JPH06105235B2 - Humidity detection element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a humidity detecting element for detecting the relative humidity of an atmosphere based on a change in electrostatic capacitance value.

(Prior Art and Problems) Moisture-sensitive elements can be roughly classified into two types according to the materials used and the operating principles thereof. One of them is an electric resistance change type that utilizes the fact that the electric conductivity changes with humidity of porous ceramics using a sintered body of metal oxide or the like. In these materials, the environment in which the humidity sensitive element is used often contains humidity, gas, oil, etc., so the resistance value increases with the period of use, causing deterioration of performance due to so-called aging. Easy to do. In order to recover the performance of the deteriorated element, there is a method of performing heating cleaning, but this method requires a heater and a control circuit.

The other is a capacitance change type, which utilizes the fact that the permittivity changes and the capacitance changes depending on the amount of water in the moisture sensitive material. Examples of moisture sensitive materials include organic polymer films, metal oxide films, aluminum oxide films and the like. In these materials that have been announced so far, the change in capacitance with respect to relative humidity does not necessarily change linearly in terms of moisture sensitivity characteristics, and it shifts directly in the low or high humidity region. There are also many. Further, even in the same humidity condition, when the ambient temperature changes, the capacitance value also changes in many cases, which is so-called temperature dependency. Therefore, when the humidity sensitive element output is subjected to signal processing, it is inevitable that the circuit configuration becomes complicated. In addition, in general, the one using a polymer film has a drawback that it cannot withstand use at high temperature.

The present invention has been made to solve the problems of the prior art, and its object is to improve the chemical resistance and gas resistance of the humidity sensitive element and to improve the capacitance with respect to changes in relative humidity. An object of the present invention is to provide a reliable humidity detecting element that changes linearly, has no temperature dependence, and has a small number of manufacturing steps.

(Means for Solving Problems) In order to solve the above problems, selection of the moisture sensitive film is important. Generally, polyimide resin has excellent heat resistance, solvent resistance, cold resistance, and other electrical characteristics, in particular, its relative permittivity is almost constant even when the temperature changes, and its volume resistivity is high. It is a well-known fact to have. Some polyimide resins have a water absorption rate of several percent. It is appropriate to use the polyimide resin as the moisture sensitive film because of these comprehensive advantages.

Documents that have been published as capacitive moisture-sensitive elements using a polyimide resin include, for example, published patent publications, Sho 55-66749 and Sho 60-166854. In the case of JP-A-55-66749, an adhesive layer is provided on a metal substrate, a polyimide layer is formed on the adhesive layer, and a gold thin film permeable to water is further formed.
In this case, the upper gold electrode is easily damaged by contact with foreign matter or the like, which leads to a change in device characteristics. Next, JP-A-60-1668
In the case of No. 54, a comb-shaped tantalum metal layer is provided on a glass substrate, the surface of this metal is oxidized to form an electrical insulating layer, and a polyimide layer is formed on it, and then a part of the polyimide layer is etched. A complicated process of vapor-depositing an upper comb-shaped metal electrode on the removed portion and performing heat treatment is required. Further, the upper metal is exposed due to its structure, which causes deterioration of the humidity sensitive element. In order to solve these drawbacks, the inventors have adopted a silicon semiconductor wafer as a substrate. The reason for this is that silicon itself can be used as both the rigid substrate and the lower electrode. Therefore, it is not necessary to provide a lower electrode layer, which leads to simplification of the manufacturing process. If a moisture sensitive element is formed on a silicon substrate, it is possible to integrate a circuit element having the output signal processing function of the moisture sensitive element and a temperature detecting element on the same substrate, and it is expected that the range of application will be further expanded. Is.

Further, since the humidity detecting element according to the present invention is provided with the thin moisture-permeable polyimide protective film layer on the upper portion thereof, the humidity detecting element can be protected from mechanical contact and dust, and is a highly reliable moisture sensitive element.

(Examples) The present invention will be described by showing examples below, but the present invention is not limited thereby.

FIG. 1 and FIG. 2 show structural diagrams of the moisture sensitive element according to the embodiment.

First, after vacuum-depositing aluminum on the back surface of a P-type or N-type silicon wafer 2 having a resistivity of 10 Ω · cm or less, which is surface-polished, in the case of P-type and gold in the case of N-type, heat treatment in vacuum. Then, the ohmic contact electrode 1 is formed.

Next, after the silicon wafer 2 is thoroughly degreased and cleaned, the polyimide resin is adjusted to an appropriate viscosity and applied using a spinner, and the polyimide moisture sensitive film 3 is cured at the temperature and time specified by the polyimide resin manufacturer. When this film thickness is thick, the sensitivity of the moisture sensitivity characteristic becomes poor. When the film is thin, the resistance value of the film itself becomes low, and the resistance value formed in parallel with the capacitance decreases, which causes inconvenience in signal processing. Generally 1.0-5.0
A thickness of μm is suitable.

Next, the upper electrode 4 is formed. In the process of forming the upper electrode, there are two methods depending on the shape of the electrode. One is a method of depositing gold on the entire surface through a metal mask that shields the periphery of the sensing element. In this case, the film thickness is 500 Å in order to make water permeability through the metal film.
Limited to the front and back. Another method is to use a metal mask having a portion where metal is not vapor-deposited like a comb shape. In this case, the metal may be a metal other than gold, and the thickness thereof may be considerably thick (1000 Å or more), because moisture may permeate through the space.

In the next step, the protective film 5 is entirely coated with polyimide to a thickness of 1 μm or less and heat-treated. A hole 6 for taking out the upper electrode is formed in the protective film 5. This method may be a general photo-etching method using a photo resist.

Next, it is completed by dividing it into individual pieces using a scriber.

(Effects of the Invention) FIG. 3 shows the humidity-sensing characteristics obtained by measuring the change in capacitance with respect to the change in relative humidity. As shown in this figure, the moisture sensitivity characteristic changes completely linearly. As for the temperature characteristics, even if the ambient temperature was changed to 20 ℃, 30 ℃, and 40 ℃, there was almost no change in the humidity sensitivity characteristics and there was no temperature dependence. No hysteresis phenomenon was observed either. Despite the protective film, the humidity response is within 30 seconds for both moisture absorption and dehumidification, and there is no practical problem. As described above, the humidity detecting element of the present invention is a humidity detecting element that has substantially solved the problems of conventional products.

[Brief description of drawings]

FIG. 1 is a top view of a humidity detecting element according to the present invention, FIG. 2 is a cross-sectional view taken along the line AA in FIG. 1, and FIG. 3 is a graph showing a moisture sensitivity characteristic according to an embodiment of the present invention. . 1 ... Ohmic contact electrode, 2 ... Silicon wafer, 3 ... Polyimide moisture sensitive film, 4 ... Upper electrode, 5 ... Protective film, 6 ... Hole for taking out upper electrode

Claims (1)

[Claims] 1. A polyimide film of a moisture sensitive material, a metal thin film for electrodes, and a protective polyimide film are sequentially deposited on a semiconductor substrate,
A capacitance-type humidity detection element that sandwiches a polyimide film, which is a moisture-sensitive material, between the semiconductor substrate and the metal thin film to form a capacitance, and detects that the capacitance therebetween changes depending on humidity.