Acoustic wave filter based on AlN / AlGaN superlattice structure and preparation method thereof

Abstract

The invention discloses an acoustic wave filter based on an AlN / AlGaN superlattice structure and a preparation method of the acoustic wave filter, and relates to the technical field of filters, the acoustic wave filter comprises a superlattice main body, and is characterized in that the superlattice main body comprises a substrate and a piezoelectric superlattice layer located on one side of the substrate; wherein the substrate is a Si substrate, a sapphire substrate or a SiC substrate; the piezoelectric superlattice layer is a composite alternating layer of an AIN layer and an Al < x > Ga < 1-x > N layer, and x is a constant greater than 0. The invention has the effects of reducing strain, improving compatibility and reliability, being suitable for high-frequency operation and remarkably improving electromechanical coupling performance.

Description

Technical Field

[0001] The present application relates to the field of filter technology, and in particular to an acoustic wave filter based on an AlN / AlGaN superlattice structure and a preparation method thereof. Background Art

[0002] Aluminum nitride (AlN) is a piezoelectric material with excellent properties. Its high acoustic velocity enables the excitation and propagation of high-frequency sound waves. It also possesses excellent chemical and thermal stability, maintaining stable performance under a wide range of environmental conditions. Furthermore, AlN has a low dielectric constant, which helps reduce capacitance effects during signal transmission and improve the frequency selectivity of filters.

[0003] Acoustic wave filters utilize the piezoelectric effect of the AlN piezoelectric layer to convert electrical signals into acoustic signals that propagate through the device, and then convert the acoustic signals back into electrical signals. During this process, only sound waves of specific frequencies are allowed to propagate smoothly through the filter, while sound waves of other frequencies are attenuated or reflected, thus achieving the filtering function of signals of different frequencies.

[0004] In the prior art, the AlN piezoelectric layer prepared by physical vapor deposition (PVD) has the problem of poor material quality, (002) rocking curve half-width (FWHM) (≧1°), rough surface morphology and poor thickness uniformity, especially in the processing of large diameter wafers (≥200mm), which requires auxiliary expensive post-processing processes. Although AlN grown by metal organic chemical vapor deposition (MOCVD) has better crystal quality (002) rocking curve half-width <0.4°, better thickness uniformity (+2% variation) and smooth surface (root mean square roughness <1nm), its large lattice mismatch, such as 19% mismatch with Si, and thermal expansion coefficient (TEC) mismatch with common substrates such as Si, sapphire, and SiC will cause tensile stress, thereby inducing cracks. In order to solve the problem of tensile stress, the use of a gradient buffer layer will reduce the electromechanical coupling coefficient due to its reduced piezoelectric activity, which needs to be improved. Summary of the Invention

[0005] In view of this, the first object of this application is to provide an acoustic wave filter based on an AlN / AlGaN superlattice structure to achieve the goals of improving crystal quality, reducing strain, and enhancing compatibility and reliability. Compared to AlN, AlGaN has a larger lattice constant. Therefore, by adjusting the Al content in AlGaN and the thickness of AlGaN, the AlN / AlGaN superlattice stress can be effectively controlled, thereby effectively suppressing cracks caused by thermal expansion coefficient mismatch. The specific scheme is as follows: An acoustic wave filter based on an AlN / AlGaN superlattice structure includes a superlattice main body, wherein the superlattice main body includes a substrate and a piezoelectric superlattice layer located on one side of the substrate; wherein: The substrate is a Si substrate, a sapphire substrate or a SiC substrate; The piezoelectric superlattice layer is a composite alternating layer of AlN layer and AlxGa1-xN layer, where x is a constant greater than 0.

[0006] Preferably: the value range of x is 0.7 <x<0.9。

[0007] Preferably: the Al x Ga 1-x The N layer is provided with a doping element having a mass concentration of 0.1-30%, and the doping element is Sc, Hf and / or Mg.

[0008] Preferably, the content of Sc is 1-10%, the content of Hf is 0.1-10%, and the content of Mg is 0.5-10%.

[0009] Preferably: the electric coupling coefficient K of the superlattice main body is based on a frequency of 1.5-6 GHz t >6%.

[0010] Preferably, the interface strain of the superlattice body is lower than 0.2%.

[0011] Preferably: the composite alternating layer is provided with 10-100 periodic layers, and the periodic layers are AlN layers and Al x Ga 1-x N-layer composite combination layer.

[0012] Preferably, the composite alternating layer is grown by MOCVD process at a temperature of 800-1100° C., using TMA, TMG, NH 3 and doping precursors.

[0013] Preferably, the thickness of the AlN layer is 5-50 nm, and the thickness of the AlxGa1-xN layer is 5-50 nm.

[0014] A second object of the present invention is to provide a method for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure, which is used to prepare the acoustic wave filter based on the AlN / AlGaN superlattice structure as described above, comprising the following steps: Step 1, fixing the substrate; Step 2: AlN layers and AlxGa1-xN layers are alternately formed on one side of the substrate using an MOCVD process; Step 3: depositing electrodes; Step 4: Bond the electrode side to the new Si substrate and remove the original Si substrate; Step 5: Deposit an electrode on the side where the substrate is removed to form a resonator.

[0015] From the above scheme, it can be seen that the present application provides an acoustic wave filter based on an AlN / AlGaN superlattice structure and a preparation method thereof. The acoustic wave filter based on the AlN / AlGaN superlattice structure has the following beneficial effects: 1. Good surface and thickness uniformity: Compared with the AIN piezoelectric layer prepared by traditional PVD, the AIN piezoelectric layer grown by MOCVD process has better thickness uniformity (variation within +2%) and smoother surface (RMS roughness <1nm). The thickness uniformity of large wafers (such as 300mm Si(111) wafers) can achieve a variation of <3%, avoiding expensive post-processing processes. 2. Relieve strain and eliminate cracks: by designing AIN / Al x Ga 1-x The N superlattice structure uses the lattice and TEC gradient of alternating layers to reduce interface strain to <0.2%, eliminating cracks in layers thicker than 2μm. Furthermore, the strain hysteresis in thermal cycling tests from -40°C to 150°C is <0.1%, which is better than the 3% hysteresis of PVD-AIN and improves filter reliability. 3. Maintaining a high electromechanical coupling coefficient: Optimizing the Al content to maintain a high piezoelectric response while relieving strain, achieving d33>5pC / N; adding doping elements to AlGaN to further increase the electromechanical coupling coefficient Kt>6%; 4. Suitable for operation in the frequency range of 1.5GHz to below 6GHz, suitable for scenarios such as 5G / 6G systems that require high-frequency filters, and can meet the use requirements of equipment such as 5G base stations, smartphones and satellite communication systems.

[0016] The preparation method of the acoustic wave filter based on the AlN / AlGaN superlattice structure is convenient to construct and suitable for batch and large-scale production, realizing scalable manufacturing of large wafers. For example, the 20-period AlN / Al0.8Ga0.2N superlattice prepared on a 200mm Si(111) wafer is crack-free and has a residual strain of <0.110%, which is conducive to the batch production of filters and has industrial applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without any creative work.

[0018] Figure 1 A schematic structural diagram of an acoustic wave filter based on an AlN / AlGaN superlattice structure disclosed in this application; Figure 2 This is a schematic diagram of the structure of the piezoelectric superlattice layer disclosed in this application.

[0019] Explanation of the reference numerals: 1. Wafer bonding etching portion; 2. Piezoelectric superlattice layer; 21. AIN layer; 22. AlxGa1-xN layer; 23. Si layer; 3. Electrode; 4. Side layer; 5. Side lower layer. DETAILED DESCRIPTION

[0020] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0021] It should be mentioned that the substrates in the embodiments of the present application are all Si substrates. Of course, sapphire substrates or SiC substrates can also be used, which will not be described in detail here.

[0022] like Figure 1 As shown, an acoustic wave filter based on an AlN / AlGaN superlattice structure includes a superlattice main body. The superlattice main body consists of a wafer bonding etch 1, side layers 4 located on both sides of the upper end of the wafer bonding etch 1, and a piezoelectric superlattice layer 2 located above the wafer bonding etch 1. Electrodes 3 are provided on both the upper and lower sides of the piezoelectric superlattice layer 2, and a side lower layer 5 is provided below the side layer 4. The side layers are made of silicon dioxide (SiO2), and the side lower layer 5 is made of silicon (Si) or glass.

[0023] like Figure 2 As shown, the piezoelectric superlattice layer 2 is a composite alternating layer of an AlN layer 21 and an AlxGa1-xN layer 22, and a Si layer 23 is provided at the bottom layer.

[0024] The following describes in detail an acoustic wave filter based on an AlN / AlGaN superlattice structure and a preparation method thereof according to the present application.

[0025] like Figure 1 、 Figure 2 As shown, an acoustic wave filter based on AlN / AlGaN superlattice structure includes a superlattice body. The superlattice body includes a substrate and a piezoelectric superlattice layer located on one side of the substrate. The substrate is a Si substrate, a sapphire substrate or a SiC substrate. The piezoelectric superlattice layer is an AlN layer and an AlGaN layer. x Ga1-x N layers of composite alternating layers, x is a constant greater than 0. The value range of x is 0.7 <x<0.9。

[0026] At the same time, in order to further improve the electromechanical coupling coefficient, the Al x Ga 1-x The N layer is provided with a doping element having a mass concentration of 0.1-30%. The doping element is Sc, Hf, and / or Mg. It should be noted that the Sc content is 1-10%, the Hf content is 0.1-10%, and the Mg content is 0.5-10%.

[0027] After testing, the electric coupling coefficient K of the superlattice body based on the frequency of 1.5-6GHz t >6%. And the interface strain of the superlattice body is less than 0.2%.

[0028] In the embodiment of the present application, the composite alternating layer is provided with 10-100 periodic layers, and the periodic layers are AlN layers and Al x Ga 1-x The composite combination layer of the N layer is grown by MOCVD process at a temperature of 800-1100°C using TMA, TMG, NH3 and doping precursors.

[0029] The thickness of the AlN layer is 5-50 nm. x Ga 1-x The thickness of the N layer is 5-50 nm.

[0030] A method for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure, for preparing the acoustic wave filter based on the AlN / AlGaN superlattice structure as described above, comprises the following steps: Step 1, fixing the substrate; Step 2: Use MOCVD process to alternately generate AlN layer and Al x Ga 1-x N-layer; Step 3: depositing electrodes; Step 4: Bond the electrode side to the new Si substrate and remove the original Si substrate; Step 5: Deposit an electrode on the side where the substrate is removed to form a resonator. Example

[0031] like Figure 1 、 Figure 2 As shown, an acoustic wave filter based on AlN / AlGaN superlattice structure includes a superlattice body. The superlattice body includes a substrate and a piezoelectric superlattice layer located on one side of the substrate. The piezoelectric superlattice layer is composed of an AlN layer and an AlGaN superlattice layer. x Ga1-x N layers of composite alternating layers, x is 0.8.

[0032] In the embodiment of the present application, the composite alternating layer is provided with 20 periodic layers, and the periodic layers are AlN layers and Al 0.8 Ga 0.2 The composite combination layer of the N layer is grown by MOCVD process at a temperature of 800℃ using TMA, TMG, NH3 and doping precursors.

[0033] The thickness of the AlN layer is 20 nm, and the thickness of the AlxGa1-xN layer is 20 nm.

[0034] A method for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure, for preparing the acoustic wave filter based on the AlN / AlGaN superlattice structure as described above, comprises the following steps: Step 1, fixing the substrate; Step 2: Use MOCVD process to alternately generate AlN layer and Al x Ga 1-x N-layer; Step 3: depositing electrodes; Step 4: Bond the electrode side to the new Si substrate and remove the original Si substrate; Step 5: Deposit an electrode on the side where the substrate is removed to form a resonator.

[0035] Based on a 200mm Si(111) wafer, the AlN / Al with 20 periodic layers was generated. 0.8 Ga 0.2 The piezoelectric superlattice layer of N was tested to have no cracks after deposition, with a residual strain of <0.110%, an operating frequency of about 4 GHz, and an electrical coupling coefficient K t >7%. Example

[0036] like Figure 1 、 Figure 2 As shown, an acoustic wave filter based on AlN / AlGaN superlattice structure includes a superlattice body. The superlattice body includes a substrate and a piezoelectric superlattice layer located on one side of the substrate. The piezoelectric superlattice layer is composed of an AlN layer and an AlGaN superlattice layer. x Ga 1-x N layers of composite alternating layers, x is 0.75.

[0037] In the embodiment of the present application, the composite alternating layer is provided with 20 periodic layers, and the periodic layers are AlN layers and Al 0.75 Ga 0.25The composite combination layer of the N layer is grown by MOCVD process at a temperature of 1000 ° C using TMA, TMG, NH3 and doping precursors.

[0038] The thickness of the AlN layer is 20 nm. 0.75 Ga 0.25 The thickness of the N layer is 20 nm.

[0039] At the same time, in order to further improve the electromechanical coupling coefficient, the Al x Ga 1-x The N layer is provided with Sc at a mass concentration of 10%.

[0040] A method for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure, for preparing the acoustic wave filter based on the AlN / AlGaN superlattice structure as described above, comprises the following steps: Step 1, fixing the substrate; Step 2: Use MOCVD process to alternately generate AlN layer and Al x Ga 1-x N-layer; Step 3: depositing electrodes; Step 4: Bond the electrode side to the new Si substrate and remove the original Si substrate; Step 5: Deposit an electrode on the side where the substrate is removed to form a resonator.

[0041] Based on a 200mm Si(111) wafer, the AlN / Al with 20 periodic layers was generated. 0.75 Ga 0.25 The piezoelectric superlattice layer of N was tested to have no cracks after deposition, the residual strain was <0.110%, the operating frequency was about 4 GHz, and the electrical coupling coefficient K t >8.4%.

[0042] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 is based on SiC as the substrate, and the -40°C to 150°C thermal cycle test shows that the strain hysteresis is <0.1%, which is significantly better than the 3% hysteresis of PVD-AIN.

[0043] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 uses a 300 mm Si (111) wafer, and the thickness uniformity obtained by testing is less than 3%.

[0044] In summary, the present application provides an acoustic wave filter based on an AlN / AlGaN superlattice structure and a preparation method thereof. The acoustic wave filter based on the AlN / AlGaN superlattice structure has good surface and thickness uniformity, relieves strain and eliminates cracks, and maintains a high electromechanical coupling coefficient. In particular, the AlN piezoelectric layer grown by the MOCVD process has better thickness uniformity (variation within +2%) and a smoother surface (RMS roughness <1nm) than the AlN piezoelectric layer prepared by traditional PVD. The thickness uniformity of large wafers (such as 300mm Si(111) wafers) can achieve a variation of <3%, avoiding expensive post-processing processes. In addition, by designing the AlN / AlxGa1-xN superlattice structure and utilizing the lattice and TEC gradient of the alternating layers, the interface strain is reduced to <0.2%, cracks in layers with a thickness greater than 2μm are eliminated, and the strain hysteresis is <0.1% in a -40°C to 150°C thermal cycle test, which is better than the 3% hysteresis of PVD-AlN, thereby improving the reliability of the filter. At the same time, by optimizing the Al content, a high piezoelectric response is maintained while relieving strain, achieving d33>5pC / N; adding doping elements to AlGaN further increases the electromechanical coupling coefficient Kt>6%. Therefore, the acoustic wave filter based on the AlN / AlGaN superlattice structure is suitable for operating in the frequency range of 1.5GHz to below 6GHz, and is suitable for scenarios such as 5G / 6G systems that require high-frequency filters. It can meet the requirements of equipment such as 5G base stations, smartphones, and satellite communication systems. The preparation method of the acoustic wave filter based on the AlN / AlGaN superlattice structure has the advantages of convenient construction and suitability for batch and large-scale production, realizing scalable manufacturing of large wafers. For example, a 20-period AlN / Al0.8Ga0.2N superlattice prepared on a 200mm Si(111) wafer is crack-free and has a residual strain of <0.110%, which is conducive to the batch production of filters and has industrial applicability.

[0045] References to "first," "second," "third," "fourth," and the like (if any) herein are intended to distinguish similar objects and are not necessarily intended to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate so that the embodiments described herein can be implemented in an order other than that illustrated or described herein. In addition, the terms "including" and "having," as well as any variations thereof, are intended to cover non-exclusive inclusions, e.g., a process, method, or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such processes, methods, or apparatus.

[0046] It should be noted that the descriptions of "first", "second", etc. in this application are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" or "second" may explicitly or implicitly include at least one of such features. In addition, the technical solutions between the various embodiments can be combined with each other, but this must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0047] This document uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. An acoustic wave filter based on an AlN / AlGaN superlattice structure, comprising a superlattice main body, characterized in that: The superlattice main body includes a substrate and a piezoelectric superlattice layer located on one side of the substrate; wherein: The substrate is a Si substrate, a sapphire substrate or a SiC substrate; The piezoelectric superlattice layer is an AlN layer and an Al x Ga 1-x A composite alternating layer of N layers, where x is a constant greater than 0.

2. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The value range of x is 0.7 <x<0.9。 3. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The AlxGa1-xN layer is provided with a doping element having a mass concentration of 0.1-30%, and the doping element is Sc, Hf and / or Mg.

4. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 3, characterized in that: The content of Sc is 1-10%, the content of Hf is 0.1-10%, and the content of Mg is 0.5-10%.

5. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The electrical coupling coefficient K of the superlattice master is based on the frequency of 1.5-6 GHz. t >6%.

6. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The interfacial strain of the superlattice body is less than 0.2%.

7. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The composite alternating layer is provided with 10-100 periodic layers, and the periodic layers are AlN layers and Al x Ga 1-x N-layer composite combination layer.

8. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 1, characterized in that: The composite alternating layer is grown by adopting MOCVD process at a temperature of 800-1100° C. and is obtained by adopting TMA, TMG, NH 3 and doping precursor.

9. The acoustic wave filter based on the AlN / AlGaN superlattice structure according to claim 8, characterized in that: The thickness of the AlN layer is 5-50 nm. x Ga 1-x The thickness of the N layer is 5-50 nm.

10. A method for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure, for preparing an acoustic wave filter based on an AlN / AlGaN superlattice structure according to any one of claims 1 to 9, characterized in that: The steps include: Step 1, fixing the substrate; Step 2: Use MOCVD process to alternately generate AlN layer and Al x Ga 1-x N-layer; Step 3: depositing electrodes; Step 4: Bond the electrode side to the new Si substrate and remove the original Si substrate; Step 5: Deposit an electrode on the side where the substrate is removed to form a resonator.

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