Bulk acoustic wave resonator and method of manufacturing the same

Abstract

The application relates to a bulk wave resonator in the technical field of semiconductors, which comprises a substrate, a piezoelectric layer, a bottom electrode and a top electrode; the piezoelectric layer comprises a support part, a resonant part and a transverse wave blocking area between the support part and the resonant part, the piezoelectric layer is fixedly supported on the substrate through the support part, a bulk wave reflection structure is arranged between the resonant part and the substrate, and the top electrode and the bottom electrode are arranged on the upper surface and the lower surface of the resonant part respectively; the area edge of the top electrode does not exceed the area edge of the bottom electrode, and the width b of the transverse wave blocking area ranges from 0.5 lambda to 10 lambda, wherein lambda is the bulk wave wavelength; the characteristic frequency and the effective electromechanical coupling coefficient of the bulk wave resonator are adjusted by changing the width of the electrode strip, and the process difficulty is greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and more specifically, to a bulk wave resonator and its fabrication method. Background Technology

[0002] A thin-film bulk acoustic resonator (FBAR) is a device that, unlike traditional filters, is fabricated using a silicon substrate and employing MEMS and thin-film technologies. It is used in wireless transceivers to achieve functions such as image cancellation, parasitic filtering, and channel selection, and features a high Q value and ease of miniaturization.

[0003] In the prior art, the performance of the device or the frequency is often improved by changing the longitudinal dimension. For example, CN109889178A discloses a bulk wave resonator, which includes a substrate, an acoustic mirror structure, a lower electrode, a piezoelectric thin film structure and an upper electrode arranged from bottom to top. The upper and / or lower surfaces of the upper electrode and / or the lower electrode have auxiliary structures, which have protrusions or depressions in a direction perpendicular to the surface of the upper electrode.

[0004] However, as is well known to those skilled in the art, vertical dimensions require multiple coating, photolithography and etching processes. In particular, the consistency of film thickness is much higher in the FBAR field than in integrated circuits, making the process complex and difficult. In addition, the selectivity between layers must be considered, which undoubtedly increases the design and process difficulty significantly. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this invention is to provide a bulk wave resonator and its fabrication method.

[0006] According to the present invention, a bulk wave resonator includes a substrate, a piezoelectric layer, a bottom electrode, and a top electrode. The piezoelectric layer includes a support portion, a resonant portion, and a transverse wave blocking region located between the support portion and the resonant portion. The piezoelectric layer is fixedly supported on the substrate by the support portion. A bulk wave reflection structure is provided between the resonant portion and the substrate. The top electrode and the bottom electrode are respectively disposed on the upper and lower surfaces opposite to the resonant portion. The edge of the top electrode region does not extend beyond the edge of the bottom electrode region. The width b of the transverse wave blocking region is in the range of 0.5λ≤b≤10λ, where λ is the bulk wave wavelength.

[0007] In some embodiments, the distance 'a' between the edge of the top electrode region and the edge of the bottom electrode region is in the range of: 1 / 16λ ≤ a ≤ 3 / 16λ.

[0008] In some embodiments, the bulk wave reflection structure is a Bragg reflector, which is embedded in the substrate, and the edge of the bottom electrode region does not extend beyond the edge of the Bragg reflector region.

[0009] In some embodiments, the bulk wave reflection structure is a cavity, which is formed by a predetermined distance between the lower surface of the resonant portion and the upper surface of the substrate, or the cavity is formed by a groove structure extending a predetermined distance from the upper surface of the substrate to the lower surface.

[0010] In some embodiments, the top electrode includes a busbar and an electrode bar. Multiple electrode bars are connected in parallel to the same side of a busbar to form a single-sided open interdigitated electrode, or multiple electrode bars are connected in parallel between two busbars to form a V-shaped electrode. The characteristic frequency is fine-tuned by adjusting the width of the electrode bars.

[0011] In some embodiments, the busbar is a straight strip or a non-straight strip.

[0012] In some embodiments, the electrode width of the electrode strip is in the range of: 1 / 8λ≤d≤3 / 8λ.

[0013] In some embodiments, when the top electrode is a single-sided open interdigitated electrode, there are two sets of interdigitated electrodes, which are respectively referred to as the first interdigitated electrode and the second interdigitated electrode. The electrode strips of the first interdigitated electrode and the second interdigitated electrode are arranged alternately, and there is a potential difference between the first interdigitated electrode and the second interdigitated electrode.

[0014] In some embodiments, when one set of the first interdigital electrode and the second interdigital electrode is used for grounding and the other set is used for radio frequency signals, the bottom electrode is either suspended, connected to radio frequency signals, or not formed as the bottom electrode.

[0015] The present invention also provides a method for fabricating a bulk wave resonator, comprising the following steps:

[0016] S1, Substrate cleaning: The substrate is made of silicon material and is cleaned using a mixture of sulfuric acid and hydrogen peroxide or a mixture of ammonia and hydrogen peroxide.

[0017] S2, Sacrificial layer growth and patterning: The sacrificial layer is made of PSG material. The SiO2 layer and the PSG layer are grown sequentially on the substrate using PECVD process. Then, the patterned sacrificial layer is obtained by sequentially using photolithography → dry etching → dry and / or wet deintercalation process.

[0018] S3, Bottom electrode fabrication: The bottom electrode is a single-layer or multi-layer electrode structure, and the growth and patterning of the bottom electrode is completed by PVD → photolithography → dry etching → dry and / or wet resist removal.

[0019] S4, Piezoelectric layer preparation: The material of the piezoelectric layer is AlN, AlScN or PZT, and the piezoelectric layer is grown by PVD process;

[0020] S5, Top electrode fabrication: The top electrode is a single-layer or multi-layer electrode structure, and the growth and patterning of the top electrode is completed by PVD → photolithography → dry etching → dry and / or wet resist removal.

[0021] S6, Cavity Release: The PSG / SiO2 inside the cavity is removed by using a HF solution with a certain ratio.

[0022] In some embodiments, the bottom electrode is made of one or more of Mo, Ag, Au, Cu, Ti, Al, Ru, or Pt, and the top electrode is made of one or more of Mo, Ag, Au, Cu, Ti, Al, Ru, or Pt.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. This invention improves the Q value of the device by blocking transverse waves propagating in the horizontal direction from escaping into the substrate through the transverse wave blocking region and by the reflection effect of the bulk wave reflecting structure. More importantly, by changing the width of the electrode strip, the characteristic frequency and effective electromechanical coupling coefficient of the bulk wave resonator can be adjusted. Compared with the existing technology that improves the performance or frequency of the device by changing the longitudinal dimension, which requires multiple coating, photolithography and etching processes and is therefore complex and difficult, this invention greatly simplifies the process and reduces the difficulty of the process by adjusting the transverse dimension of the electrode strip.

[0025] 2. This invention improves device performance and frequency adjustment by optimizing the structural layout of the top electrode and changing the electrode connection method, thereby increasing the design freedom of the device. Attached Figure Description

[0026] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0027] Figure 1 This is a schematic diagram of the overall structure of one embodiment of the present invention;

[0028] Figure 2 This is a schematic diagram of the cavity structure formed on the substrate according to the present invention;

[0029] Figure 3 This is a schematic diagram of the structure of the present invention, which is a Bragg reflector for reflecting bulk waves.

[0030] Figure 4 is a schematic diagram of the mounting and arrangement structure when the top electrode of the present invention is an interdigital electrode;

[0031] Figure 5 is a schematic structural diagram when the top electrode of the present invention is an interdigital electrode;

[0032] Figure 6 is a schematic structural diagram when the top electrode of the present invention is a grid-shaped electrode;

[0033] Figure 7 is a schematic diagram of a non-linear structure of the bus bar in the top electrode of the present invention;

[0034] Figure 8 is a schematic structural diagram of two groups of interdigital electrodes arranged in a staggered manner according to the present invention;

[0035] Figure 9 is a schematic structural diagram of a suspended bottom electrode when two groups of interdigital electrodes are arranged in a staggered manner according to the present invention;

[0036] Figure 10 is a schematic structural diagram without a bottom electrode when two groups of interdigital electrodes are arranged in a staggered manner according to the present invention;

[0037] Figure 11 is a flow chart of the manufacturing method of the bulk acoustic wave resonator of the present invention. DETAILED DESCRIPTION

[0038] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those skilled in the art, several variations and modifications can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0039] Embodiment 1

[0040] The present invention provides a bulk acoustic wave resonator, as shown in Figure 1-11As shown, the structure includes a substrate 100, a piezoelectric layer 300, a bottom electrode 400, and a top electrode 500. The piezoelectric layer 300 is connected to the substrate 100 and includes a support portion 310, a resonant portion 320, and a transverse wave blocking region 330 located between the support portion 310 and the resonant portion 320. The resonant portion 320 is located in the innermost layer of the piezoelectric layer 300 and occupies a large portion of the area. The transverse wave blocking region 330 surrounds the resonant portion 320, and the support portion 310 surrounds the transverse wave blocking region 330. All three are integrally formed. The support portion 310 is fixed to the substrate 100 and supports the entire piezoelectric layer 300. A bulk wave reflecting structure 200 is provided between the piezoelectric layer 300 and the substrate 100. The bulk wave reflecting structure 200 is either a Bragg mirror 210 embedded in the substrate 100 or a cavity 220 of a cavity structure located between the piezoelectric layer 300 and the substrate 100. When the bulk wave reflecting structure 200 is a Bragg reflector 210, preferably, the Bragg reflector 210 is composed of at least two sets of films with alternating high acoustic impedance to improve the reflection effect of sheared bulk waves. When the bulk wave reflecting structure 200 is a cavity 220, the cavity 220 can be formed by a piezoelectric layer 300 with an overall bridge-shaped structure and a flat substrate 100. In this case, the main body of the cavity 220 is located below the resonant part 320. Alternatively, the cavity 220 can also be formed by directly opening a groove structure on the substrate 100, and then covering the substrate 100 with a basically flat piezoelectric layer 300. In this case, the main body of the cavity 220 is still located below the resonant part 320.

[0041] The bottom electrode 400 and the top electrode 500 are respectively disposed on the lower end face and the upper end face of the piezoelectric layer 300. Specifically, the bottom electrode 400 and the top electrode 500 are disposed on the lower end face and the upper end face of the resonance portion 320. When the bottom electrode 400 and the top electrode 500 are grounded, connected to a signal source or connected to an external circuit, the connection is implemented through connection portions 600 respectively connected thereto, and the connection portions connected to the bottom electrode 400 and the top electrode 500 are respectively denoted as a first connection portion 610 and a second connection portion 620. The top electrode 500 is an interdigital electrode, which is composed of bus bars 501 and electrode strips 502. There are mainly two structural forms of the formed top electrode 500: one is a comb-shaped interdigital electrode, which is formed by connecting a plurality of electrode strips 502 at intervals in parallel to the same side of one bus bar 501; the other is an electrode with a grid-like structure, which is formed by connecting a plurality of electrode strips 502 at intervals in parallel between two bus bars 501. The bus bar 501 constituting the top electrode 500 may be a linear strip or a non-linear strip. For example, it may be a folded-lined type, or a structure formed by a straight line segment plus an arc line segment, which excites shear bulk waves together with the bottom electrode 400. The center distance between adjacent electrode strips 502 of the top electrode 500 is 0.5λ, and the width of the electrode strip 502 ranges from 1 / 8λ to 3 / 8λ, where λ is the wavelength of the shear bulk wave excited after the resonator receives an external electrical signal, and is positively correlated with the total thickness of the piezoelectric layer and the electrodes (the top electrode and the bottom electrode). Changing the electrode width of the electrode strip 502 is equivalent to changing the mass load on the upper part of the resonance portion 320, further changing the sound velocity, and finally adjusting the characteristic frequency and effective electromechanical coupling coefficient of the bulk acoustic wave resonator.

[0042] After the bottom electrode 400 and the top electrode 500 are disposed on the opposite lower end face and upper end face of the resonance portion 320, the area edge of the top electrode 500 is located within the area edge of the bottom electrode 400, that is, in a front projection view along the vertical direction, the top electrode 500 is completely projected within the bottom electrode 400. Preferably, the distance between the area edge of the top electrode 500 and the area edge of the bottom electrode 400 is a, and the value range of a is 1 / 16λ ≤ a ≤ 3 / 16λ. A transverse wave blocking region 330 is defined between the area edge of the bottom electrode 400 and the area edge of the support portion 310, and the width of the transverse wave blocking region 330 is b. Preferably, the value range of b is 0.5λ ≤ b ≤ 10λ. Since the region from the area edge of the bottom electrode 400 to the edge of the resonance portion 320 has neither the bottom electrode 400 nor the top electrode 500, no shear bulk wave is excited therein, so that the transverse wave blocking region 330 can block transverse waves propagating in the horizontal direction from escaping and leaking into the substrate 100, thereby increasing the Q value of the device.

[0043] The bulk resonator provided in this application has a bottom electrode 400 grounded through a first connection portion 610 and a top electrode 500 connected to a radio frequency signal through a second connection portion 620. A potential difference is generated between the top electrode 500 connected to the radio frequency signal and the grounded bottom electrode 400, which excites the resonant portion 320 to form a sheared bulk wave. The transverse wave blocking region 330 blocks the transverse wave propagating in the horizontal direction from escaping into the substrate 100 and the reflection effect of the bulk wave reflecting structure 200 improves the Q value of the device. Importantly, the characteristic frequency and effective electromechanical coupling coefficient of the bulk resonator can be adjusted by changing the width of the electrode strip 502. Compared with the existing technology that improves the performance or frequency of the device by changing the vertical dimension, which requires multiple coating, photolithography and etching processes, resulting in complex and difficult processes, the process is greatly simplified and the process difficulty is reduced by adjusting the transverse dimension of the electrode strip.

[0044] Example 2

[0045] This embodiment 2 is a variation based on embodiment 1. By optimizing the structural layout of the top electrode and changing the electrode connection method, it improves device performance and frequency adjustment, thereby increasing the design freedom of the device. Specifically:

[0046] The top electrode 500 has a comb-shaped interdigitated electrode structure, consisting of two sets of interdigitated electrodes, referred to as the first interdigitated electrode 510 and the second interdigitated electrode 520, respectively. The first interdigitated electrode 510 and the second interdigitated electrode 520 are arranged on the resonant part 320 in an alternating manner. The alternating arrangement means that the electrode strips 502 of the first interdigitated electrode 510 and the second interdigitated electrode 520 are arranged in an alternating manner, and the center distance between the electrode strips 502 of the first interdigitated electrode 510 and the electrode strips 520 of the adjacent second interdigitated electrode 520 is still 0.5λ.

[0047] When two sets of interdigitated electrodes are used to form the top electrode 500, the connection methods of the electrodes can be varied. One implementation is that one of the first interdigitated electrode 510 and the second interdigitated electrode 520 is connected to a radio frequency signal, and the other is grounded. For example, the first interdigitated electrode 510 is connected to a radio frequency signal, and the second interdigitated electrode 520 is grounded. It works normally by exciting a shear body wave based on the potential difference between the first interdigitated electrode 510 and the second interdigitated electrode 520. In this case, the bottom electrode 400 can be suspended without any external connection, or the bottom electrode 400 can be omitted. In particular, when the structure of omitting the bottom electrode 400 is located in the Bra The piezoelectric layer 300 above the reflector 210 or cavity 220 will have a very flat structure. The flat piezoelectric layer 300 can improve the electromechanical coupling coefficient of the device. Another implementation is that one of the first interdigital electrode 510 and the second interdigital electrode 520 is connected to the radio frequency signal and the other is grounded. For example, the first interdigital electrode 510 is connected to the radio frequency signal and the second interdigital electrode 520 is grounded. The bottom electrode 400 is also connected to the radio frequency signal. At this time, a potential difference can be formed between the two sets of interdigital electrodes of the top electrode 500 and between the top electrode 500 and the bottom electrode 400, thereby exciting the shear body wave through the potential difference.

[0048] Example 3

[0049] This embodiment 3 provides a method for fabricating a bulk wave resonator, which forms the bulk wave resonator of embodiment 1 or embodiment 2. The method specifically includes the following steps:

[0050] S1, Substrate cleaning: Substrate 100 is a silicon substrate made of silicon material. Substrate 100 is cleaned with a mixture of sulfuric acid and hydrogen peroxide (SPM) or a mixture of ammonia and hydrogen peroxide (SC1) to obtain a clean surface.

[0051] S2, Sacrificial layer growth and patterning: The sacrificial layer is a P-doped SiO2 material (PSG). The SiO2 layer and the PSG layer are grown sequentially on the substrate 100 using PECVD process. Then, the patterned sacrificial layer is obtained by sequentially using photolithography → dry etching → dry and / or wet resist removal process.

[0052] S3, Bottom electrode fabrication: The electrode material of the bottom electrode 400 is one or more of Mo, Ag, Au, Cu, Ti, Al, Ru or Pt. When the bottom electrode 400 is a multilayer electrode structure, two or more of them are selected to form a multilayer electrode structure. When the bottom electrode 400 is a single-layer electrode structure, one of them is selected to form a single-layer electrode structure. Then, the growth and patterning of the bottom electrode 400 are completed by PVD → photolithography → dry etching → dry and / or wet resist removal.

[0053] S4, Piezoelectric layer preparation: The material of piezoelectric layer 300 is AlN, AlScN or PZT, and piezoelectric layer 300 is grown by PVD process;

[0054] S5, Top electrode fabrication: The electrode material of the top electrode 500 is one or more of Mo, Ag, Au, Cu, Ti, Al, Ru or Pt. Similarly, when the top electrode 500 is a multilayer electrode structure, two or more of them are selected to form a multilayer electrode structure. When the top electrode 500 is a single-layer electrode structure, one of them is selected to form a single-layer electrode structure. Then, the growth and patterning of the top electrode 500 are completed by PVD → photolithography → dry etching → dry and / or wet resist removal.

[0055] S6, Cavity preparation: PSG / SiO2 in the cavity 220 region is removed by using a certain proportion of HF solution to form cavity 220.

[0056] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They 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, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0057] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A bulk wave resonator, characterized in that, It includes a substrate (100), a piezoelectric layer (300), a bottom electrode (400), and a top electrode (500); The piezoelectric layer (300) includes a support portion (310), a resonant portion (320), and a transverse wave blocking region (330) located between the support portion (310) and the resonant portion (320). The piezoelectric layer (300) is fixedly supported on the substrate (100) by the support portion (310). A bulk wave reflection structure (200) is provided between the resonant portion (320) and the substrate (100). The top electrode (500) and the bottom electrode (400) are respectively provided on the upper and lower surfaces opposite to the resonant portion (320). The edge of the region of the top electrode (500) does not exceed the edge of the region of the bottom electrode (400), and the width b of the transverse wave blocking region (330) is in the range of 0.5λ≤b≤10λ, where λ is the bulk wavelength; The top electrode (500) includes a busbar (501) and an electrode bar (502). Multiple electrode bars (502) are connected in parallel to the same side of a busbar (501) to form a single-sided open interdigitated electrode, or multiple electrode bars (502) are connected in parallel between two busbars (501) to form a shaped electrode. The characteristic frequency can be fine-tuned by adjusting the width of the electrode bars (502). The resonant part (320) is surrounded by a transverse wave blocking region (330), and the support part (310) is surrounded by the transverse wave blocking region (330). The resonant part (320) is excited by the potential difference generated between the electrodes to form a shear body wave. When the top electrode (500) is a single-sided open interdigitated electrode, there are two sets of interdigitated electrodes, which are respectively referred to as the first interdigitated electrode (510) and the second interdigitated electrode (520). The electrode strips (502) of the first interdigitated electrode (510) and the second interdigitated electrode (520) are arranged alternately, and there is a potential difference between the first interdigitated electrode (510) and the second interdigitated electrode (520). When one set of the first interdigital electrode (510) and the second interdigital electrode (520) is used for grounding and the other set is used for radio frequency signals, the bottom electrode (400) is suspended, the bottom electrode (400) is connected to radio frequency signals or does not form the bottom electrode (400), and the shear body wave is excited by the potential difference between the first interdigital electrode (510) and the second interdigital electrode (520).

2. The bulk resonator according to claim 1, characterized in that, The range of distance 'a' between the edge of the region of the top electrode (500) and the edge of the region of the bottom electrode (400) is: 1 / 16λ≤a≤3 / 16λ.

3. The bulk resonator according to claim 1, characterized in that, The bulk wave reflection structure (200) is a Bragg reflector (210), which is embedded in the substrate (100), and the edge of the bottom electrode (400) does not extend beyond the edge of the Bragg reflector (210).

4. The bulk resonator according to claim 1, characterized in that, The bulk wave reflection structure (200) is a cavity (220). The cavity (220) is formed by setting a predetermined distance between the lower surface of the resonant part (320) and the upper surface of the substrate (100), or the cavity (220) is formed by a groove structure extending a predetermined distance from the upper surface of the substrate (100) to the lower surface.

5. The bulk resonator according to claim 1, characterized in that, The busbar (501) can be a straight strip or a non-straight strip.

6. The bulk resonator according to claim 1, characterized in that, The electrode width range of the electrode strip (502) is: 1 / 8λ≤d≤3 / 8λ.

7. A method for fabricating a bulk wave resonator according to any one of claims 1 to 6, characterized in that, The steps include the following: S1, Substrate cleaning: The substrate (100) is made of silicon material and is cleaned using a mixture of sulfuric acid and hydrogen peroxide or a mixture of ammonia and hydrogen peroxide. S2, Sacrificial layer growth and patterning: The sacrificial layer is made of PSG material. The SiO2 layer and the PSG layer are grown sequentially on the substrate (100) using PECVD process. Then, the patterned sacrificial layer is obtained by sequentially using photolithography → dry etching → dry and / or wet deintercalation process. S3, Bottom electrode fabrication: The bottom electrode (400) is a single-layer or multi-layer electrode structure. The growth and patterning of the bottom electrode (400) are completed by PVD → photolithography → dry etching → dry and / or wet resist removal. S4, Piezoelectric layer preparation: The material of the piezoelectric layer (300) is AlN, AlScN or PZT, and the piezoelectric layer (300) is grown by PVD process; S5, Top electrode fabrication: The top electrode (500) is a single-layer or multi-layer electrode structure. The growth and patterning of the top electrode (500) are completed by PVD → photolithography → dry etching → dry and / or wet resist removal. S6, Cavity Release: The PSG / SiO2 inside the cavity (220) is removed by using a certain proportion of HF solution.

8. The method for fabricating a bulk wave resonator according to claim 7, characterized in that, The bottom electrode (400) is made of one or more of Mo, Ag, Au, Cu, Ti, Al, Ru or Pt, and the top electrode is made of one or more of Mo, Ag, Au, Cu, Ti, Al, Ru or Pt.

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