Film bulk acoustic resonator and manufacturing method therefor

Abstract

The present application relates to the technical field of semiconductor devices, and specifically discloses a film bulk acoustic resonator and a manufacturing method therefor. The film bulk acoustic resonator comprises a substrate, and a lower electrode, a piezoelectric layer, a thickening layer and an upper electrode which are stacked on the substrate. An overlapping portion of projections of the lower electrode, the piezoelectric layer and the upper electrode on the substrate is an active region. An air wing and an air bridge located on two opposite sides of the active region are formed between the thickening layer and the piezoelectric layer. At a position corresponding to the air bridge, the thickening layer and the upper electrode are recessed towards the side of the piezoelectric layer, so that the thickening layer is in contact with the piezoelectric layer to cause a piezoelectric effect, and the air bridge is divided into a first air sub-cavity and a second air sub-cavity. The present application can effectively reduce the strong parasitic peak introduced by the thickening structure, so that the resonator has better properties.

Description

Thin-film bulk acoustic resonator and its fabrication method

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411427898.0, filed on October 12, 2024, entitled "Thin Film Bulk Acoustic Resonator and Preparation Method Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of semiconductor device technology, and more specifically, to a thin-film bulk acoustic resonator and its fabrication method. Background Technology

[0004] To improve the quality factor (Q value), existing technologies typically add a thickening structure to the sandwich structure of a thin-film bulk acoustic resonator (FBAR). This thickening makes the frequency of the resonator boundary region lower than that of the active region, thereby increasing the reflection of acoustic energy and suppressing transverse energy leakage. While the thickening structure effectively improves the Q value, it introduces a serious problem: the thickening structure itself also resonates at its corresponding frequency, which is often lower than the main resonant frequency. This introduces a strong parasitic peak in the low-frequency range, deteriorating the out-of-band rejection performance of the bandpass filter constructed by the FBAR and failing to meet the out-of-band rejection requirements of the device.

[0005] Application content

[0006] The purpose of this application is to provide a thin-film bulk acoustic resonator and its fabrication method, which can effectively reduce the strong parasitic peaks introduced by the thickened structure, thereby enabling the resonator to have better performance.

[0007] The embodiments of this application are implemented as follows:

[0008] In a first aspect, embodiments of this application provide a thin-film bulk acoustic resonator, including a substrate and a lower electrode, a piezoelectric layer, a thickening layer, and an upper electrode stacked on the substrate; the overlapping portion of the projection of the lower electrode, the piezoelectric layer, and the upper electrode onto the substrate is an active region; an air wing and an air bridge are formed between the thickening layer and the piezoelectric layer on opposite sides of the active region; at positions corresponding to the air bridge, the thickening layer and the upper electrode are recessed toward the piezoelectric layer to make the thickening layer contact the piezoelectric layer to generate a piezoelectric effect, and divide the air bridge into a first sub-air cavity and a second sub-air cavity.

[0009] As an alternative implementation, the edge thickness of the lower electrode gradually decreases to form an inclined structure at the edge of the active region, and the thickened layer and the recess of the upper electrode are located on the projection of the inclined structure onto the substrate.

[0010] As an optional implementation, a passivation layer is provided on the side of the upper electrode away from the piezoelectric layer, and the passivation layer is recessed towards the piezoelectric layer at the position corresponding to the air bridge.

[0011] As an alternative implementation, the thickened layer is hollowed out at a position corresponding to the active region so that the upper electrode and the piezoelectric layer form a contact area, and an annular groove is etched on the passivation layer at the edge of the contact area.

[0012] As an alternative implementation, the annular groove includes an annular groove that extends circumferentially along the contact area and is connected end to end, or it includes a plurality of arc-shaped grooves arranged circumferentially around the contact area.

[0013] As an optional implementation, the upper electrode is made of aluminum scandium nitride, wherein the atomic ratio of aluminum to scandium is 3-5:1.

[0014] Secondly, embodiments of this application provide a method for fabricating the aforementioned thin-film bulk acoustic resonator, comprising:

[0015] A lower electrode and a piezoelectric layer are sequentially disposed on the substrate, and a lead-out hole is formed on the piezoelectric layer;

[0016] A thickened layer and an upper electrode are sequentially disposed on a piezoelectric layer with lead-out holes. The overlapping portion of the projection of the lower electrode, the piezoelectric layer, and the upper electrode onto the substrate is the active region. A first sacrificial layer and a second sacrificial layer are disposed between the piezoelectric layer and the thickened layer, located on opposite sides of the active region.

[0017] The first and second sacrificial layers are released to form an air wing and an air bridge in the active region. The thickened layer on the air bridge is subjected to tensile stress collapse and contacts the piezoelectric layer to divide the air bridge into a first sub-air cavity and a second sub-air cavity.

[0018] Furthermore, a lower electrode and a piezoelectric layer are sequentially disposed on the substrate, and a lead-out hole is formed on the piezoelectric layer, including:

[0019] A lower electrode is deposited on a substrate, and the edge thickness of the lower electrode is gradually reduced by etching or photolithography.

[0020] Deposit a piezoelectric layer to form a tilted structure.

[0021] Furthermore, before releasing the first and second sacrificial layers to form an air wing and an air bridge in the active region, and before the thickened layer on the air bridge collapses under tensile stress and contacts the piezoelectric layer to divide the air bridge into a first sub-air cavity and a second sub-air cavity, the process further includes:

[0022] The positions corresponding to the thickened layer and the active region are etched and hollowed out to form a contact area between the upper electrode and the piezoelectric layer.

[0023] Furthermore, before releasing the first and second sacrificial layers to form an air wing and an air bridge in the active region, and before the thickened layer on the air bridge collapses under tensile stress and contacts the piezoelectric layer to divide the air bridge into a first sub-air cavity and a second sub-air cavity, the process further includes:

[0024] A passivation layer is deposited on the upper electrode, and an annular groove is etched on the passivation layer at the edge of the contact area. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 is a schematic diagram of one of the structures of a thin-film bulk acoustic resonator according to an embodiment of this application;

[0027] Figure 2 is a second schematic diagram of the structure of the thin-film bulk acoustic resonator according to an embodiment of this application;

[0028] Figure 3 is a third schematic diagram of the structure of the thin-film bulk acoustic resonator according to an embodiment of this application;

[0029] Figure 4 is a fourth schematic diagram of the structure of the thin-film bulk acoustic resonator according to an embodiment of this application;

[0030] Figure 5 is a fifth schematic diagram of the structure of the thin-film bulk acoustic resonator according to an embodiment of this application;

[0031] Figure 6a shows the serial and parallel FBAR constructed using existing technologies;

[0032] Figure 6b shows the test curves of a bandpass filter constructed using existing technology;

[0033] Figure 7 is an impedance comparison diagram of the thin-film bulk acoustic resonator provided by the prior art and the embodiments of this application;

[0034] Figure 8 shows the test curve of the bandpass filter constructed in this application.

[0035] Icons: 101-Substrate; 102-Cavity; 103-Lower Electrode; 1031-Lower Electrode Tilt Angle; 1032-Seed Layer; 104-Piezoelectric Layer; 1041-Tap-out; 1051-First Sacrificial Layer; 1052-Second Sacrificial Layer; 106-Thickening Layer; 1061-Tap-out Thickening Layer; 1062-Left Thickening Layer; 1063-Right Thickening Layer; 107-Upper Electrode; 1071-Tap-out Upper Electrode; 108-Passivation Layer; 109-Annular Groove; 113-Air Wing; 114-Air Bridge; 1141-First Sub-Air Cavity; 1142-Recess; 1143-Second Sub-Air Cavity; 1101-First Protective Layer; 1102-Second Protective Layer; 401-Second Parasitic Peak; 402-First Parasitic Peak; 403-Protrusion; 404-Left Out-of-Band Suppression Condition. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of this application can be combined with each other, and the combined embodiments are still within the protection scope of this application.

[0037] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and therefore should not be construed as limiting this application. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0039] Referring to Figures 3 and 5, this application provides a thin-film bulk acoustic resonator, including a substrate 101 and a lower electrode 103, a piezoelectric layer 104, a thickening layer 106, and an upper electrode 107 stacked on the substrate 101; the overlapping portion of the projection of the lower electrode 103, the piezoelectric layer 104, and the upper electrode 107 onto the substrate 101 is the active region; air wing 113 and air bridge 114 are formed between the thickening layer 106 and the piezoelectric layer 104 on opposite sides of the active region; at the position corresponding to the air bridge 114, the thickening layer 106 and the upper electrode 107 are recessed towards the piezoelectric layer 104, so that the thickening layer 106 contacts the piezoelectric layer 104 to generate a piezoelectric effect, and divide the air bridge 114 into a first sub-air cavity 1141 and a second sub-air cavity 1143.

[0040] It should be noted that the existing technology can maximize the performance of the device, such as the K value, Q value and FOM value, by optimizing the width and thickness of the three structures: thickened layer 106, air wing 113 and air bridge 114.

[0041] This application embodiment solves the problem of strong parasitic peaks caused by the thickened layer 106 while retaining the above-mentioned performance.

[0042] It should be noted that, in the embodiment of this application, at the position corresponding to the air bridge 114, an additional electric field effect is generated through the recess 1142 of the thickened layer 106 and its contact with the piezoelectric layer 104. Through this electric field effect, the strong parasitic peak introduced by the thickened layer 106 structure is effectively reduced, and the out-of-band suppression performance of the filter constructed by the thin film bulk acoustic resonator is effectively improved.

[0043] As shown in Figure 6a, existing low-frequency parallel FBARs or high-frequency series FBARs exhibit a first parasitic peak 402 and a second parasitic peak 401 on the left side, respectively. During the construction of the bandpass filter shown in Figure 6b, a bulge 403 inevitably forms on the left side of the filter's out-of-band suppression, causing it to fail to meet the left-side out-of-band suppression condition 404. Generally, out-of-band suppression is below -30dB; if it conflicts with specific frequency bands, the out-of-band suppression requirement may be higher.

[0044] Figure 7 shows a comparison of the impedance curves of the prior art and the thin-film bulk acoustic resonator provided in this application. The prior art is represented by a dashed line, while the present application is represented by a solid line, which can effectively eliminate the strong parasitic peak on the left.

[0045] As shown in Figure 8, the bandpass filter constructed using the thin-film bulk acoustic resonator provided in this application has an effective enhanced out-of-band suppression performance.

[0046] In the process of preparing the thickened layer 106 and the piezoelectric layer 104 by vapor deposition, the gas flow rate can be controlled to make the formed thickened layer 106 and piezoelectric layer 104 thin film have tensile stress. In the preparation, after the sacrificial layer is removed, the above-mentioned recess 1142 is formed by tensile stress.

[0047] For example, in the vapor deposition process for preparing the thickened layer 106 and the upper electrode 107, the target material is scandium aluminum nitride, the argon gas flow rate is 19-24 cm³ / min, the nitrogen gas flow rate is 95-120 cm³ / min, and the radio frequency bias power is 15-30 W. These settings can generate a thin film tensile stress of approximately 50 MPa.

[0048] In aluminum scandium nitride, the atomic ratio of aluminum to scandium is 3-5:1.

[0049] It should be noted that the recess 1142 between the thickened layer 106 and the piezoelectric layer 104 can be located at the center of the air bridge 114, or it can be located at a certain distance from the center. Furthermore, the contact area between the thickened layer 106 and the piezoelectric layer 104 is not specifically limited in this embodiment; those skilled in the art can choose according to their needs.

[0050] It should be noted that, as shown in FIG5, the thickened layer 106 and the upper electrode 107 are recessed toward the piezoelectric layer 104 so that the thickened layer 106 and the piezoelectric layer 104 come into contact to generate a piezoelectric effect, and divide the air bridge 114 into a first sub-air cavity 1141 and a second sub-air cavity 1143.

[0051] The first sub-air cavity 1141 and the second sub-air cavity 1143 can be two independent air cavities, or they can be connected to each other. Those skilled in the art can make the configuration as needed.

[0052] More preferably, the edge thickness of the lower electrode 103 gradually decreases to form an inclined structure at the edge of the active region, and the thickened layer 106 and the recess 1142 of the upper electrode 107 are located on the projection of the inclined structure onto the substrate 101.

[0053] In this embodiment, the lower electrode 103 is located at the position opposite to the contact portion of the piezoelectric layer 104 and the thickened layer 106, and the edge thickness of the lower electrode 103 gradually decreases, resulting in a tilt angle.

[0054] The tilt angle of the lower electrode 103 can be 10-30°. Since the piezoelectric layer 104 is deposited on the lower electrode 103, it also has a corresponding tilted structure. In this case, the thickened layer 106 and the recess 1142 of the upper electrode 107 are located on the projection of the tilted structure onto the substrate 101. When the thickened layer 106 contacts the tilted structure of the piezoelectric layer 104, the resulting electric field effect can more effectively eliminate the parasitic peak problem caused by the thickened layer 106.

[0055] Referring to FIG5, as an optional embodiment, the upper electrode 107 is provided with a passivation layer 108 on the side away from the piezoelectric layer 104, and the passivation layer 108 is recessed towards the piezoelectric layer 104 at the position corresponding to the air bridge 114.

[0056] The passivation layer 108 can be any one of AlN, SiC, SiO2, and SiN. It should be noted that the passivation layer 108 is generally not prone to absorbing moisture, preventing oxidation of the underlying film and providing good protection.

[0057] Referring to FIG5, as an optional embodiment, the thickened layer 106 is hollowed out at a position corresponding to the active region so that the upper electrode 107 and the piezoelectric layer 104 form a contact area, and an annular groove 109 is etched on the passivation layer 108 at the edge of the contact area.

[0058] It should be noted that the width of the annular groove 109 can be kept constant or inconsistent, and those skilled in the art can set it as needed.

[0059] As an alternative implementation, the annular groove 109 includes an annular groove that extends circumferentially along the contact area and is connected end to end, or it includes a plurality of arc-shaped grooves arranged circumferentially around the contact area.

[0060] This application provides a method for fabricating the above-mentioned thin-film bulk acoustic resonator, comprising:

[0061] Referring to Figures 1 and 2, a lower electrode 103 and a piezoelectric layer 104 are sequentially disposed on a substrate 101, and an outlet hole 1041 is formed on the piezoelectric layer 104.

[0062] A thickening layer 106 and an upper electrode 107 are sequentially disposed on the piezoelectric layer 104 with the lead-out hole 1041. The overlapping portion of the projection of the lower electrode 103, the piezoelectric layer 104, and the upper electrode 107 onto the substrate 101 is the active region. A first sacrificial layer 1051 and a second sacrificial layer 1052 located on opposite sides of the active region are also disposed between the piezoelectric layer 104 and the thickening layer 106.

[0063] Referring to FIG5, the first sacrificial layer 1051 and the second sacrificial layer 1052 are released to form an air wing 113 and an air bridge 114 in the active region. The thickened layer 106 on the air bridge 114 is subjected to tensile stress and collapses to contact the piezoelectric layer 104. At this time, due to tensile stress collapse, the thickened layer 106 moves downward until it contacts the piezoelectric layer 104 to divide the air bridge 114 into a first sub-air cavity 1141 and a second sub-air cavity 1143. In addition, the mass distribution of the thickened layer 106 is uneven, and the mass of the thickened layer 106 in the area projected downward by the recess 1142 is greater than that of other parts of the thickened layer 106.

[0064] The preparation method provided in this application embodiment utilizes the thin film tensile stress of the thickened layer 106 and the upper electrode 107 to form a recess 1142 between the thickened layer 106 and the upper electrode 107, thereby achieving contact between the thickened layer 106 and the piezoelectric layer 104, effectively reducing the strong parasitic peaks introduced by the structure of the thickened layer 106, and effectively improving the out-of-band suppression performance of the filter constructed by the thin film bulk acoustic resonator.

[0065] Furthermore, a lower electrode 103 and a piezoelectric layer 104 are sequentially disposed on the substrate 101, and an exit hole 1041 is formed on the piezoelectric layer 104, including:

[0066] Referring to Figures 2 and 3, a lower electrode 103 is deposited on a substrate 101, and the edge thickness of the lower electrode 103 is gradually reduced by etching.

[0067] A piezoelectric layer 104 is deposited to form a tilted structure.

[0068] It should be noted that a cavity 102 is etched on the substrate 101, and a cavity sacrificial layer is filled in the cavity 102; then a seed layer 1032 is deposited on the substrate 101, and then a patterned lower electrode 103 is deposited. The lower electrode tilt angle 1031 is formed by etching or photolithography.

[0069] Furthermore, before releasing the first sacrificial layer 1051 and the second sacrificial layer 1052 to form an air wing 113 and an air bridge 114 in the active region, and before the thickened layer 106 on the air bridge 114 collapses under tensile stress and contacts the piezoelectric layer 104 to divide the air bridge 114 into a first sub-air cavity 1141 and a second sub-air cavity 1143, the process further includes:

[0070] The thickened layer 106 is etched and hollowed out at the position corresponding to the active region so that the upper electrode 107 and the piezoelectric layer 104 form a contact area. The mass distribution of the thickened layer 106 is uneven, and the mass of the thickened layer 106 in the area projected downward from the recess 1142 is greater than that of other parts of the thickened layer 106.

[0071] Specifically, the thickened layer 106 is deposited and patterned to form a lead-out thickened layer 1061, a left thickened layer 1062, and a right thickened layer 1063. Additionally, the lead-out thickened layer 106 serves to lead out the lower electrode 103.

[0072] Furthermore, before releasing the first sacrificial layer 1051 and the second sacrificial layer 1052 to form an air wing 113 and an air bridge 114 in the active region, and before the thickened layer 106 on the air bridge 114 collapses under tensile stress and contacts the piezoelectric layer 104 to divide the air bridge 114 into a first sub-air cavity 1141 and a second sub-air cavity 1143, the process further includes:

[0073] Referring to FIG4, a passivation layer 108 is deposited on the upper electrode 107, and an annular groove 109 is etched on the passivation layer 108 at the edge of the contact area.

[0074] The lead-out thickening layer 106 is covered with the lead-out upper electrode 1071. The passivation layer 108 is made hollow by patterning the passivation layer 108. Then, the lead-out hole 1041 and the upper electrode 107 are respectively covered with the first protective layer 1101 and the second protective layer 1102.

[0075] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the scope of protection of this application. Industrial applicability

[0076] The thin-film bulk acoustic resonator and its fabrication method disclosed in this application can effectively reduce the strong parasitic peaks introduced by the thickened structure, thereby enabling the resonator to have better performance in industrial applications.

Claims

1. A thin-film bulk acoustic resonator, characterized in that, It includes a substrate and a lower electrode, a piezoelectric layer, a thickening layer, and an upper electrode stacked on the substrate; the overlapping portion of the projection of the lower electrode, the piezoelectric layer, and the upper electrode onto the substrate is an active region; an air wing and an air bridge are formed between the thickening layer and the piezoelectric layer on opposite sides of the active region; At the position corresponding to the air bridge, the thickened layer and the upper electrode are recessed towards the piezoelectric layer so that the thickened layer contacts the piezoelectric layer to generate a piezoelectric effect, and the air bridge is divided into a first sub-air cavity and a second sub-air cavity.

2. The thin-film bulk acoustic resonator according to claim 1, characterized in that, The thickness of the lower electrode gradually decreases to form an inclined structure at the edge of the active region, and the thickened layer and the recess of the upper electrode are located on the projection of the inclined structure onto the substrate.

3. The thin-film bulk acoustic resonator according to claim 1, characterized in that, The upper electrode has a passivation layer on the side away from the piezoelectric layer, and the passivation layer is recessed towards the piezoelectric layer at the position corresponding to the air bridge.

4. The thin-film bulk acoustic resonator according to claim 3, characterized in that, The thickened layer is hollowed out at a position corresponding to the active region so that the upper electrode and the piezoelectric layer form a contact area, and an annular groove is etched on the passivation layer at the edge of the contact area.

5. The thin-film bulk acoustic resonator according to claim 4, characterized in that, The annular groove includes an annular groove that extends circumferentially along the contact area and is connected end to end, or it includes multiple arc-shaped grooves arranged circumferentially around the contact area.

6. The thin-film bulk acoustic resonator according to claim 1, characterized in that, The upper electrode is made of aluminum scandium nitride, wherein the atomic ratio of aluminum to scandium is 3-5:

1.

7. A method for preparing the thin-film bulk acoustic resonator according to any one of claims 1-6, characterized in that, include: A lower electrode and a piezoelectric layer are sequentially disposed on the substrate, and a lead-out hole is formed on the piezoelectric layer; A thickened layer and an upper electrode are sequentially disposed on a piezoelectric layer with lead-out holes. The overlapping portion of the projection of the lower electrode, the piezoelectric layer, and the upper electrode onto the substrate is an active region. A first sacrificial layer and a second sacrificial layer are disposed between the piezoelectric layer and the thickened layer, located on opposite sides of the active region. The first and second sacrificial layers are released to form an air wing and an air bridge in the active region. The thickened layer on the air bridge is subjected to tensile stress and collapses to contact the piezoelectric layer, thereby dividing the air bridge into a first sub-air cavity and a second sub-air cavity.

8. The preparation method according to claim 7, characterized in that, The step of sequentially depositing a lower electrode and a piezoelectric layer on a substrate, and forming an outlet hole on the piezoelectric layer, includes: The lower electrode is deposited on the substrate, and the edge thickness of the lower electrode is gradually reduced by etching or photolithography. The piezoelectric layer is deposited to form a tilted structure.

9. The preparation method according to claim 7, characterized in that, Before releasing the first and second sacrificial layers to form an air wing and an air bridge in the active region, and before the thickened layer on the air bridge collapses under tensile stress and contacts the piezoelectric layer to divide the air bridge into a first sub-air cavity and a second sub-air cavity, the method further includes: The thickened layer is etched and hollowed out at the position corresponding to the active region so that the upper electrode and the piezoelectric layer form a contact area.

10. The preparation method according to claim 9, characterized in that, Before releasing the first and second sacrificial layers to form an air wing and an air bridge in the active region, and before the thickened layer on the air bridge collapses under tensile stress and contacts the piezoelectric layer to divide the air bridge into a first sub-air cavity and a second sub-air cavity, the method further includes: A passivation layer is deposited on the upper electrode, and an annular groove is etched on the passivation layer at the edge of the contact area.

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