High performance thin film bulk acoustic resonator and method of making same

Abstract

This invention discloses a high-performance thin-film bulk acoustic resonator and its fabrication method, belonging to the field of third-generation semiconductor technology and radio frequency front-end devices. From bottom to top, it includes a substrate, a support layer, a bottom electrode, a piezoelectric layer, and a top electrode. A cavity is formed on the substrate, and a boundary ring is formed on the piezoelectric layer. The center of the top electrode contacts the piezoelectric layer, and its edge is positioned on a second-order step of the boundary ring. The first-order step is a piezoelectric material layer in contact with the piezoelectric layer, and the second-order step consists of alternating layers of metal material and silicon dioxide disposed on the first-order step. This invention introduces piezoelectric material into the boundary ring, exciting a Lamb wave at the boundary that has a phase opposite to that of the active region's piezoelectric material, thereby achieving phase cancellation of the Lamb wave and suppressing energy leakage. Furthermore, targeting the intrinsic spurious modes of the piezoelectric material, a multi-layer acoustic impedance-matched boundary ring structure is constructed to form a leakage path for spurious modes, thus improving the out-of-band suppression capability of the filter.

Description

Technical Field

[0001] This invention relates to a high-performance thin-film bulk acoustic resonator and its fabrication method, belonging to the field of third-generation semiconductor technology and radio frequency front-end devices. Background Technology

[0002] As wireless communication technology continues to evolve towards 6G, communication spectrum resources are becoming increasingly scarce, especially in the 2 GHz to 5 GHz range. The spectrum of major mobile communication operators and public communication bands is highly concentrated, making the contradiction of mutual interference between signals increasingly prominent. To effectively suppress adjacent channel interference and improve communication quality and spectrum utilization efficiency, more stringent requirements are placed on the out-of-band rejection performance of RF filters. Against this backdrop, thin-film bulk acoustic resonators (FBARs), with their significant advantages such as miniaturization, low insertion loss, high out-of-band rejection, and high power capacity, are gradually becoming one of the important directions for the development of high-performance RF filters and are showing broad application prospects.

[0003] AlN (aluminum nitride)-based materials commonly used in thin-film bulk acoustic resonators are typical type II dispersive piezoelectric materials. This results in the generation of longitudinal acoustic waves (TE modes) and transverse acoustic waves (A0, S0 waves, etc.) when excited by an electric field. The transverse acoustic waves propagate beyond the active region of the resonator with its vibrations, causing acoustic energy leakage, which is one of the main factors leading to a decrease in the resonator's quality factor (Q). Currently developed high-acoustic-impedance edge-pattern boundary rings with grooved and protruding electrode edges utilize acoustic impedance mismatch to reflect the leakage of transverse acoustic waves back into the active region, thereby improving the resonator's quality factor (Q). However, this structure introduces additional parasitic modes unique to boundary rings, leading to an increase in the resonator's stray modes. This creates a significant contradiction between the high quality factor and the compatibility of stray modes. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a high-performance thin-film bulk acoustic resonator and its fabrication method, which has a high quality factor and low stray modes.

[0005] The technical solution adopted by this invention to solve its technical problem is: In a first aspect, this application provides a high-performance thin-film bulk acoustic resonator, which includes, from bottom to top, a substrate, a support layer, a bottom electrode, a piezoelectric layer, and a top electrode. A cavity is provided on the substrate, and a boundary ring is provided on the piezoelectric layer. The middle part of the top electrode is in contact with the piezoelectric layer, and its edge is disposed on the boundary ring. The boundary ring includes a two-stage step, the first stage being a piezoelectric material layer in contact with the piezoelectric layer, and the second stage being a metal material layer and a silicon dioxide layer disposed on the first stage and alternately distributed inside and outside.

[0006] The high-performance thin-film bulk acoustic resonator provided in this application can effectively control the phase of transverse acoustic waves, reduce transverse energy leakage of the device, and construct a leakage path for stray modes through a multilayer boundary ring structure, suppressing parasitic vibrations and transverse acoustic wave leakage, thereby improving the quality factor of the resonator. This technology provides technical assurance for effectively enhancing RF chips to prevent interference from signals of similar frequencies.

[0007] Furthermore, the material of the piezoelectric material layer is AlN or Sc. x Al 1-x N, Al x Si 1-x One of N, LiNbO3, and LiTaO3.

[0008] Furthermore, the material of the metal layer is one of gold, molybdenum, and tungsten.

[0009] Furthermore, the width of the second step is smaller than the width of the first step, and the outer edge of the second step is aligned with the outer edge of the first step.

[0010] Furthermore, the second-level step, from the outside in, consists of the silicon dioxide layer, the metal material layer, the silicon dioxide layer, and the metal material layer.

[0011] Furthermore, the material of the bottom electrode is selected from at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium; the material of the top electrode is selected from at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium.

[0012] Furthermore, the material of the piezoelectric layer is selected from AlN, Sc x Al 1-x N, Al x Si 1-x At least one of N.

[0013] Secondly, this application provides a method for fabricating a high-performance thin-film bulk acoustic resonator, the steps of which include: Depressions are etched into the substrate; After filling the depression with sacrificial layer material and polishing it smooth, a support layer is grown. A patterned bottom electrode and a piezoelectric layer are sequentially grown on the support layer using photolithography. A boundary ring is created on the piezoelectric layer using nanoimprint technology. The boundary ring includes a two-stage step, where the first stage is a piezoelectric material layer in contact with the piezoelectric layer, and the second stage is a metal material layer and a silicon dioxide layer disposed on the first stage and alternately distributed inside and outside. A top electrode is grown on the piezoelectric layer; the middle part of the top electrode is in contact with the piezoelectric layer, and the edge is on the boundary ring; The sacrificial layer material is released to form a cavity.

[0014] This method can effectively improve the quality factor of resonators and suppress stray modes. It achieves precise growth and patterning of boundary rings of various materials through nanoimprint technology, and realizes high-precision thin film dispersion control.

[0015] Furthermore, the sacrificial layer material is at least one of amorphous silicon, SiO2, and Si3N4, and its filling thickness is 0.5 μm to 4 μm; the support layer thickness is 0.05 μm to 3 μm, and the material is at least one of Si3N4 and SiC; the sacrificial layer material is different from the support layer material.

[0016] Furthermore, the step of releasing the sacrificial layer material to form a cavity includes dry etching using halide gas and wet etching using halide liquid.

[0017] The beneficial effects of this invention are as follows: By introducing piezoelectric material into the boundary ring, a Lamb wave with the opposite phase to the active region piezoelectric material is excited at the boundary, thereby achieving phase cancellation of the Lamb wave and suppressing the leakage of its carried energy. Furthermore, a multi-layer acoustic impedance matching boundary ring structure is constructed to target the intrinsic stray modes of the piezoelectric material, forming a leakage path for the stray modes, thereby improving the out-of-band suppression capability of the filter.

[0018] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing the application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of a high-performance thin-film bulk acoustic resonator provided in an embodiment of this application.

[0020] Figure 2 This is a schematic flowchart of a method for fabricating a high-performance thin-film bulk acoustic resonator provided in an embodiment of this application.

[0021] Figure 3 This is a schematic diagram of the axial cross-section structure of the boundary ring.

[0022] Figure 4 This is the Q-value curve of the resonator in Comparative Example 1.

[0023] Figure 5 The S-parameter curves of the filter constructed using the Comparative 1 resonator are shown.

[0024] Figure 6 The image shows the Q-value curve of the resonator in Example 1.

[0025] Figure 7 The S-parameter curves of the filter constructed using the resonator of Example 1 are shown.

[0026] Reference numerals: 101, substrate; 102, cavity; 112, recess; 103, support layer; 104, bottom electrode; 105, piezoelectric layer; 106, top electrode; 107, boundary ring; 108, sacrificial layer; 201, piezoelectric material layer; 202, metallic material layer; 203, silicon dioxide layer. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0028] The following disclosure provides many different embodiments or examples for implementing different structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. Of course, these are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples; such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed.

[0029] Reference Figure 1 and Figure 3 This application provides a high-performance thin-film bulk acoustic resonator, which includes, from bottom to top, a substrate 101, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, and a top electrode 106. A cavity 102 is provided on the substrate 101 (the top of the substrate 101 is recessed and surrounds the cavity 102 with the bottom surface of the support layer 103). A boundary ring 107 is provided on the piezoelectric layer 105. The middle part of the top electrode 106 is in contact with the piezoelectric layer 105, and the edge is provided on the boundary ring 107. The boundary ring 107 includes two steps. The first step is a piezoelectric material layer 201 in contact with the piezoelectric layer 105, and the second step is a metal material layer 202 and a silicon dioxide layer 203 disposed on the first step and alternately distributed inside and outside.

[0030] Specifically, the top-view shape of the resonator (especially the shape of the boundary ring) can be circular, rectangular, pentagonal, etc. "Alternating distribution inside and outside" means that both the metal material layer 202 and the silicon dioxide layer 203 are ring-shaped (circular ring, rectangular ring, pentagonal ring, etc.) and are concentric rings on the same plane, distributed in this form from the inside out: one ring of metal material layer 202, one ring of silicon dioxide layer 203, one ring of metal material layer 202, one ring of silicon dioxide layer 203, and so on.

[0031] Accordingly, refer to Figure 2 This application provides a method for fabricating a high-performance thin-film bulk acoustic resonator, the steps of which include: S1: A recess 112 is etched into the substrate 101.

[0032] S2: After filling the recess 112 with sacrificial layer material and polishing it flat, the support layer 103 is grown.

[0033] S3: Patterned bottom electrode 104 and piezoelectric layer 105 are sequentially grown on support layer 103 using photolithography.

[0034] S4: A boundary ring 107 is formed on the piezoelectric layer 105 using nanoimprint technology. The boundary ring 107 includes a two-stage step. The first stage is a piezoelectric material layer 201 in contact with the piezoelectric layer 105. The second stage is a metal material layer 202 and a silicon dioxide layer 203 disposed on the first stage and alternately distributed inside and outside.

[0035] S5: A top electrode 106 is grown on the piezoelectric layer 105; the middle part of the top electrode 106 is in contact with the piezoelectric layer 105, and the edge is on the boundary ring 107.

[0036] S6: Release the sacrificial layer material to form cavity 102.

[0037] Typically, boundary rings are fabricated using dry etching, which introduces extra elements, leading to a decrease in the electrical performance of the electrodes. Furthermore, the high etching rate results in poor boundary ring morphology, which excites Lamb waves of different frequencies, causing significant parasitic vibrations. Nanoimprinting technology can effectively obtain highly controllable boundary ring structures, thereby suppressing parasitic vibrations. In addition, nanoimprinting growth technology reduces the increase in film defect density during patterned boundary ring fabrication, which is beneficial for improving the thermal conductivity and power capacity of the resonator.

[0038] Step S6 can be performed by etching the surface of the top electrode 106 down to the sacrificial layer material, or by creating a release hole on the side to expose the sacrificial layer material. The latter is preferred, as the sacrificial layer release is not in the active region, and even if dry etching is used to remove the sacrificial layer material, it will not affect the performance of the device structure.

[0039] Preferably, step S4 utilizes nanoimprinting technology to obtain a patterned boundary ring seed layer on the piezoelectric layer and grows the boundary ring structure along the seed layer. Specifically, the seed layer is grown by exposing only specific regions through nanoimprinting, and subsequent film growth only occurs along the adsorption of the seed layer. This allows for selective growth of various materials through multiple nanoimprinting processes. Films grown on the basis of nanoimprinted seed layers do not introduce additional elements that affect the quality of the film.

[0040] Furthermore, the nanoimprint growth technology allows for the selection of various material structures for the boundary ring structure. By adjusting the material properties and thickness, high-precision dispersion control can be achieved, thereby suppressing stray modes and improving the quality factor Q of the resonator.

[0041] This invention reduces transverse acoustic leakage in thin-film bulk acoustic resonators, avoids electrode performance loss caused by traditional dry etching, provides a high-quality factor resonator structure, constructs a spurious mode-guided leakage channel, and thereby improves the in-band insertion loss, out-of-band rejection, and power capacity of thin-film bulk acoustic filters.

[0042] Preferably, a protective layer may also be grown on the top electrode.

[0043] The piezoelectric material layer 201 is made of AlN and Sc. x Al 1-x N, Al x Si 1-x One of N, LiNbO3, and LiTaO3. The metal material layer 202 is made of one of gold, molybdenum, and tungsten. The bottom electrode 104 is made of at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium; the top electrode 106 is made of at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium. The piezoelectric layer 105 is made of AlN, Sc x Al 1-x N, Al x Si 1-x At least one of N. The sacrificial layer material is at least one of amorphous silicon, SiO2, and Si3N4, with a filling thickness of 0.5 μm to 4 μm; the support layer 103 has a thickness of 0.05 μm to 3 μm and is made of at least one of Si3N4 and SiC. When fabricating the same resonator, the sacrificial layer material and the support layer material are different. For example, the sacrificial layer is SiO2 or Si3N4, and the support layer is SiC; the sacrificial layer is amorphous silicon, and the support layer is Si3N4.

[0044] Example 1 according to Figure 1The resonator structure includes a silicon substrate 101, a cavity 102, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, a top electrode 106, and a boundary ring 107. The width (radial) of the second-level step is smaller than the width of the first-level step, and the outer edge of the second-level step is aligned with the outer edge of the first-level step. From the outside in, the second-level step consists of a silicon dioxide layer 203, a metal material layer 202, another silicon dioxide layer 203, and another metal material layer 202. The bottom electrode and the top electrode are both 500 nm thick, and the piezoelectric layer is 1 μm thick.

[0045] The production steps are as follows: (1) A (111) Si wafer was selected as substrate 101. The substrate was cleaned and dried using acetone and hydrofluoric acid. A 3 μm deep depression was prepared on the surface of the silicon substrate using plasma etching.

[0046] (2) A sacrificial layer 108 was grown by PVD. The material was amorphous silicon and the thickness of the sacrificial layer was 3.1 μm. The sacrificial layer was then polished and a support layer 103 was grown by plasma-enhanced CVD. The material was Si3N4 and the thickness was 50 nm.

[0047] (3) A 500 nm thick layer of metal Mo is deposited on the surface of the sacrificial layer as the bottom electrode 104 using PVD. A piezoelectric layer 105 is grown on the metal Mo using PVD. The material is AlN and the thickness is 1 μm.

[0048] (4) Boundary rings 107 are patterned and grown on the surface of piezoelectric layer 105 using nanoimprinting, as shown in the figure. Figure 3 The boundary ring includes a two-stage step. The first stage is a piezoelectric material layer in contact with the piezoelectric layer, and the second stage consists of alternating layers of metal material and silicon dioxide disposed on the first stage. The piezoelectric material layer 201 is made of AlScN, and the metal material layer 202 is made of tungsten.

[0049] (5) A 500 nm thick layer of metallic Mo was deposited on the surface of the piezoelectric layer using PVD as the top electrode 106.

[0050] (6) The sacrificial layer material is removed by dry etching. Specifically, the sacrificial layer 108 is released in gaseous hydrogen fluoride and the sacrificial layer material is removed by dry etching, thereby preparing a resonator.

[0051] Comparative Example 1 Steps (1) to (3) and (6) are exactly the same as in Example 1.

[0052] The difference from Example 1 is that (4) and (5) are changed to: Mo is grown on the piezoelectric layer and dry etched into a ring-shaped stepped structure with a central depression, that is, the shape is the same as the solid of the top electrode 106 plus the boundary ring 107 in Example 1, but it is made of only molybdenum.

[0053] The performance of the resonators in Example 1 and Comparative Example 1 was tested, and the Q-value curve of the resonator in Comparative Example 1 is shown in the figure. Figure 4 The S-parameter curves of the filter constructed using the resonator of Comparative Example 1 are shown in the figure. Figure 5 The Q-value curve of the resonator in Example 1 is shown below. Figure 6 The S-parameter curves of the filter constructed using the resonator of Example 1 are shown in Figure 1. Figure 7 . Figure 4 and Figure 6 In the diagram, the horizontal axis represents frequency, and the vertical axis represents Q value (a concept in the field of resonators, center frequency / bandwidth). Figure 5 and Figure 7 In the diagram, the horizontal axis represents frequency, and the vertical axis represents S-parameters (a concept in the field of resonators, specifically scattering parameters).

[0054] The resonator in Comparative Example 1 can only reach a maximum Q value of 2652, while the resonator using the embodiment of this application can reach a Q value of 3975. Furthermore, the filter prepared in Example 1 shows a significantly smaller in-band ripple compared to Comparative Example 1, with a marked improvement in smoothness, demonstrating that the structure of this invention significantly improves the Q value of the resonator and the suppression of spurious modes. The boundary ring structure provided by this invention does not introduce additional elements during its construction process, improving the power capacity and performance of the resonator, constructing a leakage path for spurious modes, and effectively improving the smoothness of the left side of the filter passband (the portion above -3dB in the S-parameter curve), thereby ensuring the smoothness of the filter passband.

[0055] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A high-performance thin-film bulk acoustic resonator, comprising, from bottom to top, a substrate (101), a support layer (103), a bottom electrode (104), a piezoelectric layer (105), and a top electrode (106), wherein a cavity (102) is provided on the substrate (101), characterized in that, A boundary ring (107) is provided on the piezoelectric layer (105); the middle part of the top electrode (106) is in contact with the piezoelectric layer (105), and the edge is provided on the boundary ring (107); the boundary ring (107) includes two steps, the first step is a piezoelectric material layer (201) in contact with the piezoelectric layer (105), and the second step is a metal material layer (202) and a silicon dioxide layer (203) disposed on the first step and alternately distributed inside and outside.

2. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The piezoelectric material layer (201) is made of AlN or Sc. x Al 1-x N, Al x Si 1-x One of N, LiNbO3, and LiTaO3.

3. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The metal material layer (202) is made of one of gold, molybdenum, or tungsten.

4. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The width of the second step is smaller than the width of the first step, and the outer edge of the second step is aligned with the outer edge of the first step.

5. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The second-level step, from the outside to the inside, consists of the silicon dioxide layer (203), the metal material layer (202), the silicon dioxide layer (203), and the metal material layer (202).

6. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The material of the bottom electrode (104) is selected from at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium; the material of the top electrode (106) is selected from at least one of gold, silver, ruthenium, tungsten, molybdenum, iridium, aluminum, platinum, niobium, and hafnium.

7. The high-performance thin-film bulk acoustic resonator according to claim 1, characterized in that, The material of the piezoelectric layer (105) is selected from AlN, Sc x Al 1-x N, Al x Si 1-x At least one of N.

8. A method for fabricating a high-performance thin-film bulk acoustic resonator, characterized in that the steps include... include: A recess (112) is etched on the substrate (101). After the sacrificial layer material is filled into the recess (112) and polished flat, a support layer (103) is grown. A patterned bottom electrode (104) and a piezoelectric layer (105) are sequentially grown on the support layer (103) using photolithography. A boundary ring (107) is formed on the piezoelectric layer (105) using nanoimprint technology. The boundary ring (107) includes two steps. The first step is a piezoelectric material layer (201) in contact with the piezoelectric layer (105). The second step is a metal material layer (202) and a silicon dioxide layer (203) disposed on the first step and alternately distributed inside and outside. A top electrode (106) is grown on the piezoelectric layer (105); the middle part of the top electrode (106) is in contact with the piezoelectric layer (105), and the edge is on the boundary ring (107); The sacrificial layer material is released to form a cavity (102).

9. The method for fabricating a high-performance thin-film bulk acoustic resonator according to claim 8, characterized in that, The sacrificial layer material is at least one of amorphous silicon, SiO2 and Si3N4, and its filling thickness is 0.5 μm to 4 μm; the support layer (103) has a thickness of 0.05 μm to 3 μm and is made of at least one of Si3N4 and SiC; the sacrificial layer material is different from the support layer material.

10. The method for fabricating a high-performance thin-film bulk acoustic resonator according to claim 9, characterized in that, The step of releasing the sacrificial layer material to form a cavity (102) includes dry etching using a halide gas and wet etching using a halide liquid.

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