Investigation on sensitivity of a contact-type thermal sensor for surface defect inspections

This paper presents an investigation on the sensitivity of a thermal sensor, which will be used as a contact detection sensor for surface defect inspections. In the proposed concept, frictional heat generated at a slight contact between a defect on a measuring surface and the thermal sensor will be utilized to find out existences of defects on the measuring surface. The frictional heat will be detected as a deviation of the electrical resistance of the sensing element in the thermal sensor. According to the principle, the sensor temperature will increase at the contact with defects. However, in the previous research by the authors, the sensor temperature was found to decrease at the contact with the glass-ball probe, whose tip diameter was on the order of several-ten μm. Following the experiments in the previous study, in this paper, further experimental investigation is carried out by employing an AFM probe as a nano-tip probe so that the sensitivity of the thermal sensor as a contact detection sensor for nanoscale defects inspection can be verified. Furthermore, a possible mechanismof the heat flow at the contact interface, which can explain the results observed in these experiments, is also introduced.