CMOS Tin Oxide Gas Sensor And Circuit Design

Tin Oxide gas sensor is one kind of chemical sensors for measuring the gas concentration ,by using the gas chemisorption and physisorption between the semiconductor surface and gas molecule or atom. It has a broad scope of gas measurement (oxygen, moisture, hydrogen, the carbon monoxide, etc.). this sensor is widely used such as environmental protection, chemistry, chemical industry and biomedicine,and so on.However the traditional gas sensor is taken the ceramics as a basis and sintered , the disadvantage of traditional method is high cost, low performance . In recent years , with the great progress of silicon technology, using the standard CMOS process to fabricate gas sensor has become a hot topic , the advantages of this method is to deal with the sensor and signal processing circuit onto the single chip, and to realize low cost, small size , high reliability and gas sensitivity . The computer-aided design (CAD)has played the very vital role in the integrated circuit design and the simulation analysis as a powerful tool. We can not only simulate system circuit ( including Operational Amplifier and Decoder ) and layout sensor by Hspice of EDA tool, but also simulate sensor model by Ansys. By doing this, we can design a good sensor model ,such as the heater . But it is difficult to simulate sensor and elicit its parameters by Hspice at present. So we need to study in this field in future.By understanding the surface adsorption principle very well, we can determine this sensor structure and the design parameters through Ansys simulation. On the experiment of many kinds of resistant materials ( p+ diffusion, poly , n+ diffusion, nwell), we can analyze their heating characteristic and choose poly as the heater which this sensor needs, and we compares each kind of escharotics in post-CMOS process and choose the potassium hydroxide to etch . Then we design the system circuit, including Decoder, Operational-amplifier. All will be fabricated by TSMC 0.6μm 1P3M CMOS process.We finished the total design of gas sensor system, including circuity design and simulation ,and will tape-out.