Semiconductor Gas Sensors for Detection of Combustible and Toxic Gases

In this Abstract, we review the results obtained during last several years by a research group working at the Russian Research Center Kurchatov Institute. Our activity could be classified into four main directions. The first is the investigation of materials and physical chemistry of metal-oxide gas sensors made using thick film technology. The main aim of this activity is the fabrication of most stable at high temperature, typical for operation of this kind of sensors (up to 6000C) materials and sensing layers. On the base of these materials, we designed gas sensors with lowest power consumption available for this type of devises. The second field of our interests is the application of combination of thick film materials and deposition technology with sensor chip made by micromachining technology, This provides a possibility to use the advantages of both technologies for optimization of sensor parameters. The third area of our interests concerns the investigation of a new type of gas sensors based on application of Metal-Solid electrolyte-Semiconductor (MSS) structures. These devices were applied for the determination of low concentrations of toxic gases such as fluorine and hydrogen fluoride. The forth field of our interests is the application of gas sensors in non-traditional areas such as fire protection systems, monitoring of pollutions in specific area of radio-chemical industry, in nuclear power reactors, etc

Membrane-type Gas Sensor with Thick Film Sensing Layer: Optimization of Heat Loses

We report the results of application of combined technology for the manufacturing of metal oxide gas sensors. This technology includes the manufacturing of micromachined thin dielectric membrane with microheater used as a support for thick film metal oxide gas sensing layer. The optimization of geometry of the membrane performed by means of finite-element computer simulation enabled the fabrication of methane gas sensor with power consumption of ~35 mWatt at optimal temperature equal to about 500°C. The microheater and the sensing layer have satisfactory long-term stability

Low power Silicon microheaters on a thin dielectric membrane with Thick Film Sensing Layer for gas sensor applications

We report on the design, fabrication, and characterisation of a microheater module for chemoresistive, metal-oxide semiconductor gas sensors. The microheater consists of a dielectric stacked membrane with a polysilicon resistor heater element as well as a polysilicon temperature sensing element. The geometry of both, the membrane and the heater have been optimised by means of finite element computer simulation in order to maximise heating efficiency, these devices complete of the sensing layer require only 30 mW to achieve a temperature in excess of 500°C. At present, the main limitation for the development of a battery operated thick film gas sensing devices, is power consumption. Conventional thick film sensors fabricated on aluminia substrates require typically more than 200 mW to reach their working temperature (300-500°C). The proposed micromachining technology allows low-power microheaters to be fabricated at low cost and compatible with mass production technology. Furthermore silicon micromachining is potentially suitable for the integration of the sensing and the heating element as well as the required electronics into the same battery-operated low-cost portable microsystem. The measured electrothermal characteristics of the devices are in good agreement with the outcomes of 3D numerical simulations. Overmore extensive thermomechanical finite-element numerical simulations have been carried out, to predict mechanical stability, which are confirmed by experimental tests. The electrical response to various gases of the sensor prototypes will be presented and the results, including power consumption, will be compared with the corresponding ones valid for thick film sensors fabricated on conventional ceramic substrates

Low-power thick-film gas sensor obtained by a combination of screen printing and micromachining techniques

A novel prototype of low-power thick-film gas sensor deposited by screen-printing onto a micromachined hotplate is presented. The micro-heater is designed to maintain a film temperature of 400°C with less than 30mW of input power. The fabrication process involves a combination of standard, VLSI-compatible, micromachining procedures and computer-aided screen-printing. A dielectric membrane of Si3N4 and SiO2 has been obtained with an embedded poly-Si resistor acting as a heating element. The bonding pad and contacts have been realised by a Ti/TiN/Cr/Au structure and the sensing film has been deposited by a screen-printing technique. Here follows a characterisation of a device, based on SnO2 sensing film, at working conditions together with re response curve for CH4 and NO2. We will also address some important improvements to the micro-hotplate structure, which leads to an increased flexibility of the device

Low-power thick-film gas sensor obtained by a combination of screen printing and micromachining techniques

A novel prototype of low-power thick-film gas sensor deposited by screen-printing onto a micromachined hotplate is presented. The micro-heater is designed to maintain a film temperature of 400°C with less than 30mW of input power. The fabrication process involves a combination of standard, VLSI-compatible, micromachining procedures and computer-aided screen-printing. A dielectric membrane of Si3N4 and SiO2 has been obtained with an embedded poly-Si resistor acting as a heating element. The bonding pad and contacts have been realised by a Ti/TiN/Cr/Au structure and the sensing film has been deposited by a screen-printing technique. Here follows a characterisation of a device, based on SnO2 sensing film, at working conditions together with re response curve for CH4 and NO2. We will also address some important improvements to the micro-hotplate structure, which leads to an increased flexibility of the device