CN104764511A - C-axis tilt gallium nitride FBAR piezoelectric mass sensor - Google Patents

Abstract

The present invention provides a c-axis inclined gallium nitride FBAR piezoelectric mass sensor, which includes: a sensitive layer, an upper electrode, a signal terminal, a ground terminal, a c-axis inclined gallium nitride piezoelectric film, an etching hole, a lower electrode, Bragg reflection layer and substrate; the signal terminal and the ground terminal are arranged on the top of the c-axis tilted gallium nitride piezoelectric film; the upper electrode is connected to the signal terminal and coated with the sensitive layer; the lower electrode passes through The etching hole arranged on the piezoelectric film is connected to the ground terminal; the lower electrode is deposited on the Bragg reflective layer, and the Bragg reflective layer is deposited on the substrate. The present invention proposes a c-axis inclined GaN FBAR piezoelectric mass sensor. The piezoelectric film adopts a c-axis inclined gallium nitride piezoelectric film. A certain c-axis inclination angle is preferred, so that the mass sensor can be used in a humid environment or in a liquid phase. work normally in the environment.

Description

A c-axis tilted Gallium Nitride FBAR piezoelectric mass sensor

technical field

The invention relates to a mass sensor, in particular to a piezoelectric mass sensor.

Background technique

In recent years, the research and detection of proteins, microorganisms, nucleic acids, enzyme cells, etc. in the fields of molecular biology, pathology, medical diagnostics, and bacteriology have become a research hotspot. In the process of experimental research, it is necessary to detect their extreme Micromass, which requires mass sensors with mass sensitivity down to the molecular weight level and the ability to work in wet or liquid phase environments. At present, in the detection of protein molecules and DNA, the piezoelectric mass sensor is a relatively effective means. Its mass sensitivity has reached the single molecular weight level, and it meets the requirements for detecting extremely small masses. It has a very wide application in the field of biological mass sensors. prospect.

At present, there are mainly three types of piezoelectric crystal mass sensors: quartz crystal microbalance (QCM), surface acoustic wave mass sensor (SAW), and film bulk acoustic wave mass sensor (FBAR). The quartz wafer of QCM cannot be made very thin, resulting in low sensitivity and large volume of the QCM mass sensor, which cannot be miniaturized and integrated. The mass sensitivity of the SAW mass sensor is limited by the distance between the interdigitated electrodes. It is difficult to further improve the mass sensitivity of the SAW mass sensor by the current photolithography process. In addition, some SAW mass sensors have specific requirements for the device substrate, which is not conducive to the realization of the SAW mass sensor. Miniaturization and integration. The reported FBAR mass sensor has high mass sensitivity and is easy to miniaturize and integrate, but the technology is not yet mature. In the humid environment and liquid phase environment, the sound wave is greatly attenuated in the device, which leads to the failure of the FBAR mass sensor. Work.

From the above analysis, it can be seen that the existing piezoelectric mass sensor does not solve the problem of being able to work in a wet or liquid environment while still having high mass sensitivity and miniaturization and integration. The present invention can be used in wet environments and liquids. It is of great significance to detect extremely small masses in phase environments and to promote the wide application of mass sensors with FBAR structures.

Contents of the invention

The main technical problem to be solved by the present invention is to provide a piezoelectric mass sensor that can work in a wet or liquid environment and has high mass sensitivity.

The secondary technical problem to be solved by the present invention is that the above-mentioned piezoelectric mass sensor can be miniaturized and integrated.

In order to solve the above-mentioned technical problems, the present invention provides a c-axis tilted gallium nitride FBAR piezoelectric mass sensor, including: a sensitive layer, an upper electrode, a signal terminal, a ground terminal, a c-axis tilted gallium nitride piezoelectric film, an engraved Etch holes, bottom electrodes, Bragg reflectors and substrates;

The signal terminal and the ground terminal are arranged on the top of the c-axis inclined gallium nitride piezoelectric film; the upper electrode is connected to the signal terminal and coated with the sensitive layer; The etch hole is connected to the ground; the lower electrode is deposited on the Bragg reflective layer, and the Bragg reflective layer is deposited on the substrate.

In a preferred embodiment: the Bragg reflection layer is composed of high acoustic resistance layers and low acoustic resistance layers stacked alternately.

In a preferred embodiment: the material of the substrate is gallium nitride.

In a preferred embodiment: the tilt angle of the c-axis tilt GaN piezoelectric thin film is 0°-360°.

In a preferred embodiment: the inclination angle of the c-axis inclined GaN piezoelectric film is 42.8°.

In a preferred embodiment: there are two ground terminals.

In a preferred embodiment: peripheral circuits are etched on the gallium nitride substrate.

In a preferred embodiment: the Bragg reflection layer is composed of three layers of high acoustic resistance layers and three layers of low acoustic resistance layers alternately laminated.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

1. A c-axis tilted gallium nitride FBAR piezoelectric mass sensor proposed by the present invention, the piezoelectric film adopts a c-axis tilted gallium nitride piezoelectric film, preferably with a certain c-axis tilt angle, so that the mass sensor can be used in a humid environment or Works well in a liquid environment.

2. A c-axis inclined gallium nitride FBAR piezoelectric mass sensor proposed by the present invention adopts an FBAR structure, and its process can be compatible with traditional semiconductor processes. It has the characteristics of miniaturization and integration, and the sensor mass sensitivity is extremely high. high.

Description of drawings

Fig. 1 is the structural representation of piezoelectric mass sensor in the embodiment of the present invention;

Fig. 2 is in the embodiment of the present invention the GaN piezoelectric thin film c-axis inclines 42.8 ° when the _SiO to be measured The change in frequency when the quality changes;

Fig. 3 is in the embodiment of the present invention, when the c-axis of GaN piezoelectric film is tilted 60°, the _SiO2 to be measured is changed in frequency shift when the quality changes;

Fig. 4 is a graph showing the relationship between the mass change of the _SiO2 to be measured and the absolute frequency shift when the c-axis of the gallium nitride piezoelectric thin film is tilted by 0-90° in an embodiment of the present invention.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

As shown in Figure 1, a c-axis tilted gallium nitride FBAR piezoelectric mass sensor includes a sensitive layer 1, an upper electrode 2, a signal terminal 3, a ground terminal 4, a piezoelectric film 5, an etching hole 6, and a lower electrode 7 , Bragg reflection layer 8 and substrate 9 .

In this specific embodiment, the gallium nitride substrate 9, on the one hand, serves as the supporting layer of the sensor, and on the other hand, as a semiconductor, the peripheral circuit can be etched to integrate with the piezoelectric mass sensor, and on the upper surface of the gallium nitride substrate 9 Depositing the Bragg reflection layer 8; the Bragg reflection layer 8 is formed by alternately laminating three layers of high acoustic resistance layers and three layers of low acoustic resistance layers. A lower electrode 7 is deposited on the upper surface of the Bragg reflective layer 8, and a c-axis tilted gallium nitride piezoelectric film 5 is deposited on the upper surface of the lower electrode 7. The c-axis inclination of the gallium nitride piezoelectric film is adjustable, and the gallium nitride piezoelectric film 5 is A surface arrangement device signal terminal 3 , two ground terminals 4 and an upper electrode 2 , and the upper electrode 2 is connected to the signal terminal 3 . A sensitive layer 1 is coated on the surface of the upper electrode 2 , and the two ground terminals 4 are connected to the lower electrode 7 through the etched holes 6 in the gallium nitride piezoelectric film 5 .

When the c-axis tilted GaN FBAR piezoelectric mass sensor is working, the c-axis tilted GaN piezoelectric film vibrates under the piezoelectric effect to generate shear waves, which have little attenuation in humid environments and liquid phase environments. , using the generated shear wave, when the mass of the sensitive layer 1 changes in a humid environment and a liquid phase environment, the resonant frequency of the c-axis tilted gallium nitride FBAR piezoelectric mass sensor will shift in frequency, by detecting the resonant frequency The frequency shift detects the mass of the substance to be measured, and realizes that the c-axis tilted gallium nitride FBAR piezoelectric mass sensor works in a humid environment and a liquid phase environment.

In order to verify the feasibility of the c-axis tilted gallium nitride FBAR piezoelectric mass sensor proposed by the present invention, a simulation is carried out. The effective area of the upper electrode 2 is 300 μm×300 μm, the thickness of the c-axis tilted gallium nitride piezoelectric thin film 5 is 2 μm, the object to be tested is SiO ₂ , and other materials can be selected for the object to be tested, just change the sensitive layer 1. .

Figures 2 and 3 show the frequency shift of the resonant frequency of the c-axis tilted gallium nitride piezoelectric film 5 when tilted at 42.8° and 60° with different masses of SiO ₂ , and the c-axis tilted gallium nitride FBAR when tilted at 42.8° There are only shear waves inside the piezoelectric mass sensor, and when the tilt is 60°, shear waves and longitudinal waves exist simultaneously. Figure 4 shows the relationship between the mass change of the _SiO2 to be measured and the absolute frequency shift when the c-axis tilted GaN piezoelectric film 5 is tilted from 0° to 90°, the slope of the straight line is the mass sensitivity of _SiO2 at each angle, About -820cm ² /g. It can be seen that the c-axis tilted gallium nitride FBAR piezoelectric mass sensor proposed by the present invention can work normally in a wet or liquid phase environment, and has high mass sensitivity.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present invention can easily think of changes or Replacement should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (8)

1. a c-axis inclination gallium nitride FBAR piezoelectric mass sensor, is characterized in that comprising: sensitive layer, top electrode, signal end, earth terminal, c-axis inclination gallium nitride piezoelectric membrane, etched hole, bottom electrode, Bragg reflecting layer and substrate;

Described signal end and earth terminal are at the routed on top of c-axis inclination gallium nitride piezoelectric membrane; Described top electrode is connected with signal end, and is coated with described sensitive layer; Bottom electrode is connected with earth terminal by the etched hole being arranged on piezoelectric membrane; Bottom electrode is deposited on Bragg reflecting layer, and Bragg reflection is deposited upon on substrate.

2. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 1, is characterized in that: described Bragg reflecting layer is by loud resistance layer and resistance layer is alternately laminated in a low voice forms.

3. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 1, is characterized in that: the material of described substrate is gallium nitride.

4. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 1, is characterized in that: the angle of inclination of described c-axis inclination gallium nitride piezoelectric membrane is 0 °-360 °.

5. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 1, is characterized in that: the angle of inclination of described c-axis inclination gallium nitride piezoelectric membrane is 42.8 °.

6. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 1, is characterized in that: described earth terminal is 2.

7. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 3, is characterized in that: described gallium nitride substrate etching peripheral circuit.

8. a kind of c-axis inclination gallium nitride FBAR piezoelectric mass sensor according to claim 2, is characterized in that: resistance layer is alternately laminated in a low voice forms by three floor height acoustic resistance layers and three layers for described Bragg reflecting layer.