Bulk acoustic wave sensor and method of manufacturing the same

Abstract

The application provides a bulk acoustic wave sensor manufacturing method, comprising the following steps: providing a substrate and forming a first Bragg reflection layer on the substrate; sequentially forming a lower electrode, a piezoelectric layer and an upper electrode on the first Bragg reflection layer, the upper electrode, the piezoelectric layer, the lower electrode and the first Bragg reflection layer form an overlapping area in the sensor thickness direction, the lower electrode comprises a lower electrode main body part and a lower electrode frame part, the lower electrode frame part is formed on the lower electrode main body part and located at the edge of the overlapping area, wherein the lower electrode frame part comprises a first protruding part and / or a first recessed part; forming a second Bragg reflection layer on the upper electrode. The application also provides a bulk acoustic wave sensor. The application can improve the Q value, sensitivity of the device and simplify the manufacturing process.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a bulk acoustic wave sensor and its manufacturing method. Background Technology

[0002] Please refer to Figure 1 , Figure 1 This is a cross-sectional schematic diagram of a common bulk acoustic wave sensor in the prior art. As shown in the figure, the bulk acoustic wave sensor includes, from bottom to top, a substrate 10, a Bragg reflector layer 11 (the Bragg reflector layer is formed by alternating layers of high acoustic impedance material and low acoustic impedance material; for simplicity...) Figure 1 The device does not distinguish between acoustic impedance material layers and low acoustic impedance material layers, and includes a lower electrode 12, a piezoelectric layer 13, an upper electrode 14, and a sensitive film 15. The sensitive layer 15, upper electrode 14, piezoelectric layer 13, lower electrode 12, and Bragg reflector layer 11 overlap in the device thickness direction. The sensitive layer 15 is primarily used to sense physical, chemical, and biological information and convert it into electrical information.

[0003] The shortcomings of the existing bulk acoustic wave sensors mentioned above include: (1) When the existing bulk acoustic wave sensors operate in a liquid environment, the sound waves operating in longitudinal wave mode will leak into the body fluid through the sensitive layer after propagating to the upper electrode, resulting in a decrease in the quality factor (i.e., Q value) of the bulk acoustic wave sensor, and thus a decrease in the detection sensitivity of the bulk acoustic wave sensor. (2) Existing bulk acoustic wave sensors have always had the problem of lateral sound wave leakage, which leads to a decrease in the Q value of the device and thus a decrease in the detection sensitivity of the device. Therefore, how to reduce sound wave leakage to improve the Q value of the device and thus improve the detection performance of the device has always been a technical problem that those skilled in the art have been committed to solving. Summary of the Invention

[0004] To overcome the aforementioned deficiencies in the prior art, the present invention provides a method for manufacturing a bulk acoustic wave sensor, the method comprising:

[0005] A substrate is provided, and a first Bragg reflector layer is formed on the substrate;

[0006] A lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the first Bragg reflector layer. The upper electrode, the piezoelectric layer, the lower electrode, and the first Bragg reflector layer have an overlapping area in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping area. The lower electrode frame includes a first protrusion and / or a first recess.

[0007] A second Bragg reflective layer is formed on the upper electrode.

[0008] According to one aspect of the present invention, the manufacturing method includes the step of forming a lower electrode on a first Bragg reflector layer, which comprises: depositing a lower electrode metal layer on the first Bragg reflector layer, etching the lower electrode metal layer to form a lower electrode body portion; etching a first region on the upper surface of the lower electrode body portion to form a first recess portion, and / or depositing a first protrusion portion on a second region on the upper surface of the lower electrode body portion.

[0009] According to another aspect of the invention, in this manufacturing method, the upper electrode includes an upper electrode body portion and an upper electrode connecting portion connected to the upper electrode body portion; after forming the piezoelectric layer, the manufacturing method further includes: etching a third region on the upper surface of the piezoelectric layer located below the upper electrode connecting portion to be formed to form a groove, and forming a material layer in the groove with an upper surface higher than the upper surface of the piezoelectric layer, the material layer having the characteristic of shrinking in volume when heated and maintaining a stable volume after shrinkage; the step of forming the upper electrode includes: depositing an upper electrode metal layer covering the piezoelectric layer and the material layer; etching the upper electrode metal layer to form the upper electrode, wherein the upper electrode body portion is located in the overlapping region, and at least a portion of the upper electrode connecting portion is formed on the material layer; and heat-treating the material layer to form an air gap between the upper electrode connecting portion and the material layer.

[0010] According to another aspect of the invention, in this manufacturing method, the upper surface of the material layer after heat treatment is lower than the upper surface of the piezoelectric layer; or the upper surface of the material layer after heat treatment is flush with the upper surface of the piezoelectric layer; or the upper surface of the material layer after heat treatment is higher than the upper surface of the piezoelectric layer.

[0011] According to another aspect of the invention, in this manufacturing method, the upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape.

[0012] According to another aspect of the invention, in the manufacturing method, after forming the upper electrode body portion and the upper electrode connecting portion, the step of forming the upper electrode further includes: forming an upper electrode frame portion corresponding to the lower electrode frame portion on the upper electrode body portion, the upper electrode frame portion including a second protrusion portion and / or a second recess portion.

[0013] According to another aspect of the invention, the manufacturing method further includes forming a sensitive film on the second Bragg reflective layer.

[0014] The present invention also provides a bulk acoustic wave sensor, which includes:

[0015] Substrate;

[0016] A first Bragg reflector layer is formed on the substrate;

[0017] A lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the substrate. The lower electrode, the piezoelectric layer, the upper electrode, and the first Bragg reflective layer have an overlapping region in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping region. The lower electrode frame includes a first protrusion and / or a first recess.

[0018] A second Bragg reflector layer is formed on the upper electrode.

[0019] According to one aspect of the present invention, in the bulk acoustic wave sensor, the upper electrode includes an upper electrode body portion and an upper electrode connecting portion connected thereto, at least a portion of the lower surface of the upper electrode connecting portion being higher than the upper surface of the piezoelectric layer; the bulk acoustic wave sensor further includes a groove, a heat-treated material layer, and an air gap; the groove is formed on the upper surface of the piezoelectric layer at a position below the upper electrode connecting portion; the heat-treated material layer is located within the groove, wherein the material layer has the characteristic of shrinking in volume upon heating and maintaining a stable volume after shrinkage; the air gap is located between the heat-treated material layer and the upper electrode connecting portion, wherein the air gap is formed by the volume shrinkage of the material layer upon heating.

[0020] According to another aspect of the invention, in this bulk acoustic wave sensor, the upper surface of the heat-treated material layer is lower than the upper surface of the piezoelectric layer; or the upper surface of the heat-treated material layer is flush with the upper surface of the piezoelectric layer; or the upper surface of the heat-treated material layer is higher than the upper surface of the piezoelectric layer.

[0021] According to another aspect of the invention, in this bulk acoustic wave sensor, the upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape.

[0022] According to another aspect of the invention, in the bulk acoustic wave sensor, the upper electrode further includes an upper electrode frame portion formed on the upper electrode body portion and corresponding to the lower electrode frame portion, wherein the upper electrode frame portion includes a second protrusion and / or a second recess.

[0023] According to another aspect of the invention, the bulk acoustic wave sensor further includes a sensitive membrane formed on the second Bragg reflector layer.

[0024] The bulk acoustic wave sensor and its manufacturing method provided by this invention, on the one hand, form a second Bragg reflector layer on the upper electrode. When the bulk acoustic wave sensor operates in a liquid environment, the presence of the second Bragg reflector layer effectively reflects sound waves operating in longitudinal wave mode, thereby effectively preventing sound wave leakage into the liquid. This effectively prevents the decrease in the Q value of the bulk acoustic wave sensor, and thus prevents a decrease in the sensor's sensitivity. On the other hand, a lower electrode frame portion is formed on the lower electrode. This lower electrode frame portion includes protrusions and / or recesses, and is located at the edge of the overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode, and acoustic reflection structure (i.e., the first Bragg reflector layer) in the sensor's thickness direction. The presence of the lower electrode frame portion effectively reduces lateral sound wave leakage, thereby increasing the Q value of the bulk acoustic wave sensor and thus improving its sensitivity. Attached Figure Description

[0025] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0026] Figure 1 This is a cross-sectional schematic diagram of a common bulk acoustic wave sensor in the prior art;

[0027] Figure 2 This is a flowchart of a method for manufacturing a bulk acoustic wave sensor according to a specific embodiment of the present invention;

[0028] Figures 3(a) to 3(h) According to Figure 2 The diagram shows cross-sectional schematics of each stage in the process of manufacturing a bulk acoustic wave sensor.

[0029] Figure 3(i) is a cross-sectional schematic diagram of the bulk acoustic wave sensor obtained after forming a sensitive membrane on the structure shown in Figure 3(h);

[0030] Figures 4(a) to 4(h) This is a cross-sectional schematic diagram of the various stages of forming a bulk acoustic wave sensor on the structure shown in FIG3(f) according to a preferred embodiment of the present invention;

[0031] Figure 5 This is a cross-sectional schematic diagram of a bulk acoustic wave sensor according to a preferred embodiment of the present invention;

[0032] Figure 6 This is a cross-sectional schematic diagram of a bulk acoustic wave sensor according to a preferred embodiment of the present invention.

[0033] The same or similar reference numerals in the accompanying drawings represent the same or similar parts. Detailed Implementation

[0034] To better understand and explain the present invention, a further detailed description of the invention will be provided below in conjunction with the accompanying drawings.

[0035] This invention provides a method for manufacturing a bulk acoustic wave sensor. Please refer to [link / reference]. Figure 2 , Figure 2 This is a flowchart illustrating a method for manufacturing a volume acoustic wave sensor according to a specific embodiment of the present invention. As shown, the manufacturing method includes:

[0036] In step S100, a substrate is provided and a first Bragg reflective layer is formed on the substrate;

[0037] In step S200, a lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the first Bragg reflective layer. The upper electrode, the piezoelectric layer, the lower electrode, and the first Bragg reflective layer have an overlapping area in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping area. The lower electrode frame includes a first protrusion and / or a first recess.

[0038] In step S300, a second Bragg reflective layer is formed on the upper electrode.

[0039] Below, we will combine Figures 3(a) to 3(i) The steps S100 to S300 described above will be explained in detail with reference to a specific embodiment.

[0040] Specifically, in step S100, as shown in FIG3(a), a substrate 100 is provided and a Bragg reflector layer 101 (hereinafter referred to as the first Bragg reflector layer 101) is formed on the substrate 100. The substrate 100 can be implemented using existing conventional substrate materials. The first Bragg reflector layer 101 is formed by alternating layers of high acoustic impedance material and low acoustic impedance material.

[0041] In step S200, a lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the first Bragg reflector layer 101. The formation process of the lower electrode is as follows:

[0042] First, as shown in Figure 3(b), a lower electrode metal layer 102 is deposited on the first Bragg reflector layer 101. The lower electrode metal layer 102 is preferably made of a metal material such as Mo or W.

[0043] Next, as shown in FIG3(c), the lower electrode metal layer 102 is etched to form the lower electrode body portion 103.

[0044] Next, as shown in FIG3(d), a first recess 104a is formed in a first region on the upper surface of the lower electrode body 103. Specifically, a photoresist layer (not shown) covering the first Bragg reflector layer 101 and the lower electrode body 103 is formed. This photoresist layer is patterned to expose the first region, and the first region is etched using the patterned photoresist layer as a mask to form the recessed first recess 104a. After the first recess 104a is formed, the photoresist layer is removed. Preferably, the depth of the first recess 104a (indicated by H1 in FIG3(d)) ranges from... to The width (represented by W1 in Figure 3(d)) ranges from 0.1 μm to 20 μm.

[0045] Next, as shown in FIG3(e), a first protrusion 104b is formed in the second region on the upper surface of the lower electrode body 103. Specifically, a photoresist layer (not shown) covering the first Bragg reflector layer 101, the lower electrode body 103, and the first recess 104a is formed. This photoresist layer is patterned to expose the second region, and the first protrusion 104b is formed in the second region by deposition. After the first protrusion 104b is formed, the photoresist layer is removed. In this embodiment, as shown in FIG3(e), the second region is located outside the first region and the two are disposed adjacent to each other. Thus, the first protrusion 104b is located outside the first recess 104a, and the two share the same sidewall. Preferably, the depth of the first protrusion 104b (indicated by H2 in FIG3(e)) ranges as follows: to The width (denoted as W2 in FIG3(e)) ranges from 0.1 μm to 20 μm. Furthermore, the material of the first protrusion 104b is preferably the same as that of the lower electrode body 103, but may also be different from that of the lower electrode body 103.

[0046] The manufacturing of the lower electrode is now complete. The first recessed portion 104a and the first protruding portion 104b are defined as the lower electrode frame portion.

[0047] After the lower electrode is formed, a piezoelectric layer 105 is formed on the lower electrode as shown in FIG3(f), and an upper electrode 106 is formed on the piezoelectric layer 105 as shown in FIG3(g). It should be noted that (1) the piezoelectric layer 105 shown in FIG3(f) is formed by planarizing the piezoelectric material after depositing the piezoelectric material on the first Bragg reflector layer 101 and the lower electrode. In other embodiments, the piezoelectric material may not be planarized, but the piezoelectric material may be deposited directly to form the piezoelectric layer. (2) The piezoelectric layer 105 can be implemented using conventional piezoelectric materials such as aluminum nitride (AlN), and the upper electrode 106 is preferably implemented using metal materials such as Mo or W.

[0048] In this embodiment, the upper electrode 106, piezoelectric layer 105, lower electrode, and first Bragg reflective layer 101 overlap in the sensor thickness direction, and the lower electrode frame is located at the edge of this overlapping region. Here, "the lower electrode frame is located at the edge of the overlapping region" means that the horizontal projection of the lower electrode frame is outside the horizontal projection of the overlapping region, and the inner edge of the former's projection coincides with the outer edge of the latter's projection. Those skilled in the art will understand that in other embodiments, the lower electrode frame being located at the edge of the overlapping region can also mean that the inner edge region of the horizontal projection of the lower electrode frame overlaps with the outer edge region of the horizontal projection of the overlapping region.

[0049] It should be noted that (1) in other embodiments, the first protrusion may be formed first and then the first recess may be formed; (2) in other embodiments, the lower electrode frame may only include the first recess or only the first protrusion; (3) the first recess 104a and the first protrusion 104b are preferably annular in shape, and the specific shape is related to the shape of the overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode and first Bragg reflective layer in the thickness direction of the device. For example, it may be a regular pentagon, a regular hexagon, an irregular shape, etc. (4) in other embodiments, a seed layer may be formed on the first Bragg reflective layer or a passivation layer may be formed on the upper electrode before forming the lower electrode body, and the present invention does not limit this in any way.

[0050] In step S300, as shown in FIG3(h), a Bragg reflector layer 200 (hereinafter referred to as the second Bragg reflector layer 200) is formed on the upper electrode 106. The second Bragg reflector layer 200 can be formed by alternately depositing high acoustic impedance material layers and low acoustic impedance material layers on the structure shown in FIG3(g) and patterning it. The material of the second Bragg reflector layer 200 can be the same as or different from the material of the first Bragg reflector layer 101, and no limitation is made herein. In addition, the number and thickness of the high acoustic impedance material layers and low acoustic impedance material layers in the second Bragg reflector layer 200 can be determined according to actual design requirements.

[0051] In this embodiment, the bulk acoustic wave sensor shown in Figure 3(h) can be used as a mass sensor in a liquid environment. In other embodiments, as shown in Figure 3(i), depending on the specific type of bulk acoustic wave sensor, a sensitive membrane 201 is often formed on the second Bragg reflector layer 200. The main function of the sensitive membrane 201 is to sense physical, chemical, and biological information and convert it into electrical information. It should be noted that: (1) The present invention does not limit the specific material of the sensitive membrane, which can be selected according to the specific type of bulk acoustic wave sensor. For example, if the bulk acoustic wave sensor is an Hg ion sensor, the sensitive layer can be made of TiO2. For the sake of simplicity, all possible materials of the sensitive membrane in bulk acoustic wave sensors will not be listed here. (2) The shape of the sensitive membrane is preferably the same as the shape of the upper electrode. (3) The thickness of the sensitive membrane can be determined according to the actual design needs. (4) The formation of the sensitive membrane can refer to existing processes, which will not be described in detail here.

[0052] The method for manufacturing a bulk acoustic wave sensor provided by this invention comprises, on the one hand, forming a second Bragg reflector layer on the upper electrode. When the bulk acoustic wave sensor operates in a liquid environment, the presence of the second Bragg reflector layer effectively reflects sound waves operating in longitudinal wave mode, thereby effectively preventing sound waves from leaking into the liquid. This effectively prevents a decrease in the Q value of the bulk acoustic wave sensor, and consequently, a decrease in the sensor's sensitivity. On the other hand, a lower electrode frame portion is formed on the upper surface of the lower electrode. This lower electrode frame portion includes a first protrusion and / or a first recess, and is located at the edge of the overlapping region of the upper electrode, piezoelectric layer, lower electrode, and first Bragg reflector layer in the thickness direction of the device. The lower electrode frame portion provides acoustic impedance discontinuity. Specifically, the overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode, and first Bragg reflector layer in the thickness direction of the device has a first acoustic impedance, the first recess has a second acoustic impedance, and the first protrusion has a third acoustic impedance. Since the first acoustic impedance of the overlapping area does not match the second acoustic impedance of the first recess and the third acoustic impedance of the first protrusion, when the sound wave propagates to the lower electrode frame, it will be reflected back to the overlapping area, thereby effectively reducing the lateral leakage of the sound wave, and thus effectively improving the Q value of the bulk acoustic wave sensor and enhancing the sensitivity of the bulk acoustic wave sensor.

[0053] In a preferred embodiment, the upper electrode includes an upper electrode body and an upper electrode connecting portion connected to the upper electrode body. The upper electrode connecting portion may include both a wing and a bridge, or it may include only a wing or a bridge. Please refer to the following... Figures 4(a) to 4(h) The following explanation will be based on a bulk acoustic wave sensor with an upper electrode including a wing and a bridge, formed on the basis of the structure shown in Figure 3(f).

[0054] Specifically, as shown in FIG4(a), the third region on the upper surface of the piezoelectric layer 105 (i.e., the region located below the upper electrode connection to be formed, which is usually located at the edge of the overlapping region) is etched to form grooves 107a and 107b, wherein groove 107a corresponds to the wing to be formed and groove 107b corresponds to the bridge to be formed (more precisely, corresponds to the portion of the bridge that is suspended above the piezoelectric layer 105).

[0055] Next, as shown in Figure 4(b), a material 108 covering the piezoelectric layer 105, groove 107a, and groove 107b is deposited on the structure shown in Figure 4(a), and the material 108 is planarized, wherein the upper surface of the planarized material 108 is higher than the upper surface of the piezoelectric layer 105. In this embodiment, the material 108 has the characteristic that its volume shrinks when heated and remains stable after shrinkage, that is, the volume of the material 108 decreases when heated, and the already reduced volume does not change significantly after heating. The material 108 is preferably a material containing volatile substances (such as carbon dioxide containing water vapor) or a loose and porous material (such as porous silicon oxide, porous silicon, etc.).

[0056] Next, as shown in Figure 4(c), the material 108 is patterned to expose a portion of the upper surface of the piezoelectric layer 105. Subsequently, the upper electrode body and the bridge portion are formed on this exposed area. The portions of the patterned material 108 located within grooves 107a and 107b are hereinafter referred to as material layer 109a and material layer 109b, respectively. The portion of the patterned material 108 located on the upper surface of the piezoelectric layer 105 is hereinafter referred to as material layer 109c.

[0057] Next, as shown in Figure 4(d), an upper electrode metal layer 110 covering the piezoelectric layer 105, material layers 109a, 109b, and 109c is deposited on the structure shown in Figure 4(c), and preferably, as shown in Figure 4(e), a passivation material layer 111 is deposited on the upper electrode metal layer 110. The passivation material layer 111 is used to form a passivation layer and can be implemented using existing conventional materials used to form passivation layers.

[0058] Next, as shown in Figure 4(f), the passivation material layer 111 and the upper electrode metal layer 110 are etched to remove the portion of the passivation material layer 111 and the upper electrode metal layer 110 above the material layer 109c, thereby forming the upper electrode and the passivation layer 113. In this embodiment, the upper electrode includes three parts: one part is the upper electrode body portion 112a, which overlaps with the piezoelectric layer 105, the lower electrode, and the first Bragg reflector layer 101 in the device thickness direction; another part is the wing portion 112b, which is connected to the upper electrode body portion 112a and located above the material layer 109a; and the third part is the bridge portion 112c, which is formed on the piezoelectric layer 105 at one end, connected to the upper electrode body portion 112a at the other end, and located above the material layer 109b between the two ends. In this embodiment, the material layer 109c is retained; in other embodiments, the material layer 109c may also be removed.

[0059] Finally, as shown in Figure 4(g), the structure shown in Figure 4(f) is subjected to heat treatment. Material layers 109a, 109b, and 109c shrink in volume upon heating. The shrinkage of material layer 109a releases space to form an air gap 114a below the wing 112a, in which case the wing 112a is suspended above material layer 109a. Similarly, the shrinkage of material layer 109b releases space to form an air gap 114b below the portion between the two ends of the bridge 112b, in which case the portion between the two ends of the bridge 112b is suspended above material layer 109b. It should be noted that the upper surface of the material layer 109a after shrinkage can be higher than, flush with, or lower than the upper surface of the piezoelectric layer 105. Furthermore, the present invention does not impose any limitations on the heat treatment method for material layer 109a and material layer 109b, but preferably adopts a second-level or even millisecond-level annealing method (such as laser annealing, flash lamp annealing, or spike annealing) to improve the air gap formation efficiency.

[0060] The upper electrode, including the bridge and wing sections, is now complete. It should be noted that the materials of material layer 109a and material layer 109b can also be different.

[0061] Finally, as shown in FIG4(h), a second Bragg reflector layer 200 is formed on the passivation layer 113, and a sensitive film 201 is formed on the second Bragg reflector layer 200. The second Bragg reflector layer 200 is located above the upper electrode body portion 112a, and preferably has the same shape as the upper electrode body portion 112a. Those skilled in the art will understand that in other embodiments, the passivation layer 113 may be etched to expose the upper electrode body portion 112a, and then the second Bragg reflector layer 200 and the sensitive film 201 may be sequentially formed on the upper electrode body portion 112a.

[0062] For the sake of simplicity, the fabrication process of a bulk acoustic wave sensor whose upper electrode only includes a bridge or wing portion will not be described again in this invention. Regarding the bulk acoustic wave sensor provided by this invention, the upper electrode connection portion and the groove filled with a material layer on the upper surface of the piezoelectric layer can provide acoustic impedance mismatch, reflecting sound waves back to the overlapping area of ​​the bulk acoustic wave sensor. This further reduces lateral leakage of sound waves, thereby further improving the Q value and sensitivity of the bulk acoustic wave sensor.

[0063] It should be noted here that (1) in this embodiment, the heat treatment of the material layer is performed after the passivation layer is formed. In other embodiments, it may be performed after the upper electrode is formed or after the second Bragg reflective layer is formed. Considering that the heat treatment may affect the performance of the sensitive film, the heat treatment is usually performed before the sensitive film is formed. (3) Preferably, the materials of the material layer 109a and the material layer 109b have opposite temperature coefficients to the material of the piezoelectric layer. For example, the former material has a positive temperature coefficient and the latter material has a negative temperature coefficient, or the former material has a negative temperature coefficient and the latter material has a positive temperature coefficient. In this way, the temperature compensation can be effectively achieved.

[0064] In another preferred embodiment, the upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape. For cases where the upper electrode connection includes a bridge portion and a wing portion, such as... Figure 5 As shown, the upper surface of the bridge portion 112c near the upper electrode body portion 112a has an undulating shape (the part of the bridge portion 112c circled in dashed lines in the figure), specifically a stepped shape, and this stepped shape shows a trend from low to high in the direction from the bridge portion 112c near the upper electrode body portion 112a away from the upper electrode body portion 112a. Similarly, the upper surface of the wing portion 112b near the upper electrode body portion 112a also has an undulating shape (the part of the wing portion 112b circled in dashed lines in the figure), specifically a stepped shape, and this stepped shape also shows a trend from low to high in the direction from the wing portion 112b near the upper electrode body portion 112a away from the upper electrode body portion 112a. Those skilled in the art will understand that only the upper surface of the bridge portion near the upper electrode body portion, or only the upper surface of the wing portion near the upper electrode body portion, may have an undulating shape. The portion of the upper electrode connection near the upper electrode body has an undulating upper surface, which further enhances sound wave reflection, thereby reducing lateral sound wave leakage and further improving the Q value and sensitivity of the bulk acoustic wave sensor. Furthermore, the present invention does not impose any limitation on the specific dimensions of the undulating shape, which can be determined according to actual design requirements.

[0065] In another preferred embodiment, after forming the upper electrode body and the upper electrode connecting portion, an upper electrode frame portion is formed on the upper surface of the upper electrode body, the position of which corresponds to the position of the lower electrode frame portion (i.e., the upper electrode frame portion is also formed at the edge of the overlapping area). In this embodiment, the upper electrode frame portion includes a second protrusion and / or a second recess. The step of forming the upper electrode frame portion on the upper electrode body can refer to the step of forming the lower electrode frame portion on the lower electrode body, and will not be repeated here for the sake of simplicity. The provision of the upper electrode frame portion can provide acoustic impedance discontinuity, so that when sound waves are transmitted to the upper electrode frame portion, they are reflected back to the overlapping area of ​​the bulk acoustic wave sensor, thereby effectively reducing the lateral leakage of sound waves, and thus effectively improving the Q value of the bulk acoustic wave sensor and enhancing the sensitivity of the bulk acoustic wave sensor. Figure 6 The structure shown illustrates a case where only a second recess 115 (circled in dashed lines in the figure) corresponding to the position of the first recess is formed on the upper electrode body 112a. For the sake of simplicity, the case where both a second protrusion and a second recess are formed on the upper electrode body is not illustrated in the figures.

[0066] Accordingly, the present invention also provides a bulk acoustic wave sensor, which includes:

[0067] Substrate;

[0068] A first Bragg reflector layer is formed on the substrate;

[0069] A lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the substrate. The lower electrode, the piezoelectric layer, the upper electrode, and the first Bragg reflective layer have an overlapping region in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping region. The lower electrode frame includes a first protrusion and / or a first recess.

[0070] A second Bragg reflector layer is formed on the upper electrode.

[0071] The components of the above-mentioned bulk acoustic wave sensor will now be described with reference to Figure 3(h).

[0072] Specifically, as shown in the figure, the bulk acoustic wave sensor provided by the present invention includes a substrate 100 and a first Bragg reflector layer 101 formed on the substrate 100. The substrate 100 can be made using existing conventional substrate materials. The first Bragg reflector layer 101 is formed by alternating layers of high acoustic impedance material and low acoustic impedance material.

[0073] As shown in the figure, the bulk acoustic wave sensor provided by the present invention further includes a lower electrode, a piezoelectric layer 105, and an upper electrode 106 sequentially formed on a first Bragg reflector layer 101. The lower electrode, piezoelectric layer 105, upper electrode 106, and first Bragg reflector layer 101 have an overlapping region in the thickness direction of the sensor. The materials and dimensions of the lower electrode, piezoelectric layer 105, and upper electrode 106 can be referred to the relevant sections of the manufacturing method described above; for the sake of brevity, they will not be repeated here.

[0074] In this embodiment, the lower electrode includes a lower electrode body 103 and a lower electrode frame. The lower electrode frame is located at the edge of the aforementioned overlapping region. This means that the horizontal projection of the lower electrode frame is located outside the horizontal projection of the overlapping region, and the inner edge of the former coincides with the outer edge of the latter's projection. Those skilled in the art will understand that in other embodiments, the lower electrode frame being located at the edge of the overlapping region may also mean that the inner edge region of the horizontal projection of the lower electrode frame overlaps with the outer edge region of the horizontal projection of the overlapping region.

[0075] In this embodiment, the lower electrode frame includes a first recess 104a and a first protrusion 104b. The first protrusion 104b is located outside the first recess 104a, and both share the same sidewall. The depth of the first recess 104a (i.e., the vertical distance between the bottom surface of the first recess 104a and the upper surface of the lower electrode body 103) ranges from... to The width (denoted as W1 in Figure 3(d)) ranges from 0.1 μm to 20 μm. The depth of the first protrusion 104b (i.e., the vertical distance between the top surface of the first protrusion 104b and the upper surface of the lower electrode body 103) ranges from... to The width (denoted as W2 in FIG. 3(e)) ranges from 0.1 μm to 20 μm. Furthermore, the material of the first protrusion 104b is preferably the same as that of the lower electrode body 103, but may also be different. In other embodiments, the lower electrode frame portion may include only the first recess 104a or only the first protrusion 104b.

[0076] Furthermore, it should be noted that (1) the first recess 104a and the first protrusion 104b are preferably annular in shape, and the specific shape is related to the shape of the overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode and the first Bragg reflective layer in the thickness direction of the device. For example, it can be a regular pentagon, a regular hexagon, an irregular shape, etc. (2) In other embodiments, a seed layer is formed between the first Bragg reflective layer and the lower electrode, or a passivation layer is formed on the upper electrode, etc., and the present invention does not limit this in any way.

[0077] As shown in the figure, the bulk acoustic wave sensor provided by the present invention further includes a second Bragg reflector layer 200 formed on the upper electrode 106. This second Bragg reflector layer 200 is formed by alternating layers of high acoustic impedance material and low acoustic impedance material. The material of the second Bragg reflector layer 200 can be the same as or different from the material of the first Bragg reflector layer 101; no limitation is made herein. Furthermore, the number and thickness of the high acoustic impedance material layers and low acoustic impedance material layers in the second Bragg reflector layer 200 can be determined according to actual design requirements.

[0078] In this embodiment, the bulk acoustic wave sensor shown in Figure 3(h) can be used as a mass sensor in a liquid environment. In other embodiments, as shown in Figure 3(i), depending on the specific type of bulk acoustic wave sensor, the bulk acoustic wave sensor often also includes a sensitive membrane 201 formed on the second Bragg reflector layer 200. The main function of the sensitive membrane 201 is to sense physical, chemical, and biological information and convert it into electrical information. It should be noted that: (1) The present invention does not limit the specific material of the sensitive membrane, which can be selected according to the specific type of bulk acoustic wave sensor. For example, if the bulk acoustic wave sensor is an Hg ion sensor, the sensitive layer can be made of TiO2. For the sake of simplicity, all possible materials of the sensitive membrane in bulk acoustic wave sensors will not be listed here. (2) The shape of the sensitive membrane is preferably the same as the shape of the upper electrode. (3) The thickness of the sensitive membrane can be determined according to the actual design needs.

[0079] The bulk acoustic wave sensor provided by this invention has, on the one hand, a second Bragg reflector layer formed on the upper electrode. When the bulk acoustic wave sensor operates in a liquid environment, the presence of the second Bragg reflector layer effectively reflects acoustic waves operating in longitudinal wave mode, thereby effectively preventing longitudinal acoustic waves from leaking into the liquid. This effectively prevents a decrease in the Q value of the bulk acoustic wave sensor, and consequently, a decrease in the sensor's sensitivity. On the other hand, a lower electrode frame portion is formed on the upper surface of the lower electrode. This lower electrode frame portion includes a first protrusion and / or a first recess, and is located at the edge of the overlapping region of the upper electrode, piezoelectric layer, lower electrode, and first Bragg reflector layer in the thickness direction of the device. The lower electrode frame portion provides acoustic impedance discontinuity. Specifically, the overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode, and first Bragg reflector layer in the thickness direction of the device has a first acoustic impedance, the first recess has a second acoustic impedance, and the first protrusion has a third acoustic impedance. Since the first acoustic impedance of the overlapping area does not match the second acoustic impedance of the first recess and the third acoustic impedance of the first protrusion, when the sound wave propagates to the lower electrode frame, it will be reflected back to the overlapping area, thereby effectively reducing the lateral leakage of the sound wave, and thus effectively improving the Q value of the bulk acoustic wave sensor and enhancing the sensitivity of the bulk acoustic wave sensor.

[0080] In a preferred embodiment, as shown in FIG4(h), the upper electrode includes an upper electrode body portion 112a and an upper electrode connecting portion connected to the upper electrode body portion 112a, wherein at least a portion of the lower surface of the upper electrode connecting portion is higher than the upper surface of the piezoelectric layer 105. In this embodiment, the upper electrode connecting portion includes a wing portion 112b and a bridge portion 112c, wherein one end of the wing portion 112b is connected to the upper electrode body portion 112a and the other end is suspended above the piezoelectric layer 105, and one end of the bridge portion 112c is connected to the upper electrode body portion 112a and the other end is formed on the piezoelectric layer 105, with the portion between the two ends suspended above the piezoelectric layer 105. Grooves are formed on the upper surface of the piezoelectric layer 105 at positions corresponding to the upper electrode connecting portion. In this embodiment, grooves are formed on the upper surface of the piezoelectric layer 105 corresponding to the portions between the two ends of the wing portion 112b and the bridge portion 112c, respectively. A heat-treated material layer 109a is formed in the groove corresponding to the wing 112b of the piezoelectric layer 105, and an air gap 114a is formed between the heat-treated material layer 109a and the wing 112b. Similarly, a heat-treated material layer 109b is formed in the groove corresponding to the bridge 112c of the piezoelectric layer 105, and an air gap 114b is formed between the heat-treated material layer 109b and the bridge 112c. The upper surface of the heat-treated material layer (including material layer 109a and material layer 109b) may be higher than the upper surface of the piezoelectric layer 105, flush with the upper surface of the piezoelectric layer 105, or lower than the upper surface of the piezoelectric layer 105.

[0081] In this embodiment, the material layers (including material layers 109a and 109b) have the characteristic of shrinking in volume upon heating and maintaining a stable volume after shrinkage; that is, the volume of the material layer decreases after heating, and the already reduced volume remains essentially unchanged after heating. The material of the material layers is preferably a material containing volatile substances (e.g., carbon dioxide containing water vapor) or a porous material (e.g., porous silica, porous silicon). Those skilled in the art will understand that the materials of material layers 109a and 109b can also be different. Furthermore, this invention does not limit the heating treatment method of the material layers, but preferably uses annealing methods at the second or even millisecond level (e.g., laser annealing, flash annealing, or peak annealing) to improve the air gap formation efficiency. Accordingly, air gap 114a is formed by the space released by the volume shrinkage of material layer 109a after heating, and air gap 114b is formed by the space released by the volume shrinkage of material layer 109b after heating.

[0082] Preferably, as shown in FIG4(h), the bulk acoustic wave sensor provided by the present invention further includes a passivation layer 113, which is formed on the upper electrode. It should be noted that in FIG4(h), the second Bragg reflector layer 200 is formed on the passivation layer 113. In other embodiments, the passivation layer 113 may have an opening to expose the upper electrode body portion 112a, and the second Bragg reflector layer 200 may be formed on the upper electrode body portion 112a.

[0083] Regarding the bulk acoustic wave sensor provided by the present invention, the upper electrode connection portion and the groove filled with material layer on the upper surface of the piezoelectric layer can provide acoustic impedance mismatch, which can reflect sound waves back to the overlapping area of ​​the bulk acoustic wave sensor, thereby further reducing the lateral leakage of sound waves, and further improving the Q value and sensitivity of the bulk acoustic wave sensor.

[0084] Preferably, the materials of material layers 109a and 109b have opposite temperature coefficients to the material of the piezoelectric layer. For example, the former material has a positive temperature coefficient while the latter material has a negative temperature coefficient, or the former material has a negative temperature coefficient while the latter material has a positive temperature coefficient. In this way, temperature compensation can be effectively achieved.

[0085] In another preferred embodiment, the upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape. For cases where the upper electrode connection includes a bridge portion and a wing portion, such as... Figure 5As shown, the upper surface of the bridge portion 112c near the upper electrode body portion 112a has an undulating shape (the part of the bridge portion 112c circled in dashed lines in the figure), specifically a stepped shape, and this stepped shape shows a trend from low to high in the direction from the bridge portion 112c near the upper electrode body portion 112a away from the upper electrode body portion 112a. Similarly, the upper surface of the wing portion 112b near the upper electrode body portion 112a also has an undulating shape (the part of the wing portion 112b circled in dashed lines in the figure), specifically a stepped shape, and this stepped shape also shows a trend from low to high in the direction from the wing portion 112b near the upper electrode body portion 112a away from the upper electrode body portion 112a. Those skilled in the art will understand that only the upper surface of the bridge portion near the upper electrode body portion, or only the upper surface of the wing portion near the upper electrode body portion, may have an undulating shape. The upper surface of a portion of the upper electrode connection near the upper electrode body has an undulating shape, which can further improve the lateral reflection of sound waves, thereby further reducing the lateral leakage of sound waves, and thus further improving the Q value and sensitivity of the bulk acoustic wave sensor. Furthermore, the present invention does not impose any limitation on the specific dimensions of the undulating shape, which can be determined according to actual design requirements.

[0086] In another preferred embodiment, the upper electrode further includes an upper electrode frame portion formed on the upper electrode body portion and corresponding to the lower electrode frame portion (i.e., the upper electrode frame portion is also formed at the edge of the overlapping area). The upper electrode frame portion includes a second protrusion and / or a second recess. The position, structure, and dimensions of the second protrusion and the second recess can be referenced to the first protrusion and the first recess in the lower electrode frame portion, and will not be elaborated further here for simplicity. The upper electrode frame portion provides acoustic impedance discontinuity, allowing sound waves to be reflected back into the overlapping area of ​​the bulk acoustic wave sensor when transmitted to it. This effectively reduces lateral leakage of sound waves, thereby effectively improving the Q value and sensitivity of the bulk acoustic wave sensor. Figure 6 The structure shown illustrates a case where only a second recess 115 (circled in dashed lines in the figure) corresponding to the position of the first recess is formed on the upper electrode body 112a. For the sake of simplicity, the case where both a second protrusion and a second recess are formed on the upper electrode body is not illustrated in the figures.

[0087] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other components, units, or steps, and the singular does not exclude the plural. Multiple components, units, or devices recited in the system claims may also be implemented by a single component, unit, or device in software or hardware.

[0088] The above-disclosed embodiments are merely some preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for manufacturing a bulk acoustic wave sensor, characterized in that, The manufacturing method includes: A substrate is provided and a first Bragg reflector layer is formed on the substrate; A lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the first Bragg reflector layer. The upper electrode, the piezoelectric layer, the lower electrode, and the first Bragg reflector layer have an overlapping area in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping area. The lower electrode frame includes a first protrusion and / or a first recess. A second Bragg reflector layer is formed on the upper electrode; A sensitive film is formed on the second Bragg reflector layer. The sensitive film is used to sense physical, chemical and biological information and convert it into electrical information. The third region on the upper surface of the piezoelectric layer, located below the upper electrode connection to be formed, is etched to form a groove, and a material layer with an upper surface higher than the upper surface of the piezoelectric layer is formed in the groove; the material layer is heat-treated to form an air gap between the upper electrode connection and the material layer; The overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode and first Bragg reflector layer in the thickness direction of the device has a first acoustic impedance, the first recess has a second acoustic impedance, and the first protrusion has a third acoustic impedance. The first acoustic impedance of the overlapping area does not match the second acoustic impedance of the first recess and the third acoustic impedance of the first protrusion, thus reflecting the sound wave back into the overlapping area of ​​the bulk acoustic wave sensor.

2. The manufacturing method according to claim 1, characterized in that, in, The steps for forming the lower electrode on the first Bragg reflector layer include: A lower electrode metal layer is deposited on the first Bragg reflector layer, and the lower electrode metal layer is etched to form the lower electrode body. The first region on the upper surface of the lower electrode body is etched to form a first recess, and / or a first protrusion is deposited in the second region on the upper surface of the lower electrode body.

3. The manufacturing method according to claim 1, characterized in that, in: The upper electrode includes an upper electrode body portion and an upper electrode connecting portion connected to the upper electrode body portion; The step of forming the upper electrode includes: depositing an upper electrode metal layer covering the piezoelectric layer and the material layer; etching the upper electrode metal layer to form the upper electrode, wherein the upper electrode body is located in the overlapping region, and at least a portion of the upper electrode connection portion is formed on the material layer.

4. The manufacturing method according to claim 3, characterized in that, in: The upper surface of the heat-treated material layer is lower than the upper surface of the piezoelectric layer; or After heat treatment, the upper surface of the material layer is flush with the upper surface of the piezoelectric layer; or After heat treatment, the upper surface of the material layer is higher than the upper surface of the piezoelectric layer.

5. The manufacturing method according to claim 3, characterized in that, in, The upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape.

6. The manufacturing method according to claim 3, characterized in that, in: After forming the upper electrode body portion and the upper electrode connection portion, the step of forming the upper electrode further includes: forming an upper electrode frame portion corresponding to the lower electrode frame portion on the upper electrode body portion, the upper electrode frame portion including a second protrusion portion and / or a second recess portion.

7. A bulk acoustic wave sensor, characterized in that, The bulk acoustic sensor includes: Substrate; A first Bragg reflector layer is formed on the substrate; A lower electrode, a piezoelectric layer, and an upper electrode are sequentially formed on the substrate. The lower electrode, the piezoelectric layer, the upper electrode, and the first Bragg reflective layer have an overlapping region in the thickness direction of the sensor. The lower electrode includes a lower electrode body and a lower electrode frame. The lower electrode frame is formed on the lower electrode body and located at the edge of the overlapping region. The lower electrode frame includes a first protrusion and / or a first recess. A second Bragg reflector layer is formed on the upper electrode; A sensitive membrane, formed on the second Bragg reflector layer, is used to sense physical, chemical, and biological information and convert it into electrical information. The bulk acoustic wave sensor also includes a groove, a heat-treated material layer, and an air gap; The groove is formed on the upper surface of the piezoelectric layer at a position below the upper electrode connection portion; The heat-treated material layer is located within the groove; The air gap is located between the heat-treated material layer and the upper electrode connection portion, wherein the air gap is formed by the volume shrinkage of the material layer after being heated; The overlapping area of ​​the upper electrode, piezoelectric layer, lower electrode and first Bragg reflector layer in the thickness direction of the device has a first acoustic impedance, the first recess has a second acoustic impedance, and the first protrusion has a third acoustic impedance. The first acoustic impedance of the overlapping area does not match the second acoustic impedance of the first recess and the third acoustic impedance of the first protrusion, thus reflecting the sound wave back into the overlapping area of ​​the bulk acoustic wave sensor.

8. The bulk acoustic wave sensor according to claim 7, characterized in that, in: The upper electrode includes an upper electrode body and an upper electrode connection portion connected thereto, wherein at least a portion of the lower surface of the upper electrode connection portion is higher than the upper surface of the piezoelectric layer.

9. The bulk acoustic wave sensor according to claim 7, characterized in that, in: The upper surface of the heat-treated material layer is lower than the upper surface of the piezoelectric layer; or The upper surface of the heat-treated material layer is flush with the upper surface of the piezoelectric layer; or The upper surface of the material layer after heat treatment is higher than the upper surface of the piezoelectric layer.

10. The bulk acoustic wave sensor according to claim 8, characterized in that, in, The upper surface of the portion of the upper electrode connection near the upper electrode body has an undulating shape.

11. The bulk acoustic wave sensor according to claim 7, characterized in that, in: The upper electrode further includes an upper electrode frame portion, which is formed on the upper electrode body portion and corresponds to the lower electrode frame portion, wherein the upper electrode frame portion includes a second protrusion and / or a second recess.

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