The widespread use of Liquid Petroleum Gas (LPG) for cooking and as fuel for automobile vehicles requires fast and selective detection of LPG to precisely measure the leakage of gas for preventing the occurrence of accidental explosions. The adoption of Micro-Electro-Mechanical-System (MEMS) technology for fabricating the gas sensor provides other potential advantages for sensing applications, which includes low power consumption, low fabrication cost, high quality, small size and reliability. MEMS based gas sensor requires a sensitive layer of oxide material like ZnO, SnO2, TiO2, Fe2O3, etc. The tin oxide material used in the present work changes its electrical properties, as it interacts with the reducing gas like LPG. The sensor material becomes active only at high temperature such as 400ºC, thereby realizing the need of a micro heater to reach the desired temperature. To control the temperature of micro heater and to determine the change in electrical properties of the sensor due to its interaction with LPG an Application Specific Integrated Circuit (ASIC) forms an essential constituent of the MEMS based gas sensor. In the present work, an attempt has been made to improve the sensitivity of LPG gas sensor and it is correlated with other properties by different characterization techniques. The work also includes the design as well as testing of ASIC for gas sensor system. Process parameters particularly deposition time and substrate temperature have a profound influence on the microstructure of the tin oxide film, which in turn affects the gas sensing properties. To study the effects of these parameters, RF magnetron sputtering system is used for depositing tin oxide films onto the silicon substrate, which is compatible with CMOS technology. The effects of structural properties, optical properties and the porosity of the films are also studied and correlated with the gas sensing properties. In this direction the deposited films are characterized using X-Ray Diffraction (XRD) to determine the structure orientation. The morphology of the sensor films are analyzed by Scanning Electron Microscope (SEM) while the refractive index, thickness and porosity of the films are determined using ellipsometry studies. The thickness of the deposited films is also confirmed by the surface profilometer. The change in composition of the deposited film along its depth is determined using Secondary Ion Mass Spectrometer (SIMS). Maximum sensitivity 5.5 is obtained for 470 nm thick films, which corresponds to a grain size of 38nm at the operating temperature of 4000C. Following these studies, an ASIC has been designed using Tanner EDA Tools on AMIS 0.7 µm CMOS process, fabricated through Euro practice’s ASIC prototyping service, Belgium and tested successfully after fabrication. The temperature control module of ASIC has been designed using relaxation oscillator technique to control the temperature of the in house developed heater. The resistance to period conversion technique is explored for the design of the sensor read out module of ASIC. The heater is integrated successfully with the sensor film, ASIC and microcontroller based LCD module. The test results show good agreement with the simulation results.

Today there is a great deal of interest in the development of gas sensors for applications like air pollution monitoring, indoor environment control, detection of harmful gases in mines etc. Based on different sensing principles, a large variety of sensors such as semiconductor gas sensors, thermoelectric gas sensors, optical sensors and thermal conductivity sensors have been developed. The present thesis reports a detailed account of a novel method followed for the design and development of a thermoelectric gas sensor for sensing of Volatile Organic Compounds. Thermoelectric effect is one of the highly reliable and important working principles that is widely being put into practical applications. The thermoelectric property of semiconducting tin oxide film has been utilized in the sensor that has been developed. The thermoelectric property of semiconducting tin oxide film has been utilized in the sensor. The deposition parameters for sputtering of tin oxide film have been optimized to obtain a high seebeck coefficient. A test set-up to characterize the deposited films for their thermoelectric property has been designed and developed. A novel method of increasing the seebeck coefficient of tin oxide films has been successfully implemented. Thin films of chromium, copper and silver were used for this purpose. Deposition of the semiconducting oxide on strips of metal films has led to a noticeable increase in the seebeck coefficient of the oxide film without significantly affecting its thermal conductivity. The next part of our work involved development of a gas sensor using this thermoelectric film. These sensors were further tested for their response to volatile organic compounds. The sensor showed significant sensitivity to the test gases at relatively low temperatures. In addition to this, the developed sensor is also selective to acetone gas.

Recently, there has been an increasing interest in the electronics world for those aspects related to semiconducting gas sensor (SGS) materials. In view of the increasingly strict legal limits for pollutant gas emissions, there is a great interest in developing high performance gas sensors for applications such as controlling air pollution and exhaust gases in automotive industry. In this way, semiconductor gas sensors offer good advantages with respect to other gas sensor devices, due to their simple implementation, low cost and good stability and sensitivity. The first part of the thesis is dedicated to the synthesis, film structural and sensitivity study of the Tin Oxide film deposited by RF sputtering, doped with noble metal Palladium (Pd). Effects on the Gas Sensitivity due to the deposition parameters like thickness of the film, Substrate temperature, Ar /O2 ratio of the sputtering environment, annealing temperature and duration and doping metal weight % into the Tin Oxide films are studied and the results are shown in detail. The sensitivity and selectivity of the gas sensing film is decided by the operating temperature i.e. the temperature of the gas sensing film while it is in the target gas ambience, Microheaters happen to be the very important component in the gas sensor especially with wide band gap semiconducting metal oxides films such as tin oxide, gallium oxide or indium oxides. Other than gas sensing microheater also finds applications in many areas like thermal dip pen nanolithography, polymerase chain reaction (PCR), fluid pumping with bubbles, in vitro fertilization etc. So in this report due importance was given for the design and fabrication of the microheater. Microheaters are the most power consuming element of the integrated Gas sensors. This is also an important reason for the extensive microheater work in this research. Six different heater patterns were simulated by considering low power and temperature uniformity as an important goals. Among them the best three patterns named Double spiral, “Fan” Shape and “S” shape were chosen for fabrication and both thermal and electrical characterization results of them were presented in detail in the Microheater section of the thesis. It is believed that the intelligent design and integration of the electronic circuitry (for drive, signal conditioning/compensation, and read-out) with the gas sensing element can mitigate some of the significant issues inherent in solid-state gas sensors, such as strong temperature and humidity dependence, signal drift, aging, poisoning, and weak selectivity. The sensitivity of the gas sensors which has been indicated as the dynamic change of resistance in wide range should be read out properly. Towards this aim a low cast high efficient readout circuit is designed and implemented. Temperature monitoring and controlling is a key phenomenon in the metal Oxide based gas sensors since the selectivity mainly depends on the operating temperature of the sensing film. So focus was also shown on the design and implementation of the temperature monitoring and control unit, which been presented in the last part of this thesis.