CN103487474A - MEMS (micro-electromechanical systems) capacitive humidity sensor with high sensitivity and fast response - Google Patents

Abstract

The invention discloses an MEMS capacitive humidity sensor with high sensitivity and fast response. The sensor comprises a substrate (1) and an interdigital positive electrode (1-2) covered with a humidity sensing medium (2), wherein the substrate (1) is located at the bottom of a detection capacitor and has an action of a base; the interdigital positive electrode (1-2) and the surface of an interdigital negative electrode (1-3) are covered with the humidity sensing medium (2), a cavity (1-5) is formed between the interdigital negative electrode (1-3) and the substrate (1), and the humidity sensing medium (2) and an air layer (3) between the interdigital positive electrode (1-2) and the interdigital negative electrode (1-3) form a humidity sensing structure of the detection capacitor which adopts an interdigital cantilever beam structure. The capacitive humidity sensor has the advantages of high sensitivity, fast response, simple structure, convenience in processing, small stray capacitance and the like.

Description

A MEMS capacitive humidity sensor with high sensitivity and fast response

technical field

The invention relates to a MEMS (micro-electro-mechanical system) capacitive humidity sensor based on bulk silicon technology, in particular to a capacitive humidity sensor with an interdigital structure using porous silicon and an air layer as a medium.

Background technique

Humidity measurement is widely used in industry and agriculture as well as people's daily life, and it is also an indispensable factor for studying meteorological conditions. Humidity sensors have been developed for many years as an important part of humidity measurement systems. Humidity sensors made of silicon have also existed for more than ten years, and can be divided into capacitive, resistive, piezoresistive, cantilever beam, and thermocouple types according to their working types. Among them, the capacitive humidity sensor has the advantages of high sensitivity, low power consumption, good temperature characteristics, firm structure, and high sensitivity to external stress, making it the most widely studied.

At present, there are two main capacitive humidity sensors, one is the interdigital capacitive humidity sensor, the commonly used interdigital capacitive humidity sensor is formed by surface processing technology, its sensitive capacitance is small, and the parasitic capacitance is large, which is not conducive to measurement , and the other is a sandwich-structured humidity sensor. This sensor places a moisture-sensitive material between sensitive capacitor plates as a moisture-sensing medium. Although it has high sensitivity and small parasitic capacitance, its response speed is slow.

Contents of the invention

Technical problem: The purpose of the present invention is to provide a MEMS capacitive humidity sensor with high sensitivity and fast response. The technical problem to be solved is to propose a simple structure, convenient processing, sensitive Capacitive humidity sensor with large capacitance and small parasitic capacitance.

Technical solution: The MEMS capacitive humidity sensor with high sensitivity and fast response of the present invention includes a substrate and an interdigitated positive electrode covered with a moisture-sensitive medium; wherein, the substrate is located at the bottom of the detection capacitor and acts as a base, and the moisture-sensitive medium covers On the surface of the interdigital positive electrode and interdigital negative electrode, there is a cavity between the interdigital negative electrode and the substrate, and the air layer between the moisture-sensing medium and the interdigital positive electrode and interdigital negative electrode constitutes a moisture-sensing structure for detecting capacitance .

The moisture-sensing layer is a porous silicon layer.

The interdigitated positive electrode and the interdigitated negative electrode are low-resistance silicon.

The interdigital positive electrode and the interdigital negative electrode are interdigital structures with a high aspect ratio processed by bulk silicon technology.

There is an air layer between the interdigitated positive electrode and the interdigitated negative electrode and the substrate.

The substrate is glass.

The working principle of the capacitive humidity sensor with high sensitivity in the present invention is: in the technical solution of the present invention, the capacitive humidity sensor includes a medium layer, an air layer and interdigital electrodes, wherein the interdigital capacitance is in the form of a cantilever The beam structure is in which the dielectric layer is above the interdigital electrodes, and there is an air layer between the interdigital electrodes covering the dielectric layer and between the interdigital fingers and the substrate. When the moisture-sensitive medium layer absorbs moisture, its dielectric constant will change, which will cause the detection capacitor to deform, thereby realizing the humidity measurement function.

Beneficial effects: As an improvement to the technical solution of the present invention, the interdigital electrode is an interdigital structure with a high aspect ratio processed by bulk silicon technology. In terms of the processing cost of the material, the realization of the manufacturing process, and the size of the sensitive capacitor, the interdigitated electrode processed by the bulk processing process has the advantages of low cost, simple manufacturing process, and large sensitive capacitor.

As an improvement to the technical solution of the present invention, the substrate is a glass substrate, and a structure is formed with low-resistance silicon through a bonding process. In terms of the cost of the selected material, the manufacturing process and the performance of the material, choosing a glass substrate can reduce parasitic capacitance and has the advantage of a mature silicon-glass bonding process.

As an improvement to the technical solution of the present invention, there is an air cavity between the interdigital structure and the glass substrate, so that the interdigital structure with a high aspect ratio can sense moisture on both sides and improve the response time.

As an improvement to the technical solution of the present invention, there is an air cavity between the interdigital structures, so that the response time is improved.

Description of drawings

Fig. 1 is a top view of the capacitive relative humidity sensor of the present invention.

Fig. 2 is a cross-sectional view of the capacitive relative humidity sensor of the present invention.

In the figure, there are: substrate 1, interdigitated positive electrodes 1-2, interdigitated negative electrodes 1-3, air gaps 1-4, cavities 1-5, moisture sensitive medium 2, and air layer 3.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Preferred embodiments of the present invention are as follows:

As shown in Figure 1, the capacitive humidity sensor described in the present embodiment comprises the detection capacitance that is cantilever beam structure, and this sensor comprises substrate 1, is covered with the interdigital positive electrode 1-2 of moisture sensing medium 2; Wherein, substrate 1 is located at the bottom of the detection capacitor and acts as a base. The moisture-sensitive medium 2 covers the surface of the positive interdigital electrode 1-2 and the negative interdigital electrode 1-3. The positive interdigital electrode 1-2, the negative interdigital electrode 1-3 and the There are cavities 1-5 between the substrates 1, and the air layer 3 between the moisture-sensitive medium 2 and the interdigital positive electrode 1-2 and the interdigital negative electrode 1-3 constitutes the medium layer of the detection capacitance for sensing humidity. The variation of the dielectric constant between the electrodes; the detection capacitance is in the structure of interdigitated cantilever beams.

In this embodiment, the substrate 1 is a glass substrate, the moisture-sensitive medium 2 is porous silicon, and the interdigital positive electrode 1-2 and interdigital negative electrode 1-3 are both low-resistance silicon.

As shown in Figure 2, the manufacturing process of the capacitive humidity sensor described in this embodiment is as follows: first, low-resistance silicon is selected as the initial material, and a photolithography process and a wet etching process are performed on the back thereof to form a cavity 1- 5. Bond the silicon wafer and the glass substrate 1 to form a cavity structure with a base; perform photolithography and deep reactive ion etching processes on the front of the silicon wafer to form an interdigitated capacitor structure with a high aspect ratio, that is, to form The interdigitated positive electrode 1-2 and the interdigitated negative electrode 1-3; the molded silicon interdigitated structure is used as an anode to pass an electric current in HF acid solution for anodic oxidation, that is, the moisture-sensitive medium 2 can be obtained on the surface of the silicon wafer.

In this embodiment, the positive and negative electrodes, the porous silicon moisture-sensing layer and the air layer constitute the detection capacitance of the interdigitated structure. When the humidity changes, the porosity of the porous silicon will change its dielectric constant, which will cause capacitance to occur. deformation, and because there is an air layer between the porous silicon, there is no problem of slow diffusion of the polymer when it senses moisture, and the response time of the capacitive humidity sensor is greatly improved.

It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should belong to the protection scope of the appended claims of the present invention.

Claims (6)

1. one kind has the high sensitivity MEMS capacitance type humidity sensor of response fast, it is characterized in that, this sensor comprises substrate (1), is coated with the interdigital positive electrode (1-2) of humidity-sensitive medium (2); Wherein, substrate (1) is positioned at the bottom of Detection capacitance, play the pedestal effect, humidity-sensitive medium (2) covers the surface of interdigital positive electrode (1-2), interdigital negative electrode (1-3), be provided with cavity (1-5) between interdigital negative electrode (1-3) and substrate (1), the air layer (3) between humidity-sensitive medium (2) and interdigital positive electrode (1-2), interdigital negative electrode (1-3) forms the wet structure of sense of Detection capacitance.

2. a kind of high sensitivity MEMS capacitance type humidity sensor of response fast that has according to claim 1, is characterized in that, described humidity sensing layer (2) is porous silicon layer.

3. a kind of high sensitivity MEMS capacitance type humidity sensor of response fast that has according to claim 1, is characterized in that, described interdigital positive electrode (1-2), interdigital negative electrode (1-3) are low-resistance silicon.

4. a kind of high sensitivity MEMS capacitance type humidity sensor of response fast that has according to claim 1, is characterized in that the interdigital structure that described interdigital positive electrode (1-2), interdigital negative electrode (1-3) are bulk silicon technological processing.

5. a kind of high sensitivity MEMS capacitance type humidity sensor of response fast that has according to claim 1, is characterized in that, between the interdigital structure of described interdigital positive electrode (1-2), interdigital negative electrode (1-3) and substrate (1), is air layer.

6. a kind of high sensitivity MEMS capacitance type humidity sensor of response fast that has according to claim 1, is characterized in that, described substrate (1) is glass.

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