JPS63293459A - Detecting element - Google Patents

Abstract

PURPOSE:To enhance the detection sensitivity of a detecting element laminated with a conductive layer on an insulating layer molded to the shape of a bridge, etc. on a base plate and to increase the response speed thereof by using a metallic material having <=100W/m.k thermal conductivity as a material of the conductive layer. CONSTITUTION:After the bridge-shaped insulating layer 2 formed of a thin film is formed on the base plate 1, the base plate 1 is subjected to crystal axis anisotropic etching of Si which is the base plate. A hollow structure is thereby formed between the base plate 1 and the microbridge 3 as the element structure having excellent thermal insulation; furthermore, the surface of the bridge 3 is fixed to a sensor material 4 made of a thin film. The metallic material, such as titanium, having <=100W/m.k thermal conductivity is used as the material of the conductive layer. The absolute humidity is thus detected in humidity measurement. The detection sensitivity in particular is thereby enhanced and the response speed is increased.

Description

[Detailed Description of the Invention] Technical Field> The present invention aims to improve detection sensitivity and high-speed response by improving the thermal insulation of a sensor material whose temperature changes due to changes in the thermal conductivity of the detection atmosphere. The present invention relates to a sensing element capable of detecting moisture, and in particular to a moisture sensing element electrode material capable of improving the detection sensitivity and high-speed response of an absolute humidity sensor that directly detects the amount of water vapor in humidity measurement.

<Prior art and its problems> Many types of humidity sensing elements or humidity sensors have been developed in the past, and in particular sensors for detecting relative humidity in the atmosphere are based on the electrical resistance or capacitance of humidity sensitive materials. The following methods are mainly known, taking advantage of the fact that water changes in response to humidity or water vapor in the atmosphere.

■Iron oxide (Fe203.Fe304), tin oxide (5no
2) Those using sintered bodies of metal oxides or metal oxide films, ■ Those using hydrophilic polymer membranes or polymer electrolytes, and even fiber polymers, ■ Solithium chloride (Li)
ck), etc., and (2) those in which conductive particles or fibers such as carbon are dispersed in a hygroscopic resin or a hygroscopic polymer membrane.

The above sensors have many advantages and disadvantages, such as detection humidity range, detection sensitivity and accuracy, response speed, reliability, and environmental resistance. In order to detect minute changes in water vapor in an environment where humidity changes rapidly, changes in relative humidity, which is a function of temperature, can be considered as follows, which is disadvantageous for detecting the amount of water vapor. For example, if we assume that the amount of water vapor in the detection atmosphere is constant and the temperature of this atmosphere increases,
Even if the amount of water vapor is constant, relative humidity decreases due to the saturated water vapor pressure, and if the temperature rises rapidly, the slight increase in water vapor will be offset by the temperature increase or the relative humidity will decrease. This poses a major problem in detection. Therefore, absolute humidity detection, which can directly detect the amount of water vapor, is more advantageous than relative humidity detection in measuring the humidity of the environment as described above.

As means for detecting the amount of water vapor, measuring devices that utilize the attenuation of microwaves by water vapor, the absorption of infrared rays, etc. have been conventionally used. Since these devices can directly detect water vapor using physical methods, they are advantageous in detecting small changes in water vapor even in environments with rapid temperature changes as mentioned above, but on the other hand, the device configuration is large-scale and the cost is quite high. Become something. There is also a thermal conduction type absolute humidity sensor that uses two thermistors with the same characteristics, making use of the difference in thermal conductivity between humid air and dry air.It is small and has excellent environmental resistance, but compared to conventional However, there were problems in terms of high pressure detection sensitivity and high-speed response.

In order to solve the above problems, the present inventors developed a moisture sensitive element as described below. In other words, the absolute humidity detection method uses the fact that the thermal conductivity of air changes depending on the amount of water vapor contained in the air, and exposes an element heated to a constant temperature to the detection atmosphere, and detects the temperature as a result of a change in water vapor. The amount of water vapor is detected based on the temperature change caused by the change in thermal conductivity. Furthermore, micromachining technology was used for the element structure, and a micro bridge was formed to reduce the heat capacity of the element as much as possible, and a thin film of a material with a large thermistor constant, such as Ge, was used as the sensor material. Although the moisture-sensitive elements fabricated using these methods showed improvements in detection sensitivity, response characteristics, etc. compared to conventional methods, it was not possible to improve the detection sensitivity and response characteristics of the moisture-sensitive elements due to the use of common metal materials with high thermal conductivity such as Au1Ae as the material for the conductive layer. However, the thermal insulation of the sensor thin film on the bridge was insufficient, and therefore the advantage of the microbridge, which had a reduced heat capacity as much as possible, was not utilized, and good detection sensitivity and response characteristics could not be obtained.

As mentioned above, there are problems with conventional moisture sensing elements, and there is a strong desire for a method to solve these problems, particularly the development of a conductive layer material on a bridge in a crosslinked moisture sensing element.

<Purpose of the Invention> The present invention has been made in order to eliminate the drawbacks of the conventional moisture sensing elements as described above, and it detects absolute humidity in humidity measurement, and in particular improves the detection sensitivity. The aim is to achieve unprecedented high sensitivity and high-speed response.

<Summary of the Invention> The present invention provides a sensing element having a structure in which a conductive layer is laminated on an insulating layer formed in the shape of a bridge, a cantilever, or a diaphragm on a substrate. It is characterized by using a metal material such as titanium having a particle diameter of k or less.

The thermal conductivity of SiO3, a typical insulating layer, is 1.4 W/
mek, and on the other hand, the thermal conductivity of the metal material of the conductive layer formed on the insulating layer is higher than that of 5i02, and the general conductive materials A g and Cu + A uv A 6 are 428, 403, and 403, respectively. It is 319,236W/rn@. Therefore, as a conductive material, the thermal conductivity is 20W/m@
By using titanium, which is the lowest class of metal materials, by forming the insulating layer into a cross-linked structure, the sensor material on the bridge can be sufficiently thermally insulated, further enhancing the advantage of the structure that reduces heat capacity as much as possible. You can make use of it.

In addition, since the electrical conductivity and thermal conductivity of metal materials are generally proportional, materials such as titanium, which have low thermal conductivity, also have low electrical conductivity, resulting in higher wiring resistance than wiring such as AAN. However, since the sensor material, such as a Ge thin film, has even higher resistance, the wiring resistance of titanium can be ignored.

Furthermore, titanium is stable because it is a high melting point metal, and Si
It also has good adhesion with insulating layers such as O, and a highly reliable device structure can be constructed.

Therefore, water vapor can be directly detected, and the micro-bridge structure reduces the element heat capacity, the construction of a conductive layer metal material with low thermal conductivity, and the construction of a thin film sensor material with a large thermistor constant provide unprecedented superior detection. High-speed response of water vapor detection can be obtained due to sensitivity and accuracy and good thermal response of the element. In addition, since detection is performed using a physical method that utilizes the dependence of thermal conductivity on the amount of water vapor, it is less likely to contaminate the sensor material, etc., than detection using a chemical method that uses changes in electrical characteristics due to adsorption and desorption of moisture. The device is stable even when exposed to sunlight, has excellent environmental resistance, and is inexpensive because the fabrication of the microbridge device or sensor thin film can be carried out in batches using a normal semiconductor process or its applied process. be able to.

As described above, an object of the present invention is to provide a moisture-sensitive element which has the above-mentioned many advantages and is particularly excellent in high detection sensitivity and high-speed response.

<Example> FIGS. 1 and 2 are a schematic structural diagram and a cross-sectional view of a moisture-sensitive element showing an example of the present invention. After forming a bridge-shaped thin film insulating layer 2 on a Si substrate 1, etching the Si substrate 1 with crystal axis anisotropy etches the area below the insulating layer bridge to form a structure between the substrate 1 and the insulating layer bridge portion (
Hereinafter, it will be referred to as a microbridge. °) A hollow structure is formed between the microbridges 3 to provide an element structure excellent in thermal insulation, that is, low heat capacity, and furthermore, a thin film sensor material 4 is fixed on the microbridge 3. To describe the manufacturing process of this device in detail, first, a thin film insulating layer 2, which will become a microbridge 3 and a mask during etching, is heated on a Si substrate 1 whose chemical etching speed differs depending on the orientation of the crystal axis, depending on the material. Lamination is formed by an oxidation method, vacuum evaporation method, sputtering method, CVD method, etc., and microfabrication into a bridge shape is performed by photolithography technology. In addition, as an insulating layer material, 5
It is preferable to use materials such as i02, A1203, and ZrO2 that have a low heat capacity and a coefficient of thermal expansion relatively similar to that of the substrate 1, and cantilever or diaphragm structures are also useful.

Next, a comb-shaped electrode 5 made of a metal material with low thermal conductivity such as titanium is provided on the micro bridge 3 by EB (electron beam) evaporation, vacuum evaporation, sputtering, etc., and then on the electrode 5. The sensor thin film is deposited using vacuum evaporation method, sputtering method, C
Manufactured by VD method etc.

Note that Ge, SiC, TaN, etc. can be used as the thin film sensor material as a material having a large thermistor constant. After the above steps, the Si of the substrate 1 is chemically etched from the insulating layer side for a predetermined time using a solution such as E, P, W (ethylenediamine-pyrocatechol-water), that is, crystal axis anisotropic etching. By stacking thin film sensor materials with a large thermistor constant, a microchip moisture sensing element with a microbridge structure, which is sufficiently thermally insulated by electrodes with low thermal conductivity and has a small heat capacity, can be obtained.

Therefore, by reducing the element heat capacity through the microbridge structure, constructing a conductive layer material with low thermal conductivity, and constructing a thin film sensor material with a large thermistor constant, detection sensitivity and responsiveness superior to the conventional ones can be obtained.

As described above, the humidity sensing element of the above embodiment is suitable for application to an absolute humidity sensor, and because it is of a thermal conduction type, it can directly detect the amount of water vapor, and has unprecedented high detection sensitivity and high-speed response. Since it is detected using a physical method, it has excellent environmental resistance and is extremely useful in practice.

<Effects of the Invention> The moisture-sensitive element according to the present invention has the following practically extremely useful characteristics.

That is, the heat capacity of the element is made extremely small by the element configuration of a micro bridge, cannalever, or diaphragm structure, and a material with low thermal conductivity such as titanium is used as the wiring material, and furthermore, Ge, Ge, etc. are used as the thin film sensor material.
By using materials with large thermistor constants such as SiC and TaN, it has unprecedented high sensitivity characteristics and high-speed response.

[Brief explanation of drawings]

1 and 2 are a schematic structural diagram and a sectional view of a moisture-sensitive element showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Insulating layer, 3... Micro bridge, 4... Sensor thin film, 5... Electrode. Agent Patent attorney Takeshi Sugiyama (and 1 other person) Figure 1 Figure 2

Claims (4)

[Claims] 1. A substrate provided with a void, an insulating layer layered on the substrate and forming a bridge, cantilever, or diaphragm shape in the void, and a pair of conductive layers laminated on the insulating layer with a constant gap between each other. and a sensor thin film layer in contact with both of the conductive layer, and detects a temperature change of the sensor thin film corresponding to a change in thermal conductivity of the detection atmosphere as a change in resistance value, the conductive layer comprising: A sensing element characterized in that it is made of a metal material with a thermal conductivity of 100 W/m·k or less. 2. The sensing element according to claim 1, wherein the material of the conductive layer is titanium. 3. 2. The sensing element according to claim 1, wherein the change in thermal conductivity of the sensing atmosphere is caused by a change in the amount of water vapor in the atmosphere. 4. The material of the sensor thin film layer is Ge, SiC or TaN.
The sensing element according to claim 1, which is a thin film of a material consisting of or having these as main components.