Pixel-by-pixel calibration of a CCD camera based thermoreflectance thermography system with nanometer resolution

This work presents for the first time a method for calibrating pixel-by-pixel and in-situ a CCD camera-based thermoreflectance thermography system with nanometer spatial resolution. Using the thermoreflectance method to determine the temperature map of an activated device requires two steps: first, the thermal image is acquired using a CCD camera or laser-diode set-up and, second, the obtained thermal image is converted to the actual temperature map by multiplying each pixel of the thermal image with the corresponding thermoreflectance coefficient. The critical aspect is that even if the thermoreflectance coefficient is known, or measured independently for each surface material, converting the thermal image to the temperature map requires building manually the exact corresponding map of the thermoreflectance coefficient, which sometimes can be difficult. In addition, the thermoreflectance coefficient is highly dependent on the wavelength of the probing light, numerical aperture, focus level, light uniformity, and other measurement effects. To mitigate these issues, one must obtain the thermoreflectance coefficient map of the same measurement area of interest, while ensuring that the same objective lens is used, the same focus level is maintained, and the same exact position is kept for frame acquisition at both the low and high temperature settings. To satisfy all of these requirements, the position of the sample must be adjusted in 3D space with nanometer spatial resolution.