A thin film bulk acoustic resonator with double-layer pentagonal electrodes

Abstract

The present invention discloses a thin film bulk acoustic wave resonator with a double-layer pentagonal electrode. The thin film bulk acoustic wave resonator includes a piezoelectric oscillation stack structure composed of a top electrode, a piezoelectric layer, and a bottom electrode from top to bottom, as well as a support layer (connection layer) and a substrate. The top electrode described in the present invention is composed of two layers of inner and outer pentagons, which are obtained by rotating the inner and outer pentagons of the same circle at a certain angle. The outer layer thickness of the top electrode described in the present invention is higher than the inner layer pentagon thickness, forming a step frame at the edge, and the rest of the position is a plane, and any two sides of the inner and outer pentagons are not parallel, thereby forming an asymmetric figure, so that the lateral parasitic sound waves are attenuated and dispersed. The present invention suppresses the lateral shear wave of the resonator without increasing the process steps by designing the shape and size of the electrode layer, thereby improving the Q value of the resonator and optimizing the resonance characteristics of the thin film bulk acoustic wave resonator.

Description

Technical Field

[0001] The invention relates to the technical field of bulk acoustic wave resonators, and in particular to a thin film bulk acoustic wave resonator with double-layer pentagonal electrodes. Background Art

[0002] With the rapid development of microwave wireless technology, acoustic wave filtering technology is particularly important in today's mobile communication terminals due to its excellent high-frequency performance. The further development of communication technology has put forward new requirements for filters working in the radio frequency band, such as integration, miniaturization, high performance, and low cost. Film Bulk Acoustic Resonator (FBAR) has broad application prospects in the fields of sensing, measurement and control, and communication due to its excellent performance, such as small size, low loss, high power capacity, and integration.

[0003] The core structure of the film bulk acoustic wave resonator is a piezoelectric oscillation stack structure composed of electrode-piezoelectric layer-electrode. Its working principle is that when the alternating electrical signal is on the electrodes at both ends, the inverse piezoelectric effect of the material will convert the electrical signal into a mechanical signal. The mechanical signal propagates in the film in the form of sound waves. When the wavelength and thickness of the sound wave in the vertical direction meet certain conditions, a standing wave is generated. At this time, the energy loss is minimal. Finally, the device converts the sound signal into an electrical signal for frequency selection through the piezoelectric effect. The most important part of the bulk acoustic wave resonator is the piezoelectricity of the piezoelectric oscillation stack structure. The high quality factor (Q value) enables it to show excellent suppression and insertion loss performance even in crowded frequency bands and tight passband edges. As the frequency band used gradually increases, the influence of the lateral parasitics of the film bulk acoustic wave resonator on the Q value becomes more and more significant. Suppressing lateral parasitics can further improve the high-frequency performance and Q value of the resonator.

[0004] The growing development of radio frequency microwave technology has put forward more stringent requirements on the working conditions of radio frequency devices. As the operating frequency continues to increase, there are also higher requirements for device size, performance, stability, and integration. Film Bulk Acoustic Resonator (FBAR) has broad application prospects in the fields of sensing, measurement and control, and communication due to its excellent performance, such as small size, low loss, high power capacity, and integration. Summary of the invention

[0005] In order to overcome the above-mentioned deficiencies in the prior art, an object of the present invention is to provide a thin film bulk acoustic resonator with double-layer pentagonal electrodes.

[0006] The double-layer pentagonal electrode thin film bulk acoustic wave resonator provided by the present invention is an improved double-layer pentagonal electrode thin film bulk acoustic wave resonator. The present invention suppresses the lateral parasitic effect generated when the FBAR device is vertically excited through the design of the electrode shape and the step. The FBAR using the electrode can have a higher Q value and avoid the generation of clutter. On the basis of not adding additional process steps, the transverse wave is suppressed and the manufacturing cost is controlled.

[0007] The purpose of the present invention is achieved by at least one of the following technical solutions.

[0008] The present invention provides a double-layer pentagonal electrode thin film bulk acoustic wave resonator, which includes, from top to bottom, a piezoelectric oscillation stack structure composed of a top electrode, a piezoelectric layer, and a bottom electrode, as well as a supporting layer (connecting layer) and a substrate; the outline of the piezoelectric oscillation stack structure is a pentagonal figure in which any two sides of the inner and outer circles are not parallel; an acoustic reflection interface is provided on the substrate, the piezoelectric oscillation stack structure is arranged on the acoustic reflection interface, and the effective area of ​​the piezoelectric oscillation stack structure is larger than the acoustic reflection interface.

[0009] Furthermore, the top electrode is composed of two circles of inner and outer pentagonal electrodes, and the two circles of pentagonal electrodes are an inscribed pentagon and a circumscribed pentagon of a circle with the same radius.

[0010] Furthermore, from a top view, there is an angle between the inner and outer circles of the top electrode, the angle ranges from 0° to 360° and is not equal to n×36°, where n is an integer and the value range of n is 1-9.

[0011] Furthermore, the thickness of the inner pentagonal electrode of the top electrode is 100-300 nm, and the thickness of the outer pentagonal electrode of the top electrode is 300-1200 nm.

[0012] Furthermore, the inner and outer pentagonal circles of the top electrode are made of the same material, and the material of the top electrode is one or more of molybdenum, tungsten, gold, aluminum, silver, titanium, etc.

[0013] Furthermore, the substrate is one of high-resistance silicon, lithium niobate, sapphire substrate or SOI substrate. The substrate is suitable for thin film bulk acoustic resonator.

[0014] Furthermore, the top electrode and the bottom electrode are both metal films.

[0015] Furthermore, the piezoelectric layer is a thin film material with piezoelectric effect, and the support layer is a physical support layer or a metal bonding layer. The physical support layer is an insulating film such as silicon nitride or silicon dioxide. The metal bonding layer is an intermetallic compound such as Au / Sn, Au / Au, Ni / Sn, etc.

[0016] Furthermore, the piezoelectric layer is a thin film material having a piezoelectric effect; the piezoelectric layer is one or more of PZT, AlN, GaN, ZnO, CdS and LiNbO3.

[0017] Furthermore, the acoustic reflection interface is an air cavity or a Bragg reflection layer formed by overlapping high and low acoustic impedances.

[0018] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0019] The present invention utilizes the design of electrode geometry to enhance the reflection of longitudinal waves in a thin film bulk acoustic wave resonator and reduce the loss of shear waves; the designed electrode structure is composed of two inner and outer layers of pentagons rotated at a certain angle, wherein any two sides are not parallel, thereby forming an asymmetric geometric figure, so that the transverse sound waves generated by the excitation cannot generate standing waves, and the propagation direction and phase of the transverse reflected sound waves do not meet the oscillation conditions, thereby dispersing and attenuating; the present invention sets steps in the longitudinal dimension to suppress parasitic effects, and sets double pentagonal figures in the transverse dimension to suppress parasitic effects, thereby further reducing transverse standing waves; without increasing process steps, the manufacturing cost of the device is controlled, and the device performance is further improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A top view of a thin film bulk acoustic wave resonator with double-layer pentagonal electrodes according to an embodiment of the present invention;

[0021] Figure 2 It is a cross-sectional view of the first double-layer pentagonal electrode thin film bulk acoustic resonator in Example 1 of the present invention;

[0022] Figure 3 is a cross-sectional view of a second type of double-layer pentagonal electrode thin film bulk acoustic resonator in Example 2 of the present invention;

[0023] Figure 4 This is a cross-sectional view of a third type of double-layer pentagonal electrode thin film bulk acoustic wave resonator in Example 3 of the present invention. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described below in conjunction with examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. If the manufacturer of the reagents or instruments used is not indicated, they are deemed to be conventional products that can be purchased commercially.

[0025] Example 1

[0026] This embodiment provides an air gap type thin film bulk acoustic wave resonator with double-layer pentagonal electrodes, such as Figure 1 and Figure 2 As shown, the resonator includes a substrate 105, a bottom electrode 104, a piezoelectric layer 103, an inner top electrode 101, and an outer top electrode 102, which are sequentially distributed from bottom to top. In this embodiment, the air cavity is used as the reflection interface, and the area of ​​the bottom electrode 104 is larger than the air cavity, and larger than the top electrodes 101 and 102. The double-layer pentagon of the top electrode is divided into an inner top electrode 101 and an outer top electrode 102.

[0027] The substrate 105 is single crystal Si; the piezoelectric layer material is 1 μm thick polycrystalline AlN material; the bottom electrode 104 and the inner ring top electrode 101 are both 200nm thick metal Mo electrodes; the outer ring top electrode 102 is 400nm thick metal Mo;

[0028] The double-layer pentagonal electrode is obtained by two PVD magnetron sputterings. The first sputtering obtains the inner circle top electrode 101 of 200nm, and the second sputtering obtains the outer circle top electrode 102 of 400nm.

[0029] The angle between the double-layer pentagonal electrodes is Figure 1 As shown, the phase difference is 17°, and any two sides of the inner and outer double-layer pentagons are not parallel, and the area is smaller than the bottom electrode 104, forming an asymmetric geometric figure.

[0030] Example 2

[0031] This embodiment provides a solid-state assembled thin film bulk acoustic resonator with double-layer pentagonal electrodes, such as Figure 3 As shown, the resonator includes a substrate 105, a Bragg reflection layer 108, a bottom electrode 104, a piezoelectric layer 103, an inner top electrode 101, and an outer top electrode 102, which are sequentially distributed from bottom to top. In this embodiment, the Bragg reflection layer is used as a reflection interface, and the Bragg reflection layer is formed by alternating thin film materials with high and low acoustic impedance and a thickness of 1 / 4 wavelength. The double-layer pentagon of the top electrode is divided into an inner top electrode 101 and an outer top electrode 102.

[0032] The substrate 105 is single crystal Si; the piezoelectric layer material is 1 μm thick polycrystalline AlN material; the bottom electrode 104 and the inner ring top electrode 101 are both 200 nm thick metal Mo electrodes; the outer ring top electrode 102 is 400 nm thick metal Mo; the Bragg reflection layer 108 is an Al-W multilayer film system alternately deposited on a silicon wafer by DC magnetron sputtering technology, and a thermal annealing process is used to improve the performance of the Bragg reflection layer.

[0033] The double-layer pentagonal electrode is obtained by two PVD magnetron sputterings. The first sputtering obtains the inner circle top electrode 101 of 200nm, and the second sputtering obtains the outer circle top electrode 102 of 400nm.

[0034] The angle between the double-layer pentagonal electrodes is Figure 1As shown, the phase difference is 20°, and any two sides of the inner and outer double-layer pentagons are not parallel, and the area is smaller than the bottom electrode 104, forming an asymmetric geometric figure.

[0035] Example 3

[0036] This embodiment provides a bulk silicon back-etched thin film bulk acoustic wave resonator with double-layer pentagonal electrodes, such as Figure 4 As shown, the resonator includes a substrate 105, a support layer 106, a bottom electrode 104, a piezoelectric layer 103, an inner top electrode 101, and an outer top electrode 102, which are sequentially distributed from bottom to top. In this embodiment, the substrate at the bottom of the working area is removed, and the air interface is used as the reflection interface. Since the bottom substrate is penetrated, the support layer 106 is provided to increase the mechanical strength of the device. The double-layer pentagon of the top electrode is divided into an inner top electrode 101 and an outer top electrode 102.

[0037] The substrate 105 is single crystal Si; the piezoelectric layer material is 1 μm thick polycrystalline AlN material; the bottom electrode 104 and the inner ring top electrode 101 are both 200 nm thick metal Mo electrodes; the outer ring top electrode 102 is 400 nm thick metal Mo; the support layer material is a 150 nm silicon nitride film;

[0038] On the one hand, the supporting layer material improves the mechanical strength of the resonator during operation, and on the other hand, it serves as a barrier layer (self-stop layer) during the etching process of the substrate.

[0039] The angle between the double-layer pentagonal electrodes is Figure 1 As shown, the phase difference is 20°, and any two sides of the inner and outer double-layer pentagons are not parallel, and the area is smaller than the bottom electrode 104, forming an asymmetric geometric figure.

[0040] The above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A double-layer pentagonal electrode thin film bulk acoustic wave resonator, comprising from top to bottom a piezoelectric oscillation stack structure consisting of a top electrode, a piezoelectric layer, a bottom electrode, a support layer and a substrate; characterized in that: The outline of the piezoelectric oscillation stack structure is a pentagonal figure in which any two sides of the inner and outer circles are not parallel; an acoustic reflection interface is provided on the substrate, the piezoelectric oscillation stack structure is arranged on the acoustic reflection interface, and the effective area of ​​the piezoelectric oscillation stack structure is larger than the acoustic reflection interface; the top electrode is composed of two inner and outer circles of pentagonal electrodes, and these two circles of pentagonal electrodes are inscribed pentagons and circumscribed pentagons of the same radius; from a top-down perspective, there is an angle between the inner and outer circles of the top electrode, the degree of the angle ranges from 0° to 360° and the degree of the angle is not equal to n×36°, n is an integer and the value range of n is 1-9; the thickness of the inner circle pentagonal electrode of the top electrode is 100-300nm, and the thickness of the outer circle pentagonal electrode of the top electrode is 300-1200nm.

2. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 1, characterized in that: The inner and outer circles of the top electrode are made of the same material, and the material of the top electrode is one or more of molybdenum, tungsten, gold, aluminum, silver, and titanium.

3. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 1, characterized in that: The substrate is one of high-resistance silicon, sapphire substrate or SOI substrate.

4. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 1, characterized in that: The top electrode and the bottom electrode are both metal films.

5. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 1, characterized in that: The piezoelectric layer is a thin film material with piezoelectric effect, the supporting layer is a physical supporting layer or a metal bonding layer; the physical supporting layer is an insulating film; the physical supporting layer is silicon nitride or silicon dioxide.

6. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 5, characterized in that: The piezoelectric layer is a thin film material with piezoelectric effect; the piezoelectric layer is one or more of PZT, AlN, GaN, ZnO, CdS and LiNbO3.

7. The double-layer pentagonal electrode thin film bulk acoustic resonator according to claim 1, characterized in that: The acoustic reflection interface is an air cavity or a Bragg reflection layer formed by overlapping high and low acoustic impedances.

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