CN219009917U

CN219009917U - MEMS structure

Info

Publication number: CN219009917U
Application number: CN202223275941.5U
Authority: CN
Inventors: 李现飞; 刘端
Original assignee: Anhui Aofei Acoustics Technology Co ltd
Current assignee: Anhui Aofei Acoustics Technology Co ltd
Priority date: 2022-12-07
Filing date: 2022-12-07
Publication date: 2023-05-12
Anticipated expiration: 2032-12-07

Abstract

The application discloses MEMS structure includes: a substrate having a cavity; a vibration supporting layer formed over the substrate and covering the cavity; a first electrode layer formed over the vibration supporting layer; a seed layer formed over the first electrode layer; a piezoelectric layer formed over the seed layer; and a second electrode layer formed over the piezoelectric layer. In summary, in the MEMS structure provided by the application, the seed layer induces the piezoelectric layer to grow according to the crystal column structure, so that the piezoelectric layer has a better Z-axis crystal column growth structure and has better compactness.

Description

MEMS structure

Technical Field

The present application relates to the field of MEMS (Micro Electro Mechanical Systems, i.e., microelectromechanical systems) technology, and in particular, to a MEMS structure.

Background

Piezoelectric MEMS sensors and actuators are often made of piezoelectric materials such as piezoelectric ceramics, quartz (SiO 2), lithium niobate (libbo 3), aluminum nitride (AlN), zinc oxide (ZnO), lead zirconate titanate (PZT), and polyvinylidene fluoride (PVDF). Zinc oxide is nontoxic and harmless due to good semiconductor dielectric property and piezoelectric property, and is easy to form Z-axis preferred orientation. And the preparation of the zinc oxide film with high quality, high speed, large area and low cost can be realized by adopting the magnetron sputtering method, so that the zinc oxide material is widely applied to various piezoelectric devices such as micro-electromechanical systems, sensors, actuators and the like.

However, when the magnetron sputtering equipment is used for preparing zinc oxide, a zinc oxide film which grows and is compact in Z-axis crystal column is difficult to obtain. If the zinc oxide piezoelectric film has only a Z-axis crystal column growth structure but is not compact, the leakage current of the device can be increased, and the overall performance of the device is not improved. If the zinc oxide piezoelectric film has no Z-axis crystal column growth structure or has poor structure, the piezoelectric performance of the zinc oxide piezoelectric film can be reduced.

Disclosure of Invention

Aiming at the problems in the related art, the application provides a MEMS structure, and a piezoelectric layer with better compactness and piezoelectric performance can be obtained.

The technical scheme of this application is so realized, provides a MEMS structure, includes:

a substrate having a cavity;

a vibration supporting layer formed over the substrate and covering the cavity;

a first electrode layer formed over the vibration supporting layer;

a seed layer formed over the first electrode layer;

a piezoelectric layer formed over the seed layer;

and a second electrode layer formed over the piezoelectric layer.

Wherein the MEMS structure is applied to a microphone or a speaker.

Wherein the material of the seed layer comprises zinc oxide, and the material of the piezoelectric layer comprises zinc oxide.

Wherein the deposition air pressure of the seed layer is 1 to 2 Pa, and the deposition air pressure of the piezoelectric layer is 0.6 to 0.8Pa.

The surface roughness of the first electrode layer is less than 5 nanometers, and the surface roughness of the second electrode layer is less than 5 nanometers.

In summary, in the MEMS structure provided herein, a seed layer is formed over a vibration supporting layer, and then a piezoelectric layer is grown over the seed layer. The seed layer induces the piezoelectric layer to grow according to the crystal column structure, so that the piezoelectric layer has a better Z-axis crystal column growth structure and has better compactness. The better Z-axis crystal column growth structure shows the better piezoelectric performance of zinc oxide.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 illustrates a schematic cross-sectional view during fabrication of a MEMS structure according to some embodiments;

FIG. 2 illustrates a cross-sectional schematic view of a MEMS structure in accordance with some embodiments;

fig. 3 shows an SEM (scanning electron microscope, i.e., scanning electron microscope) surface view of a piezoelectric layer with a seed layer, according to some embodiments.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application are within the scope of the protection of the present application.

Referring to fig. 1 and 2, according to an embodiment of the present application, a MEMS structure is provided, which may be applied to a sensor such as a microphone, or an actuator such as a speaker. The MEMS structure comprises a substrate 1, a vibration supporting layer 2, a first electrode layer 3, a seed layer 4, a piezoelectric layer 5 and a second electrode layer 6. The MEMS structure will be described in detail below.

The substrate 1 has a cavity 11. The vibration supporting layer 2 is formed over the substrate 1 and covers the cavity 11. The first electrode layer 3 is formed above the vibration supporting layer 2. A seed layer 4 is formed over the first electrode layer 3. A piezoelectric layer 5 is formed over the seed layer 4. A second electrode layer 6 is formed over the piezoelectric layer 5.

In some embodiments, the substrate 1 comprises silicon or any suitable silicon-based compound or derivative (e.g., silicon wafer, SOI, polysilicon on SiO 2/Si).

In some embodiments, the vibration supporting layer 2 comprises a single-layer or multi-layer composite film structure of silicon nitride (Si 3N 4), silicon oxide, single crystal silicon, polysilicon, or other suitable supporting material.

In some embodiments, the material of the seed layer 4 comprises zinc oxide and the material of the piezoelectric layer 5 comprises zinc oxide. The deposition pressure of the seed layer 4 is 1 to 2 Pa, and the deposition pressure of the piezoelectric layer 5 is 0.6 to 0.8Pa.

In some embodiments, the first electrode layer 3 and the second electrode layer 6 comprise aluminum, gold, platinum, molybdenum, titanium, chromium, and composite films or other suitable materials composed thereof. The surface roughness of the first electrode layer 3 is less than 5nm and the surface roughness of the second electrode layer 6 is less than 5nm.

In some embodiments, the seed layer 4 and the piezoelectric layer 5 may convert the applied pressure into a voltage, and the first electrode layer 3 and the second electrode layer 6 may transmit the generated voltage to other integrated circuit devices.

Referring to fig. 3, an SEM surface microstructure of the piezoelectric layer 5 is shown in fig. 3, and it can be seen that the piezoelectric layer 5 of zinc oxide has a good microstructure.

In summary, in the MEMS structure provided by the present application, the seed layer 4 is formed above the vibration supporting layer 2, and then the piezoelectric layer 5 is grown above the seed layer 4, and the seed layer 4 and the piezoelectric layer 5 are zinc oxide layers formed by a magnetron sputtering method. The seed layer 4 induces the piezoelectric layer 5 to grow according to the crystal column structure, so that the piezoelectric layer 5 has a better Z-axis crystal column growth structure and has better compactness. The better Z-axis crystal column growth structure shows the better piezoelectric performance of zinc oxide.

In addition, methods of forming the MEMS structure are provided. The flow of the method will be described in detail below.

Step 1, cleaning the substrate 1 by using a chemical cleaning method.

And 2, forming a vibration supporting layer 2 on the cleaned substrate 1.

Step 3, the first electrode layer 3 is prepared over the vibration supporting layer 2 using PVD (Physical Vapor Deposit, physical vapor deposition) equipment.

And 4, preparing a seed layer 4 on the first electrode layer 3 by using PVD radio frequency magnetron sputtering equipment under the high-pressure condition. The material of the seed layer 4 comprises zinc oxide. The zinc metal target material prepared by using the radio frequency magnetron reactive sputtering method has the purity of better than 99.95%, the purity of the reaction gases of argon and oxygen is better than 99.95%, the temperature of the substrate 1 is 150-200 ℃, the power is 120W, and the deposition air pressure is 1.0-2.0 Pa.

And 5, preparing the piezoelectric layer 5 on the seed layer 4 by using PVD radio frequency magnetron sputtering equipment under the condition of low air pressure. The purity of Zn metal target is better than 99.95%, the purity of reaction gases such as argon and oxygen is better than 99.95%, the temperature of the substrate 1 is 150-200 ℃, the power is 120W, and the deposition pressure is 0.6-0.8 Pa.

In the MEMS structure obtained based on the preparation method, the piezoelectric layer 5 of zinc oxide has a better Z-axis crystal column growth structure and better compactness, and an XRD (X-ray diffraction) test has very good (0002) crystal orientation preferred orientation. In addition, the piezoelectric layer 5 of zinc oxide prepared under the low pressure condition is more beneficial to mass production of MEMS structures.

The foregoing description of the preferred embodiments of the present utility model is not intended to limit the utility model to the precise form disclosed, and any modifications, equivalents, and variations which fall within the spirit and principles of the present utility model are intended to be included within the scope of the present utility model.

Claims

1. A MEMS structure, comprising:

a substrate having a cavity;

a vibration supporting layer formed over the substrate and covering the cavity;

a first electrode layer formed over the vibration supporting layer;

a seed layer formed over the first electrode layer;

a piezoelectric layer formed over the seed layer;

and a second electrode layer formed over the piezoelectric layer.

2. The MEMS structure of claim 1, wherein the MEMS structure is applied to a microphone or speaker.

3. The MEMS structure of claim 1, wherein the material of the seed layer comprises zinc oxide and the material of the piezoelectric layer comprises zinc oxide.

4. The MEMS structure of claim 3 wherein the seed layer has a deposition pressure of 1 to 2 pa and the piezoelectric layer has a deposition pressure of 0.6 to 0.8pa.

5. The MEMS structure of claim 1 wherein the surface roughness of the first electrode layer is less than 5 nanometers and the surface roughness of the second electrode layer is less than 5 nanometers.