RU2065601C1 - Method of manufacture of gas composition monitor - Google Patents

Abstract

FIELD: manufacture of gas composition monitors. SUBSTANCE: the method consists in cleaning of the backing ceramic surface, sputtering of lands, deposition of metal film, thermal oxidation of it and connection of leads to the lands. A metal film, 0.01-to 0.03-mcm thick, is formed by successive deposition of tin and dope, featuring catalytic properties, to gas under analysis and maxing up 5 to 15 mass percent of the tin layer. Oxidation is performed successively in the atmosphere of dry oxygen at a temperature of 50 to 10 C for 0.8 to 1.2 h, in the atmosphere of humid oxygen at a temperature of 200 to 500 C for 2.5 to 3.5 h, and in the atmosphere of dry oxygen at a temperature of 550 to 650 C for 20 to 40 min at atmospheric pressure. EFFECT: facilitated procedure. 1 dwg, 1 tbl

Description

 The invention relates to the field of creating materials and manufacturing technology of sensors for detecting combustible and harmful gases in measurement, control and detection devices, and can be used in petrochemistry, mechanical engineering, energy, ecology and everyday life.

 Known methods for the manufacture of gas composition sensors based on a change in the electrical conductivity of a semiconductor film due to adsorption of gas on its surface [1] As the main component of the semiconductor film, oxides of tin, zinc or titanium are used. The selectivity and sensitivity of the sensors are determined by their temperature and the introduction of a substance with catalytic properties into the oxide layer.

 The main disadvantages of the known methods are the low selectivity and instability of their parameters over time, due to the non-optimal concentration of the catalyst and manufacturing technology.

Closest to the proposed invention, the technical essence is a method of manufacturing a film gas composition sensor [2], which includes preparing a ceramic substrate of Al ₂ O ₃ , applying electron-beam sputtering from silver electrodes, and then SnO _x film, followed by annealing.

 The disadvantage is the non-optimal choice of interrelated technological parameters: film thickness, dopant concentration, annealing mode, which does not allow to obtain high selectivity, stability and durability of the sensor.

 The objective of the invention is to increase the selectivity, stability and durability of the gas composition sensor.

This problem is solved due to the fact that in the method of manufacturing a gas composition sensor, including cleaning the surface of the ceramic substrate, sputtering the contact pads, sputtering a metal film, thermally oxidizing it, attaching pins to the pads, form a metal film 0.10 thick before sputtering the pads ± 0.03 μm by sequential deposition of tin and an alloying metal impurity, which has catalytic properties for the test gas and constitutes from the mass of the tin layer from 5 to 10 wt. and its oxidation is carried out sequentially in an atmosphere of dry oxygen at a temperature of 50-100 ^o C for 0.8-1.2 hours, in an atmosphere of wet oxygen at a temperature of 200-500 ^o C for 2.5-3.5 hours and dry oxygen atmosphere at a temperature of 550-560 ^o C for 20-40 minutes at atmospheric pressure.

When carrying out the invention, the following technical result is achieved:
1. A complex experimentally selected thermal oxidation regime activates diffusion, oxidation, and porous processes that increase the selectivity of the gas-sensitive layer and stabilize its characteristics.

 2. Separate (in this case sequential) sputtering of tin and dopant makes it possible to obtain a reproducible ratio of the components of the gas-sensitive layer.

The invention is illustrated in the drawing, which schematically shows a gas composition sensor, where:
1-ceramic substrate, 2-gas sensitive layer, 3-pin pads, 4-leads.

The sensor works as follows:
Using conclusions 4, the sensor is connected to a secondary device sensitive to the electrical resistance of the gas-sensitive layer 2, the sensor is heated to operating temperature. Under the influence of a gas mixture in which the analyzed gas is present, a catalytic oxidation reaction occurs on the surface of the gas-sensitive film, as a result of which the electrical conductivity of the film increases, which is recorded by a secondary device.

 An example implementation of the method.

 The experimental samples of the sensors were made on glass-ceramic substrates with a thickness of 0.5 mm square in shape, 10x10 mm in size, at the VUP-4 vacuum station. A metal film was formed by sequentially spraying a certain amount of dopants and tin and various thermal oxidation modes. Contact pads were made of nickel, gold wire leads. Their connection to the contact pads was carried out by contact welding. Achieving the required temperature was carried out using a nichrome heater sprayed onto the opposite side of the gas-sensitive layer of the substrate. The temperature of the sensor was controlled by a chromel-kopel thermocouple. The experimental results are summarized in the table "Production and study of the gas composition sensor."

где G₀ проводимость датчика при нулевой объемной концентрации исследуемого газа в воздухе,
G₁ проводимость датчика при объемной концентрации исследуемого газа,
β объемная концентрация исследуемого газа в воздухе.The sensor prepared according to the proposed technology was placed in a sealed chamber made of quartz glass, in which a controlled atmosphere was created, consisting of a mixture of air with the analyzed gas. Selectivity and stability were evaluated by the ratio of the relative change in conductivity to the volume concentration of the test gas in its mixture with air, which is called sensitivity (see table)

where G _{0 the} conductivity of the sensor at zero volume concentration of the test gas in the air,
G _{1 the} conductivity of the sensor at a volume concentration of the test gas,
β volume concentration of the test gas in air.

где R_k сопротивление датчика по истечении месяца при концентрации исследуемого газа в воздухе 2000 млн^-1,
R_н сопротивление датчика перед началом эксплуатации при концентрации исследуемого газа в воздухе 2000 млн^-1.Temporary stability was estimated by the change in the sensor resistance after a month with daily 4-hour operation

where R _{k the} resistance of the sensor after a month at a concentration of the test gas in the air of 2000 million ^-1 ,
R _n sensor resistance before use at a concentration of the test gas in air 2000 million ^-1.

 Using the proposed method for manufacturing a gas composition sensor allows, in comparison with existing methods, to increase selectivity and stability, to increase the output of suitable products, it allows for the production of large batches of samples with reproducible parameters in a single technological cycle using traditional semiconductor manufacturing equipment. TTT1

Claims (1)

A method of manufacturing a gas composition sensor, including cleaning the surface of a ceramic substrate, spraying the contact pads, spraying a metal film, thermally oxidizing it, attaching pins to the contact pads, characterized in that before coating the contact pads a metal film is formed with a thickness of 0.10 ± 0.03 μm by successive deposition of tin and an alloying metal impurity having catalytic properties to the test gas and constituting from the mass of the tin layer 5 15 wt. and its oxidation is carried out sequentially in an atmosphere of dry oxygen at 50 1 ^° C for 0.8 1.2 hours, in an atmosphere of wet oxygen at 200 500 ° C for 2.5 3.5 hours and in an atmosphere of dry oxygen at 550 - 650 ^o C for 20-40 minutes at atmospheric pressure.

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