JPH03202798A - Thin film moisture sensitive element - Google Patents

Abstract

PURPOSE:To improve the sensitivity, responding property and resistances to heat and medicines by forming a moisture sensitive element including a polyimide thin film which is mainly in the structure composed of repeated units of a specific formula. CONSTITUTION:A substance in the structure of repeated units expressed by this formula (R<1> is a tetravalent group containing at least two carbons) is laminated on various kinds of substrates, for example, by Langmuir-Blodgett technique. As a result, a moisture sensitive element is produced with the use of a polyimide thin film obtained through the succeeding imide reaction. The thickness of the polyimide thin film is preferably 1,000Angstrom or smaller from the viewpoint of easy separation of the moisture in the whole of the thin film. An insulative substrate IS or semiconductor substrate is used in the metal/ moisture sensitive film/metal structure (MIM structure), onto which metal, moisture sensitive film I and metal are sequentially formed. The metal and semiconductor S are enough to form an oxide film and the metal forming an upper electrode M is necessary to be porous and as thick as to display metallic electric conductivity.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 or semiconductors such as Se, Ge, Si, etc. (2) Metal oxides such as Sn, Fe, Ti, etc. (3)
Porous metal oxides such as A 1 z O3 (4) LiC
1st Class Electrolyte Salt (5) Thick Polymer Film Made of Organic or Inorganic MaterialsHowever, moisture sensing 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-Prodgett method have a regular structure that allows them to desorb water quickly, and the presence of a small amount of water increases the dielectric constant and Or the electrical 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 focused on the polyimide thin film obtained using the Langmuir-Prodgett method, and found that the film is very dense and has very few pinholes, so it has good insulation properties and has excellent responsiveness. By using a polyimide thin film with fluorine atoms introduced into its skeleton as a moisture-sensitive membrane, we have developed a new technology that improves both sensitivity and responsiveness, instead of conventional moisture-sensitive elements that have problems with maintenance, reliability, and responsiveness. It is an object of the present invention to provide a thin film moisture-sensitive element having excellent heat resistance and chemical resistance.

In the present invention, an amphiphilic polymer substance having a repeating unit represented by the following formula is used. For example, a thin film moisture-sensitive element was created by using a polyimide thin film that was laminated on various substrates using the Langmuir-Prodgett method and then subjected to a chemical reaction. The thickness of the polyimide thin film is preferably 1000 Å or less, preferably 500 Å or less, and most preferably 300 Å or less so that moisture can be easily desorbed over the entire thin film.

It is difficult to obtain such a thin film with few pinholes by any method other than the LB method.

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.

Using an insulating substrate (Is) or a semiconductor substrate (SS),
On top of that, metal, moisture sensitive film, and metal are formed in this order. The metal and semiconductor used may also 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.

These MIM and MIS type devices are highly resistant because the polyimide thin film obtained by the Langmuir-Prodgett method has good electrical insulation properties even at a thickness of several people and is not affected by commonly used chemicals. It becomes a capacitor with excellent chemical properties, that is, a thin film moisture-sensitive element. Furthermore, since polyimide 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 present 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.

Sharp treatment group Next, the present invention will be explained by examples.

Example 1 On a glass substrate on which electrodes were formed by vapor-depositing aluminum, 41 layers of an amphiphilic polymer material having repeating units shown in the figure below were accumulated by the Langmuir-Prodgett method. Thereafter, heat treatment was performed at 400"C for 1 hour to complete imidization. The obtained polyimide thin film had a thickness of 200 Å
It is. On the formed polyimide thin film, an electrode width of 10
A MIM-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 using a resistance heating method.

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 the humidity test layer 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.

Changes in capacitance and electrical conductivity in response to changes in relative humidity were completed within 5 seconds, confirming that this thin film moisture-sensitive element had high-speed response.

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 using a resistance heating method.

The thin film moisture sensitive element constructed in this manner also has the structure of Example 1O.
It has properties similar to MIM type thin film moisture sensitive elements, and its effectiveness as a thin film moisture sensitive element has been confirmed.

In this example, a vertical immersion method as a Langmuir-Prodgett method was used as a method for forming the moisture-sensitive film, but a generally known rotating cylinder method or horizontal deposition method may also be used.

Example 3 A MIM type thin film moisture sensitive element was produced in the same manner as in Example 1 using an amphiphilic polymer substance having the repeating units shown in the figure below.

The thin film moisture sensitive element produced in this way also has the same properties as Example 1, and the thin film moisture sensitive element produced in this way as a thin film humidity sensitive element also has the same properties as Example 1. , and its effectiveness as a thin film moisture-sensitive element was confirmed.

[Brief explanation of drawings]

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 shows the M I M described in Example 1.
2 is a graph showing changes in capacitance with respect to relative humidity of a type of thin film moisture sensitive element. (Explanation of symbols) M...Electrode I...Moisture sensitive film S...Semiconductor Is...Insulating substrate SS...Semiconductor substrate The effectiveness was confirmed. Example 4 Example 1 except that an amphiphilic polymer material having the repeating unit shown in the figure below was used and the heat treatment temperature was 300 degrees.
An MIM-type thin film moisture-sensitive element was produced in the same manner as described above. Figure 1 Figure 2 @ Figure 3 Figure 4

Claims (2)

[Claims] (1) Mainly has a repeating unit structure of the following formula (1),
▲There are mathematical formulas, chemical formulas, tables, etc.▼ (1) (In the formula, R^1 is a tetravalent group containing at least two carbon atoms) A thin film moisture-sensitive element containing a polyimide thin film with a thickness of 1000 Å or less. (2) Mainly has a repeating unit structure of the following formula (2),
▲There are mathematical formulas, chemical formulas, tables, etc.▼ (2) [In the formula, R^1 is a tetravalent group containing at least two carbon atoms, and R^2 is ▲There are mathematical formulas, chemical formulas, tables, etc.▼ R ^3, R^4, R^5 and R^6 are aliphatic, cycloaliphatic or aromatic (these may be combined with each other) monovalent groups having 1 to 30 carbon atoms (these The group may be substituted with a halogen atom, a nitro group, an amino group, a cyano group, a methoxy group, an acetoxy group) or a hydrogen atom, and at least R^3, R^4, R^5 and R^6 One is a group having 12 to 30 carbon atoms. ] An amphoteric polyimide precursor was laminated on a substrate by the Langmuir-Blodgett method, and at a temperature of 200°C to 450°C, it was partially or completely converted into an imide ring, and a thickness of 1.
A thin film moisture sensitive element containing a polyimide thin film with a thickness of 000 Å or less.