Bulk acoustic wave resonator based on piezoelectric thin film structure on silicon and preparation method thereof

Abstract

The present invention provides a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon and a preparation method thereof, comprising: an electrode, an aluminum nitride piezoelectric thin film layer (3) and a silicon on insulator (SOI); the electrode comprises: a top electrode (1); the aluminum nitride piezoelectric thin film layer (3) and the silicon on insulator (SOI) are arranged below the top electrode (1); the silicon on insulator comprises: a single crystal silicon top layer (4), an insulating silicon dioxide middle layer (5), and a silicon substrate layer; the thickness of the silicon substrate layer is greater than a set threshold; the thickness of the insulating silicon dioxide middle layer (5) is less than a set threshold; the thickness of the single crystal silicon top layer (4) is greater than the insulating silicon dioxide middle layer (5); the thickness of the single crystal silicon top layer (4) is less than the silicon substrate layer; the piezoelectric thin film structure on silicon proposed in this patent combines the advantages of the above two types of resonators, thereby facilitating the design of a resonator with both high Q value and low motional impedance.

Description

Technical Field

[0001] The present invention relates to the technical field of resonators, and in particular to a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon and a preparation method thereof. Background Art

[0002] With the rapid development of 5G communication systems, resonators based on micro-electromechanical systems (MEMS) have become one of the most promising devices due to their small size and high compatibility. There are two main types of resonators: capacitive resonators.

[0003] Patent document CN106992768A discloses a capacitive MEMS resonator with multiple pairs of driving and sensing electrodes; Patent document CN111010138A proposes a high-Q bulk acoustic wave resonator. The shortcomings of the existing technology are: the motional impedance of conventional capacitive resonators is too high, and the Q value of piezoelectric resonators is low. However, the piezoelectric thin film resonator on silicon proposed in this patent can greatly improve the Q value of the resonator while ensuring low motional impedance; the mechanical strength and temperature stability of conventional oscillating stack suspended resonators are poor, while the resonator proposed in this patent has silicon and silicon dioxide layers placed under the oscillating stack, which can effectively help improve the mechanical strength and temperature stability of the resonator; the top electrode shape of conventional resonators is single and has limited applicability, while this patent proposes three basic top electrode shapes that can effectively excite lambda wave resonance, providing multiple options for different practical environments; the processing technology of conventional resonators is complex and difficult, while this patent provides a set of processing methods for the proposed resonator, which can simplify the processing technology and obtain high-quality resonators. Summary of the Invention

[0004] In view of the defects in the prior art, the present invention aims to provide a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon and a preparation method thereof.

[0005] According to the present invention, a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon includes: an electrode, an aluminum nitride piezoelectric thin film layer 3, and a silicon-on-insulator (SOI). The electrode includes: a top electrode 1; the aluminum nitride piezoelectric thin film layer 3 and the silicon-on-insulator (SOI) are arranged below the top electrode 1; the silicon-on-insulator includes: a single crystal silicon top layer 4, an insulating silicon dioxide intermediate layer 5, and a silicon substrate layer; the thickness of the silicon substrate layer is greater than a set threshold; the thickness of the insulating silicon dioxide intermediate layer 5 is less than a set threshold; the thickness of the single crystal silicon top layer 4 is greater than the insulating silicon dioxide intermediate layer 5; and the thickness of the single crystal silicon top layer 4 is less than the silicon substrate layer.

[0006] Preferably, the electrode further comprises: a bottom electrode 2; the bottom electrode 2 is arranged below the top electrode 1; the bottom electrode is electrically floating; and the bottom electrode is grounded.

[0007] Preferably, the electrode adopts the following electrode materials: - platinum Pt; - aluminum Al; - molybdenum Mo; - gold Au; - silver Ag; - ruthenium Ru; the piezoelectric film layer adopts any one of the following materials: - aluminum nitride AlN; - scandium-doped aluminum nitride AlScN; - zinc oxide ZnO; - lead zirconate titanate PzT.

[0008] When a signal is applied to the top electrode, a lambda wave resonance mode is excited in the aluminum nitride piezoelectric film layer, thereby obtaining a resonator with a high Q value and low motional impedance.

[0009] The silicon dioxide layer at the bottom of the resonator can also compensate the frequency temperature coefficient of the piezoelectric film layer to a certain extent, thereby reducing the drift of the resonant frequency caused by temperature changes and improving its temperature stability.

[0010] Preferably, the top electrode 1 adopts any one of the following structures: - an annular structure; - a concentric ring structure; - an interdigitated electrode.

[0011] Preferably, it further comprises: a pad; the annular structure adopted by the top electrode 1 is equally divided into four parts, wherein the opposite quarter parts are connected to each other and to the pad on one side.

[0012] In this structure, the electrical signals applied to two adjacent quarters will have opposite phases, thereby effectively exciting lambda wave resonance in the aluminum nitride thin film layer.

[0013] Preferably, the device further comprises a pad; the central disc-shaped electrode of the concentric ring structure of the top electrode 1 is connected to the pad at one end; and the ring surrounding the central disc-shaped electrode of the concentric ring structure of the top electrode 1 is connected to the pad at the other end. When a signal with a potential difference is applied to the pads at both ends, the generated electric field can excite lambda wave resonance in the aluminum nitride thin film layer.

[0014] Preferably, the device further comprises: a bonding pad; the interdigitated electrodes of the interdigitated electrodes used in the top electrode 1 are connected to the bonding pads at both ends. When a signal is applied to both ends of the interdigitated electrodes, a horizontal electric field is formed between the interdigitated electrodes, thereby exciting lambda wave resonance in the aluminum nitride film.

[0015] Preferably, a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon is prepared, characterized by comprising: step S1: preparing silicon on insulator;

[0016] Step S2: preparing a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon on the basis of silicon on insulator;

[0017] The step S1 comprises:

[0018] Step S1.1: Cleaning and preparing the first silicon wafer and the second silicon wafer;

[0019] Step S1.1.2: Under set conditions, a set dose of hydrogen ions or helium ions is implanted into the first silicon wafer at a set energy to generate a bubble layer at a specific depth below the silicon surface;

[0020] Step S1.3: Oxidizing the surface of the second silicon wafer to obtain an insulating silicon dioxide layer of a specific thickness;

[0021] Step S1.4: Bonding the first silicon wafer to the second silicon wafer. The silicon dioxide layer on the surface of the second silicon wafer will serve as the insulating layer in the future silicon-on-insulator structure, and the second silicon wafer will become the substrate of the silicon-on-insulator structure.

[0022] Step S1.5: heat-treating the bonded first silicon wafer and the second silicon wafer so that the first silicon wafer is separated from the hydrogen ion bubble layer and the upper silicon film is bonded to the second silicon wafer, thereby obtaining silicon-on-insulator.

[0023] Preferably, step S2 includes:

[0024] Step S2.1: Cleaning and preparing the silicon-on-insulator;

[0025] Step S2.2: growing a metal layer on the surface of the silicon-on-insulator as a bottom electrode;

[0026] Step S2.3: growing an aluminum nitride piezoelectric thin film layer of a set thickness on the surface of the bottom electrode;

[0027] Step S2.4: applying photoresist, exposing, and etching the shape of the top electrode;

[0028] Step S2.5: depositing a metal layer, and using a peeling and stripping process to obtain a top electrode of a predetermined shape;

[0029] Step S2.6: Etch out the area where the resonator oscillation stack is located from the back side of the silicon substrate using a dry or wet method, thereby obtaining the required resonator.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. By employing a piezoelectric thin-film-on-silicon structure, this invention addresses both the low Q problem of resonators based on piezoelectric transduction mechanisms and the high motional impedance problem of resonators based on capacitive transduction mechanisms. The piezoelectric thin-film-on-silicon structure proposed in this patent combines the advantages of both types of resonators, facilitating the design of resonators with both high Q and low motional impedance.

[0032] 2. This invention addresses the problems of poor mechanical strength and low power capacity of conventional oscillator stack suspension resonators by employing a piezoelectric thin film on silicon structure. Furthermore, the silicon dioxide layer at the bottom of the resonator proposed in this patent can also compensate for the frequency temperature coefficient of the piezoelectric thin film layer to a certain extent, improving the temperature stability of the resonator.

[0033] 3. This invention addresses the limited applicability of conventional BAW resonators due to their single structure by proposing three top electrode shapes to stimulate different forms of lambda wave resonance. The proposed annular, concentric, and interdigitated top electrodes provide more design options for different applications, and further top electrode designs can be developed based on these three top electrode shapes.

[0034] 4. The present invention adopts intelligent stripping technology to prepare silicon-on-insulator structures, thereby solving the problems of high annealing temperature, great process difficulty and low quality of the silicon-on-insulator prepared in conventional preparation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0036] Figure 1 Schematic diagram of a bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure in an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of a novel top electrode ring structure in an embodiment of the present invention.

[0038] Figure 3 Schematic diagram of a novel concentric ring structure of a top electrode in an embodiment of the present invention.

[0039] Figure 4 Schematic diagram of a novel top electrode interdigitated electrode in an embodiment of the present invention.

[0040] Figure 5 1 is a flow chart of a method for preparing a bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure according to an embodiment of the present invention.

[0041] Figure 6 1 is a flow chart of a second method for preparing a bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure according to an embodiment of the present invention.

[0042] In the picture:

[0043] 1-top electrode 5-insulating silicon dioxide intermediate layer

[0044] 2- bottom electrode 6- silicon substrate (Si)

[0045] 3-Aluminum nitride piezoelectric film layer 7-Photoresist

[0046] 4-Single crystal silicon top layer DETAILED DESCRIPTION

[0047] The present invention will be described in detail below with reference to specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those skilled in the art, several changes and improvements can be made without departing from the scope of the present invention. These all fall within the scope of protection of the present invention.

[0048] Conventional resonators based on micro-electromechanical systems are mainly divided into two types: resonators based on capacitive transduction mechanisms and resonators based on piezoelectric transduction mechanisms. There is a contradictory balance between resonators based on these two transduction mechanisms - motional impedance and quality factor Q. On the one hand, the motional impedance of resonators based on piezoelectric transduction mechanisms is generally less than 50Ω, but due to the high loss characteristics of the piezoelectric material itself, the Q value of such resonators is difficult to improve. On the other hand, due to the low loss characteristics of silicon materials, resonators based on capacitive conversion mechanisms can achieve extremely high Q values. However, due to the weak capacitive electroacoustic coupling, the motional impedance of such resonators is generally at the kΩ level. Based on this, this patent combines the advantages of the above two resonators and proposes a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon. By combining high-Q silicon (Si) material and low-motional impedance piezoelectric thin film material, the designed resonator has both high Q value and low motional impedance.

[0049] Figure 1 The figure shows a bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure proposed in this patent. The resonator consists of a top electrode 1, a bottom electrode 2, an aluminum nitride piezoelectric thin film layer 3, and a silicon-on-insulator (SOI) structure. The SOI structure consists of a thin single-crystal silicon top layer 4, a very thin insulating silicon dioxide intermediate layer 5, and a thick silicon substrate layer. The bottom electrode can be electrically floating, grounded, or not used at all. Electrode materials can include platinum (Pt), aluminum (Al), molybdenum (Mo), gold (Au), silver (Ag), ruthenium (Ru), etc. The aluminum nitride piezoelectric thin film layer can also be replaced with other effective piezoelectric thin film materials, such as scandium-doped aluminum nitride (AlScN), zinc oxide (ZnO), and lead zirconate titanate (PzT). When a signal is applied to the top electrode, a lambda wave resonant mode is excited in the aluminum nitride piezoelectric thin film layer, resulting in a resonator with a high Q value and low motional impedance. The silicon dioxide layer at the bottom of the resonator can also compensate the frequency temperature coefficient of the piezoelectric film layer to a certain extent, thereby reducing the drift of the resonant frequency caused by temperature changes and improving its temperature stability.

[0050] Based on the piezoelectric film structure on silicon, this patent also proposes three new top electrode structures. One is Figure 2 The ring structure is divided into four equal parts, where the opposite quarters are connected to each other and to the pads on one side. In this structure, the electrical signals applied to the two adjacent quarters will have opposite phases, thus well exciting the lambda wave resonance in the aluminum nitride film layer. Another is as Figure 3 The concentric ring structure shown in the figure has a disc-shaped electrode in the center connected to a pad at one end, and a ring surrounding the disc is connected to a pad at the other end. When a signal with a potential difference is applied to the pads at both ends, the generated electric field can excite lambda wave resonance in the aluminum nitride film layer. The last top electrode shape is as follows Figure 4 The interdigitated electrodes shown are connected to pads at both ends. When a signal is applied to the interdigitated electrodes, a horizontal electric field is formed between the interdigitated electrodes, which stimulates lambda wave resonance in the aluminum nitride film.

[0051] The bulk acoustic wave resonator based on the piezoelectric thin film structure on silicon proposed in this patent can be processed and prepared by standard photolithography technology. Its processing flow is mainly divided into two parts: the preparation of silicon on insulator and the preparation of the resonator. The preparation of silicon on insulator mainly adopts the smart peeling technology, and its preparation process is as follows: Figure 5 As shown: 1. The first silicon wafer and B are cleaned and prepared; 2. Under specific conditions, a certain dose of hydrogen ions or helium ions are injected into the first silicon wafer with a certain energy to produce a bubble layer at a specific depth below the silicon surface; 3. The surface of the second silicon wafer is oxidized to obtain an insulating silicon dioxide layer of a specific thickness; 4. The first silicon wafer and B are bonded, and the silicon dioxide layer on the surface of the second silicon wafer serves as the insulating layer in the future silicon-on-insulator structure, and the second silicon wafer will become the substrate of the silicon-on-insulator; 5. The bonded first silicon wafer and B are heat-treated to separate the first silicon wafer from the hydrogen ion bubble layer, and the upper silicon film is bonded to the second silicon wafer, thereby obtaining a silicon-on-insulator structure. After obtaining the silicon-on-insulator, the resonator preparation process on this substrate is as follows. Figure 6 As shown: 1. Cleaning and preparation of silicon on insulator; 2. Growing a metal layer on the surface of silicon on insulator as the bottom electrode; 5. Growing an aluminum nitride piezoelectric film layer of a specific thickness on the surface of the bottom electrode; 6. Applying photoresist, exposing and etching the shape of the top electrode; 7. Depositing a metal layer, and using a lift-off process to obtain a top electrode of a specific shape; 8. Using a dry or wet method to etch out the area where the resonator oscillation stack is located from the back of the silicon substrate, thereby obtaining the required resonator.

[0052] In the description of this application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this 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 cannot be understood as a limitation on this application.

[0053] The above describes specific embodiments of the present invention. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. The embodiments of this application and the features in the embodiments may be combined with each other in any manner unless there is a conflict.

Claims

1. A bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon, characterized in that: include: Electrodes, aluminum nitride piezoelectric film layer (3) and silicon on insulator; The electrodes include: a top electrode (1); The aluminum nitride piezoelectric film layer (3) and the silicon-on-insulator are arranged below the top electrode (1); The silicon-on-insulator comprises: a single crystal silicon top layer (4), an insulating silicon dioxide middle layer (5), and a silicon substrate layer; The thickness of the silicon substrate layer is greater than a set threshold; The thickness of the insulating silicon dioxide intermediate layer (5) is less than a set threshold; The thickness of the single crystal silicon top layer (4) is greater than the insulating silicon dioxide middle layer (5); The thickness of the single crystal silicon top layer (4) is smaller than that of the silicon substrate layer; The electrode further comprises: a bottom electrode (2); The bottom electrode (2) is arranged below the top electrode (1); The bottom electrode can be electrically floating; The bottom electrode can be grounded; The top electrode (1) adopts any one of the following structures: - Ring structure; - Concentric ring structure; Also includes: solder pads; The ring structure is divided into four equal parts, with opposite quarters connected to each other and to pads on one side. The electrical signals applied to two adjacent quarters will have opposite phases, thereby exciting lambda wave resonance in the aluminum nitride piezoelectric film layer. The disc-shaped electrode at the center of the concentric ring structure is connected to the pad at one end, and the ring surrounding the disc is connected to the pad at the other end. When a signal with a potential difference is applied to the pads at both ends, the generated electric field excites lamb wave resonance in the aluminum nitride piezoelectric film layer.

2. The bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure according to claim 1, characterized in that: The electrodes are made of the following materials: - Platinum; - aluminum; - Molybdenum; - gold; - silver; - Ruthenium; The piezoelectric film layer is made of any of the following materials: - Aluminum nitride; - Scandium-doped aluminum nitride; - Zinc oxide; - Lead zirconate titanate.

3. The bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure according to claim 1, characterized in that: Also includes: pads; The top electrode (1) adopts a ring-shaped structure which is equally divided into four parts, wherein opposite quarter parts are connected to each other and to a pad on one side.

4. A method for preparing a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon, characterized in that: A bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon according to any one of claims 1 to 3 is prepared, characterized in that it comprises: Step S1: preparing silicon-on-insulator; Step S2: preparing a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon on the basis of silicon on insulator; The step S1 comprises: Step S1.1: Cleaning and preparing the first silicon wafer and the second silicon wafer; Step S1.1.2: Under set conditions, a set dose of hydrogen ions or helium ions is implanted into the first silicon wafer at a set energy to generate a bubble layer at a specific depth below the silicon surface; Step S1.3: oxidizing the surface of the second silicon wafer to obtain an insulating silicon dioxide layer of a specific thickness; Step S1.4: Bonding the first silicon wafer to the second silicon wafer. The silicon dioxide layer on the surface of the second silicon wafer serves as the insulating layer in the silicon-on-insulator structure, and the second silicon wafer becomes the substrate of the silicon-on-insulator structure. Step S1.5: heat-treating the bonded first silicon wafer and the second silicon wafer so that the first silicon wafer is separated from the hydrogen ion bubble layer and the upper silicon film is bonded to the second silicon wafer, thereby obtaining silicon-on-insulator.

5. The method for preparing a bulk acoustic wave resonator based on a piezoelectric thin film on silicon structure according to claim 4, characterized in that: Step S2 further includes: Step S2.1: Cleaning and preparing the silicon-on-insulator; Step S2.2: growing a metal layer on the surface of the silicon-on-insulator as a bottom electrode; Step S2.3: growing an aluminum nitride piezoelectric thin film layer of a set thickness on the surface of the bottom electrode; Step S2.4: applying photoresist, exposing, and etching the shape of the top electrode; Step S2.5: depositing a metal layer, and using a peeling and stripping process to obtain a top electrode of a predetermined shape; Step S2.6: Etching the area where the resonator oscillation stack is located from the back side of the silicon substrate by dry or wet etching, thereby obtaining a bulk acoustic wave resonator based on a piezoelectric thin film structure on silicon.

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