Sensitivity improved thermal infrared sensor cell applying the heat insulating phononic crystals

Improving heat insulation in microelectromechanical system based thermal-type infrared sensor is crucial to increase its performance. The concept of phonon engineering allows us to change material thermal conductivity by several orders of magnitudes, which can be a potential technique for thermal management of such microelectronic devices. Here, we introduced a phononic crystal structure in a prototype thermopile sensor to investigate the effectiveness of phonon engineering. We demonstrate that ultrafine phononic crystal structure, which was consisted of through-holes periodically arranged at 38 nm, resulted in ten-fold reduction in Si thermal conductivity. This led to improvement of the sensitivity of IR detection by a factor of ten. In addition, our phononic crystal could suppress thermal conductivity while maintaining the electrical conductivity, which enable us to increase the noise equivalent temperature difference by 5.6 times. The present study demonstrates great potential of phonon engineering for infrared sensor technology to reach for smaller pixel size and lower device cost.