JP4298637B2 - Gas sensor and gas sensing device using the same - Google Patents

Description

The present invention is installed in a chamber that shuts off the flow of ambient gas, and is provided with a heater and a temperature sensor that are individually formed on a thin film that is thermally separated from the substrate, realizing temperature measurement and temperature control with high sensitivity and high accuracy. The present invention relates to a gas sensor and a gas sensing device that can analyze the degree of vacuum and gas components in a chamber using the gas sensor.

Conventional vacuum sensors that use a gas sensor as a heat conduction type vacuum sensor include a Pirani vacuum gauge and a thermocouple vacuum gauge. In the Pirani gauge, heat is generated when an electric current is passed through a thin metal wire (hereinafter referred to as a thin wire heater), and the heat is dissipated by heat conduction of gas molecules, solid conduction and radiation transmitted through the fine wire heater, and the amount of heat taken by the gas molecules is reduced. Utilizes the dependence on pressure. This gas sensor stretches a thin metal wire heater inside a metal cylinder, and controls the current flowing through the thin wire heater in order to keep the temperature of the thin wire heater constant. The current flowing through the thin wire heater changes depending on the amount of heat taken by the gas molecules, and the pressure is displayed using this amount of change.

Thermocouple vacuum gauges include a gas sensor in which a thin wire heater and a thermocouple are thermally separated, and a gas sensor in which a thin wire heater and a thermocouple are in close contact. A gas sensor in which a thin wire heater and a thermocouple are thermally separated uses the heat conduction of surrounding gas molecules, a constant current is passed through the thin wire heater, and the heat conduction between the thin wire heater and the thermocouple is pressurized. It is a gas sensor using the dependence on. The gas sensor device in which the thin wire heater and the thermocouple are thermally separated is a device that displays the pressure using the electromotive force of the thermocouple.

On the other hand, a gas sensor in which a thin wire heater and a thermocouple are in close contact uses the amount of heat taken by gas molecules from the thin wire heater, and a constant current is passed through the thin wire heater in close contact with the thermocouple, so that the electromotive force of the thermocouple against the pressure is It is a gas sensor that utilizes the dependence, and a device that displays pressure using the electromotive force of a thermocouple.

In the Pirani vacuum apparatus, the fact that the resistance value of the metal increases in proportion to the temperature is utilized, so the circuit for detecting the change in the resistance value is an AC bridge circuit or a DC bridge circuit. In order to keep the required temperature of the thin wire heater constant, the current fed to the thin wire heater is controlled by a negative feedback circuit so that the resistance value becomes a constant value. The output of the bridge circuit is converted into pressure and displayed.
In the thermocouple vacuum device, there are a vacuum sensor in which the fine wire heater and the thermocouple are thermally separated, and a vacuum sensor in which the fine wire heater and the thermocouple are in close contact, but both vacuum sensors require a constant current circuit for the fine wire heater. A constant current is passed, and a temperature change in which the amount of heat taken by gas molecules depends on pressure is detected by a thermocouple, and the electromotive force is converted into voltage, converted into pressure, and displayed.

  However, a vacuum sensor in which a thin wire heater is stretched inside a metal cylinder uses a small resistance temperature coefficient of the metal that is the thin wire heater, and therefore, the output change with respect to the temperature change is small and the sensitivity is small. In addition, the vacuum sensor in which the thin wire heater and the thermocouple are arranged at a certain distance has the thin wire heater and the thermocouple uniformly approached, so thermal radiation also contributes, and the accuracy is inferior. Although it is desired to use, the surface area of the thin wire heater is small, so the temperature change is small and the sensitivity is poor. The vacuum sensor where the thin wire heater and thermocouple are bonded has a small surface area in contact with the thin wire heater, and the thermocouple is bonded to a part of the thin wire heater and also uses solid heat conduction. Sensitivity is poor because one point is detected by a thermocouple. The thin wire heater is mainly a platinum or tungsten thin wire heater. To obtain the required resistance, the thin wire heater is arranged in a straight line or meandering to obtain the required temperature. There was a problem of becoming.

In order to solve the above problem, a sensor chip of a gas sensor according to claim 1 of the present invention is shown in FIG. Two thin films (4a, 4b) thermally separated from the substrate 1 are opposed to each other through a gap 300. The thin film 4a is individually provided with a heater 6 and a temperature sensor TSa in the vicinity of the heater. A temperature sensor TSb for measurement is installed on the thin film 4b facing the thin film 4a. The temperature raised by the heater 6 on the thin film 4a is measured by the temperature sensor TSa and controlled to a constant temperature. This heat is transmitted to the thin film 4b by heat conduction through the gap 300, and this temperature is measured by the temperature sensor TSb to obtain information on the type and density of the gas filling the gap. A heater and a thin film temperature sensor were individually formed on a thin film that was installed in a chamber where the flow of ambient gas was cut off and thermally separated from the substrate.

  Further, the sensing device according to claim 2 is a heat conduction type temperature sensor, and the heater 6 of the thin film 4a has a required temperature in the relationship between the thin films 4a and 4b and the gap 300 between them. At the same time, the temperature of the heater 6 is measured by the temperature sensor TSa, and at the same time, the temperature is controlled at a required temperature by a negative feedback circuit. This heat makes the width of the gap 300 smaller than both the width of the thin film 4a and the thickness of the thin film 4b, so that heat is transferred through the gap 300 and is transmitted to the thin film 4b. This temperature was measured by the temperature sensor TSb to obtain information on the type and density of the gas filling the gap. A vacuum sensor with low power consumption, high-speed response, small size and higher sensitivity has been made possible. And the gas sensing apparatus using this was able to be provided.

Further, as a sensing device according to claim 3, in the gas sensor according to claim 1 and claim 2, by using the outputs of the temperature sensor TSa and the temperature sensor TSb, the atmospheric pressure of the surrounding gas in the chamber or In the gas sensor capable of measuring the component, the temperature output of the temperature sensor TSa and the temperature sensor TSb is affected by the change in the ambient gas temperature. In order to reduce this, a temperature sensor TSc for detecting the ambient gas temperature Tc is provided on the substrate 1. Thus, the influence is reduced by correcting the temperature outputs of the temperature sensor TSa and the temperature sensor TSb. As a result, a vacuum sensor with low power consumption, high-speed response, small size, higher sensitivity, and high accuracy has become possible. In addition, a gas sensing device using this can be provided.

According to a fourth aspect of the present invention, there is provided a sensing device according to any one of the first to third aspects, wherein the temperature sensor TSa, the temperature sensor TSb, and the temperature sensor TSc are bipolar transistors or semiconductor diodes. The forward characteristic is driven at a constant voltage, and the current change with respect to the temperature is converted into a voltage after voltage conversion. Since the semiconductor diode is driven at a constant voltage, the current change greatly changes with respect to the temperature change. Bipolar transistors can obtain the same characteristics as semiconductor diodes by using the base and emitter diode characteristics. As a result, a vacuum sensor with low power consumption, high-speed response, small size, higher sensitivity, and high accuracy has become possible. In addition, a gas sensing device using this can be provided.

Further, as a gas sensing device according to claim 5, by using the gas sensor according to any one of claims 1 to 4, the temperature of the temperature sensor TSa, the temperature sensor TSb, and the temperature sensor TSc is changed to a signal amplification circuit. Then, the temperature is controlled by a drive power supply circuit, and this temperature signal is processed by an arithmetic circuit, a memory circuit, and a display unit so that the atmospheric pressure of the ambient gas in the chamber or its component can be measured. As a result, it is possible to provide a gas sensing device that has a high-speed response, is small, and has higher sensitivity and accuracy.

Since the present invention is configured as described above, the following effects can be obtained. Since the thin film 4a and the thin film 4b thermally separated from the respective substrates perform heat transfer as surfaces through the gap and the surrounding gas, the sensitivity can be increased. In addition, it is small in size and can reduce the amount of heat dissipated by solid heat conduction and radiation, enabling low-power consumption, high-speed response, compact and highly sensitive vacuum sensors. By forming the heater and the temperature sensor individually, it is possible to use the best one of them, and it is possible to measure with improved performance so that there is no mutual influence.
The thin film heater 6 and the temperature sensor are concentrated and integrated in the thin film 4a and the thin film 4b thermally separated from the substrate, and the gap 300, so that the heat capacity of the thin film heater 6 can be small, low power consumption and small size. A measuring device using a gas sensor can be formed. Further, since the thin film is divided into the thin film 4a and the thin film 4b, the heat from the heater is transferred only through the surrounding gas, so that a thermal gas sensor such as a highly sensitive vacuum sensor can be provided. Since the temperature sensor for detecting the temperature of the surrounding gas is provided, the influence of the ambient temperature can be corrected, and a more accurate measuring device can be provided.

In order to achieve the above object, a gas sensor according to claim 1 of the present invention includes a substrate 1 installed in a chamber in which the flow of ambient gas is blocked, two thin films 4a thermally separated from the substrate 1, and a thin film 4b is disposed through a gap 300, and one thin film 4a is provided with at least one heater 6 and a temperature sensor TSa for detecting the temperature Ta at the location A of the heater 6, and the other thin film 4a. 4b includes a temperature sensor TSb that detects the temperature Tb, and is configured such that the temperature of the location B rises due to the heat conduction of the surrounding gas in contact with the thin film 4b. The outputs of the temperature sensor TSa and the temperature sensor TSb are Utilizing the sensor to measure the atmospheric pressure or its components in the chamber and the cylinder or polygonal cylinder that blocks the flow of the ambient gas, In some cases, the component is measured without being influenced by the flow of the surrounding gas. In addition, there is a cylinder or polygonal cylinder in which the flow of ambient gas is blocked, and a small hole is formed on the gas sensor detection surface so as to be the same as the ambient gas atmosphere, and measurement is performed with high sensitivity.

A gas sensor according to a second aspect of the present invention is the gas sensor according to the first aspect of the present invention, wherein the width of the gap 300 spaced apart from the temperature sensor TSa at the location A of the thin film 4a is smaller than either of the widths of the thin film 4a and the thin film 4b. Since the thin film 4a and the thin film 4b are close to each other, heat is easily transferred from the thin film 4a to the thin film 4b through the ambient gas to be measured, so that the sensitivity is high.

The gas sensor according to claim 3 of the present invention is the case where the temperature sensor TSc for detecting the temperature Tc of the surrounding gas in the first and second aspects is provided on the substrate 1, and is measured more than the temperature Tc of the surrounding gas by measurement. It is preferable to control the heater so that the temperature becomes several tens of degrees.

The gas sensor according to claim 4 of the present invention is a gas sensor structure according to claims 1 to 3, as a temperature sensor that is highly sensitive and accurate as a temperature sensor used therefor, and that can be simply integrated. This is the case when a bipolar transistor or a semiconductor diode is used.

  A gas sensing device according to claim 5 of the present invention uses the gas sensor according to any one of claims 1 to 5 and outputs of the temperature sensor TSa and the temperature sensor TSb of the gas sensor to perform signal amplification. The gas sensing device is provided with a circuit, an arithmetic circuit, a memory circuit, a drive power supply circuit, and a display unit as necessary, and can measure the atmospheric pressure of the ambient gas in the chamber or its component.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of a gas sensor of the present invention and a gas sensing device using the same will be described in detail with reference to the drawings.
FIG. 1A is a schematic plan view of a sensor chip that is a gas sensing unit of a gas sensor, and FIG. 1B is a cross-sectional view taken along line XX ′ in FIG. 2 shows a system diagram of a gas sensing device including a gas sensor.

FIG. 1A is a schematic plan view of a sensor chip that is a gas sensing unit of a gas sensor, and FIG. 1B is a cross-sectional view taken along line XX ′ in FIG. 2 shows a system diagram of a gas sensing device including a gas sensor.
This sensor chip is an embodiment in which a substrate 1 which is a silicon SOI substrate is used. A cavity 3 is formed in the base substrate 2, and a groove 40 is formed above the cavity 3 for thermal separation from the substrate 1. The thin film 4a and the thin film 4b left for this purpose are formed of a thin film 4a supported by four beams 5a and a thin film 4b supported by three beams 5b via a gap 300. The thin films 4a and 4b and the beams 5a and 5b are mainly composed of the BOX layer 10 and the single crystal silicon thin film 20 of the SOI substrate. For this reason, the thin film 4a and the thin film 4b are structures that are suspended in the air and are thermally separated from the substrate.

  The single crystal silicon thin film 20 is a p-type layer 210, and an n-type layer 220 formed by n-type impurity diffusion can be used as the thin film heater 6 here. Since the heater 6 which is a thin film of the n-type layer 220 has a conductivity type different from that of the surrounding p-type layer 210, a pn junction is formed between them, and the heater 6 is electrically connected to the surrounding p-type layer 210. It is a structure that is electrically isolated. Therefore, when a current is passed through the heater electrode 140, the current can flow only in the heater 6, and only the heater 6 can be Joule-heated.

  In addition, the n-type layer 220 at the same time as the thin film heater 6 includes a pn junction diode formed on the thin film 4a and the thin film 4b, and the temperature sensor TSa for detecting the temperature Ta of the heater 6 at the location A is used. It is used as a temperature sensor TSb for detecting the temperature Tb. The temperature sensor TSc for detecting the temperature Tc of the surrounding gas also has an n-type layer 220 region formed simultaneously with the thin film heater 6, and a pn junction diode is formed.

  In addition, since current is applied to the wiring 150 and the p-type electrode 120 of the pn junction diode and the n-type electrode 130 of the pn junction diode, the wiring 150 and the p-type electrode 120 of the pn junction diode and the n-type electrode 130 of the pn junction diode A silicon oxide film 51 is formed and insulated between the single crystal silicon thin films 20.

  In the above description, the pn junction diode 7a is used as the temperature sensor TSa, the pn junction diode 7b is used as the temperature sensor TSb, and the pn junction diode 7c is used as the temperature sensor TSc. Alternatively, a pn junction of may be used. An element having a temperature coefficient may be used.

The sensor chip shown in FIG. 1a and FIG. 1b can be formed by using a known semiconductor microfabrication technique of single crystal silicon, an illegal etching technique, and by using an impurity diffusion process, a thermal oxidation process, etc. The formation of the wiring 150, the p-type electrode 120 of the pn junction diode, the n-type electrode 130 of the pn junction diode, and the like can be easily formed by an existing technology. For metallization of the electrodes and the like, it is preferable to use a metal that is resistant to an alkaline etching solution which is anisotropic etching used when forming the cavity 3 in the substrate 1. However, when using a non-resistant metal such as aluminum, it is necessary to make it resistant as an alloy of aluminum and silicon, or to perform an illegal etching after forming a protective film on it. is there. Here, a silicon oxide film 52 is used.

Next, the thin film 4 a heated by the heater 6, the temperature Ta of the temperature sensor TSa composed of the pn junction diode 7 a at the location A, and the location B of the thin film 4 b away from the location A through the air gap 300, A description will be given of the atmospheric gas pressure measurement and apparatus by the temperature Tb of the temperature sensor TSb composed of the pn junction diode 7b at the location B of the thin film 4b heated by heat conduction.

The thickness of the thin film 4a, 4b (including the single crystal silicon thin film 20) of the SOI thin film portion of the silicon SOI substrate which is the substrate 1 is 6 μm, and the size of the thin film surrounded by the groove 40 is 400 μm (including the thin films 4a, 4b). When the thickness of the BOX layer 10 is 1 μm and n-type impurity diffusion is performed to form the n-type layer 220, the resistance value of the thin film heater 6 is approximately 60Ω, depending on the impurity diffusion temperature and time. Met. When a direct current was passed through the heater electrode 140 by several tens of mA, the temperature rose to 200 ° C. or higher. The heater 6 is disposed in the vicinity of the location A of the thin film 4a thermally separated from the substrate 1 by providing the heater 6 and the temperature sensor TSa separately. The temperature sensor TSb (pn junction) of the thin film 4b heated by the temperature Ta detected by the sensor TSa (pn junction diode 7a) and the heat conduction through the air gap 300 and the surrounding gas away from the place A. The temperature Tb detected by the diode 7b) has a temperature gradient due to heat radiation by heat conduction and heat conduction through the air gap 300, and the temperature Tb is always lower than the temperature Ta.

The embodiment including the system diagram of FIG. 2 supplies a bias voltage required to operate the temperature sensor TSa from the “signal amplifier circuit” to the “temperature sensor TSa” for measuring the temperature Ta, The “signal amplifier circuit” converts the voltage to a voltage corresponding to a predetermined temperature, and supplies power from the “signal amplifier circuit” to the “heater 6” so that the temperature Ta at the point A becomes a predetermined temperature. To maintain.

A necessary bias voltage for operating the temperature sensor TSb is supplied from the “signal amplifying circuit” to the “temperature sensor TSb” for measuring the temperature Tb of the place B, and the ambient gas pressure is changed from the atmospheric pressure to the ambient gas pressure. If the temperature is lowered, the thermal conductivity of the surrounding gas at the temperature Ta at the location A and the temperature Tb at the location B is lowered and the heat radiation is deteriorated, and the cooling effect at the location A and the location B is lowered. In order to maintain the temperature at a predetermined temperature, the power supplied to the “heater 6” must be lowered. Since the temperature Ta at the location A is maintained at a predetermined temperature, the location B of the thin film 4b is heated by the heat conduction of the thin film 4a and the gap 300 from the heater 6, but the thermal conductivity of the surrounding gas is large. The temperature difference between the temperature Ta at the location A of the heater 6 and the temperature Tb at the location B increases.

These temperature differences are detected by a “signal amplification circuit”, and the temperature difference information and the ambient gas temperature Tc information (the system for measuring the temperature Tc is the same as the temperature Ta and the temperature Tb). As a vacuum gauge that converts the voltage corresponding to the temperature difference into a vacuum degree, and information on the temperature Tc as temperature information in the chamber, signal processing is performed in the “arithmetic circuit” and “memory circuit”, and the “display circuit”. Can be displayed.

Further, the temperature can be set with a short wave so that a voltage is applied to the heater 6 with a short wave, and a vacuum gauge with low power consumption can be obtained. The output voltage of the “signal amplifier circuit” can be digitized by the “arithmetic circuit”, required data can be stored in the “memory circuit”, and required signal processing can be performed to display the “display circuit”. The “drive power supply circuit” is a circuit that supplies power necessary for operation to each circuit.

The single crystal silicon thin film 20 is a p-type layer 210, and an n-type layer 220 formed by n-type impurity diffusion can be used as the thin film heater 6 here. Since the heater 6 which is a thin film of the n-type layer 220 has a conductivity type different from that of the surrounding p-type layer 210, a pn junction is formed between them, and the heater 6 is electrically connected to the surrounding p-type layer 210. It is a structure that is electrically isolated. Therefore, when a current is passed through the heater electrode 140, the current can flow only in the heater 6, and only the heater 6 can be joule-heated.

Since the substrate 1 can be formed on a silicon semiconductor substrate, the circuit necessary for the gas sensing system and the circuit necessary as a part of the measuring device can be integrated, so that the measuring device is extremely small, consumes little power, and has high reliability. Can be provided.

(a) It is the schematic which shows one Example of the gas sensor of this invention. (b) It is sectional drawing in XX 'of Fig.1 (a). It is a systematic diagram which shows one Example of the gas sensing apparatus of this invention.

Explanation of symbols

1 Substrate 2 Base substrate 3 Cavity 4a, 4b Thin film
5a, 5b Beam 6 Heater 7a, 7b, 7c pn junction diode (temperature sensor)
10 BOX layer 20 single crystal silicon thin film 40 groove 51, 52 silicon oxide film
120 p-type electrode of pn junction diode 130 n-type electrode of pn junction diode
140 heater electrode 150 wiring 210 p-type layer
220 n-type layer
300 gap

Claims (5)

A substrate (1) installed in a chamber in which the flow of ambient gas is blocked and two thin films (4a, 4b) thermally separated from the substrate (1) are arranged via a gap (300) that is independent of each other. One thin film (4a) is individually provided with at least one heater (6) and a temperature sensor TSa for detecting the temperature Ta at the location A of the heater (6), and the other thin film (4b) ) Is provided with a temperature sensor TSb for detecting the temperature Tb, and the temperature of the place B is increased only by the heat conduction of the surrounding gas in contact with the thin film (4b). The temperature sensor TSa and the temperature sensor TSb A gas sensor characterized in that it can measure the atmospheric pressure of the ambient gas in the chamber or its component by using the output of. The gas sensor according to claim 1, wherein the width of the gap (300) is made smaller than any of the widths of the thin film (4a) and the thin film (4b). The gas sensor according to any one of claims 1 and 2, wherein a temperature sensor TSc for detecting a temperature Tc of the surrounding gas is provided on the substrate (1). The gas sensor according to any one of claims 1 to 3, wherein the temperature sensor TSa, the temperature sensor TSb, and the temperature sensor TSc are bipolar transistors or semiconductor diodes. 5. A signal amplifier circuit, an arithmetic circuit, a memory circuit, a drive power circuit, a display using the gas sensor according to claim 1 and outputs of the temperature sensor TSa and the temperature sensor TSb of the gas sensor A gas sensing device characterized in that a part is provided as required so that the atmospheric pressure of the surrounding gas in the chamber or its component can be measured.