CN205067412U - Poroid electrode parallel -plate capacitive moisture sensor of going up of miniature quick response - Google Patents

Abstract

The utility model discloses a miniature fast-response hole-shaped upper electrode parallel-plate capacitive humidity sensor, which respectively includes a hole-shaped upper electrode, a PI moisture-sensitive film, a flat lower electrode, an _SiO2 insulating layer and a Si substrate from top to bottom. Among them, the upper electrode is provided with a number of neatly arranged upper electrode holes, and the PI moisture-sensitive film is provided with 2 lower electrode lead holes. During production, the silicon wafer is first cleaned, the silicon wafer is oxidized to form an insulating layer, the lower electrode is evaporated, the lower electrode is coated with polyimide acid, imidized, the upper electrode is evaporated, and the hole pattern of the upper electrode is etched with phosphoric acid. Etch electrodes and plasma etch the moisture-sensitive film to form a scribing line, use the plasma-etched moisture-sensitive film to form the lower electrode lead hole, and finally slice, argon welding, and package. The beneficial effect of the utility model is that under the same conditions, the response time of the humidity sensitive element with the hole-shaped upper electrode can be improved to the greatest extent compared with that of the grid-shaped upper electrode.

Description

A miniature fast-response hole-shaped upper electrode parallel plate capacitive humidity sensor

technical field

The utility model belongs to the technical field of humidity measurement and control, and relates to a miniature fast-response hole-shaped upper electrode parallel plate capacitive humidity sensor.

Background technique

Humidity measurement and control are closely related to social life, industrial and agricultural production, etc. Some fields, such as the diagnosis and treatment of respiratory diseases, fuel cell vehicles, etc., not only require the humidity sensor to have accurate and reliable static characteristics, but also require the humidity sensor to be able to quickly respond to the transient change of the measured environmental humidity. The static characteristics of existing humidity sensitive elements are relatively good, but the dynamic characteristics of their marketed products are not satisfactory (usually tens of seconds).

At present, the widely used grid-shaped upper electrode parallel plate capacitive humidity sensor is mostly based on Si substrate and polyimide moisture-sensitive film (PI). The polyimide (PI) polymer moisture-sensitive film is a porous medium and can absorb Gas, and the dielectric constant is small, and the dielectric constant of water vapor molecules is relatively large. When the moisture-sensing film absorbs water vapor molecules in the humid air, the dielectric constant ε _s of the humidity-sensing film changes significantly linearly, and corresponds to the moisture-sensing The membrane adsorbs varying concentrations of water vapor molecules. When the ambient humidity suddenly increases, due to the difference in the concentration of water vapor molecules in the environment and the moisture-sensitive film, the water vapor molecules in the ambient gas enter the surface of the wet-sensitive film from the grid teeth gap of the grid-shaped upper electrode, and then vertically downward and horizontally Spread left and right to the moisture-sensitive film area covered by the grid teeth of the upper electrode. The faster the diffusion, the shorter the response time of the humidity sensor. It can be seen that under the same conditions, the narrower the grid teeth of the grid-shaped upper electrode (the narrower the coverage area) and the thinner the moisture-sensitive film, the shorter the diffusion distance of water vapor molecules, the faster the diffusion of water vapor molecules, and the faster the response time of the humidity sensor. shorter; and vice versa.

In order to strengthen the structure and uniform charge distribution of the grid-shaped upper electrode, the grid-shaped upper electrode must be equipped with a current equalizing bar, the width of which is much larger than the width of the grid-shaped upper electrode grid teeth, and the area accounts for about 30% of the total area of the grid-shaped upper electrode- 40%. The existence of the equalizer strips increases the diffusion distance of water vapor molecules, so that the effect of improving the dynamic response time of the humidity sensor by pursuing too small grid-shaped upper electrode grid tooth width is not obvious. In this way, the presence of the grid-shaped upper electrode flow equalizer bar restricts the further improvement of the dynamic response time of the humidity sensor.

Utility model content

The purpose of this utility model is to provide a miniature fast response hole-shaped upper electrode parallel plate capacitive humidity sensor, which does not need a flow equalizer, and solves the problem that the existing grid-shaped upper electrode parallel plate capacitive humidity sensor must be set to occupy the total area of the upper electrode. A relatively large proportion of the upper electrode current equalizing strips leads to a too long diffusion path of water vapor molecules, so that the effect of improving the response time of the humidity sensor by reducing the width of the grid-shaped upper electrode grid teeth cannot be obvious.

The technical solution adopted by the utility model is respectively from top to bottom a hole-shaped upper electrode, a PI moisture-sensitive film, a flat lower electrode, a _SiO2 insulating layer and a Si substrate, wherein the upper electrode is provided with a number of neatly arranged upper electrode holes , There are 2 lower electrode lead holes on the PI moisture-sensitive film.

Further, the Si substrate is selected from a silicon chip, and the upper electrode and the lower electrode are Mo-Al electrodes.

Further, the hole diameter of the upper electrode holes is 2 μm, and the minimum distance between the centers of the upper electrode holes is 4 μm.

Further, the thickness of the PI moisture-sensitive film is 0.54 μm.

The beneficial effect of the utility model is that the hole-shaped upper electrode is used to replace the grid-shaped upper electrode of the existing humidity-sensitive element, and there is no need for the upper electrode structure strengthening and the flow equalizer for uniform charge distribution, so that the water entering the moisture-sensitive film through the holes of the upper electrode The diffusion path of gas molecules is approximately equal, and can be reduced with the decrease of the hole spacing. Under the same conditions, the response time of the hole-shaped upper electrode humidity sensor can be improved to the greatest extent compared with the grid-shaped upper electrode humidity sensor.

Description of drawings

Fig. 1 plan view of the hole-shaped upper electrode parallel plate capacitive humidity sensor;

Fig. 2 structure schematic diagram of hole-shaped upper electrode parallel plate capacitive humidity sensor;

Fig. 3 process flow chart of the manufacturing process of the hole-shaped upper electrode parallel plate capacitive humidity sensor;

Fig. 4 is a schematic diagram of hole distance between electrodes on the hole-shaped upper electrode parallel plate capacitive humidity sensor;

Fig. 5 Comparison diagram of the dynamic characteristics of the humidity sensor with the hole-shaped upper electrode and the grid-shaped upper electrode.

detailed description

The utility model will be described in detail below in conjunction with specific embodiments.

The hole-shaped upper electrode parallel plate capacitive humidity sensor of the utility model is shown in Figure 1 and Figure 2, from top to bottom are the hole-shaped upper electrode 2, the PI moisture-sensitive film 4, the plate lower electrode 6, and the SiO ₂ insulating layer. 7 and Si substrate 8, Si substrate 8 can be selected silicon chip, upper electrode 2 and lower electrode 6 are Mo-Al electrodes, wherein, hole-shaped upper electrode 2 is provided with several upper electrode holes 3 arranged neatly, the upper electrode hole 3 The hole diameter is preferably 2 μm, and the minimum distance between the centers of the upper electrode holes 3 is preferably 4 μm. The two lower electrode lead holes 5 formed by etching the PI moisture-sensitive film 4 are used for argon welding of the lower electrode leads. In the utility model, the PI moisture-sensitive film 4 is formed by pre-configured polyimidic acid coated on silicon wafers of a homogenizer, and then imidized, and its thickness is controlled by controlling the concentration of polyimidic acid, coating dosage, And the number of revolutions per minute of the glue homogenizer, the preferred thickness is 0.54 μm. The Mo-Al composite electrode used in the utility model is to strengthen the weldability of the electrode lead wire through molybdenum (Mo) with stronger adhesion, and the use of the aluminum electrode reduces the cost of the humidity sensitive element and increases its life. When the ambient humidity rises, the water vapor molecules 1 diffuse through the upper electrode hole 3 and enter the PI moisture-sensing film 4 , and when the ambient humidity decreases, the water vapor molecules 1 diffuse from the PI moisture-sensing film 4 through the upper electrode hole 3 and enter the environment.

The manufacturing process of the parallel plate capacitive humidity sensor of the present utility model is as shown in Figure 3. First, the silicon chip is cleaned, the silicon chip is oxidized to form an insulating layer, the lower electrode is evaporated, and the lower electrode is coated with polyimide acid and imidized. Evaporate the upper electrode, etch the hole pattern of the upper electrode with phosphoric acid, form a scribing line by etching the electrode with phosphoric acid, and etch the moisture-sensitive film by plasma, and form the lead hole of the lower electrode by plasma etching the PI moisture-sensitive film, finally slice, argon welding, and package .

The hole-shaped upper electrode of the utility model avoids the grid-shaped upper electrode considering that the grid teeth are too narrow and easy to break and uniform charge distribution. Equal, without increasing the cost and process complexity, the response time of the humidity sensor can be effectively improved.

The utility model is a capacitive humidity sensor with a hole-shaped upper electrode parallel plate, with an area of 3 mm × 3 mm, an area of the upper electrode active area of 2 mm × 2 mm, and the hole distance as shown in Figure 4, wherein the hole diameter is 2 μm, and the hole center distance S1 = S2=4μm, the area of the upper electrode is 2.5mm ² ; it has been verified by experiments that under the same conditions, the dynamic response time of the utility model's hole-shaped upper electrode parallel plate capacitive humidity sensor is faster than that of the existing grid-shaped upper electrode parallel plate capacitive humidity sensor. Sensitive components have improved by at least 30%.

Figure 5 shows the existing grid-shaped upper electrode humidity sensor (area 3mm×3mm, upper electrode active area area 2mm×2mm, grid teeth width 2μm, grid teeth gap width 2μm, upper electrode area 2.5mm ² , average Flow bar width 50 μm, accounts for upper electrode area ratio 40%) and the utility model humidity sensor dynamic characteristic comparison, wherein, the dynamic characteristic data of grid-shaped upper electrode humidity sensor originates from 25 ℃ since relative humidity is 33.2%RH (MgCl ₂ saturated salt solution) to a relative humidity of 75.8% RH (NaCl saturated salt solution) humidity response test results, the dynamic characteristics test is based on the saturated salt solution method, the equilibrium time is 5s, the test time is less than 10s, the hole-shaped upper electrode is humidity sensitive The dynamic characteristic data of the component comes from numerical simulation. The ordinate in the figure is the dimensionless capacitance value, and the abscissa is time.

It can be seen from Figure 5 that the response time of the hole-shaped upper electrode humidity sensor is obviously better than that of the grid-shaped upper electrode humidity sensor, especially in the later stage of the test.

The above description is only a preferred embodiment of the utility model, and does not limit the utility model in any form. Any simple modification made to the above implementation method according to the technical essence of the utility model is equivalent to changes and modifications. All belong to the scope of the technical solution of the utility model.

Claims (4)

1. a miniature quick response poroid top electrode parallel plate capacitor formula humidity-sensitive element, is characterized in that: be respectively poroid top electrode, PI humidity-sensitive film, dull and stereotyped bottom electrode, SiO from top to bottom ₂insulation course and Si substrate, wherein, top electrode is provided with the top electrode hole of some marshallings, and PI humidity-sensitive film is provided with 2 bottom electrode fairleads.

2., according to a kind of miniature quick response poroid top electrode parallel plate capacitor formula humidity-sensitive element described in claim 1, it is characterized in that: silicon chip is selected in described Si substrate, described top electrode and bottom electrode are Mo-Al electrode.

3., according to a kind of miniature quick response poroid top electrode parallel plate capacitor formula humidity-sensitive element described in claim 1, it is characterized in that: the aperture in described top electrode hole is 2 μm, top electrode Kong Jian center minimum spacing is 4 μm.

4., according to a kind of miniature quick response poroid top electrode parallel plate capacitor formula humidity-sensitive element described in claim 1, it is characterized in that: PI humidity-sensitive film thickness is 0.54 μm.