CN107241077B - Piezoelectric thin-film bulk acoustic wave resonator and method of making the same - Google Patents

Abstract

The invention belongs to the technical field of radio frequency micro-electromechanical systems (MEMS), and specifically provides a novel piezoelectric thin-film bulk acoustic wave resonator and a manufacturing method thereof, comprising a substrate, a support layer, a bottom electrode layer, a piezoelectric layer and a top electrode layer; the A certain number of grooves are opened on the substrate of the resonator to increase the external surface area of the substrate; a support layer is arranged on the substrate, and the interior of the groove and the upper surface of the support layer are filled with low acoustic impedance flexible material polyimide, etc. ; Then, a bottom electrode layer, a piezoelectric layer and a top electrode layer are sequentially arranged on the low acoustic impedance layer. The novel piezoelectric thin-film bulk acoustic wave resonator has novel structure, simple preparation, and more importantly, can effectively solve the problems of insufficient thermal stability and insufficient power capacity of the flexible substrate bulk acoustic wave resonator, and has a good application prospect.

Description

Piezoelectric thin-film bulk acoustic wave resonator and method of making the same

technical field

The invention belongs to the technical field of radio frequency micro-electromechanical systems (MEMS), and in particular relates to a novel piezoelectric thin-film bulk acoustic wave resonator and a manufacturing method thereof.

Background technique

With the development of wireless communication systems towards miniaturization, high frequency and integration, traditional dielectric filters and surface acoustic wave filters are also difficult to meet the requirements of miniaturization and high frequency. The device has the incomparable volume advantages of ceramic dielectric filters, the incomparable operating frequency and power capacity advantages of surface acoustic wave resonators; especially the more and more mature MEMS technology, thin film bulk acoustic wave resonators have become the development of today's wireless communication systems. trend.

The main part of the thin film bulk acoustic wave resonator is a "sandwich" structure composed of a bottom electrode, a piezoelectric film and a top electrode. Waves; since the speed of acoustic waves is 5 orders of magnitude smaller than that of electromagnetic waves, the dimensions of thin-film bulk acoustic wave resonators are smaller than conventional devices. The most important part for BAW resonators is to confine the acoustic waves in the piezoelectric layer. At present, traditional thin-film BAW resonators are divided into two categories according to the method of confining the acoustic waves:

The first is the solid-state assembly type (SMR), whose structure is shown in Figure 3. Its working principle is to use a quarter-wavelength thickness of high acoustic impedance layer and low acoustic impedance layer to form a reflection layer to realize the reflection of sound waves. ; This solid-state assembly type BAW resonator has good mechanical strength and power capacity, and can be used under high power conditions, but the Bragg reflection layer of the SMR type resonator has a great impact on the thickness and roughness of each film. High requirements, the stress control between the films also needs to be strictly controlled, otherwise it is easy to fall off, and it is difficult to achieve in the process;

Second, cavity-type thin-film bulk acoustic wave resonators, currently there are two main ways to realize a cavity: air cavity type (FBAR), whose structure is shown in Figure 4; back-etched type, whose structure is shown in Figure 5 ; The working principle of the cavity type thin film bulk acoustic wave resonator is to use the sound wave to reflect at the interface between the bottom electrode or the support layer and the air, confine the sound wave to the piezoelectric layer, and realize resonance; the resonator of this type of structure has high reflection efficiency, It has the advantages of high Q value, low insertion loss, and can be integrated, but the preparation process of the cavity-type thin-film bulk acoustic wave resonator is relatively complicated, and there are strict requirements for the control of the film stress and the preparation process; because of its high production cost, process The high threshold limits the development of the entire domestic industry.

At present, in the analysis of the performance of the device by the substrate, it is proposed to use a flexible substrate with an acoustic impedance close to the air as the substrate, which can avoid using the traditional cavity structure or the Bragg reflection structure to achieve the device performance; the proposed flexible structure can The complexity of the device preparation process is greatly reduced, and the application of the device can be extended to fields such as biochemical sensing. However, compared with rigid materials, flexible materials have poor thermal conductivity, so the thermal stability and power capacity of flexible matrix acoustic wave resonators need to be further improved and improved compared with traditional BAW resonators.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a piezoelectric thin-film bulk acoustic wave resonator and a preparation method thereof in view of the problems existing in the above-mentioned prior art. The production cycle is shortened, the production cost is reduced, and at the same time, the thermal stability and power capacity of the flexible matrix acoustic wave resonator are improved, which has a good application prospect.

In order to achieve the above object, the technical scheme adopted by the present invention is:

A piezoelectric thin-film bulk acoustic wave resonator, its structure includes a substrate, a support layer, a bottom electrode, a piezoelectric layer and a top electrode sequentially arranged on the substrate and the support layer, characterized in that the resonator also includes a low The acoustic impedance layer, the upper surface of the substrate is provided with several vertical grooves, the support layer surrounds all the vertical grooves, is arranged on the substrate, and forms a large groove together with the substrate, the low acoustic The impedance layer completely fills the groove and has a flat upper surface; the bottom electrode, the piezoelectric layer and the top electrode are sequentially arranged on the low acoustic impedance layer.

Further, the plurality of vertical grooves are distributed in an array, and each vertical groove has the same shape, and its top view shape is polygon, rectangle or circle, and its side view shape is a grooming line shape or a zigzag shape.

Further, the low acoustic impedance piezoelectric layer material is polyimide or cross-linked polyphenylene polymer.

Further, the support layer material adopts high thermal conductivity material, and the height of the support layer is 10-50um.

Further, the substrate is a silicon substrate, and the piezoelectric layer is an aluminum nitride layer with a C-axis orientation.

Further, the material of the bottom electrode and the top electrode is a metal with high acoustic impedance, such as tungsten or molybdenum.

The preparation method of the aforementioned piezoelectric thin-film bulk acoustic wave resonator comprises the following steps:

Step 1, using dry etching or wet etching process to etch a plurality of vertical grooves at preset positions on the substrate;

Step 2, using magnetron sputtering or chemical vapor deposition to deposit a layer of support layer material on the substrate of step 1, and obtain a patterned support layer by photolithography;

Step 3, uniformly coating a layer of low-acoustic impedance material on the substrate and support layer in step 2 by using spin coating and casting processes, and then performing high-temperature curing to obtain a low-acoustic impedance layer;

Step 4, using magnetron sputtering or electron beam evaporation to deposit a high acoustic impedance electrode layer on the upper surface of the low acoustic impedance layer and photoetching a bottom electrode pattern;

Step 5, growing the piezoelectric layer on the bottom electrode by magnetron sputtering and photoetching the piezoelectric layer pattern;

Step 6, using magnetron sputtering or electron beam evaporation to deposit a top electrode on the upper surface of the piezoelectric layer, and etching the top electrode pattern, that is, the preparation of the thin film bulk acoustic wave resonator is prepared.

It should be noted that in the present invention, a certain number of vertical grooves are arranged on the upper surface of the substrate to increase the contact area between the flexible low-acoustic impedance material and the silicon substrate, and the substrate with grooves can effectively suppress the reflection of acoustic waves. The parasitic modulus brought by the wave can avoid the interference of the reflected wave to the fundamental frequency signal. The specific shape can be determined according to the actual size of the resonator and the manufacturing process level, and it is ensured that the flexible low acoustic impedance material is sufficiently and uniformly filled on the surface of the substrate. The height of the support layer is to make the flexible low acoustic impedance layer have a certain thickness so as to reduce the return loss of the bulk acoustic wave resonator and improve the performance of the device.

Compared with the prior art and the structure, the present invention has the following advantages:

1. Compared with the traditional cavity type and solid-state assembly type thin-film bulk acoustic wave resonator, there is no need to form a cavity structure, which improves the mechanical strength and reduces the technological difficulty. The sacrificial layer in the cavity structure is not required, which reduces the subsequent complicated process step of releasing the sacrificial layer; the use of flexible materials with low acoustic impedance can effectively replace the Bragg reflection layer in the solid-state assembly type thin-film bulk acoustic wave resonator, It overcomes the difficult determination of the Bragg reflection layer, can well limit the leakage of acoustic waves to the bottom electrode, and ensures the performance of the thin-film bulk acoustic wave resonator. The surface of the substrate with grooves can also effectively suppress the parasitic modulus caused by the reflected wave of the acoustic wave leaking to the low acoustic impedance layer, so as to avoid the interference of the reflected wave to the main frequency signal.

2. The device of the present invention innovatively proposes to solve the problems of insufficient thermal stability and insufficient power capacity of the flexible matrix acoustic wave resonator. When the resonator is working, due to the self-heating phenomenon, it is difficult for the flexible low-impedance material to dissipate heat due to its low thermal conductivity, resulting in an excessively high temperature coefficient of the device and limiting the power capacity of the device, making the flexible matrix acoustic resonator unable to meet some market demands. Using a large area of contact between a silicon substrate with high thermal conductivity and a flexible substrate can dissipate heat more effectively, thereby reducing the thermal steady-state temperature of the device; improving device performance, high power capacity also broadens the application of flexible substrate acoustic wave resonators field.

3. The present invention can greatly simplify the manufacturing process of the thin-film bulk acoustic wave resonator, lower the technological threshold, shorten the manufacturing cycle, and reduce the manufacturing cost.

Description of drawings

FIG. 1 is a schematic structural diagram of a thin film bulk acoustic wave resonator of the present invention.

FIG. 2 is a schematic diagram of the same structure of the thin film bulk acoustic wave resonator of the present invention.

FIG. 3 is a schematic structural diagram of a solid-state assembled thin-film bulk acoustic resonator (SMR).

FIG. 4 is a schematic structural diagram of an air cavity film bulk acoustic resonator (FBAR).

FIG. 5 is a schematic structural diagram of a back-etched thin-film bulk acoustic resonator.

FIG. 6 is a cross-sectional view of the substrate after etching in Embodiment 1. FIG.

FIG. 7 is a cross-sectional view of the embodiment 1 after depositing a support layer.

FIG. 8 is a cross-sectional view of the device after the support layer is patterned in Embodiment 1. FIG.

FIG. 9 is a cross-sectional view of the device after filling with polyimide in the first embodiment.

FIG. 10 is a cross-sectional view of the device after the bottom electrode layer is prepared in Example 1. FIG.

FIG. 11 is a cross-sectional view of the device after the piezoelectric layer is prepared in Example 1. FIG.

FIG. 12 is a cross-sectional view of the device after the top electrode layer is prepared in Example 1. FIG.

FIG. 13 is a top view of the piezoelectric thin-film bulk acoustic wave resonator prepared in Example 1. FIG.

In the figure, 1 is a substrate, 2 is a support layer, 3 is a low acoustic impedance polyimide layer, 4 is a bottom electrode layer, 5 is a piezoelectric layer, and 6 is a top electrode layer.

Detailed ways

The present invention will be further described in detail below with reference to the accompanying drawings and examples.

Example 1

This embodiment provides a piezoelectric thin-film bulk acoustic resonator, the structure of which is shown in FIG. 1 , including a substrate 1 with vertical grooves, a patterned support layer 2, which completely fills the low-acoustic resonator covering the surface of the substrate. The impedance layer 3, the bottom electrode layer 4, the piezoelectric layer 5, and the top electrode layer 6; in this embodiment, the substrate material is silicon, the depth of the vertical groove in the substrate is about 10um, and the vertical groove is made of square. The holes and vertical grooves are arranged in an array, and the side view shape is in the shape of a dressing line. The low acoustic impedance layer is polyimide, the bottom electrode is molybdenum, and the piezoelectric layer is aluminum nitride with C-axis orientation. The top electrode of the upper layer is the metal molybdenum.

The specific preparation process of the above-mentioned piezoelectric thin-film bulk acoustic resonator includes the following steps:

Step 1. Use the photolithography method on the surface of the silicon substrate, first remove the photoresist in the groove part with reverse glue, expose the silicon substrate in the groove part, and then use dry etching or wet etching method to etch For the exposed part, control the etching time so that the depth of the vertical groove is about 10um, and the groove area is 20um×20um, as shown in Figure 6; the surface of the silicon substrate can be (100), (110) or ( 111) Orientation, this experiment adopts the method of reactive ion deep etching to etch the silicon substrate;

Step 2, remove the photoresist in step 1, use the method of magnetron sputtering to deposit a layer of amorphous aluminum nitride as a support layer, and control the deposition time so that the height of the support layer is 10-50um, as shown in Figure 7 Then, the shape that needs to be etched on the support layer is etched out by using the reverse glue, and the pattern of the support layer is etched by the wet etching method, as shown in Figure 8. In this example, a water bath heated at 40°C is used. TMAH solution etching;

Step 3. Coat the liquid polyimide evenly on the support layer in step 2. After the polyimide has fully entered the groove, use a glue spinner to evenly glue the polyimide on the support layer. On the support layer, and then high temperature curing liquid polyimide to obtain a cured polyimide low acoustic impedance layer, as shown in Figure 9;

Step 4. Deposit a layer of 100-200nm metal molybdenum on the polyimide low acoustic impedance layer by magnetron sputtering, and pattern the corresponding bottom electrode shape as the bottom electrode layer by photolithography, as shown in Figure 10. The process conditions of magnetron sputtering in this example are: air pressure 1Pa, power 200W, gas flow 20sccm, and substrate temperature is water cooling;

Step 5. Using the method of magnetron sputtering, deposit an AlN layer with C-axis orientation, obtain the piezoelectric layer by patterning by photolithography, and expose the bottom electrode pattern, as shown in Figure 11; The process conditions are nitrogen concentration>40%, power density>10w/cm ² , temperature>150℃;

In step 6, a layer of 100-200 nm metal molybdenum is deposited by magnetron sputtering, and the top electrode layer is obtained by patterning by photolithography, as shown in FIG. 12. In this example, the process conditions are the same as in step 4; the prepared piezoelectric The top view of the thin film bulk acoustic wave resonator structure is shown in Figure 13.

The above descriptions are only specific embodiments of the present invention, and any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all the disclosed features, or All steps in a method or process, except mutually exclusive features and/or steps, may be combined in any way.

Claims (7)

1. a piezoelectric thin-film bulk acoustic wave resonator, its structure comprises a substrate, a support layer, a bottom electrode, a piezoelectric layer and a top electrode sequentially arranged on the substrate and the support layer, it is characterized in that, described resonator also Including a low acoustic impedance layer, the upper surface of the substrate is provided with several vertical grooves, the support layer surrounds all the vertical grooves, is arranged on the substrate, and forms a large groove together with the substrate, the The low acoustic impedance layer completely fills the large groove and all the vertical grooves, and has a flat upper surface; the bottom electrode, the piezoelectric layer and the top electrode are sequentially arranged on the low acoustic impedance layer. 2. The piezoelectric thin-film bulk acoustic resonator according to claim 1, wherein the several vertical grooves are distributed in an array, and each vertical groove has the same shape, and its top view shape is a polygon, a rectangle or a circle, Its side view shape is groomed line or zigzag. 3 . The piezoelectric thin-film bulk acoustic resonator according to claim 1 , wherein the material of the low acoustic impedance layer is polyimide or cross-linked polyphenylene polymer. 4 . 4. The piezoelectric thin-film bulk acoustic wave resonator according to claim 1, wherein the material of the support layer adopts a high thermal conductivity material, and the height of the support layer is 10-50um. 5 . The piezoelectric thin-film bulk acoustic wave resonator according to claim 1 , wherein the substrate is a silicon substrate, and the piezoelectric layer is an aluminum nitride layer with a C-axis orientation. 6 . 6 . The piezoelectric thin-film bulk acoustic resonator according to claim 1 , wherein the bottom electrode and the top electrode are made of high acoustic impedance metal. 7 . 7. by the preparation method of the described piezoelectric thin-film bulk acoustic wave resonator of claim 1, it is characterized in that, comprise the following steps: Step 1, using dry etching or wet etching process to etch a plurality of vertical grooves at preset positions on the substrate; Step 2, using magnetron sputtering or chemical vapor deposition to deposit a layer of support layer material on the substrate of step 1, and obtain a patterned support layer by photolithography; Step 3, uniformly coating a layer of low-acoustic impedance material on the substrate and support layer in step 2 by using spin coating and casting processes, and then performing high-temperature curing to obtain a low-acoustic impedance layer; Step 4, using magnetron sputtering or electron beam evaporation to deposit a high acoustic impedance electrode layer on the upper surface of the low acoustic impedance layer and photoetching a bottom electrode pattern; Step 5, growing the piezoelectric layer on the bottom electrode by magnetron sputtering and photoetching the piezoelectric layer pattern; Step 6, using magnetron sputtering or electron beam evaporation to deposit a top electrode on the upper surface of the piezoelectric layer, and etching the top electrode pattern, that is, the preparation of the thin film bulk acoustic wave resonator is prepared.

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