Research on thermal conductivity measurement of submicrometer-scale silicon dioxide film in thermal flow sensor by micro-Raman technique

Thermal flow sensor can be used in tiny robot to detect the direction and velocity of the air flow around the robot. Thermal flow sensor needs a reliable thermally insulated structure. Silicon dioxide film is widely used as the thermal insulating layer in thermal flow sensors due to its characteristics such as low thermal conductivity and simple fabrication process. So it is very important to investigate the thermal conductivity of silicon dioxide film and its measurement technique for the research and design purpose of thermally insulated structure in thermal flow sensor. The technique of thermal conductivity measurement with micro-Raman spectroscopy is a direct and noncontact method, with this technique the thermal conductivity of thin film can be measured successfully while the laser diameter of the micro-Raman spectroscopy device is about several micrometers or tens of micrometers, so this technique cannot be applied directly to the thin film with submicrometer- scale thickness. An analytic heat flow model is presented in this paper to modify the micro-Raman technique. And the thermal conductivities of 200 nm, 300 nm and 500 nm thickness silicon dioxide Alms are measured with this modified technique. It is proved by the results that the modified micro-Raman technique can be applied to measure the thermal conductivity of thin film with submicrometer-scale thickness.