CN210431367U

CN210431367U - A Frequency Tunable Transverse Field Excited Thin Film Bulk Acoustic Resonator

Info

Publication number: CN210431367U
Application number: CN201921179868.7U
Authority: CN
Inventors: 章秀银; 薛艳梅; 吴子莹; 周长见
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2019-07-25
Filing date: 2019-07-25
Publication date: 2020-04-28
Anticipated expiration: 2029-07-25

Abstract

The utility model discloses a transverse field excitation film bulk acoustic resonator with adjustable frequency, which comprises an electrode aluminum, a piezoelectric substrate, a temperature compensation layer and a substrate from top to bottom in sequence; the substrate is provided with a cavity which is communicated with a release through hole penetrating through the temperature compensation layer and the piezoelectric substrate, and the piezoelectric substrate is made of single crystal materials. The utility model discloses under the thickness condition that does not change the piezoelectric substrate, the central frequency of syntonizer changes along with the electrode pair changes of excitation direction.

Description

Transverse field excitation film bulk acoustic resonator with adjustable frequency

Technical Field

The utility model relates to a microelectronic technique, concretely relates to frequency adjustable's horizontal field excitation film bulk acoustic resonator.

Background

The film bulk acoustic resonator has attracted much research attention due to the characteristics of high Q value, small volume, integration and the like, and along with the rapid development of mobile communication technology, the film bulk acoustic resonator not only has a great deal of applications in radio frequency front ends, but also has great potential in sensor detection applications, such as biochemical detection, mechanical detection and the like.

The excitation modes of the film bulk acoustic wave device are mainly divided into two modes, one mode adopts a thickness field excitation mode, two electrodes are respectively arranged on two sides of a piezoelectric substrate, and an electric field is along the thickness direction of the substrate; the other is transverse field excitation mode, two electrodes are on the same surface of the piezoelectric substrate, and the manufacture method of the bulk acoustic wave device is similar to that of a surface acoustic wave device. In practical application, the two excitation modes can cause mass points in the piezoelectric substrate body to generate thickness shear vibration, and sound waves generated by the mass points propagate in the substrate body and belong to bulk sound waves.

Compared with the bulk acoustic wave device in the thickness field excitation mode, the bulk acoustic wave device in the transverse field excitation mode has the following advantages: the part with the strongest crystal vibration activity is not provided with an electrode, so that the aging efficiency is reduced; when the method is applied to a liquid environment, a higher Q value can be obtained; the electrodes are on the same main surface, and the manufacture is relatively easy.

The existing mainstream bulk acoustic wave devices all adopt polycrystalline piezoelectric materials, such as AlN and ZnO films, and compared with single crystal materials, the polycrystalline materials have isotropic characteristics, so that the performance of an electrode on a piezoelectric substrate is generally considered to be irrelevant to the direction of the electrode. In addition, the polycrystalline thin film structure has a large number of grain boundaries and defects, and when sound waves propagate in the polycrystalline thin film structure, the scattering coefficient of the sound waves can be scattered by the grain boundaries and the defects, so that energy loss is caused, and the electromechanical coupling efficiency is reduced.

Generally, a bulk acoustic wave filter is configured by connecting resonators having a plurality of resonance frequencies in a certain structure. The bulk acoustic wave resonant frequency is mainly realized by changing the thickness of the piezoelectric substrate, and the thinner the substrate thickness is, the higher the resonant frequency is, so that the piezoelectric substrate with one thickness can only be used as a bulk acoustic wave device with one resonant frequency, and a plurality of piezoelectric substrates with different thicknesses are required for manufacturing one bulk acoustic wave filter, thereby greatly increasing the manufacturing difficulty of the filter. If the thickness of the piezoelectric substrate is consistent and the resonance frequency is inconsistent, the bulk acoustic wave filter can be manufactured only by one piezoelectric substrate, so that the design efficiency is improved, and the production cost of the filter is reduced.

SUMMERY OF THE UTILITY MODEL

In order to overcome the defects and deficiencies of the prior art, the utility model aims to provide a frequency-adjustable transverse field excitation film bulk acoustic resonator, which is based on Y-42 cutting lithium tantalate single crystal material, and provides a bulk acoustic resonator with adjustable center frequency by changing the relative direction of an electrode pair and a piezoelectric substrate, namely the electric field excitation angle under the condition of not changing the electrode size and the thickness of a piezoelectric film.

The utility model adopts the following technical scheme:

a transverse field excitation film bulk acoustic resonator with adjustable frequency sequentially comprises electrode aluminum, a piezoelectric substrate, a temperature compensation layer and a substrate from top to bottom;

the substrate is provided with a cavity which is communicated with a release through hole which penetrates through the temperature compensation layer and the piezoelectric substrate.

The piezoelectric substrate is a single crystal material.

The monocrystalline material is specifically 42-degree Y-tangential monocrystalline lithium tantalate.

The electrode aluminum is composed of two parallel electrodes.

The thickness of the temperature compensation layer is 1.5 mu m, the thickness of the substrate is 300 mu m, and the thickness of the piezoelectric substrate is 670 nm.

The thickness of the electrode is 100 nm.

A method for preparing a transverse field excitation film bulk acoustic resonator comprises the following steps:

s1, photoetching and releasing a through hole on the piezoelectric material on the uppermost layer of the wafer, and defining the shape of the through hole;

s2, etching the piezoelectric substrate and the temperature compensation layer by using an inductively coupled plasma dry method, protecting the area which does not need to be etched, forming a through hole penetrating through the piezoelectric substrate and the temperature compensation layer after etching is finished, and exposing the substrate in the etching window;

s3, photoetching and evaporating electrode aluminum on the upper surface of the piezoelectric substrate;

s4, using gas XeF₂And (4) carrying out substrate etching by releasing the through hole to form a cavity structure, thus finishing the preparation.

The utility model has the advantages that:

(1) the utility model obtains the change rule of the resonant frequency along with the direction of the electrode pair based on COMSOL simulation, adjusts the direction of the electrode pair according to the single crystal piezoelectric substrate material, and obtains the resonator with adjustable resonant frequency under the condition of not changing the size of the electrode and the thickness of the piezoelectric film;

(2) the frequency-adjustable film resonator of the utility model can realize the on-chip bulk acoustic wave filter on the same piezoelectric substrate, which is beneficial to reducing the volume and the manufacturing cost of the device;

(3) the existing preparation process obtains a polycrystalline piezoelectric film material through magnetron sputtering, and due to the existence of crystal boundaries and defects in the polycrystalline material, the absorption or scattering of bulk acoustic waves can be caused, and the transmission loss of the acoustic waves is increased. The piezoelectric layer of the utility model adopts lithium tantalate single crystal material, which is beneficial to improving the coupling coefficient, quality factor and filtering performance of the device;

(4) the utility model discloses a film bulk acoustic resonator, electrode are at same main surface, and the structure is simple relatively, and the preparation is easier, because the strongest part of crystal vibration vigor does not have the electrode simultaneously, reduces the ageing rate of device.

Drawings

FIG. 1 is a perspective view of a Comsol simulation model according to the present invention;

fig. 2 is a cross-sectional view of the present invention;

FIG. 3 is a flow chart of the manufacturing method of the present invention;

fig. 4(a) is a schematic diagram of the electrode rotation angle of 0 degree according to the present invention;

FIG. 4(b) is a graph of simulation results of the equivalent impedance Y11 of FIG. 4(a) at the center resonant frequency of 2.06 GHz;

fig. 4(c) is a schematic diagram of the electrode rotating angle of 45 degrees according to the present invention;

FIG. 4(d) is a graph of the simulation result of the equivalent impedance Y11 of FIG. 4(c) at the center resonant frequency of 2.22 GHz;

fig. 4(e) is a schematic view of the electrode of the present invention with a rotation angle of-45 degrees;

FIG. 4(f) is a graph of the simulation result of the equivalent impedance Y11 of FIG. 4(e) at the center resonant frequency of 2.21 GHz;

fig. 4(g) is a schematic diagram of the electrode rotation angle of 90 degrees according to the present invention;

fig. 4(h) is a graph of the simulation result of the equivalent impedance Y11 of fig. 4(g) at the center resonance frequency of 2.10 GHz.

Detailed Description

The present invention will be described in further detail with reference to the following examples and drawings, but the present invention is not limited thereto.

Examples

Fig. 1 is the three-dimensional structure diagram of the transverse field excitation film bulk acoustic resonator of the utility model, which comprises an electrode aluminum 1, a piezoelectric substrate 2 and a temperature compensation layer 3 which are sequentially arranged from top to bottom, wherein the piezoelectric substrate is made of Y-42 cut single crystal lithium tantalate material, and the temperature compensation layer is made of silicon dioxide.

Fig. 2 shows a cross-sectional view of a transverse field excited film bulk acoustic resonator with a temperature compensation layer arranged on a substrate, said substrate 5 being provided with cavities 4 which are symmetrical with respect to the longitudinal centre line of the substrate and which extend downwards from the upper edge. The temperature compensation layer is arranged between the piezoelectric substrate and the substrate, the electrode aluminum is positioned on the same surface of the piezoelectric substrate, the release through hole 6 is communicated with the cavity, the through hole penetrates through the piezoelectric substrate, the temperature compensation layer and the cavity, and the size and the shape of the cavity and the size and the shape of the through hole are determined according to actual conditions.

The utility model discloses the syntonizer is at the during operation, and on the signal of telecommunication loaded electrode aluminium, the electric field direction of lithium tantalate single crystal piezoelectric film excitation is on a parallel with crystal substrate's main surface direction, transverse field excitation mode promptly. If the relative direction of the electrode pair and the piezoelectric substrate is changed, crystal ions generate different vibrations due to the anisotropy of the single crystal material, and macroscopically, the resonance frequency of the resonator is changed;

the utility model discloses it is big to single crystal material temperature coefficient, and there is the problem that the temperature floats device frequency can exist, has added the silica that the one deck has positive temperature coefficient in film structure as the temperature compensation layer, reduces the temperature coefficient of compound rete, strengthens the temperature stability of device.

The utility model discloses an aluminium electrode comprises the electrode of two parallels, and through changing electrode excitation angle, the central frequency of syntonizer changes along with the electrode pair change of encouraging the direction.

In this embodiment, the excitation angles of the aluminum electrode pairs are set to 0 °, +45 °, -45 °, and 90 °, simulation results thereof correspond to fig. 4(a) -4 (h), and the center frequency of the resonator changes with the change of the excitation direction of the electrode pairs, so that on the same piezoelectric substrate, without changing the thickness of the wafer, a plurality of resonators with different resonant frequencies can be designed, and are connected by a suitable coupling topology, which provides a possibility for realizing an on-chip filter.

Referring to fig. 3, fig. 3 is a flow chart of a method for manufacturing a film bulk acoustic resonator structure according to the present invention. The utility model discloses film bulk acoustic resonator manufacturing approach includes the step:

s2, etching the piezoelectric substrate and the temperature compensation layer by adopting an inductive coupling plasma dry method, protecting the area which does not need to be etched, forming a through hole penetrating through the piezoelectric substrate and the temperature compensation layer after etching is finished, and exposing the substrate in the etching window;

The transverse excitation film bulk acoustic wave device is set according to parameters, the thickness of an electrode excited on the upper surface is 100nm, the thickness of the Y-42 cut lithium tantalate film layer is 670nm, the thickness of the temperature compensation layer silicon dioxide is 1.5 mu m, and the thickness of the substrate silicon is 300 mu m.

The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited by the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be equivalent replacement modes, and all are included in the scope of the present invention.

Claims

1. A transverse field excitation film bulk acoustic resonator with adjustable frequency is characterized by sequentially comprising electrode aluminum, a piezoelectric substrate, a temperature compensation layer and a substrate from top to bottom;

2. The transverse field excited thin film bulk acoustic resonator according to claim 1, wherein the piezoelectric substrate is a single crystal material.

3. The transverse field excited thin film bulk acoustic resonator according to claim 2, wherein the single crystal material is in particular 42 degree Y tangential single crystal lithium tantalate.

4. The transverse field excited thin film bulk acoustic resonator according to claim 1, wherein the electrode aluminum is formed by two parallel electrodes.

5. The transverse field excited thin film bulk acoustic resonator according to claim 1, wherein the temperature compensation layer is 1.5 μm thick and the substrate is 300 μm thick.

6. The transverse field excited thin film bulk acoustic resonator according to claim 4, wherein the thickness of the electrodes is 100 nm.

7. The transverse field excited thin film bulk acoustic resonator according to claim 1, wherein the thickness of the piezoelectric substrate is 670 nm.