Design and testing of a micro thermal sensor for non-contact surface defect detection

This paper presents an experimental study on a new concept of a surface defect detection method, in which surface defects will be detected by monitoring a change in heat flow between a micro thermal sensor and a smoothly-finished measuring surface such as magnetic disks, sapphire substrates and so on. In the proposed method, the micro thermal sensor is designed to detect surface defects without any contacts in between them. Since the change in heat flow across the gap is utilized, the method is expected to find out both the convex and concave defects. Searching for the possibility of the non-contact surface defect detection by the micro thermal sensor, in this paper, a simple heat transfer model is established to estimate the change in heat flow due to the change in gap between themeasuring surface and the sensor surface. Some basic experiments are also carried out by using prototype micro thermal sensors, each of which is composed of a pair of electrodes and a thin metal film resistor, fabricated on both the silicon and glass substrates.