Bulk acoustic wave resonator and preparation method thereof

Abstract

The invention discloses a bulk acoustic wave resonator and a preparation method thereof, and relates to the technical field of micro electro mechanical systems, the bulk acoustic wave resonator comprises a substrate, and a lower electrode, a piezoelectric layer, a temperature compensation layer and an upper electrode which are arranged on the substrate, the two side faces of the piezoelectric layer make contact with the piezoelectric layer and the upper electrode through the first adhesion layer and the second adhesion layer respectively, the projection overlapping portion of the lower electrode, the piezoelectric layer and the upper electrode on the substrate is an effective resonance area, the projection of the temperature compensation layer on the substrate falls within the projection range of the effective resonance area on the substrate and is located on the periphery of the temperature compensation layer, and the temperature compensation layer is located between the upper electrode and the lower electrode. A first gap is formed between the upper electrode and the piezoelectric layer. According to the bulk acoustic wave resonator and the preparation method thereof provided by the invention, the stability of the bulk acoustic wave resonator can be improved.

Description

Technical Field

[0001] The present application relates to the technical field of micro-electromechanical systems, and in particular to a bulk acoustic wave resonator and a method for preparing the same. Background Art

[0002] With the rapid development of wireless communication technology, higher and higher requirements are put forward for filters with high performance, low frequency temperature coefficient and small size. BAW filters have the advantages of high frequency, low loss, small size and high Q. When used in communication systems, they can isolate and select RF signals, limit the radiation signal of the transmitter within its operating frequency band, and prevent the interference of received noise signals. They are key components in RF systems and play a vital role in RF front-ends. Thin film BAW filters convert electrical signals into acoustic signals through the inverse piezoelectric effect, and then convert acoustic signals into electrical signals through the piezoelectric effect.

[0003] Among them, the resonant frequency of the BAW resonator is extremely sensitive to temperature changes. In order to reduce the frequency drift caused by temperature changes, the prior art introduces a temperature compensation layer into the BAW resonator. Because silicon dioxide has a positive temperature coefficient (between 20-30ppm / ℃), it can offset the negative temperature coefficient of the piezoelectric layer (between (-25)-(-30)ppm / ℃), and is often used as a temperature compensation layer material. However, there are problems with silicon dioxide as a temperature compensation layer. Specifically, silicon dioxide does not match other materials of the BAW resonator in terms of crystal structure, mechanical properties, thermal expansion coefficient, etc., which can easily cause the temperature compensation layer to fall off or crack, causing device failure. Summary of the invention

[0004] The purpose of the present application is to provide a bulk acoustic wave resonator and a preparation method thereof, which can improve the stability of the bulk acoustic wave resonator.

[0005] On the one hand, an embodiment of the present application provides a bulk acoustic wave resonator, including a substrate and a lower electrode, a piezoelectric layer, a temperature compensation layer and an upper electrode arranged on the substrate, wherein the two side surfaces of the piezoelectric layer are respectively in contact with the piezoelectric layer and the upper electrode through a first adhesion layer and a second adhesion layer, the overlapping part of the projections of the lower electrode, the piezoelectric layer and the upper electrode on the substrate is an effective resonance area, the projection of the temperature compensation layer on the substrate falls within the projection range of the effective resonance area on the substrate, and a first gap is formed between the upper electrode and the piezoelectric layer at the periphery of the temperature compensation layer.

[0006] As an implementable method, a thickening layer is further arranged between the piezoelectric layer and the upper electrode on the periphery of the first gap. In the direction of the first gap away from the temperature compensation layer, the thickening layer includes a connecting portion in contact with the piezoelectric layer and a wing portion separated from the piezoelectric layer, and a second gap is formed between the wing portion and the piezoelectric layer.

[0007] As an practicable manner, the second gap is filled with oxide.

[0008] As an practicable manner, the second gap is filled with a plurality of oxide columns arranged at intervals.

[0009] As an implementable manner, the upper electrode extends outside the effective resonance region to form a connecting portion, the thickening layer further includes a bonding portion arranged on the connecting portion, and the wing portion is connected to the bonding portion to form a bridge portion.

[0010] As an implementable manner, a projection of the bridge portion on the substrate is partially located within the effective resonance region, and partially located outside the effective resonance region.

[0011] As an practicable manner, the material of the first adhesion layer and the second adhesion layer are both one of chromium, titanium, and titanium tungsten.

[0012] As an practicable manner, the acoustic impedance of the material of the thickened layer is greater than the acoustic impedance of the material of the piezoelectric layer.

[0013] On the other hand, an embodiment of the present application provides a method for preparing a bulk acoustic wave resonator, including: providing a substrate, and forming a lower electrode and a piezoelectric layer in sequence on the substrate; forming a temperature compensating structure on the piezoelectric layer, the temperature compensating structure including a first adhesion layer, a temperature compensating layer and a second adhesion layer sequentially arranged on the piezoelectric layer, and the projection of the temperature compensating structure on the substrate falls within the projection range of the lower electrode on the substrate; forming a first sacrificial ring on the periphery of the temperature compensating structure, the first sacrificial ring contacts the side of the temperature compensating structure; forming an upper electrode on the piezoelectric layer formed with the first sacrificial ring; and releasing the first sacrificial ring to form a first gap.

[0014] As an implementable manner, before the piezoelectric layer forms a temperature compensation structure, the method also includes: forming a second sacrificial ring and a thickening ring on the piezoelectric layer, the thickening ring partially covers the second sacrificial ring and is partially located on the piezoelectric layer, and there is a gap between the inner arm of the thickening ring and the temperature compensation structure.

[0015] As an practicable manner, after releasing the first sacrificial ring to form the first gap, the method further includes: completely releasing the second sacrificial ring to form a wing with the thickened ring and the piezoelectric layer, or partially releasing the second sacrificial ring to form an oxide column in the wing.

[0016] The beneficial effects of the embodiments of the present application include:

[0017] The BAW resonator provided by the present application comprises a substrate and a lower electrode, a piezoelectric layer, a temperature compensation layer and an upper electrode arranged on the substrate, wherein the two side surfaces of the piezoelectric layer are in contact with the piezoelectric layer and the upper electrode respectively through a first adhesion layer and a second adhesion layer, so that the two side surfaces of the temperature compensation layer have good adhesion to the piezoelectric layer and the upper electrode, and in addition, the first adhesion layer and the second adhesion layer can accommodate a certain deformation, so that when the BAW resonator is heated to expand or cooled to contract, due to the difference in thermal expansion coefficients between the temperature compensation layer, the piezoelectric layer and the upper electrode, the expansion and contraction amounts of the temperature compensation layer, the piezoelectric layer and the upper electrode are different, wherein the piezoelectric layer and the temperature compensation layer have different expansion and contraction amounts. The difference in deformation between the temperature compensating layer and the upper electrode can be absorbed by the first adhesion layer, and the difference in deformation between the temperature compensating layer and the upper electrode can be absorbed by the second adhesion layer, so that the temperature compensating layer can stretch outward within the layer, and the overlapping part of the projections of the lower electrode, the piezoelectric layer and the upper electrode on the substrate is the effective resonance area. The projection of the temperature compensating layer on the substrate falls within the projection range of the effective resonance area on the substrate, and a first gap is formed between the upper electrode and the piezoelectric layer at the periphery of the temperature compensating layer. The first gap can accommodate the outward expansion of the temperature compensating layer. Therefore, the problem of film shedding caused by surface stress caused by different thermal expansion coefficients can be avoided, thereby improving the temperature stability of the bulk acoustic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 One of the structural schematic diagrams of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0020] Figure 2 A second structural schematic diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0021] Figure 3 A third structural schematic diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0022] Figure 4 A fourth structural schematic diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0023] Figure 5 A flow chart of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0024] Figure 6 One of the state diagrams of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0025] Figure 7 A second state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0026] Figure 8 A third state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0027] Fig. 9 A fourth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0028] Fig.10 A fifth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0029] Fig.11 A sixth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0030] Fig.12 A seventh state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0031] Fig.13 This is an eighth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application.

[0032] Icon: 100-bulk acoustic wave resonator; 110-substrate; 120-lower electrode; 130-piezoelectric layer; 131-upper electrode; 141-first adhesion layer; 142-temperature compensation layer; 143-second adhesion layer; 150-first gap; 160-thickening layer; 161-connecting part; 162-wing part; 163-second gap; 164-fitting part; 171-oxide; 172-oxide column; 181-seed layer; 182-passivation layer; 183-cavity; 191-first sacrificial ring; 192-second sacrificial ring; 193-thickening ring; 194-sacrificial material; 195-lead-out electrode. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application described and shown in the drawings here can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for which protection is sought, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0035] In the description of the present application, it should be noted that the terms "center", "vertical", "horizontal", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the product of the application is usually placed when in use. They are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0036] Since the piezoelectric material of the BAW resonator has a negative temperature coefficient, the BAW resonator is very sensitive to temperature, and the ambient temperature in which the BAW resonator may work has a large span. In order to reduce the temperature drift caused by temperature changes, the prior art sets a temperature compensation layer with a positive temperature coefficient in the BAW resonator to improve the temperature stability of the BAW resonator. However, the thermal expansion coefficients of the temperature compensation layer and the piezoelectric layer in the prior art are quite different, which easily causes the temperature compensation layer to fall off or crack, resulting in device failure.

[0037] The present application embodiment provides a bulk acoustic wave resonator 100, such as Figures 1 to 4 As shown, it includes a substrate 110 and a lower electrode 120, a piezoelectric layer 130, a temperature compensation layer 142 and an upper electrode 131 arranged on the substrate 110, wherein the two side surfaces of the piezoelectric layer 130 are respectively in contact with the piezoelectric layer 130 and the upper electrode 131 through a first adhesion layer 141 and a second adhesion layer 143, the overlapping part of the projections of the lower electrode 120, the piezoelectric layer 130 and the upper electrode 131 on the substrate 110 is an effective resonance area, the projection of the temperature compensation layer 142 on the substrate 110 falls within the projection range of the effective resonance area on the substrate 110, and a first gap 150 is formed between the upper electrode 131 and the piezoelectric layer 130 at the periphery of the temperature compensation layer 142.

[0038] In the BAW resonator 100 provided in the embodiment of the present application, a sandwich structure formed by the lower electrode 120, the piezoelectric layer 130 and the upper electrode 131 is used as a working unit of the BAW resonator 100. Specifically, an external electrical signal is transmitted between the upper electrode 131 and the lower electrode 120, and the electrical signal forms a voltage difference between the upper electrode 131 and the lower electrode 120. The piezoelectric layer 130 is made of piezoelectric layer material and has a piezoelectric effect. When the electrical signal forms a voltage difference between the upper electrode 131 and the lower electrode 120, the piezoelectric layer 130 vibrates and reflects at the boundary to form resonance.

[0039] In the embodiment of the present application, a temperature compensating layer 142 is arranged on the piezoelectric layer 130, so that the temperature coefficients of the temperature compensating layer 142 and the piezoelectric layer 130 cancel each other, so that the BAW resonator 100 has good temperature stability. In addition, the two side surfaces of the temperature compensating layer 142 in the embodiment of the present application are in contact with the piezoelectric layer 130 and the upper electrode 131 through the first adhesion layer 141 and the second adhesion layer 143, respectively, so that the two side surfaces of the temperature compensating layer 142 have good adhesion to the piezoelectric layer 130 and the upper electrode 131. In addition, the first adhesion layer 141 and the second adhesion layer 143 can accommodate a certain deformation. In this way, when the BAW resonator 100 expands due to heat or contracts due to cold, due to the difference in thermal expansion coefficients between the temperature compensating layer 142 and the piezoelectric layer 130 and the upper electrode 131, the expansion and contraction amount of the temperature compensating layer 142 and the piezoelectric layer 130 and the upper electrode 131 is The difference in deformation between the piezoelectric layer 130 and the temperature compensating layer 142 can be absorbed by the first adhesion layer 141, and the difference in deformation between the temperature compensating layer 142 and the upper electrode 131 can be absorbed by the second adhesion layer 143, so that the temperature compensating layer 142 can extend outward within the layer. In addition, the present application forms a first gap 150 between the upper electrode 131 and the piezoelectric layer 130 at the periphery of the temperature compensating layer 142, that is, the temperature compensating layer 142 can extend into the first gap 150. In this way, the problem of film shedding caused by surface stress caused by different thermal expansion coefficients can be avoided, thereby improving the temperature stability of the bulk acoustic wave resonator 100.

[0040] In addition, those skilled in the art should know that when the BAW resonator 100 is working, the piezoelectric layer 130 contains not only sound waves propagating longitudinally but also sound waves propagating transversely. The first gap 150 is arranged on the piezoelectric layer 130, and the first gap 150, the piezoelectric layer 130 and the temperature compensation layer 142 have different sound reflection coefficients, that is, a sound reflection structure is formed at the cross section of the first gap 150 to reflect the sound waves propagating there, thereby avoiding the sound waves from leaking from the periphery of the temperature compensation layer 142, thereby improving the Q value of the BAW resonator 100.

[0041] It can be understood that the temperature compensation layer 142 of the embodiment of the present application is used to offset the temperature coefficient of the piezoelectric layer 130, that is, the temperature compensation layer 142 is opposite to the temperature coefficient of the piezoelectric layer 130. When the piezoelectric layer 130 is aluminum nitride, its temperature coefficient is negative, between (-25)-(-30) ppm / °C, and the temperature compensation layer 142 should have a positive temperature coefficient. For example, the material of the temperature compensation layer 142 can be silicon dioxide, titanium dioxide, tantalum oxide, silicon nitride, aluminum oxide, etc. or their composite materials. Those skilled in the art can specifically select the materials of the piezoelectric layer 130 and the temperature compensation layer 142 according to actual conditions, as long as the two have opposite temperature coefficients.

[0042] Those skilled in the art should know that the better the film quality of the piezoelectric layer 130 is, the better the performance of the BAW resonator 100 is. In order to improve the film quality of the piezoelectric layer 130, a seed layer 181 may be formed on the substrate 110 before depositing the lower electrode 120, such as Figure 1 and Figure 2 As shown, the seed layer 181 is disposed on the substrate 110, and the seed layer 181 provides a guide for the crystal orientation of the piezoelectric film, so that the piezoelectric film can grow according to a preset crystal orientation, thereby improving the film quality of the piezoelectric layer 130. Specifically, the material of the seed layer 181 can be aluminum nitride or titanium nitride.

[0043] In addition, in order to achieve reflection of sound waves, a sound reflection structure is usually provided on the substrate 110. Specifically, the sound reflection structure may be as follows: Figure 1 and Figure 2 The cavity 183 shown may also be a stack formed by alternating high-sound-reflecting materials and low-sound-reflecting materials. In order to protect the surface of the BAW resonator 100 and prevent the device from being exposed to air and oxidized, the embodiment of the present application further forms a passivation layer 182 on the upper electrode 131. Specifically, the material of the passivation layer 182 may be silicon dioxide, silicon nitride, aluminum nitride, aluminum oxide, polymer materials, and the like.

[0044] The specific material of the substrate 110 is not limited in the embodiment of the present application, and those skilled in the art may select a substrate 110 commonly used in semiconductors according to actual conditions, for example, sapphire, silicon nitride or silicon, etc.

[0045] The BAW resonator 100 provided in the present application includes a substrate 110 and a lower electrode 120, a piezoelectric layer 130, a temperature compensating layer 142 and an upper electrode 131 arranged on the substrate 110, wherein the two side surfaces of the piezoelectric layer 130 are in contact with the piezoelectric layer 130 and the upper electrode 131 respectively through a first adhesion layer 141 and a second adhesion layer 143, so that the two side surfaces of the temperature compensating layer 142 have good adhesion to the piezoelectric layer 130 and the upper electrode 131. In addition, the first adhesion layer 141 and the second adhesion layer 143 can accommodate a certain deformation. In this way, when the BAW resonator 100 is heated to expand or cooled to contract, due to the difference in thermal expansion coefficients between the temperature compensating layer 142 and the piezoelectric layer 130 and the upper electrode 131, the expansion and contraction amounts of the temperature compensating layer 142, the piezoelectric layer 130 and the upper electrode 131 are different, wherein the piezoelectric layer The difference in deformation between the temperature compensating layer 130 and the temperature compensating layer 142 can be absorbed by the first adhesion layer 141, and the difference in deformation between the temperature compensating layer 142 and the upper electrode 131 can be absorbed by the second adhesion layer 143, so that the temperature compensating layer 142 can stretch outward within the layer, and the overlapping part of the projections of the lower electrode 120, the piezoelectric layer 130 and the upper electrode 131 on the substrate 110 is the effective resonance area, and the projection of the temperature compensating layer 142 on the substrate 110 falls within the projection range of the effective resonance area on the substrate 110, and a first gap 150 is formed between the upper electrode 131 and the piezoelectric layer 130 at the periphery of the temperature compensating layer 142, and the first gap 150 can accommodate the outward extension of the temperature compensating layer 142, therefore, the problem of film shedding caused by surface stress caused by different thermal expansion coefficients can be avoided, thereby improving the temperature stability of the bulk acoustic wave resonator 100.

[0046] Optional, such as Figure 2 As shown, a thickening layer 160 is further arranged between the piezoelectric layer 130 and the upper electrode 131 on the periphery of the first gap 150, and in the direction of the first gap 150 away from the temperature compensation layer 142, the thickening layer 160 includes a connecting portion 161 in contact with the piezoelectric layer 130 and a wing portion 162 separated from the piezoelectric layer 130, and a second gap 163 is formed between the wing portion 162 and the piezoelectric layer 130.

[0047] Since the temperature compensation layer 142 has a certain thickness, the slope of the inclined surface of the upper electrode 131 located in the first gap 150 is relatively large, which is not conducive to deposition. In the embodiment of the present application, a thickening layer 160 is formed on the periphery of the first gap 150, wherein the thickening layer 160 is located between the piezoelectric layer 130 and the upper electrode 131. In this way, the thickening layer 160 has a supporting effect on the upper electrode 131, thereby reducing the difficulty of depositing the upper electrode 131.

[0048] In addition, along the direction of the first gap 150 away from the temperature compensation layer 142, the thickening layer 160 includes a connecting portion 161 in contact with the piezoelectric layer 130 and a wing portion 162 separated from the piezoelectric layer 130, wherein a second gap 163 is formed between the wing portion 162 and the piezoelectric layer 130. The second gap 163 is the same as the first gap 150, and is formed between the piezoelectric layer 130 and the upper electrode 131. When the transverse wave propagates to the interface of the second gap 163, it is reflected, thereby avoiding the leakage of the transverse acoustic wave, thereby improving the Q value of the bulk acoustic wave resonator 100.

[0049] Among them, in the direction perpendicular to the layers, there are different acoustic reflection coefficients between the second gap 163 and the piezoelectric layer 130, and between the second gap 163 and the wing 162, and there is also reflection on the interface therebetween, that is, the longitudinal sound waves can also be reflected, thereby improving the Q value of the BAW resonator 100.

[0050] In one possible implementation of the embodiment of the present application, Figure 3 As shown, the second gap 163 is filled with oxide 171 .

[0051] In the layer, the oxide 171 and the thickened layer 160 have different acoustic reflection coefficients, and an acoustic reflection interface is formed between the oxide 171 and the connecting portion 161 to prevent lateral acoustic wave leakage. In the direction perpendicular to the layer, the oxide 171 and the piezoelectric layer 130, and the oxide 171 and the wing portion 162 have different acoustic reflection coefficients, which reflect the longitudinal acoustic waves and prevent the longitudinal acoustic wave leakage. In addition, the oxide 171 can further improve the temperature stability of the BAW resonator 100.

[0052] Optional, such as Figure 4 As shown, the second gap 163 is filled with a plurality of oxide pillars 172 arranged at intervals.

[0053] When a plurality of oxide columns 172 are filled in the second gap 163 , each oxide column 172 forms a reflection interface with the air filled in the first gap 150 , that is, a reflection is formed at each oxide column 172 , thereby further improving the Q value of the BAW resonator 100 .

[0054] Specifically, other materials may be filled between the oxidation columns 172 , and the acoustic reflection coefficient of the other materials is different from that of the oxidation columns 172 to improve the reflection efficiency.

[0055] In one possible implementation of the embodiment of the present application, Figure 2 As shown, the upper electrode 131 extends outside the effective resonance region to form a connecting portion 161 , and the thickened layer 160 further includes a bonding portion 164 disposed on the connecting portion 161 , and the wing portion 162 is connected to the bonding portion 164 to form a bridge portion.

[0056] The wing portion 162 and the fitting portion 164 are connected to form a bridge portion, and the fitting portion 164 can provide a certain supporting force to the wing portion 162, thereby improving the stability of the wing portion 162.

[0057] It should be noted that the upper electrode 131 extends outside the effective resonance region in order to lead out the upper electrode 131. Figure 1 and Figure 2 As shown, an extraction electrode 195 is disposed on the upper electrode 131 and connected to the upper electrode 131 . Similarly, the lower electrode 120 also needs to be extracted through the extraction hole.

[0058] Optional, such as Figure 2 As shown, the projection of the bridge portion on the substrate 110 is partially located in the effective resonance region and partially located outside the effective resonance region.

[0059] In one achievable manner of the embodiment of the present application, the material of the first adhesion layer 141 and the second adhesion layer 143 are both one of chromium, titanium, and titanium tungsten.

[0060] On one hand, chromium, titanium, and titanium tungsten have a certain adhesion layer, which can play the role of fixing the temperature compensation layer 142 . On the other hand, they can withstand certain deformation and can withstand certain deformation of the temperature compensation layer 142 on the basis of fixing the temperature compensation layer 142 .

[0061] Optionally, the acoustic impedance of the material of the thickened layer 160 is greater than the acoustic impedance of the material of the piezoelectric layer.

[0062] The present application also discloses a method for preparing a bulk acoustic wave resonator 100, such as Figure 5 As shown, including:

[0063] S10: Figure 6 , Figure 7 As shown, a substrate 110 is provided, and a lower electrode 120 and a piezoelectric layer 130 are sequentially formed on the substrate 110;

[0064] In order to achieve the reflection of the sound waves, a sound reflection structure is usually arranged on the substrate 110. Specifically, the sound reflection structure can be a cavity 183, or a stacked layer formed by alternating high sound reflection materials and low sound reflection materials. When the sound reflection structure is a cavity 183, before forming the lower electrode 120 on the substrate 110, a groove is first formed on the substrate 110, and a sacrificial material 194 is filled in the groove, wherein the sacrificial material 194 has a different etching rate from the substrate 110 layer, so that after completing the setting of other layers, the sacrificial material 194 is etched using the release hole to form the cavity 183.

[0065] Similar to the structure, before depositing the lower electrode 120 on the substrate 110 , a seed layer 181 may be disposed on the substrate 110 to improve the film quality of the piezoelectric layer 130 .

[0066] Specifically, the material of the lower electrode 120 is not limited in the embodiment of the present application, and can be, for example, one of metals such as molybdenum, aluminum, copper, tungsten, tantalum, platinum, ruthenium, rhodium, iridium, chromium, titanium, gold, osmium, rhenium, palladium, and combinations thereof. The material of the piezoelectric layer 130 can be aluminum nitride, lithium niobate, lithium tantalate, lead zirconate titanate, zinc oxide, scandium-doped aluminum nitride, quartz crystal, lead magnesium niobate, lead fluoride, and the like, and combinations thereof.

[0067] S20: Fig.10 As shown, a temperature compensation structure is formed on the piezoelectric layer 130, and the temperature compensation structure includes a first adhesion layer 141, a temperature compensation layer 142, and a second adhesion layer 143 sequentially arranged on the piezoelectric layer 130, and the projection of the temperature compensation structure on the substrate 110 falls within the projection range of the lower electrode 120 on the substrate 110;

[0068] The specific materials of the temperature compensation layer 142, the first adhesion layer 141, and the second adhesion layer 143 are as described in the structure, and are not described in detail here. The specific method can be patterning after deposition.

[0069] S30: Fig.11 As shown, a first sacrificial ring 191 is formed on the periphery of the temperature compensating structure, and the first sacrificial ring 191 is in contact with the side surface of the temperature compensating structure;

[0070] The space occupied by the first sacrificial ring 191 is the first gap 150 , on this basis, the ring width of the first sacrificial ring 191 can be a fixed value or a variable value.

[0071] S40: Fig.12 As shown, an upper electrode 131 is formed on the piezoelectric layer 130 formed with the first sacrificial ring 191;

[0072] After forming the upper electrode 131, an extraction hole can be formed on the piezoelectric layer 130, the bottom wall of the extraction hole is the lower electrode 120, and metal is deposited in the extraction hole to form an extraction electrode 195 of the lower electrode 120. Similarly, an extraction electrode 195 connected to the upper electrode 131 is formed on the passivation layer 182. Fig.13 shown.

[0073] S50: Figure 1 As shown, the first sacrificial ring 191 is released to form the first gap 150 .

[0074] The temperature coefficients of the temperature compensating layer 142 and the piezoelectric layer 130 of the embodiment of the present application offset each other, so that the BAW resonator 100 has good temperature stability, and the two sides of the temperature compensating layer 142 are in contact with the piezoelectric layer 130 and the upper electrode 131 through the first adhesion layer 141 and the second adhesion layer 143, respectively, so that the two sides of the temperature compensating layer 142 have good adhesion to the piezoelectric layer 130 and the upper electrode 131. In addition, the first adhesion layer 141 and the second adhesion layer 143 can accommodate a certain deformation. In this way, when the BAW resonator 100 is expanded by heat or contracted by cold, due to the difference in thermal expansion coefficients between the temperature compensating layer 142 and the piezoelectric layer 130 and the upper electrode 131, the temperature compensating layer 142 has different expansion and contraction amounts from the piezoelectric layer 130 and the upper electrode 131, wherein the difference in deformation between the piezoelectric layer 130 and the temperature compensating layer 142 can be absorbed by the first adhesion layer 141, and the difference in deformation between the temperature compensating layer 142 and the upper electrode 131 can be absorbed by the second adhesion layer 143, so that the temperature compensating layer 142 can stretch outward within the layer. In addition, the present application forms a first gap 150 between the upper electrode 131 and the piezoelectric layer 130 on the periphery of the temperature compensating layer 142, that is, the temperature compensating layer 142 can stretch into the first gap 150. In this way, the problem of film shedding caused by surface stress caused by different thermal expansion coefficients can be avoided, thereby improving the temperature stability of the bulk acoustic wave resonator 100.

[0075] In one achievable manner of the embodiment of the present application, before the piezoelectric layer 130 forms a temperature compensation structure, the method further includes:

[0076] like Figure 8 and Fig. 9 As shown, a second sacrificial ring 192 and a thickened ring 193 are formed on the piezoelectric layer 130 , the thickened ring 193 partially covers the second sacrificial ring 192 , and is partially located on the piezoelectric layer 130 , and there is a gap between the inner arm of the thickened ring 193 and the temperature compensation structure.

[0077] The second sacrificial ring 192 occupies space for the second gap 163 , and the gap between the inner wall of the thickening ring 193 and the temperature compensation structure is the first gap 150 .

[0078] Optionally, after releasing the first sacrificial ring 191 to form the first gap 150 , the method further includes: completely releasing the second sacrificial ring 192 to allow the thickened ring 193 and the piezoelectric layer 130 to form a wing 162 , or partially releasing the second sacrificial ring 192 to form an oxide column 172 in the wing 162 .

[0079] The space between the wing 162 and the piezoelectric layer 130 is filled with air, or the pillar 172 is oxidized to improve the Q value of the BAW resonator 100 .

[0080] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A bulk acoustic wave resonator, characterized in that: It includes a substrate and a lower electrode, a piezoelectric layer, a temperature compensation layer and an upper electrode arranged on the substrate, wherein the two side surfaces of the piezoelectric layer are respectively in contact with the piezoelectric layer and the upper electrode through a first adhesion layer and a second adhesion layer, the overlapping part of the projections of the lower electrode, the piezoelectric layer and the upper electrode on the substrate is an effective resonance area, the projection of the temperature compensation layer on the substrate falls within the projection range of the effective resonance area on the substrate, and a first gap is formed between the upper electrode and the piezoelectric layer at the periphery of the temperature compensation layer.

2. The bulk acoustic wave resonator according to claim 1, characterized in that A thickening layer is further arranged between the piezoelectric layer and the upper electrode on the periphery of the first gap. In the direction of the first gap away from the temperature compensation layer, the thickening layer includes a connecting portion in contact with the piezoelectric layer and a wing portion separated from the piezoelectric layer, and a second gap is formed between the wing portion and the piezoelectric layer.

3. The bulk acoustic wave resonator according to claim 2, characterized in that: The second gap is filled with oxide.

4. The bulk acoustic wave resonator according to claim 2, characterized in that: The second gap is filled with a plurality of oxide columns arranged at intervals.

5. The bulk acoustic wave resonator according to claim 2, characterized in that: The upper electrode extends outside the effective resonance region to form a connecting portion, the thickening layer further includes a bonding portion arranged on the connecting portion, and the wing portion is connected to the bonding portion to form a bridge portion.

6. The bulk acoustic wave resonator according to claim 5, characterized in that A projection of the bridge portion on the substrate is partially located within the effective resonance region and partially located outside the effective resonance region.

7. The BAW resonator according to claim 1, characterized in that: The material of the first adhesion layer and the second adhesion layer are both one of chromium, titanium and titanium tungsten.

8. The bulk acoustic wave resonator according to claim 2, characterized in that: The acoustic impedance of the material of the thickened layer is greater than the acoustic impedance of the material of the piezoelectric layer.

9. A method for preparing a bulk acoustic wave resonator, characterized in that: include: Providing a substrate, and sequentially forming a lower electrode and a piezoelectric layer on the substrate; forming a temperature compensation structure on the piezoelectric layer, the temperature compensation structure comprising a first adhesion layer, a temperature compensation layer, and a second adhesion layer sequentially arranged on the piezoelectric layer, and a projection of the temperature compensation structure on the substrate falls within a projection range of the lower electrode on the substrate; forming a first sacrificial ring on the outer periphery of the temperature compensating structure, wherein the first sacrificial ring contacts the side surface of the temperature compensating structure; forming an upper electrode on the piezoelectric layer having the first sacrificial ring formed thereon; The first sacrificial ring is released to form a first gap.

10. The method for preparing a bulk acoustic wave resonator according to claim 9, characterized in that: Before forming the temperature compensation structure on the piezoelectric layer, the method further includes: A second sacrificial ring and a thickening ring are formed on the piezoelectric layer. The thickening ring partially covers the second sacrificial ring and is partially located on the piezoelectric layer. There is a gap between the inner arm of the thickening ring and the temperature compensation structure.

11. The method for preparing a bulk acoustic wave resonator according to claim 10, characterized in that: After releasing the first sacrificial ring to form the first gap, the method further includes: The second sacrificial ring is fully released to allow the thickened ring and the piezoelectric layer to form a wing, or the second sacrificial ring is partially released to form an oxide column in the wing.

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