JPH022912A - Thin film moisture sensitive element - Google Patents

Abstract

PURPOSE:To make it possible to implement excellent resistance against temperature, chemicals and the like, high sensitivity and high speed response by providing a moisture sensitive element incorporating a polyimide based thin film whose thickness if 1,000Angstrom or less. CONSTITUTION:Aluminum is evaporated on a glass substrate, and an electrode is formed on the substrate. Amphoteric polyimide precursors (PIP) shown by the formula are laminated on the substrate in 41 layers by the method of Langmuir-Brodgett. Thereafter, heat treatment is performed at 400 deg.C for one hour, and imidation is completed. The thickness of the obtained polyimide thin film is 200Angstrom . Comb-shaped gold as an electrode having the width of 100mum and an interval of 500mum is evaporated on the formed polyimide thin film by a resistance heating method. In this way, an MIM type thin film moisture sensitive element is manufactured. The gold having the degree of thickness is porous and furthermore has metallic electric conductivity. The access of moisture is easy.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) The present invention relates to a thin film moisture sensitive element. More specifically, the present invention relates to a thin film moisture-sensitive element having excellent resistance to temperature, chemicals, etc., high sensitivity, and high-speed response.

Controlling the relative humidity in the air is very important in the precision industry, food industry, textile industry, building management, etc., and the moisture sensing elements that detect it have traditionally been made of the following materials. The one used is known.

(1) Metals such as Se, Ge, Si, etc. or semiconductors (21) Metal oxides (31) such as Sn, Fe, Ti, etc.
Porous metal oxide f41 L i C such as A1203
Electrolyte salts such as I (5) Polymer thick films made of organic or inorganic materials However, moisture-sensitive elements using these various materials are difficult to maintain, or have problems with reliability and responsiveness. However, we are not in a satisfactory state.

For example, when using the metal oxide of (2) above, pressing and sintering are performed to shape it, but there are problems with homogeneous pressing or cracking during sintering. Further, even if the molding is performed without any problem in the process, there is also a problem in durability, in other words, in reliability.

Further, when the thick polymer film of (5) above is used, although it is inexpensive in terms of material, there are problems such as deterioration due to chemicals such as solvents and a decrease in reliability. Furthermore, because the volume of the moisture-absorbing part is large, there are limits to increasing speed and sensitivity.
When measuring capacitance or electrical conductivity by configuring a capacitor, the stability of the detection system is an important issue because the value is small. Here, what is a polymer thick film?
A polymer film with a thickness of several thousand angstroms or more obtained by methods such as spin coding.

Polyimide thin films obtained using the Langmuir-Blodgett method have a regular structure that allows them to desorb water quickly, and the presence of a small amount of water reduces the dielectric constant or electrical property. Conductivity changes significantly. Furthermore, since it is a thin film, the capacitance and electrical conductivity of the device are relatively large, which leads to a reduction in the cost of the detection system.

The present inventors have focused on polyimide thin films obtained using the Langmuir-Blodgett method, and have
Conventional methods have problems with reliability, responsiveness, etc. An object of the present invention is to provide a thin-film moisture-sensitive element containing a polyimide-based thin film that is excellent in both sensitivity and responsiveness, and has excellent heat resistance and chemical resistance, instead of the 3-humidity element.

The present invention, which we proposed in Japanese Patent Application No. 61-275533, is based on the method of depositing an amphoteric polyimide precursor on various substrates using the Langmuir-Blodgett method, followed by an imidization reaction. This was achieved by fabricating a thin-film moisture-sensitive element using a polyimide-based thin film. The thickness of the polyimide thin film is preferably 1000 Å or less, preferably 500 Å or less, and more preferably 300 Å or less so that moisture can be easily desorbed over the entire thin film.

Schematic diagrams of a thin film moisture sensitive element having a metal/moisture sensitive membrane/metal (hereinafter referred to as MIM) structure are shown in FIGS. 1 and 2.

An insulating substrate (Is) or a semiconductor substrate ('SS) is used, and a metal, a moisture sensitive film, and a metal are formed in this order. The metal and semiconductor used may be those that form an oxide film. Further, the metal serving as the upper electrode must be porous and thick enough to have metal-like electrical conductivity in order to facilitate the entry and exit of moisture.

Schematic diagrams of a thin film moisture sensitive element having a metal/moisture sensitive film/semiconductor (hereinafter referred to as Mis) structure are shown in FIGS. 3 and 4.

A semiconductor film (S) formed on a semiconductor substrate (SS) or an insulating substrate (Is) having an electrode (M) is used, and a moisture sensitive film and a metal are formed thereon in this order.

The metal and semiconductor used may be those that form an oxide film. Further, the metal serving as the upper electrode must be porous and thick enough to have metal-like electrical conductivity in order to facilitate the entry and exit of moisture.

Further, the upper electrode has an opening, and has a structure that allows water to enter and exit through the opening, and for example, a comb-shaped or spiral-shaped electrode can be used.

These MIM and MIS type elements are made of polyimide thin films obtained by the Langmuir-Blodgett method, which have good electrical insulation properties even at a thickness of several people, and are not affected by commonly used chemicals. It becomes a capacitor with excellent chemical resistance, that is, a thin film moisture-sensitive element. Furthermore, since the polyimide resin has high heat resistance, it becomes a capacitor, that is, a thin film moisture sensitive element, which does not deteriorate at all at the temperatures at which humidity sensitive elements are normally used.

The thin film moisture-sensitive element according to the present invention effectively utilizes the property that a polyimide thin film obtained using the Langmuir-Blodgett method quickly responds to humidity. Furthermore, the thin crotch has excellent heat resistance and chemical resistance.

This invention has made it possible to provide a moisture-sensitive thin film element with excellent resistance to temperature, chemicals, etc., high sensitivity, and high-speed response.

Furthermore, the capacitance and electrical conductivity of the device are relatively large, and the cost of the detection system can be reduced.

Husband provisional Next, the present invention will be explained by examples.

Example 1 An amphoteric polyimide precursor (P
fP) was accumulated in 41 layers by the Langmuir-Blodgett method. Thereafter, PIP heat treatment was performed at 400°C for 1 hour to complete imidization. The obtained polyimide thin film has a thickness of 200. On the formed polyimide thin film, electrode width lOOμm, electrode spacing 500μm
The comb-shaped gold is deposited to a thickness of 200 mm using the resistance heating method.
An MIM type thin film moisture sensitive element was manufactured.

Gold of this thickness is porous and has metallic electrical conductivity, allowing moisture to easily enter and exit.

After attaching the thin film moisture sensitive element thus constructed to a humidity test bottle and connecting it to a YHP4192A impedance analyzer, the change in capacitance corresponding to relative humidity from 11 to 92% was measured while keeping the frequency constant (IKHz). was measured at a temperature of 20°C. The obtained results,
This is shown in the graph of FIG. This result confirmed its effectiveness as a humidity sensing element that can measure relative humidity with high sensitivity using capacitance. Of course, the corresponding humidity can also be determined by electrical conductivity.

Furthermore, this MIM type thin film moisture sensitive element has a capacitance,
It was also confirmed that there is almost no temperature dispersion in electrical conductivity, and that it can be used without temperature correction.

Changes in capacitance and electrical conductivity in response to changes in relative humidity were completed within 10 seconds, confirming that this thin film moisture-sensitive element had high-speed response.

Comparative Example 1 A MIM type thin film moisture sensitive element similar to that of Example 1 was produced, except that the thickness of the upper electrode was 500 mm. Gold of this thickness is quite dense. Changes in capacitance and electrical conductivity with respect to changes in relative humidity are 1
It was found that the response of the device decreased when the upper electrode was dense.

Comparative Example 2 A MIM type thin film moisture sensitive element similar to that of Example 1 was produced, except that the thickness of the polyimide thin film was 2000 mm. It was found that changes in capacitance and electrical conductivity with respect to changes in relative humidity were completed in about 1 minute, and that when the moisture-sensitive film was thick, the response of the element decreased.

Example 2 A polyimide thin film was formed in the same manner as in Example 1 on a silicon substrate on which ohmic contact was made with gold and a back electrode was formed. On the formed polyimide thin film, an electrode width of 10
A MIS type thin film moisture sensitive element was fabricated by depositing comb-shaped gold with a thickness of 0 μm and an electrode spacing of 500 μm to a thickness of 200 μm using a resistance heating method.

The thin film moisture sensitive element constructed in this manner also had the same properties as the MIM type thin film moisture sensitive element of Example 1, and its effectiveness as a thin film moisture sensitive element was confirmed.

In this example, the Langmuir-Blodgett method was used as a method for forming the moisture-sensitive film, but a rotating cylinder method or a horizontal deposition method known for boat fishing may also be used. In addition, the amphoteric polyimide precursor is not limited to PIP, but can be used to produce a polyimide ring through a thermal cyclization reaction.
-275533 proposed amphiphilic polymer,
It can be any substance.

[Brief explanation of the drawing]

1 to 2 are schematic diagrams of an MIM type thin film moisture sensitive element, and FIGS. 3 to 4 are schematic diagrams of an MIS type thin film moisture sensitive element. FIG. 5 is a graph showing changes in capacitance with respect to relative humidity of the MIM type thin film moisture sensitive element described in Example 1. (Explanation of symbols) M...1 Moisture sensitive film S...Semiconductor Is...Insulating substrate SS...Semiconductor substrate Figure 5 Figure 2

Claims (4)

[Claims] (1) A thin film moisture sensitive element containing a polyimide thin film having a thickness of 1000 Å or less. (2) The thin film moisture-sensitive element according to claim 1, comprising a polyimide thin film produced by accumulating an amphoteric polyimide precursor on a substrate by the Langmuir-Blodgett method and subsequent imidization reaction. (3) A metal/moisture-sensitive membrane/with an upper electrode that is porous and has an opening and is thick enough to have metallic electrical conductivity.
3. The thin-film moisture-sensitive element according to claim 1, which is made of a metal-structured element and includes the polyimide-based thin film as a moisture-sensitive film. (4) Consisting of an element having a metal/moisture-sensitive film/semiconductor structure, which has an upper electrode that is porous and has an opening and is thick enough to have metallic electrical conductivity, and the polyimide thin film is made of a moisture-sensitive material. Claim 1 or 2 including as a film
Thin-film moisture-sensitive element described in .