Electro-thermal properties of integrated circuit microbolometers

Abstract

The use of uncooled infrared sensors in thermal imaging is a fast growing market in the fields of security and health. The integration of uncooled or room temperature infrared sensors onto a silicon CMOS chip will facilitate the manufacture of large imaging arrays. At the University of Pretoria we are researching the integration of microbolometer infrared sensors onto CMOS readout electronic circuits using post processing techniques. The microbolometer utilises the change in resistance of a temperature sensitive resistive material, e.g. vanadium oxide or a thin metal film, to measure the amount of infrared radiation falling onto the device and heating the device. The microbolometer structure should be thermally isolated from the bulk silicon to achieve the required sensitivity. In this paper we will describe the device structures, as well as the techniques we used to determine experimentally the electrical, thermal and electro-thermal properties of the devices. Of interest to us are the following parameters: 1) temperature coefficient of the bolometer resistive layer, 2) thermal conductivity of the device, 3) thermal capacitance of the total sensor structure and 4) the thermal time constant. The microbolometer thermal characteristics can also be modelled and simulated using CoventorWare software.