CN101620197B - Rapid response CMOS relative humidity sensor - Google Patents

Abstract

A fast-response CMOS relative humidity sensor, which is composed of a substrate, an oxide layer, a capacitive electrode, and a humidity-sensitive medium. The sensitive medium is set between the capacitor electrodes and above the capacitor electrodes, corroding the substrate and the oxide layer above it to form a cavity, so that the lower surface of the humidity sensitive medium between the capacitor electrodes is also in contact with the air, and the capacitor electrodes are interdigitated The electrodes are arranged in a staggered manner, and the common ends of each group of interdigitated electrodes and the free ends of the interdigitated electrodes are fixed on the oxide layer to ensure the mechanical strength of the electrodes. The invention adopts polyimide as the humidity sensitive medium, corrodes the substrate and the oxide layer above it to form a cavity, and the upper and lower sides of the humidity sensitive medium between the capacitor electrodes are air, and the sensor has fast response speed and high sensitivity. High, small substrate parasitic and other advantages.

Description

A Fast Response CMOS Relative Humidity Sensor

technical field

The invention relates to a relative humidity sensor based on a standard CMOS process, in particular to a fast-response CMOS relative humidity sensor.

Background technique

Humidity measurement is widely used in national defense aviation, weather forecast, industrial manufacturing, agricultural production, medical and health, food processing and other fields. As an important part of the humidity measurement system, the humidity sensor has been developed for many years. From the original traditional humidity sensors such as wet and dry bulb hygrometers and hair hygrometers to the miniature humidity sensors that can be manufactured by standard CMOS technology. Humidity sensors processed by standard CMOS technology have the advantages of small size, low price, and good product consistency. They are the hotspots of humidity sensor research in recent years. In addition, it is easy to monolithically integrate the humidity sensor and detection circuit by using a standard CMOS process, which can improve the stability and anti-interference ability of the humidity detection system. In 2001, Y.Y.Qiu (name) proposed a humidity sensor made using CMOS technology. The humidity sensor uses polyimide as the humidity sensitive medium, integrates the detection circuit and the humidity sensitive capacitor monolithically, and directly converts the change of the humidity sensitive capacitor It is a voltage change output, which is convenient for the back-end detection system to perform signal sampling and processing, but the response speed of the humidity sensor with this structure is slow. In 2004, Chinese Gu Lei proposed a humidity sensor made using CMOS technology. The sensitive unit of the humidity sensor is an interdigital capacitor structure. The grid-shaped polysilicon heating resistor is placed under the interdigital electrode, and polyimide is used As a humidity sensitive medium, it has high sensitivity and good linearity, but the hysteresis characteristic of the sensor is not very good, and the response is slow. The heating circuit can increase the temperature of the humidity sensitive unit, thereby speeding up the response speed of the sensor, but this will inevitably make The power consumption of the sensor increases.

Contents of the invention

Technical problem: The purpose of this invention is to propose a CMOS relative humidity sensor with fast response compatible with standard CMOS technology, which has the advantages of fast response speed, high sensitivity, simple structure and small substrate parasitic.

Technical solution: The present invention is a high-speed response CMOS relative humidity sensor, which is composed of a substrate, an oxide layer, a capacitor electrode, and a humidity-sensitive medium. The oxide layer is arranged on the substrate, and the capacitor electrode is arranged on the oxide layer. The capacitor electrode consists of The pressure welding block is drawn out, and the humidity sensitive medium is arranged between and above the capacitor electrodes, corroding the substrate and the oxide layer above it, forming a cavity, so that the lower surface of the humidity sensitive medium between the capacitor electrodes is also in contact with the air, The capacitor electrodes are interdigitated electrodes arranged in a staggered manner, and the common ends of each group of interdigitated electrodes and the free ends of the interdigitated electrodes are fixed on the oxide layer to ensure the mechanical strength of the capacitor electrodes.

Beneficial effects: the invention has simple process steps, is manufactured by combining standard CMOS process and MEMS processing technology, has low cost, high precision and good long-term stability. The humidity sensor proposed by the present invention uses polyimide as the humidity sensitive medium, which has high sensitivity, and the substrate and the oxide layer above it are corroded to form a cavity, so that the upper and lower sides of the humidity sensitive medium between the capacitor electrodes are air, The response speed of the sensor is accelerated, and the parasitic effect of the substrate is reduced.

Description of drawings

Fig. 1 is a top view of the present invention, in which there are: an oxide layer 2, a first capacitance electrode 3, a second capacitance electrode 4, a first common end 31 of the interdigitated electrodes, a second common end 41 of the interdigitated electrodes, The first free end 32 of the interdigitated electrode, the second free end 42 of the interdigitated electrode, the first pressure welding block 33 , the second pressure welding block 43 , the humidity sensitive medium 5 , and the cavity 6 .

FIG. 2 is a cross-sectional view of the present invention, in which there are: a substrate 1 , an oxide layer 2 , a first capacitor electrode 3 , a second capacitor electrode 4 , a humidity-sensitive medium 5 , and a cavity 6 .

Detailed ways

The present invention is a fast-response CMOS relative humidity sensor, which consists of a substrate 1, an oxide layer 2, a first capacitor electrode 3, a second capacitor electrode 4, and a humidity-sensitive medium 5. The oxide layer 2 is arranged on the substrate 1, The first capacitance electrode 3 and the second capacitance electrode 4 are arranged on the oxide layer 2, the first capacitance electrode 3 and the second capacitance electrode 4 are respectively drawn out by the first pressure soldering block 33 and the second pressure soldering block 43, and the humidity sensitive medium 5 Set between the first capacitor electrode 3 and the second capacitor electrode 4 and above the first capacitor electrode 3 and the second capacitor electrode 4, etch the substrate 1 and the oxide layer 2 above it to form a cavity 6, so that the first capacitor The lower surface of the humidity-sensitive medium 5 between the electrode 3 and the second capacitance electrode 4 is also in contact with the air, the first capacitance electrode 3 and the second capacitance electrode 4 are interdigitated electrodes and are arranged in a staggered manner, and each group of interdigitated electrodes The first common end 31 and the second common end 41 and the first free end 32 and the second free end 42 of the interdigitated electrode are all fixed on the oxide layer 2, so as to ensure the contact between the first capacitance electrode 3 and the second capacitance electrode 4 Mechanical strength.

In this embodiment, the substrate 1 is bulk silicon, the oxide layer 2 is silicon dioxide, the first capacitor electrode 3 and the second capacitor electrode 4 are aluminum electrodes, and the humidity sensitive medium 5 is polyimide. The present invention can use the following process To make: grow a layer of oxide layer 2 on the silicon substrate 1, sputter aluminum and etch to form the first capacitance electrode 3 and the second capacitance electrode 4 and the first pressure soldering block 33 and the second pressure soldering block 43, using Spin-coating spin coating a layer of polyimide, photoetching polyimide, imidization, then depositing a layer of silicon nitride barrier layer on the back side of the silicon substrate 1 and etching out the etching window of the silicon substrate 1, and then Using the anisotropic etching of bulk silicon to etch from the back of the silicon substrate 1 to the oxide layer 2, the etching rate of the oxide layer 2 by the selected etching solution is much lower than the etching rate of the substrate 1 by the etching solution. When the substrate 1 is etched When the oxide layer 2 is reached, it is considered that the corrosion of the substrate 1 has ended. At this time, a cavity is obtained in the substrate 1, and the oxide layer 2 above the cavity is etched away to obtain a cavity 6. At this time, the first capacitor electrode 3 The lower surface of the humidity sensitive medium 5 between the second capacitance electrode 4 is also in contact with the air, and finally the silicon nitride barrier layer on the back of the substrate 1 is etched away.

The capacitance formed by the first capacitance electrode 3 and the second capacitance electrode 4 uses polyimide as the humidity sensitive medium. When the ambient humidity changes, the dielectric constant of the polyimide moisture sensing layer will change, thereby making the humidity sensitive When the capacitance value changes, the environment humidity information can be obtained by using the capacitance detection circuit to detect the change of the humidity sensitive capacitance.

Claims (5)

1. a kind of CMOS relative humidity sensor of fast response is characterized in that this sensor comprises substrate (1), oxide layer (2), the first capacitive electrode (3), the second capacitive electrode (4) and humidity sensitive medium ( 5), the oxide layer (2) is arranged on the substrate (1), the first capacitor electrode (3), the second capacitor electrode (4) are arranged on the oxide layer (2), the first capacitor electrode (3) and the second capacitor electrode Two capacitor electrodes (4) are respectively drawn out by the first pressure welding block (33) and the second pressure welding block (43), and the humidity sensitive medium (5) is arranged on the first capacitor electrode (3) and the second capacitor electrode (4) Between and above the first capacitor electrode (3) and the second capacitor electrode (4), etch the substrate (1) and the oxide layer (2) above it to form a cavity (6), so that the first capacitor electrode (3 ) and the lower surface of the humidity sensitive medium (5) between the second capacitive electrode (4) is also in contact with the air. 2. A kind of fast response CMOS relative humidity sensor according to claim 1, is characterized in that the first capacitive electrode (3), the second capacitive electrode (4) are interdigitated electrodes and are arranged in a staggered manner, each group of interdigitated electrodes The first common end (31) and the second common end (41) of the shape electrode and the first free end (32) and the second free end (42) of the interdigitated electrode are all fixed on the oxide layer (2), with The mechanical strength of the first capacitor electrode (3) and the second capacitor electrode (4) is guaranteed. 3. A fast-response CMOS relative humidity sensor according to claim 1 or 2, characterized in that the humidity-sensitive medium (5) is polyimide. 4. A kind of fast-response CMOS relative humidity sensor according to claim 1 or 2, characterized in that the first capacitance electrode (3) and the second capacitance electrode (4) are aluminum electrodes. 5. A fast-response CMOS relative humidity sensor according to claim 1 or 2, characterized in that the processing technology of the sensor is fully compatible with the standard CMOS technology, and the post-treatment process of the sensor is completed by MEMS anisotropic wet etching.

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