Aluminum nitride Lamb wave resonator with arc-shaped bus and preparation method

Abstract

The invention discloses an aluminum nitride Lamb wave resonator with an arc-shaped bus and a preparation method of the aluminum nitride Lamb wave resonator, and belongs to the field of radio frequency MEMS devices. The invention provides an aluminum nitride Lamb wave resonator with an arc bus. The aluminum nitride Lamb wave resonator with the arc bus comprises a substrate, wherein a release cavity is formed in the upper surface of the substrate; the bottom plate electrode is placed above the upper surface of the substrate and is positioned in the release cavity; the piezoelectric vibration structure is located on the surface of the bottom plate electrode; the top interdigital electrode is positioned on the surface of the piezoelectric vibration structure; the supporting shafts are located on the two sides of the piezoelectric vibration structure so that the piezoelectric vibration structure, the bottom plate electrode and the top interdigital electrode can be fixed in the release cavity in a suspended mode. The aluminum nitride Lamb wave resonator with the arc-shaped bus provided by the invention has the characteristic of high quality factor, and a novel resonator capable of improving the Q value can be realized.

Description

Technical Field

[0001] The present application belongs to the field of radio frequency MEMS devices, and in particular to an aluminum nitride Lamb wave resonator with an arc-shaped bus and a preparation method thereof. Background Art

[0002] With the development and application of 5G technology, RF devices based on micro-electromechanical systems (MEMS) technology have received widespread attention. Among them, piezoelectric acoustic filters are widely used in various wireless communication devices due to their small size, low cost and excellent performance. The resonator is the core component of the filter, and its performance directly affects the important parameters of the filter. However, the high frequency f and high electromechanical coupling coefficient k of the resonator t 2 It is difficult to achieve a good balance between high bandwidth and high Q value, and requirements such as large bandwidth, low loss, and low power consumption are also important challenges in the current design of high-quality resonators.

[0003] SAW devices have low resonant frequency and Q value and can only be used in medium and low frequency bands, but they can achieve on-chip multi-band integration; BAW devices have high resonant frequency and high Q value and k t 2 , but it cannot realize on-chip multi-band integration; Lamb wave resonator (LWR), as an emerging piezoelectric microelectromechanical system (MEMS) acoustic device, combines the advantages of SAW devices and BAW devices, and exhibits the characteristics of high operating frequency, moderate electromechanical coupling coefficient, high quality factor and low power consumption. Its manufacturing process is compatible with integrated circuit technology and can realize on-chip multi-band integration.

[0004] However, with the continuous development of 5G communication technology, electronic devices are constantly updated, and acoustic devices with higher Q values ​​and lower losses are in great demand.

[0005] Therefore, there is a real need to provide an aluminum nitride Lamb wave resonator and a preparation method thereof with improved quality factor (Q value) so as to further realize low-loss filters, high-sensitivity sensors and low-phase noise oscillators. Summary of the invention

[0006] In view of this, the object of the present invention is to provide an aluminum nitride Lamb wave resonator with an arc-shaped bus to improve the Q value and a preparation method, using an arc-shaped bus structure to improve the quality factor Q value.

[0007] The present invention provides the following technical solutions:

[0008] In a first aspect of the present invention, there is provided an aluminum nitride Lamb wave resonator with an arc-shaped bus, the aluminum nitride Lamb wave resonator with an arc-shaped bus comprising:

[0009] A substrate, wherein a release cavity is disposed on an upper surface of the substrate;

[0010] a bottom plate electrode disposed above the upper surface of the substrate and within the release cavity;

[0011] A piezoelectric vibration structure is located on the surface of the bottom plate electrode;

[0012] a top interdigitated electrode, located on the surface of the piezoelectric vibrating structure;

[0013] The supporting shaft is located at both sides of the piezoelectric vibration structure so that the piezoelectric vibration structure, the bottom plate electrode and the top interdigital electrode are all suspended and fixed in the release cavity.

[0014] In some embodiments, the top interdigitated electrode includes an arc bus located on both sides and a plurality of main body electrodes located in the middle of the arc bus.

[0015] In some embodiments, the arc of the arc bus is 150°-180°.

[0016] In some embodiments, the thickness of the arc bus is the same as the thickness of the main electrode and the thickness is 100nm-200nm.

[0017] In some embodiments, the piezoelectric vibration structure uses a scandium-doped aluminum nitride film; the thickness of the scandium-doped aluminum nitride film is 500nm-1000nm.

[0018] In some embodiments, the scandium doping concentration of the scandium-doped aluminum nitride film is 10%-30%;

[0019] The top interdigital electrode and the bottom flat electrode have the same thickness, and the thickness is 100nm-200nm, and the selected material is molybdenum;

[0020] The material of the substrate is silicon.

[0021] In a second aspect of the present invention, there is provided a method for preparing the aluminum nitride Lamb wave resonator as described above, comprising the following steps:

[0022] S1 etches a release cavity on a high-resistance silicon wafer as a substrate, and then forms a SiO2 film using a wet thermal oxidation process;

[0023] S2 deposits a polysilicon layer on the SiO2 layer as a sacrificial layer;

[0024] S3 removes the polysilicon outside the release cavity by dry etching and performs chemical mechanical polishing;

[0025] S4 deposits a layer of molybdenum to form the bottom plate electrode;

[0026] S5 deposits an aluminum nitride film to form the piezoelectric vibration structure;

[0027] S6: depositing a molybdenum layer, sequentially performing plasma etching on the molybdenum layer, and then performing patterning to form a top interdigital electrode;

[0028] S7: plasma etching is performed on the molybdenum / aluminum nitride / molybdenum three-layer film to form a release hole, and the sacrificial layer is released in a corrosive gas to form the release cavity, thereby obtaining the aluminum nitride Lamb wave resonator.

[0029] In some embodiments, in steps S2, S4, S5 and S6, the depositing is performed by a magnetron sputtering process.

[0030] In some embodiments, in step S1, the etching is performed using a reactive ion etching process.

[0031] In some embodiments, the sacrificial layer material is silicon oxide; and the corrosive material is hydrofluoric acid gas.

[0032] The aluminum nitride Lamb wave resonator with an arc-shaped bus and the preparation method according to the embodiment of the present invention have at least one of the following advantages:

[0033] The invention provides an aluminum nitride Lamb wave resonator with an arc-shaped bus to improve the Q value, which effectively improves the quality factor by designing the bus area of ​​the top interdigital electrode into an arc shape and reasonably designing the depth and starting angle of the arc-shaped bus.

[0034] The aluminum nitride Lamb wave resonator with arc-shaped bus and improved Q value provided by the present invention provides an important direction for further realizing low-loss filters, high-sensitivity sensors and low-phase noise oscillators. Its high quality factor plays a key role in large-scale applications of radio frequency front ends. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] These and / or other aspects and advantages of the present invention will become apparent and readily understood from the following description of preferred embodiments in conjunction with the accompanying drawings, in which:

[0036] Figure 1 A three-dimensional structural diagram of an arc-shaped bus aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0037] Figure 2 A top view of the arc-shaped bus aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0038] Figure 3 A transverse cross-sectional view of the arc-shaped bus aluminum nitride Lamb wave resonator provided in Example 1 of the present invention;

[0039] Figure 4A three-dimensional structural diagram of a conventional rectangular bus aluminum nitride Lamb wave resonator provided in Example 4 of the present invention;

[0040] Figure 5 A top view of a conventional rectangular bus aluminum nitride Lamb wave resonator provided in Example 4 of the present invention;

[0041] Figure 6 A transverse cross-sectional view of a conventional rectangular bus aluminum nitride Lamb wave resonator provided in Example 4 of the present invention;

[0042] Figure 7 A schematic diagram of the structure after processing in step 1 of the preparation method provided in Example 1 of the present invention;

[0043] Figure 8 A schematic diagram of the structure after processing in step 2 of the preparation method provided in Example 1 of the present invention;

[0044] Fig. 9 A schematic diagram of the structure after processing in step 3 of the preparation method provided in Example 1 of the present invention;

[0045] Fig.10 A schematic diagram of the structure after processing in step 4 of the preparation method provided in Example 1 of the present invention;

[0046] Fig.11 A schematic diagram of the structure after processing in step 5 of the preparation method provided in Example 1 of the present invention;

[0047] Fig.12 A schematic diagram of the structure after processing in step 6 of the preparation method provided in Example 1 of the present invention;

[0048] Fig.13 A schematic diagram of the structure after processing in step 7 of the preparation method provided in Example 1 of the present invention;

[0049] Fig.14 A schematic diagram of the structure after processing in step 8 of the preparation method provided in Example 1 of the present invention;

[0050] Fig.15 Lamb wave vibration displacement diagram provided by Example 1 and Example 4 of the present invention;

[0051] Fig.16 The admittance diagram of the aluminum nitride Lamb wave resonator (starting angle is 160°) of the arc bus provided in Example 1 of the present invention;

[0052] Fig.17 The admittance diagram of the aluminum nitride Lamb wave resonator (starting angle is 150°) of the arc bus provided in Example 2 of the present invention;

[0053] Fig.18The admittance diagram of the aluminum nitride Lamb wave resonator (starting angle is 170°) of the arc bus provided in Example 3 of the present invention;

[0054] Fig.19 The admittance diagram of the aluminum nitride Lamb wave resonator (starting angle is 180°) of the conventional rectangular bus provided in Example 4 of the present invention;

[0055] In the figure: arc bus Lamb wave resonator 100, substrate 10, piezoelectric vibration structure 20, top interdigital electrode 30, bottom plate electrode 40, support shaft 50, release cavity 11, main body electrode 32, arc bus 31;

[0056] A conventional rectangular bus Lamb wave resonator 200 of a comparative example includes a substrate 210 , a piezoelectric structure 220 , a top interdigital electrode 230 , a bottom plate electrode 240 , a support shaft 250 , a release cavity 211 , a main electrode 232 , and a bus region 231 . DETAILED DESCRIPTION

[0057] The technical solution of the present invention is further specifically described below by examples and in conjunction with the accompanying drawings. In the specification, the same or similar reference numerals indicate the same or similar components. The following description of the embodiments of the present invention with reference to the accompanying drawings is intended to explain the overall inventive concept of the present invention and should not be construed as a limitation of the present invention.

[0058] It should be noted that the terms used in this application are generally terms commonly used by those skilled in the art. If there is any inconsistency with the commonly used terms, the terms in this application shall prevail.

[0059] In this article, the term "plasma etching" refers to placing gas in a high-frequency electric field to ionize gas molecules, generate electrons and ions, and form plasma. The generated plasma with strong chemical activity moves to the sample surface under the acceleration of the electric field, and not only chemically reacts to generate volatile gases on the sample surface, but also has a certain physical etching effect. Because the plasma source is separated from the RF acceleration source, the plasma density can be higher and the acceleration ability can be enhanced to obtain a higher etching rate and better anisotropic etching.

[0060] As used herein, the term "etching" refers to the process of selectively removing unwanted material from the surface of a substrate by chemical or physical methods.

[0061] In this article, the term "reactive ion etching" refers to the use of ion-induced chemical reactions to achieve anisotropic etching, that is, the use of ion energy to form an easily etched damaged layer on the surface of the etched layer and promote chemical reactions. At the same time, ions can also remove surface products to expose a clean etched surface.

[0062] In this article, the term "magnetron sputtering technology" refers to a method of bombarding a target material with high-energy particles, causing atoms in the target material to sputter out and deposit on the surface of a substrate to form a thin film.

[0063] In this article, the term "stripping" means that after the substrate is coated with photoresist, exposed and developed, the photoresist film with a certain pattern is used as a mask to evaporate the required metal with glue, and then the metal on the glue film is stripped off at the same time as the photoresist is removed, leaving only the metal with the original pattern on the substrate.

[0064] Herein, the term “patterning” refers to the generation of a nanoscale regular surface structure in at least one dimensional direction. Patterning can be achieved using a variety of techniques, such as photolithography, scanning probe-based micromachining, microcontact printing, and the like.

[0065] The following is a detailed description of the implementation of the present application.

[0066] Example 1

[0067] An aluminum nitride Lamb wave resonator 100 with an arc-shaped bus is provided. The aluminum nitride Lamb wave resonator 100 with an arc-shaped bus comprises:

[0068] A substrate 10, wherein a release cavity 11 is provided on an upper surface of the substrate 10;

[0069] A bottom plate electrode 40 is placed above the upper surface of the substrate 10 and located in the release cavity 11;

[0070] The piezoelectric vibration structure 20 is located on the surface of the bottom plate electrode 40;

[0071] The top interdigital electrode 30 is located on the surface of the piezoelectric vibration structure 20;

[0072] The support shaft 50 is located at both sides of the piezoelectric vibration structure 20 so that the piezoelectric vibration structure 20 , the bottom plate electrode 40 and the top interdigital electrode 30 are all suspended and fixed in the release cavity 11 .

[0073] The top interdigitated electrode 30 includes arc bus bars 31 on both sides and a plurality of main electrodes 32 in the middle of the arc bus bars 31. The width of the arc bus bars is 1.5 μm, and the starting angle or arc is 150°-180°. In the example shown in the figure, the arc is 160°. Figure 1 shown.

[0074] The thickness of the arc bus 31 is the same as the thickness of the main electrode 32 and is in the range of 100 nm to 200 nm.

[0075] The piezoelectric vibration structure 20 uses an aluminum nitride (AlN) single crystal film with a thickness of 1 μm; for example, a scandium-doped aluminum nitride film with a thickness of 500nm-1000nm and a scandium doping concentration of 10%-30%.

[0076] The thickness of the top interdigital electrode 30 and the bottom plate electrode 40 are the same, for example, the thickness of the top interdigital electrode and the bottom plate electrode are both 200 nm.

[0077] The top interdigitated electrode 30 is disposed on the upper surface of the piezoelectric vibration structure 20 and includes an arc bus 31, which is arc-shaped and has a starting angle of 160°. The top interdigitated electrode 30 also includes eight main electrodes 32 as the electrode main body. Figure 2 and Figure 3 As shown, the width of the main electrode 32 is 1 μm, and the interval between each main electrode 32 is 1 μm.

[0078] Embodiment 1 of the present invention provides a method for preparing an aluminum nitride Lamb wave resonator 100 having an arc-shaped bus. The arc-shaped bus is used to improve the Q value.

[0079] The preparation method comprises the following steps:

[0080] Step 1: A release cavity is etched on a high-resistance silicon wafer as a substrate 10 by using a reactive ion etching process, and then a SiO2 film is formed by using a wet thermal oxidation process, such as Figure 7 As shown, the structure includes a SiO2 film and a substrate 10 from top to bottom;

[0081] Step 2: depositing a silicon oxide layer as a sacrificial layer on the SiO2 layer by magnetron sputtering process, such as Figure 8 As shown;

[0082] Step 3: Fig. 9 As shown, the polysilicon outside the release cavity is first removed by dry etching, and then chemical mechanical polishing (CMP) is performed;

[0083] Step 4: deposit a layer of molybdenum by magnetron sputtering to form the bottom plate electrode 40. Fig.10 As shown;

[0084] Step 5: Deposit an aluminum nitride film with a scandium doping concentration of 20% by magnetron sputtering to form the piezoelectric vibration structure 20. Fig.11 As shown;

[0085] Step 6: deposit a molybdenum layer by magnetron sputtering, perform plasma etching on the molybdenum layer in sequence, and then perform patterning processes such as coating, exposure, development, etching and degumming to form a top interdigitated electrode structure 30, such as Fig.12 As shown, only the main electrode 32 is shown;

[0086] Step 7: Plasma etching is performed on the molybdenum / aluminum nitride film with a scandium doping concentration of, for example, 20% / molybdenum three-layer film to form release holes, such as Fig.13 As shown;

[0087] Step 8: Place the sacrificial layer in corrosive hydrofluoric acid gas to form the release cavity 11, and obtain the aluminum nitride Lamb wave resonator, such as Fig.14 shown.

[0088] Example 2

[0089] An aluminum nitride Lamb wave resonator with an arc-shaped bus is provided, wherein the width of the arc-shaped bus is 1.5 μm, the starting angle is 150°, and the remaining parameters are the same as those in Example 1.

[0090] Example 3

[0091] Example 3 provides an aluminum nitride Lamb wave resonator with an arc-shaped bus, wherein the width of the arc-shaped bus is 1.5 μm, the starting angle is 170°, and the remaining parameters are the same as those of Example 1.

[0092] Example 4 (Traditional rectangular bus structure)

[0093] Example 4 provides an aluminum nitride Lamb wave resonator with a conventional rectangular bus, wherein the width of the rectangular bus is 1.5 μm, the starting angle is 180°, and the remaining parameters are the same as those of Example 1.

[0094] Through the simulation analysis of COMSOL Multiphysics software, we get the following Fig.15 The Lamb wave vibration displacement diagram shown in Figure 16-19 The admittance diagram shown.

[0095] Fig.15 (a) is a displacement distribution diagram of the S0-type Lamb wave of the aluminum nitride Lamb wave resonator of the conventional rectangular bus provided in Example 4 when resonating, from Fig.15 In (a), it can be seen that there is an obvious displacement at the support shaft, indicating that part of the mechanical energy will be lost through the vibration of the support shaft; Fig.15 (b) is a displacement distribution diagram of the S0-type Lamb wave of the aluminum nitride Lamb wave resonator (starting angle is 160°) with an arc bus provided in Example 1 when resonating. Because the arc bus makes the energy more concentrated, Fig.15 It can be seen from (b) that the displacement at the support axis is significantly smaller than that in the aluminum nitride Lamb wave resonator of the traditional rectangular bus, which suppresses the loss and improves the Q value.

[0096] Fig.19The admittance diagram of the aluminum nitride Lamb wave resonator (starting angle is 180°) of the traditional rectangular bus provided in Example 4 is shown in FIG. Fig.19 It can be seen that the Q value of the aluminum nitride Lamb wave resonator of the traditional rectangular bus is low, which is 481, and the resonant frequency f s It is 1844MHz and there are some parasitic modes.

[0097] Figure 16-18 The admittance diagrams of the aluminum nitride Lamb wave resonators of the arc bus provided in Examples 1-3 are as follows: Fig.17 As shown in the figure, when the starting angle is 150°, the Q value of the arc-shaped bus aluminum nitride Lamb wave resonator operating at 2032MHz is 1036, which is 2.15 times higher than that of the traditional rectangular bus aluminum nitride Lamb wave resonator. Fig.18 As shown in the figure, when the starting angle is 170°, the Q value of the arc-shaped bus aluminum nitride Lamb wave resonator operating at 2032MHz is 1037, which is 2.156 times higher than that of the traditional rectangular bus aluminum nitride Lamb wave resonator. Fig.16 As shown in the figure, when the starting angle is 160°, the arc-shaped bus aluminum nitride Lamb wave resonator working at 2032MHz has the best loss suppression effect and the highest Q value of 1039, which is 2.16 times higher than that of the traditional rectangular bus aluminum nitride Lamb wave resonator. At the same time, the non-parallel arc-shaped bus makes it impossible to form standing waves in the lateral direction, suppressing the stray modes, such as Fig.16 , 17 As shown in , 18 and 19, it can be seen that compared with the aluminum nitride Lamb wave resonator with a traditional rectangular bus, the spectrum of the aluminum nitride Lamb wave resonator with an arc bus is smoother.

[0098] The aluminum nitride Lamb wave resonator with an arc-shaped bus and the preparation method according to the embodiment of the present invention have at least one of the following advantages:

[0099] The invention provides an aluminum nitride Lamb wave resonator with an arc-shaped bus to improve the Q value, which effectively improves the quality factor by designing the bus area of ​​the top interdigital electrode into an arc shape and reasonably designing the depth and starting angle of the arc-shaped bus.

[0100] The aluminum nitride Lamb wave resonator with arc-shaped bus and improved Q value provided by the present invention provides an important direction for further realizing low-loss filters, high-sensitivity sensors and low-phase noise oscillators. Its high quality factor plays a key role in large-scale applications of radio frequency front ends.

[0101] The above description is only a preferred example of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the subject matter and principles of the present application shall be included in the protection scope of the present application.

Claims

1. An aluminum nitride Lamb wave resonator with an arc bus, characterized in that: The aluminum nitride Lamb wave resonator with an arc bus comprises: A substrate, wherein a release cavity is disposed on an upper surface of the substrate; a bottom plate electrode disposed above the upper surface of the substrate and within the release cavity; A piezoelectric vibration structure is located on the surface of the bottom plate electrode; a top interdigitated electrode, located on the surface of the piezoelectric vibrating structure; The supporting shaft is located at both sides of the piezoelectric vibration structure so that the piezoelectric vibration structure, the bottom plate electrode and the top interdigital electrode are all suspended and fixed in the release cavity.

2. The aluminum nitride Lamb wave resonator according to claim 1, characterized in that: The top interdigitated electrode includes arc-shaped buses located on both sides and a plurality of main body electrodes located in the middle of the arc-shaped buses.

3. The aluminum nitride Lamb wave resonator according to claim 2, characterized in that: The arc angle of the arc bus is 150°-180°.

4. The aluminum nitride Lamb wave resonator according to claim 3, characterized in that: The thickness of the arc bus is the same as the thickness of the main electrode and is 100nm-200nm.

5. The aluminum nitride Lamb wave resonator according to any one of claims 1 to 4, characterized in that: The piezoelectric vibration structure adopts a scandium-doped aluminum nitride film; the thickness of the scandium-doped aluminum nitride film is 500nm-1000nm.

6. The aluminum nitride Lamb wave resonator according to claim 5, characterized in that: The scandium doping concentration of the scandium-doped aluminum nitride film is 10%-30%; The top interdigital electrode and the bottom flat electrode have the same thickness, and the thickness is 100nm-200nm, and the selected material is molybdenum; The material of the substrate is silicon.

7. A method for preparing an aluminum nitride Lamb wave resonator according to any one of claims 1 to 6, characterized in that: The steps include: S1 etches a release cavity on a high-resistance silicon wafer as a substrate, and then forms a SiO2 film using a wet thermal oxidation process; S2 deposits a polysilicon layer on the SiO2 layer as a sacrificial layer; S3 removes the polysilicon outside the release cavity by dry etching and performs chemical mechanical polishing; S4 deposits a layer of molybdenum to form the bottom plate electrode; S5 deposits an aluminum nitride film to form the piezoelectric vibration structure; S6: depositing a molybdenum layer, sequentially performing plasma etching on the molybdenum layer, and then performing patterning to form a top interdigital electrode; S7: plasma etching is performed on the molybdenum / aluminum nitride / molybdenum three-layer film to form a release hole, and the sacrificial layer is released in a corrosive gas to form the release cavity, thereby obtaining the aluminum nitride Lamb wave resonator.

8. The preparation method according to claim 7, characterized in that: In steps S2, S4, S5 and S6, the deposition is performed by a magnetron sputtering process.

9. The preparation method according to claim 7, characterized in that: In step S1, the etching is performed by using a reactive ion etching process.

10. The preparation method according to claim 7, characterized in that: The sacrificial layer material is silicon oxide; the corrosive material is hydrofluoric acid gas.

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