Investigation On Heat Transfer Of Micro-scale Gas In Micro Hot-plate

The heat transfer of micro-scale gas is a fundamental physical problem in the design and production of devices and research on heat transfer of micro-scale gas is greatly meaningful in improving reliability and stability of the devices. As the heat transfer or heat insulating mechanism, micro-scale gas gap widely exists in micro electronic mechanical systems, and even some micro/nano sensors, such as flow-meter, Pirani pressure sensor, depend on the principles of heat transfer of gas gap to work. As the boundary of convective heat transfer, micro-scale surface is also important to be considered in many mechanical systems. Under the condition of micro-scale, the heat transfer of gas is affected by the scale. To study the heat transfer properties of the micro-scale gas gap and surface, the paper selects micro hot-plate as the test structure to gain the curve of the heat transfer characteristics to the scale.In addition to advantages of small size and compatibility with standard CMOS technology, importantly the micro hot-plate has the objects:the micro-scale gas gap and surface, which we would like to research. Since the co-existence of two types of heat transfer, it brings great difficulty to our research. Our idea is that firstly we do the study on convective heat transfer of gas surface and then the result obtained is applied to research heat transfer of gas gap.Firstly, micro hot-plate by etching front bulk silicon is designed and manufactured.And thermal circuits of the structure are set up at atmospheric pressure and in vacuum at normal temperature.Steady hot-plate method is used to measure convective heat transfer coefficient of micro gas surface.The result shows that due to the increasing of the specific area, the convention coefficient is much larger than that at macro scale. At the same time, finite element simulation is applied to analysis method's accuracy and factors causing method's uncertainty. The result shows that the method's accuracy is high and uneven temperature distribution of heating zone is the main reason affecting the method's accuracy.Secondly, based on the sacrificial layer technology, micro hot-plates with different gas gaps are designed and manufactured.Thermal circuits of the structures are established at atmospheric pressure and in vacuum at normal temperature as well.In the same way, the same method is used to measure the thermal conductance of air and we combine the convention coefficient obtained above to calculate the thermal conductance and the thermal conductivity of the gas gap. The result shows that in the range of 220 nm-1900 nm, with the size decreasing thermal conductance increases first and then decreases.However, the thermal conductivity of the gas gap has been a decreasing trend.