There is a growing interest in infrared image for a wide range of applications from military and commercial night vision to the heat sensing for a fire alarm or for medical applications. Detection mechanism of infrared can be classified into two groups: photon detection and thermal detection. Photon detectors are too expensive for general commercial applications because of the requirement of cryogenic cooling.
Three types of thermal detectors have been reported in recent years: resistive bolometers, thermopile detectors, and pyroelectric detectors. In this work we have chosen a bolometer approach because its responsivity is much higher than that of thermopile detectors and it is easy to fabricate compared to pyroelectric detectors.
Bolometers are thermistor-based sensors that measure temperature change in a thermally-isolated membrane heated by infrared radiation absorbed on the surface. There are two major design issues on bolometers. One is a structure issue and the other is a material issue. In order to obtain high detectivity, structures must have a good thermal isolation and a high fill-factor, and materials must have a high TCR and low noise.
In this work we proposed a new structure with a high fill-factor. By using micromachined multi-level structure we have achieved high fill-factor over 92% in a 50㎛×50㎛ pixel with a detectivity of $5×10^{8}cm\sqrt{Hz}/W$. As a new material, we have studied microcrystalline SiC thin films and we have achieved a TCR of 3.27%. From a sample with the TCR of 0.8% we have estimated the detectivity improved to be $1.5×10^{9}cm\sqrt{Hz}/W$.
