阅读说明：本技术 一种薄膜体声波谐振器及其分隔制备工艺 (Film bulk acoustic resonator and separation preparation process thereof ) 是由 齐本胜 孙彬彬 蔡春华 苗红霞 华迪 谈俊燕 于 2019-10-25 设计创作，主要内容包括：本发明公开了一种薄膜体声波谐振器及其分隔制备工艺,其中薄膜体声波谐振器由下至上依次包括柔性基底和压电振荡堆,所述压电振荡堆包括耐腐蚀薄膜、下电极、压电薄膜、上电极。本发明主要针对上述薄膜体声波谐振器提出了一种新型的制备工艺,采用了聚酰亚胺与压电振荡堆分隔制备的工艺步骤,解决了聚酰亚胺的耐温性与压电振荡堆制备中退火所需的高温环境之间的矛盾,提高电极和压电薄膜的成膜质量,提升FBAR器件的谐振性能。(The invention discloses a film bulk acoustic resonator and a separation preparation process thereof, wherein the film bulk acoustic resonator sequentially comprises a flexible substrate and a piezoelectric oscillation stack from bottom to top, and the piezoelectric oscillation stack comprises a corrosion-resistant film, a lower electrode, a piezoelectric film and an upper electrode. The invention mainly provides a novel preparation process for the film bulk acoustic resonator, adopts the process steps of separating and preparing the polyimide and the piezoelectric oscillating stack, solves the contradiction between the temperature resistance of the polyimide and the high-temperature environment required by annealing in the preparation of the piezoelectric oscillating stack, improves the film forming quality of the electrode and the piezoelectric film, and improves the resonance performance of the FBAR device.)

1. A film bulk acoustic resonator characterized by: the resonator sequentially comprises a flexible substrate (10) and a piezoelectric oscillation stack from bottom to top, the piezoelectric oscillation stack comprises a corrosion-resistant film (3), a lower electrode (4), a piezoelectric film (5) and an upper electrode (7), the upper electrode (7) is arranged on the upper surface of the piezoelectric film (5), the lower electrode (4) is arranged on the lower surface of the piezoelectric film (5), and the left ends of the upper electrode (7) and the lower electrode (4) are flush with the left end of the piezoelectric film (5); the right end of the upper surface of the piezoelectric film (5) is provided with a through hole (6) from top to bottom, the bottom of the through hole (6) extends to the upper surface of the lower electrode (4), and the right end of the upper electrode (7) does not reach the orifice of the through hole (6).

2. A thin film bulk acoustic resonator according to claim 1, wherein: the material of the flexible substrate (10) is polyimide.

3. A thin film bulk acoustic resonator according to claim 1, wherein: the material of the corrosion-resistant film (3) is platinum.

4. A thin film bulk acoustic resonator according to claim 1, wherein: the lower electrode (4) and the upper electrode (7) are made of one of Al, Mo or Pt as a metal material.

5. A thin film bulk acoustic resonator according to claim 1, wherein: the piezoelectric film (5) is made of one of ZnO and AlN.

6. A thin film bulk acoustic resonator according to claim 1, wherein: the thickness of the flexible substrate (10) is 200-550 μm, the thickness of the corrosion-resistant film (3) is 5-10nm, the thicknesses of the lower electrode (4) and the upper electrode (7) are 50-200nm, and the thickness of the piezoelectric film (5) is 1-10 μm.

7. A separation preparation process for the film bulk acoustic resonator according to claim 1, characterized in that a polyimide and piezoelectric oscillating stack separation preparation method is adopted, and the separation preparation process specifically comprises the following steps:

step S1: selecting silicon dioxide, cleaning and drying for later use;

step S2: carrying out magnetron sputtering on a Cr metal thin layer and a Pt metal thin layer on the silicon dioxide layer in sequence;

step S3: preparing a three-layer piezoelectric oscillating stack structure of a lower electrode, a piezoelectric film and an upper electrode on the Pt metal thin layer by magnetron sputtering in sequence, imaging, and performing annealing treatment after the imaging is finished;

step S4: flatly covering the surface of the piezoelectric oscillation stack structure with a thermal stripping film, and then putting the piezoelectric oscillation stack structure into buffer etching liquid to corrode the silicon dioxide layer;

step S5: after the corrosion is finished, cleaning the surface and drying the surface, spin-coating a polyimide layer on the surface of one side which is not covered with the thermal peeling film, drying and curing, wherein the drying temperature is lower than 120 ℃;

step S6: adjusting to make one side of the thermal stripping film face upwards, heating to a fixed temperature for a period of time, and removing the thermal stripping film by making the thermal stripping film lose viscosity.

Technical Field

The invention relates to the technical field of radio frequency micro-electro-mechanical systems, in particular to a film bulk acoustic resonator and a separation preparation process of the film bulk acoustic resonator.

Background

A Film Bulk Acoustic Resonator (FBAR) is a novel Acoustic resonance device, the core structure is a sandwich structure of an upper layer of electrode, a lower layer of electrode and a piezoelectric Film, the principle is that the piezoelectric material can perform mutual conversion between electric energy and mechanical energy, and an external electric signal is used for exciting high-frequency Acoustic resonance by an inverse piezoelectric effect. Compared with the traditional Quartz Crystal Microbalance (QCM), the film bulk acoustic resonator has the advantages of small volume, high working frequency, low power consumption, small insertion loss and the like. At present, FBAR has been widely used in the field of wireless communication, and the application of FBAR devices in the field of sensors is attracting much research interest due to its excellent characteristics.

Typical FBAR device structures are three types, back-etched, solid-assembled (SMR), and air-gap. The back etching and air gap type forms air layers on two sides of the resonant cavity to obtain good sound wave reflection and ensure the Q value of the FBAR device, and the solid assembly type simulates air low sound impedance through a Bragg reflector formed by alternately stacking high/low sound impedance layers. However, the three methods have obvious defects, and although the back etching is simple to prepare, the structure strength is low, the yield is low, and the mass production cannot be realized; the solid assembly type and air gap type are complex in process and high in cost, and the existence of the lower cavity of the air gap type lower electrode can also reduce the stability of the device structure.

The three FBAR device structures all use silicon as a substrate, which is a significant characteristic of solid electronics, and the rapid development of solid electronics brings technological innovation, but with the increase of application scenes, people are no longer limited to rigid substrates, but hope to have flexible electronics to make up for the deficiency of rigid substrates, for example, the special requirements of the original appearance (flexible display screen and the like) can be easily changed. In recent years, due to the development of micro-processing means, the progress of advanced organic polymer materials and preparation processes thereof, flexible electronics is developed rapidly, application scenes of prepared electric appliances are increased, the reliability of the electric appliances is improved, and a good reference method is provided for a flexible film bulk acoustic resonator. How to replace the FBAR device with the three structures is one of the research focuses, that is, a low acoustic impedance material is found to replace an air cavity and a bragg reflector, polyimide in an organic polymer material has the characteristic of low acoustic impedance at the same time, and can be used as a flexible substrate of the FBAR device, the polyimide has stable chemical properties, is high temperature resistant and good in flexibility, and can be used for preparing the flexible FBAR device to obtain a better application scene.

Currently, researches on polyimide as a flexible substrate of an FBAR device have been reported, and a conventional preparation method is to directly deposit each layer of film of the FBAR device on the polyimide. However, there are many problems in practical preparation, for example, polyimide is used as an organic polymer material, and surface partial regions of the polyimide are prone to wrinkle under high-temperature environments of sputtering substrate heating and annealing in the piezoelectric oscillation stack preparation process, so that the surface is not flat enough, and the film forming quality of subsequent electrodes and piezoelectric films is affected. Meanwhile, the high temperature of the annealing heat treatment environment required by the preparation of the electrode and the piezoelectric film is close to or exceeds the upper limit of the heat-resistant temperature of polyimide, the effect of removing residual stress in the film in the annealing process can be limited, the quality of the film is influenced, and the resonance performance of the FBAR device is reduced.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a structural design of a film bulk acoustic resonator, a polyimide layer ensures the limitation of acoustic waves in a piezoelectric oscillation stack of a device, the structural reliability of the device is high, and the device has good resonance performance, and a separation preparation process of the film bulk acoustic resonator.

The technical scheme of the invention is as follows:

the utility model provides a film bulk acoustic resonator, from supreme flexible base and the piezoelectric oscillation heap of including in proper order down, piezoelectric oscillation piles including corrosion-resistant film, bottom electrode, piezoelectric film, upper electrode, the upper electrode sets up the upper surface at piezoelectric film, and the bottom electrode sets up at piezoelectric film lower surface, and the left end of upper electrode and bottom electrode flushes with the left end of piezoelectric film. The right end of the upper surface of the piezoelectric film is provided with a through hole from top to bottom, the bottom of the through hole extends to the upper surface of the lower electrode, and the right end of the upper electrode does not reach the orifice of the through hole.

Preferably, the material of the flexible substrate is polyimide.

Preferably, the material of the corrosion-resistant thin film is a Pt metal material.

Preferably, the material of the lower electrode and the lower electrode is one of metal materials of Al, Mo, or Pt.

Preferably, the material of the piezoelectric thin film is one of ZnO and AlN.

Preferably, the thickness of the flexible substrate is 200 μm to 550 μm, the thickness of the corrosion-resistant film is 5nm to 10nm, the thickness of the lower electrode and the upper electrode is 50 nm to 200nm, and the thickness of the piezoelectric film is 1 μm to 10 μm.

The invention also provides a separation preparation process of the film bulk acoustic resonator, which adopts a method for separating and preparing polyimide and the piezoelectric oscillation stack, and specifically comprises the following steps:

step S1: quartz glass (silicon dioxide) is selected to be cleaned and dried for standby;

step S2: carrying out magnetron sputtering on a Cr metal thin layer and a Pt metal thin layer on the silicon dioxide layer in sequence;

step S3: preparing a three-layer piezoelectric oscillating stack structure of a lower electrode, a piezoelectric film and an upper electrode by magnetron sputtering in sequence on the Pt metal thin layer, imaging, and performing annealing treatment after the imaging is finished;

step S4: flatly covering the surface of the piezoelectric oscillation stack structure with a thermal stripping film, and then putting the piezoelectric oscillation stack structure into buffer etching liquid to corrode the silicon dioxide layer;

step S5: after the corrosion is finished, cleaning the surface and drying the surface, spin-coating a polyimide layer on the surface of one side which is not covered with the thermal peeling film, drying and curing, wherein the drying temperature is lower than 120 ℃;

step S6: adjusting to make one side of the thermal stripping film face upwards, heating to a fixed temperature for a period of time, and removing the thermal stripping film by making the thermal stripping film lose viscosity.

The invention ensures a good sound wave reflecting layer of a classic FBAR structure through the polyimide layer made of the flexible material, reduces sound wave leakage as much as possible, improves the Q value of the device, ensures the structural strength of the FBAR device, and improves the yield of the device compared with back etching and air gap type. And the use of the flexible material also enables the FBAR device to have certain bending characteristics, so that the FBAR device can be used for more application scenes.CThe r metal improves the adhesive force of the film on the quartz glass to prevent separation, the Pt metal and the thermal stripping film are not easy to react with the corrosive liquid to isolate the electrode and the corrosive liquid when corroding the substrate, the thermal stripping film can be used as a medium for transferring the piezoelectric oscillation stack structure to prevent the structural layer from being broken due to lack of support, and the thermal stripping film can be heated for a period of time at a fixed temperature and then loses viscosity to strip without polluting the piezoelectric oscillation stack. The process step of separating and preparing the polyimide and the piezoelectric oscillating stack is skillfully adopted, so that the annealing high-temperature environment in the preparation of the electrode and the piezoelectric film is not limited by the temperature resistance of the polyimide, the film quality of the electrode and the piezoelectric film is further improved, and the resonance performance of the FBAR device is improved. Compared with the solid assembly type of the classic FBAR structure, the process also reduces the process complexity, reduces the process cost and finally can realize batch production.

Drawings

Fig. 1 is a schematic diagram of an overall structure of a film bulk acoustic resonator according to an embodiment of the present invention;

FIG. 2 is a schematic flow chart of the preparation process of the invention.

In the figure: 1 quartz glass, 2 metal Cr, 3 corrosion-resistant film, 4 lower electrode, 5 piezoelectric film, 6 through holes, 7 upper electrode, 8 thermal stripping film, 9 buffer corrosive liquid and 10 flexible substrate.

Detailed Description

The present invention is specifically illustrated below with reference to examples: