Micro-hotplate (MHP) provides a platform for thin-film gas sensor operating at elevated temperature. It is proposed elsewhere that temperature programmed desorption technique can be used to improve the selectivity of gas detection. For this reason, the temperature uniformity and the ease of controlling the operating temperature on a MHP become more and more important. In this thesis, the author intended to address the thermal management problem. In the first part of this work, the use of mechanical engineering software to simulate the thermal behavior of MHP is demonstrated. The simulation can be used to estimate the temperature distribution and heater power of the MHP under design. Next, a novel MHP structure is proposed. The approach uses frontside anisotropic etching of silicon toget...[ Read more ]

Micro-hotplate (MHP) provides a platform for thin-film gas sensor operating at elevated temperature. It is proposed elsewhere that temperature programmed desorption technique can be used to improve the selectivity of gas detection. For this reason, the temperature uniformity and the ease of controlling the operating temperature on a MHP become more and more important. In this thesis, the author intended to address the thermal management problem. In the first part of this work, the use of mechanical engineering software to simulate the thermal behavior of MHP is demonstrated. The simulation can be used to estimate the temperature distribution and heater power of the MHP under design. Next, a novel MHP structure is proposed. The approach uses frontside anisotropic etching of silicon together with special layout to create the thermally isolated structure. Sandwich of inter-dielectric layers and aluminum interconnection provides the supporting material while highly doped boron diffusion provides the heating and temperature sensing. The design incorporates guard heater layout that improves the temperature uniformity. Simulation result shows that the temperature variation on a sensor film of 50 x 60 [mu square metres] is less than 25℃ when the operating temperature is 350℃. The micro-hotplate fabricated exhibits heating efficiency of about 7℃/mW and CMOS compatibility.

Finally, tin dioxide was identified as the gas sensing material and was deposited using RF reactive sputtering of tin under oxygen ambient. The film composition and grain structure have been characterized by XPS and STM techniques. We have also designed the preliminary schematic of an automatic gas sensor characterization system. With the foundation laid by this work, many research activities in integrated gas sensor such as gas sensitivities and selectivity investigation can be carried out.