafer 20 includes an inner ring film 201 fixedly connected to one end of the inner ring wall 1031 and having an opening in the middle, an outer ring film 202 fixedly connected to one end of the outer ring wall 1032 and surrounding the outside of the inner ring film 201, and an annular vibration film 203 with its inner peripheral edge connected to the outside of the inner ring film 201 and its outer peripheral edge connected to the inside of the outer ring film 202. The shapes of the inner ring wall 1031 and the outer ring wall 1032 can be square, circular, pentagonal, hexagonal, etc. Correspondingly, the annular slit 110 can also be square, circular, pentagonal, hexagonal, etc.

[0105] Since the piezoelectric layer 101 and the base layer 102 are provided with an annular slit 110, and an elastic annular diaphragm 203 is connected between the inner annular film 201 and the outer annular film 202, the annular diaphragm 203 can play the role of a spring, so that the central portion 120 can vibrate in the thickness direction of the first wafer 10 relative to the outer annular portion 130, and the inner annular film 201 can vibrate in the thickness direction of the second wafer 20 relative to the outer annular film 202, which is equivalent to the transducer having two drivers, which can increase the vibration frequency of the piezoelectric transducer, improve SPL (sensitivity), and connecting the inner annular film 201 and the outer annular film 202 together improves the stability of the structure.

[0106] Further, in order to prepare the above-mentioned piezoelectric transducer, as Figure 2 - 20 As shown, this embodiment provides a method for preparing a piezoelectric transducer, comprising the steps of:

[0107] S100, preparing a first wafer: providing a first substrate 1010, forming a piezoelectric layer 101 on one side of the first substrate 1010 to obtain a first substrate; removing part of the material on the piezoelectric layer 101 side of the first substrate, forming a first annular groove 1231 on the piezoelectric layer 101 side of the first substrate, wherein the first annular groove 1231 separates the first substrate into an initial central portion 120 located in the middle region and an initial outer annular portion 130 enclosed outside the initial central portion 120; forming an inner annular wall 1031 located within the encircled region of the first annular groove 1231 and an outer annular wall 1032 enclosed outside the inner annular wall 1031 and located outside the encircled region of the first annular groove 1231 on the side of the first substrate away from the piezoelectric layer 101;

[0108] S200, preparing a second wafer: providing a second substrate 2011, removing part of the material on one side of the second substrate 2011, forming a middle groove 2081 and a second annular groove 2041 enclosed outside the middle groove 2081 on one side of the second substrate 2011; forming an initial film layer on the side of the second substrate 2011 where the middle groove 2081 is formed, the initial film layer comprising an intermediate film covering the inner surface of the middle groove 2081, an annular film covering the inner surface of the second annular groove 2041, an inner annular film 201 connecting the intermediate film and the annular film, and an outer annular film 202 connected to the outer periphery of the annular film;

[0109] S300. Bond the first wafer and the second wafer: Fix one end of the inner ring wall 1031 to the inner ring film 201, and fix one end of the outer ring wall 1032 to the outer ring film 202; Remove the material on the side of the second wafer away from the initial film layer, leaving the initial film layer; Remove the material at the bottom of the first annular groove 1231 of the first wafer to separate the initial central part 120 and the initial outer ring part 130, forming the central part 120 and the outer ring part 130, and remove the intermediate film to form an annular diaphragm 203 connecting the inner ring wall 1031 and the outer ring wall 1032 with the initial film layer.

[0110] Specifically, in this embodiment, the specific steps for preparing the first wafer are as follows:

[0111] As Figure 3 and 4 shown:

[0112] S101. Provide a silicon-based substrate, the silicon-based substrate includes an intermediate layer 1011 in the middle, grow silicon dioxide on both sides of the silicon-based substrate, so that the silicon-based substrate forms a first outer layer 1012 and a second outer layer 1013 respectively located on both sides of the silicon-based substrate, forming the first substrate 1010; Specifically, the intermediate layer 1011, the first outer layer 1012 and the second outer layer 1013 are all made of silicon dioxide material, and the material between the intermediate layer 1011 and the first outer layer 1012, and between the intermediate layer 1011 and the second outer layer 1013 is silicon material.

[0113] Form a bottom electrode layer 1061 on the first outer layer 1012 side of the first substrate 1010, including:

[0114] S102. Deposit a metal material on the first outer layer 1012 side of the first substrate 1010 to form an initial bottom electrode layer 1021; Specifically, the metal material in this step can include Cr (chromium), Au (gold), Pt (platinum), Al (aluminum), Ti (titanium), etc.; The deposition method can adopt physical vapor deposition, chemical vapor deposition, atomic layer deposition or coating process, etc.

[0115] S103. Coat a photoresist on the side of the initial bottom electrode layer 1021 away from the first substrate 1010 to form a first photoresist layer 1033;

[0116] S104. Form a first etching pattern 1041 on the first photoresist layer 1033 by photoresist development; The first etching pattern 1041 is annular;

[0117] S105. Etch the initial bottom electrode layer 1021 to remove the material of the initial bottom electrode layer 1021 corresponding to the first etching pattern 1041;

[0118] S106. Remove the remaining first photoresist layer 1033 to obtain the bottom electrode layer 1061. The area of the bottom electrode layer 1061 is smaller than the area of the first substrate 1010, that is, the bottom electrode layer 1061 is located within the area enclosed by the edge of the first substrate 1010. In this embodiment, the center of the bottom electrode layer 1061 coincides with the center of the first substrate 1010.

[0119] As Figure 5 and 6 shown:

[0120] Form a piezoelectric ceramic layer 1111 on the side of the bottom electrode layer 1061 away from the first substrate 1010, including

[0121] S107. Deposit PZT (lead zirconate titanate piezoelectric ceramic) on the side of the first substrate 1010 where the bottom electrode layer 1061 is formed to form an initial piezoelectric ceramic layer 1071; PZT can include PZT materials with different zirconium-titanium component ratios, lead manganese zirconate titanate piezoelectric ceramic PMnZT, etc.

[0122] S108. Coat a photoresist on the side of the initial piezoelectric ceramic layer 1071 away from the first substrate 1010 to form a second photoresist layer 1081;

[0123] S109. Form a second etching pattern 1091 on the second photoresist layer 1081 by photoresist development; the second etching pattern 1091 is annular;

[0124] S110. Etch the initial piezoelectric ceramic layer 1071 to remove the material of the initial piezoelectric ceramic layer 1071 corresponding to the second etching pattern 1091;

[0125] S111. Remove the remaining second photoresist layer 1081 to obtain the piezoelectric ceramic layer 1111. The area of the piezoelectric ceramic layer 1111 is slightly smaller than that of the bottom electrode layer 1061;

[0126] As Figure 7 and 8 shown:

[0127] Form a top electrode layer 1161 on the side of the piezoelectric ceramic layer 1111 away from the first substrate 1010, including:

[0128] S112. Deposit a metal material on the side of the first substrate 1010 where the piezoelectric ceramic layer 1111 is formed to form an initial top electrode layer 1121; the metal material in this step can include W (tungsten), Au (gold), Pt (platinum), Al (aluminum), Ti (titanium), etc.; the deposition method can adopt physical vapor deposition, chemical vapor deposition, atomic layer deposition or coating process, etc.;

[0129] S113. Coat a photoresist on the side of the initial top electrode layer 1121 away from the first substrate 1010 to form a third photoresist layer 1131;

[0130] S114. Form a third etching pattern 1141 in the third photoresist layer 1131 by photoresist development; the third etching pattern 1141 is annular;

[0131] S115. Etch the initial top electrode layer 1121 to remove the material of the initial top electrode layer 1121 corresponding to the third etching pattern 1141;

[0132] S116. Remove the remaining third photoresist layer 1131 to obtain the top electrode layer 1161, thereby obtaining the first substrate.

[0133] As Figure 9 and 10 shown:

[0134] Remove part of the material on the piezoelectric layer 101 side of the first substrate, and form a first annular groove 1231 on the piezoelectric layer 101 side of the first substrate, including:

[0135] S117. Coat a photoresist on the side of the first substrate where the piezoelectric layer 101 is formed to form a fourth photoresist layer 1171;

[0136] S118. Form a fourth etching pattern 1181 in the fourth photoresist layer 1171 by photoresist development, and the fourth etching pattern 1181 corresponds to the first annular groove 1231; the fourth etching pattern 1181 is annular;

[0137] S119. Etch the piezoelectric layer 101 and the first substrate 1010 from the side of the first substrate where the piezoelectric layer 101 is formed to form an initial first annular groove 1191;

[0138] Specifically, this step includes:

[0139] Etch the top electrode layer 1161, the piezoelectric ceramic layer 1111, and the bottom electrode layer 1061 in sequence; to remove the materials of the top electrode layer 1161, the piezoelectric ceramic layer 1111, and the bottom electrode layer 1061 corresponding to the fourth etching pattern 1181;

[0140] Perform oxide etching on the first outer layer 1012 to remove the silicon dioxide material at the position corresponding to the fourth etching pattern 1181 of the first outer layer 1012;

[0141] S120. Remove the remaining part of the fourth photoresist layer 1171;

[0142] S121, coating a photoresist on the side of the first substrate where the piezoelectric layer 101 is formed to form a fifth photoresist layer 1211;

[0143] S122, forming a fifth etching pattern 1221 on the fifth photoresist layer 1211 by a photoresist development method, wherein the fifth etching pattern 1221 is located in the initial first annular groove 1191; specifically, the fifth etching pattern 1221 is adjacent to the outer edge of the initial first annular groove 1191;

[0144] S123, etching the silicon material between the middle layer 1011 and the first outer layer 1012 to form the first annular groove 1231. In this step, a portion of the silicon material between the first outer layer 1012 and the middle layer 1011 corresponding to the fifth etching pattern 1221 is removed.

[0145] S124, removing the remaining portion of the fifth photoresist layer 1211; and performing oxide protection deposition to form an oxide protection layer; to isolate the surface of the silicon dioxide material;

[0146] like Figure 11 and 12 As shown:

[0147] An inner ring wall 1031 located within the area defined by the first annular groove 1231 and an outer ring wall 1032 enclosed outside the inner ring wall 1031 and located outside the area defined by the first annular groove 1231 are formed on the side of the first substrate facing away from the piezoelectric layer 101, and an inner ring metal connecting end 1281 is formed on the end surface of the inner ring wall 1031, and an outer ring metal connecting end 1282 is formed on the end surface of the outer ring wall 1032, including:

[0148] S125, depositing a metal material on the side of the first substrate away from the piezoelectric layer 101 to form a first metal bonding layer 1251; the metal material in this step may include W (tungsten), Au (gold), Pt (platinum), Al (aluminum), Ti (titanium), etc.; the deposition method may be physical vapor deposition, chemical vapor deposition, atomic layer deposition or coating process, etc.;

[0149] S126, coating a photoresist on the side of the first metal bonding layer 1251 facing away from the first substrate to form a sixth photoresist layer 1261;

[0150] S127. Form a sixth etching pattern 1271 on the sixth photoresist layer 1261 by means of photoresist development; in this embodiment, the sixth etching pattern 1271 includes a square pattern in the middle and a square ring pattern surrounding the outer periphery of the square pattern; the specific shape of the sixth etching pattern 1271 can be set according to the shapes of the inner ring wall 1031 and the outer ring wall 1032. For example, when the inner ring wall 1031 and the outer ring wall 1032 are circular rings, the sixth etching pattern 1271 includes a circular pattern in the middle and a circular ring pattern surrounding the outer periphery of the circular pattern.

[0151] S128. Etch the first metal bonding layer 1251 to remove the metal material of the first metal bonding layer 1251 corresponding to the sixth etching pattern 1271, and form the inner ring metal connection end 1281 and the outer ring metal connection end 1282; perform oxide etching on the second outer layer 1013 of the first substrate to remove the silicon dioxide material of the second outer layer 1013 corresponding to the sixth etching pattern 1271, and perform silicon etching on the side of the first substrate close to the sixth photoresist layer 1261 to remove the silicon material between the intermediate layer 1011 and the second outer layer 1013 corresponding to the sixth etching pattern 1271.

[0152] S129. Remove the remaining part of the sixth photoresist layer 1261.

[0153] The specific steps for preparing the second wafer are as follows:

[0154] As Figure 13 and 14 shown:

[0155] S201. Provide a silicon-based substrate as the second substrate 2011.

[0156] S202. Coat a photoresist on one side of the second substrate 2011 to form a seventh photoresist layer 2021.

[0157] S203. Form a seventh etching pattern 2031 on the seventh photoresist layer 2021 by means of photoresist development, and the seventh etching pattern 2031 corresponds to the second annular groove 2041.

[0158] S204. Perform silicon etching on the side of the second substrate 2011 coated with the seventh photoresist layer 2021 to remove the silicon material in the area of the second substrate 2011 corresponding to the seventh etching pattern 2031, and form the second annular groove 2041 on the second substrate 2011; the silicon etching can adopt the TMHA (tetramethylammonium hydroxide) silicon etching method, that is, wet etching. The cross-section of the obtained second annular groove 2041 is arched, and can be circular arched, trapezoidal, elliptical arched, etc.

[0159] S205. Remove the remaining portion of the seventh photoresist layer 2021.

[0160] S206. Coat a photoresist on one side of the second substrate 2011 to form an eighth photoresist layer 2061. The eighth photoresist layer 2061 covers the inner wall of the second annular groove 2041. The thickness of the eighth photoresist layer 2061 is uniform and can be within 50um - 500um, preferably 200um.

[0161] S207. Form an eighth etching pattern 2071 on the eighth photoresist layer 2061 by photoresist development. The eighth etching pattern 2071 corresponds to the intermediate groove 2081. The intermediate groove 2081 is square.

[0162] S208. Perform silicon etching on the side of the second substrate 2011 coated with the eighth photoresist layer 2061 to remove the silicon material in the area of the second substrate 2011 corresponding to the eighth etching pattern 2071, and form the intermediate groove 2081 in the second substrate 2011.

[0163] S209. Remove the remaining portion of the eighth photoresist layer 2061.

[0164] As Figure 15 and 16 shown:

[0165] S210. Perform an oxidation treatment on one side of the second substrate 2011 to convert the silicon material on one side of the second substrate 2011 into a silicon dioxide material, and form a first silicon dioxide layer 2101. The thickness of the first silicon dioxide layer 2101 can be within 50um - 500um, such as 100um, 150um, 200um, 250um, 300um, 350um, 400um, 450um, etc.

[0166] S211. Perform silicon deposition on the side of the first silicon dioxide layer away from the second substrate 2011 to form a silicon deposition layer 2111. The thickness of the silicon deposition layer 2111 can be within 50um - 500um, such as 100um, 150um, 200um, 250um, 300um, 350um, 400um, 450um, etc.

[0167] S212. Coat a photoresist on the side of the silicon deposition layer 2111 facing away from the first silicon dioxide layer to form a ninth photoresist layer 2121.

[0168] S213. Perform photoresist development on the ninth photoresist layer 2121 to form a ninth etching pattern 2131. The ninth etching pattern 2131 corresponds to the intermediate groove 2081.

[0169] S214. Perform silicon etching on the silicon deposition layer 2111 to remove the part of the silicon deposition layer 2111 located within the intermediate groove 2081;

[0170] S215. Remove the remaining part of the ninth photoresist layer 2121;

[0171] S216. Deposit silicon dioxide on the side of the silicon deposition layer 2111 away from the second substrate 2011 to form a second silicon dioxide layer 2161. The first silicon dioxide layer 2101 and the second silicon dioxide layer 2161 jointly wrap the silicon deposition layer 2111 to obtain an initial film layer.

[0172] As Figure 17 and 18 shown:

[0173] Form an inner metal connection end 2201 on the side of the inner ring film 201 away from the second substrate 2011, and form an outer metal connection end 2202 on the side of the outer ring film 202 away from the second substrate 2011, including:

[0174] S217. Deposit a metal material on the side of the initial film layer away from the second substrate 2011 to form a second metal bonding layer 2171; the metal material may include W (tungsten), Au (gold), Pt (platinum), Al (aluminum), Ti (titanium), etc.; the deposition method may adopt physical vapor deposition, chemical vapor deposition, atomic layer deposition or coating process, etc.;

[0175] S218. Coat a photoresist on the side of the second metal bonding layer 2171 away from the second substrate 2011 to form a tenth photoresist layer 2181;

[0176] S219. Form a tenth etching pattern 2191 on the tenth photoresist layer 2181 by photoresist development;

[0177] S220. Etch the second metal bonding layer 2171 to remove the metal material of the second metal bonding layer 2171 corresponding to the tenth etching pattern 2191, and form the inner metal connection end 2201 and the outer metal connection end 2202;

[0178] S221. Remove the remaining part of the tenth photoresist layer 2181.

[0179] As Figure 19 and 20 shown, the specific steps for bonding the first wafer and the second wafer are as follows:

[0180] S301. Bond the inner ring metal connection end 1281 to the inner side metal connection end 2201, and bond the outer ring metal connection end 1282 to the outer side metal connection end 2202, so that the inner ring wall 1031 is fixedly connected to the inner ring film 201, and the outer ring wall 1032 is fixedly connected to the outer ring film 202;

[0181] S302. Grind the side of the second wafer facing away from the initial film layer to thin the second substrate 2011;

[0182] S303. Etch the second substrate 2011 to remove the material of the second substrate 2011, leaving the initial film layer. Specifically, it is a dry etching of silicon (DRIE Si etch). Since an oxide protection deposition is carried out during the preparation of the first wafer and there is an oxide protection layer, the silicon material of the first wafer can be protected, that is, the silicon material of the first wafer will not be affected, while the silicon material of the second wafer that is not isolated by silicon dioxide is removed;

[0183] S304. Use the method of VHF (hydrofluoric acid vapor) oxide release to process the intermediate layer 1011 and the intermediate film, remove the material of the intermediate layer 1011 corresponding to the first annular groove 1231, form an annular slit 110 in the first annular groove 1231, remove the material of the second silicon dioxide layer 2161, and remove the material of the region of the first silicon dioxide layer corresponding to the intermediate groove 2081 to form the annular diaphragm 203, and the annular diaphragm 203 is arched.

[0184] The above are only the embodiments of the present invention. It should be noted here that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, improvements can still be made, but these all belong to the protection scope of the present invention.

Claims

1. A piezoelectric transducer, comprising a first wafer and a second wafer fixedly connected to one side of the first wafer, characterized in that, The first wafer includes a connecting wall fixedly connected to the second wafer, a base layer fixedly connected to the side of the connecting wall away from the second wafer, and a piezoelectric layer stacked on the side of the base layer away from the second wafer. The piezoelectric layer and the base layer are jointly provided with an annular slit, and the annular slit divides the piezoelectric layer and the base layer into a central portion located in the middle region and an outer ring portion surrounding the central portion. The connecting wall includes an inner ring wall fixedly connected to the central portion and an outer ring wall fixedly connected to the outer ring portion and surrounding the outer side of the inner ring wall; the second wafer includes an inner ring film fixedly connected to one end of the inner ring wall and having an opening in the middle, an outer ring film fixedly connected to one end of the outer ring wall and surrounding the outer side of the inner ring film, and an annular vibrating film with an inner peripheral edge connected to the outer side of the inner ring film and an outer peripheral edge connected to the inner side of the outer ring film, and the annular vibrating film has elasticity.

2. A preparation method of a piezoelectric transducer, characterized in that, Including steps: Preparing the first wafer: providing a first substrate, and forming a piezoelectric layer on one side of the first substrate to obtain a first substrate sheet; Removing a part of the material on the piezoelectric layer side of the first substrate sheet, forming a first annular groove on the piezoelectric layer side of the first substrate sheet, and the first annular groove divides the first substrate sheet into an initial central portion located in the middle region and an initial outer ring portion surrounding the initial central portion; forming an inner ring wall located within the area defined by the first annular groove on the side of the first substrate sheet away from the piezoelectric layer side and an outer ring wall surrounding the outer side of the inner ring wall and located outside the area defined by the first annular groove; Preparing the second wafer: providing a second substrate, removing a part of the material on one side of the second substrate, forming a middle groove and a second annular groove surrounding the middle groove on one side of the second substrate; forming an initial film layer on the side of the second substrate where the middle groove is opened, and the initial film layer includes a middle film covering the inner surface of the middle groove, an annular film covering the inner surface of the second annular groove, an inner ring film connecting the middle film and the annular film, and an outer ring film connected to the outer periphery of the annular film; Bonding the first wafer and the second wafer: fixedly connecting one end of the inner ring wall to the inner ring film, and fixedly connecting one end of the outer ring wall to the outer ring film; Removing the material on the side of the second wafer away from the initial film layer, leaving the initial film layer; Removing the material at the bottom of the first annular groove of the first wafer, separating the initial central portion and the initial outer ring portion to form a central portion and an outer ring portion, removing the middle film, and making the initial film layer form an annular vibrating film connecting the inner ring wall and the outer ring wall, and the annular vibrating film has elasticity.

3. The preparation method of the piezoelectric transducer according to claim 2, characterized in that, The providing the first substrate, forming a piezoelectric layer on one side of the first substrate to obtain a first substrate sheet includes: Providing a silicon-based substrate, growing silicon dioxide on both sides of the silicon-based substrate, making the silicon-based substrate form a first outer layer and a second outer layer respectively located on both sides of the silicon-based substrate, and forming the first substrate; Forming a bottom electrode layer on the first outer layer side of the first substrate; Forming a piezoelectric ceramic layer on the side of the bottom electrode layer away from the first substrate; A top electrode layer is formed on the side of the piezoelectric ceramic layer away from the first substrate.

4. The method for preparing a piezoelectric transducer according to claim 3, wherein, The formation of the bottom electrode layer on the first outer layer side of the first substrate includes: Depositing a metal material on the first outer layer side of the first substrate to form an initial bottom electrode layer; Coating a photoresist on the side of the initial bottom electrode layer away from the first substrate to form a first photoresist layer, and forming a first etching pattern in the first photoresist layer by photoresist development; Etching the initial bottom electrode layer to remove the material of the initial bottom electrode layer corresponding to the first etching pattern; Removing the remaining first photoresist layer to obtain the bottom electrode layer.

5. The preparation method of the piezoelectric transducer according to claim 3, wherein, The formation of the piezoelectric ceramic layer on the side of the bottom electrode layer away from the first substrate includes: Performing PZT deposition on the side of the first substrate where the bottom electrode layer is formed to form an initial piezoelectric ceramic layer; Coating a photoresist on the side of the initial piezoelectric ceramic layer away from the first substrate to form a second photoresist layer, and forming a second etching pattern in the second photoresist layer by photoresist development; Etching the initial piezoelectric ceramic layer to remove the material of the initial piezoelectric ceramic layer corresponding to the second etching pattern; Removing the remaining second photoresist layer to obtain the piezoelectric ceramic layer.

6. The manufacturing method of the piezoelectric transducer according to claim 3, characterized in that The formation of the top electrode layer on the side of the piezoelectric ceramic layer away from the first substrate includes: Depositing a metal material on the side of the first substrate where the piezoelectric ceramic layer is formed to form a second initial electrode layer; Coating a photoresist on the side of the second initial electrode layer away from the first substrate to form a third photoresist layer, and forming a third etching pattern in the third photoresist layer by photoresist development; Etching the second initial electrode layer to remove the material of the second initial electrode layer corresponding to the third etching pattern; Removing the remaining third photoresist layer to obtain the top electrode layer.

7. The preparation method of the piezoelectric transducer according to claim 3, characterized in that, Removing a part of the material on the piezoelectric layer side of the first substrate, and forming a first annular groove on the piezoelectric layer side of the first substrate, includes: Coating a photoresist on the side of the first substrate where the piezoelectric layer is formed to form a fourth photoresist layer, and forming a fourth etching pattern in the fourth photoresist layer by photoresist development, the fourth etching pattern corresponding to the first annular groove; Etching the piezoelectric layer and the first substrate from the side of the first substrate where the piezoelectric layer is formed to form an initial first annular groove; Removing the remaining part of the fourth photoresist layer.

8. The preparation method of the piezoelectric transducer according to claim 7, characterized in that, The etching of the piezoelectric layer and the first substrate from the side of the first substrate where the piezoelectric layer is formed to form an initial first annular groove includes: Sequentially etching the top electrode layer, the piezoelectric ceramic layer, and the bottom electrode layer; Performing oxide etching on the first outer layer to remove the silicon dioxide material at the position corresponding to the fourth etching pattern of the first outer layer.

9. The preparation method of the piezoelectric transducer according to claim 8, wherein, The silicon-based substrate includes an intermediate layer; removing a part of the material on the piezoelectric layer side of the first substrate, and forming a first annular groove on the piezoelectric layer side of the first substrate, further includes: After removing the remaining part of the fourth photoresist layer, coating the piezoelectric layer-forming side of the first substrate with photoresist to form a fifth photoresist layer, and forming a fifth etching pattern on the fifth photoresist layer by photoresist development, wherein the fifth etching pattern is located in the initial first annular groove; The silicon material between the middle layer and the first outer layer is subjected to silicon etching to form the first annular groove.

10. The preparation method of the piezoelectric transducer according to claim 9, wherein, The inner ring wall located in the area defined by the first ring groove and the outer ring wall enclosed outside the inner ring wall and located outside the area defined by the first ring groove are formed on the side of the first substrate facing away from the piezoelectric layer, and include: Coating a photoresist on the second outer layer side of the first substrate to form a sixth photoresist layer, and forming a sixth etching pattern on the sixth photoresist layer by developing the photoresist; The second outer layer of the first substrate is subjected to oxide etching to remove the silicon dioxide material of the second outer layer corresponding to the sixth etching pattern, and the side of the first substrate close to the sixth photoresist layer is subjected to silicon etching to remove the silicon material between the middle layer and the second outer layer corresponding to the sixth etching pattern.

11. The method for preparing a piezoelectric transducer according to claim 9, wherein The removing of the material at the bottom of the first annular groove of the first wafer to separate the initial central portion and the initial outer ring portion to form a central portion and an outer ring portion comprises: The intermediate layer is processed by VHF oxide release, so that the material of the intermediate layer corresponding to the first annular groove is removed, so that the first annular groove forms an annular slit.

12. The manufacturing method of the piezoelectric transducer according to claim 2, characterized in that, The method of providing a second substrate, removing part of the material on one side of the second substrate, and forming a middle groove and a second annular groove surrounding the middle groove on one side of the second substrate comprises: Providing a silicon-based substrate as a second substrate, coating a photoresist on one side of the second substrate to form a seventh photoresist layer, and forming a seventh etching pattern on the seventh photoresist layer by a photoresist development method, wherein the seventh etching pattern corresponds to the second annular groove; Performing silicon etching on the side of the second substrate coated with the seventh photoresist layer to remove silicon material in the area of ​​the second substrate corresponding to the seventh etching pattern, and forming the second annular groove on the second substrate; The remaining portion of the seventh photoresist layer is removed.

13. The method for preparing a piezoelectric transducer according to claim 12, wherein The method of providing a second substrate, removing part of the material on one side of the second substrate, forming a middle groove and a middle groove enclosed outside the middle groove on one side of the second substrate, further includes: Coating a photoresist on one side of the second substrate to form an eighth photoresist layer, and forming an eighth etching pattern on the eighth photoresist layer by developing the photoresist, wherein the eighth etching pattern corresponds to the middle groove; Performing silicon etching on the side of the second substrate coated with the eighth photoresist layer to remove silicon material in the area of ​​the second substrate corresponding to the eighth etching pattern, and forming the middle groove on the second substrate; The remaining portion of the eighth photoresist layer is removed.

14. The preparation method of the piezoelectric transducer according to claim 2, wherein, The forming of the initial film layer on the side of the second substrate where the middle groove is opened comprises: Performing an oxidation treatment on one side of the second substrate to convert the silicon material on one side of the second substrate into a silicon dioxide material to form a first silicon dioxide layer; Silicon deposition is performed on the side of the first silicon dioxide layer away from the second substrate to form a silicon deposition layer; A ninth photoresist layer is coated on the side of the silicon deposition layer facing away from the first silicon dioxide layer, and photoresist development is performed on the ninth photoresist layer to form a ninth etching pattern, and the ninth etching pattern corresponds to the intermediate groove; The silicon deposition layer is subjected to silicon etching to remove the part of the silicon deposition layer located in the intermediate groove and remove the remaining part of the ninth photoresist layer; Silicon dioxide deposition is performed on the side of the silicon deposition layer away from the second substrate to form a second silicon dioxide layer.

15. The method for preparing a piezoelectric transducer according to claim 14, characterized in that, The removing the intermediate film to form an annular diaphragm connecting the inner ring wall and the outer ring wall from the initial film layer includes: Processing the intermediate film by means of VHF oxide release to remove the material of the second silicon dioxide layer and remove the material of the region of the first silicon dioxide layer corresponding to the intermediate groove to form the annular diaphragm.

16. The method for preparing a piezoelectric transducer according to claim 2, characterized in that, The preparation of the first wafer further includes: forming an inner ring metal connection end on the end face of the inner ring wall and forming an outer ring metal connection end on the end face of the outer ring wall; The preparation of the second wafer includes: forming an inner side metal connection end on the side of the inner ring film facing away from the second substrate and forming an outer side metal connection end on the side of the outer ring film facing away from the second substrate; The fixing one end of the inner ring wall to the inner ring film and fixing one end of the outer ring wall to the outer ring film includes: Bonding the inner ring metal connection end to the inner side metal connection end and bonding the outer ring metal connection end to the outer side metal connection end.

17. The method for preparing a piezoelectric transducer according to claim 16, wherein, The forming an inner ring metal connection end on the end face of the inner ring wall and forming an outer ring metal connection end on the end face of the outer ring wall includes: Depositing a metal material on the side of the first substrate facing away from the piezoelectric layer to form a first metal bonding layer; Coating a photoresist on the side of the first metal bonding layer facing away from the first substrate to form a sixth photoresist layer, and forming a sixth etching pattern in the sixth photoresist layer by means of photoresist development; Etching the first metal bonding layer to remove the metal material of the first metal bonding layer corresponding to the sixth etching pattern to form the inner ring metal connection end and the outer ring metal connection end.

18. The method for preparing a piezoelectric transducer according to claim 16, wherein, The forming an inner side metal connection end on the side of the inner ring film facing away from the second substrate and forming an outer side metal connection end on the side of the outer ring film facing away from the second substrate includes: Depositing a metal material on the side of the initial film layer facing away from the second substrate to form a second metal bonding layer; Coating a photoresist on the side of the second metal bonding layer facing away from the second substrate to form a tenth photoresist layer, and forming a tenth etching pattern in the tenth photoresist layer by means of photoresist development; Etching the second metal bonding layer to remove the metal material of the second metal bonding layer corresponding to the tenth etching pattern to form the inner side metal connection end and the outer side metal connection end; Removing the remaining part of the tenth photoresist layer.

19. The preparation method of the piezoelectric transducer according to claim 2, wherein The removing the material on the side of the second wafer facing away from the initial film layer and leaving the initial film layer includes: Grind the side of the second wafer facing away from the initial film layer to thin the second substrate; Etch the second substrate to remove the material of the second substrate, leaving the initial film layer.

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