Fabrication of a sensitive germanium microbolometer for tympanic thermometry

Abstract

Fabrication of a complementary-metal-oxide-semiconductor (CMOS)-process-compatible microbolometer for tympanic thermometry using an amorphous germanium thin film as the temperature-sensitive element has been studied. Heat treatment of the deposited films, with or without passivation, at different annealing temperatures was investigated for optimizing the sensitivity of the material and for considering the compatibility of the CMOS process. Microbolometers structured with a thermally isolated membrane to enhance the thermal responsivity were fabricated by micromachining. The fabricated devices were characterized by conducting appropriate experiments and evaluated for the necessary thermal and electrical parameters useful in applications. It has been found that, for an annealing condition around 370 degrees C for two hours, the passivated floating Ge thermistor has a 3%/degrees C temperature coefficient of resistance (TCR) and a comparably low flicker noise relative to other conditions. In a vacuum, the passivated device with an area of 250x250 mu m(2) shows a responsivity up to 400 kV/W at 1 Hz, and a normalized detectivity D* of 1.2x10(8) and 5.2x10(7) cmHz(1/2)/W at 3 Hz and 30 Hz, respectively. These measured values also prove that the device, in its current structure, can be used as a sensitive radiation detector for tympanic thermometers.