Noise Reduction of Amorphous SixGeyO1-x-y Thin Films for Uncooled Microbolometers by Si3N4 Passivation and Annealing in Vacuum

This paper presents the fabrication and reduction of noise voltage power spectral density (PSD) of SixGeyO1-x-y uncooled infrared microbolometers with four different compositions. The noise reduction was achieved by passivating SixGeyO1-x-y with Si3N4 layers and by annealing the devices in vacuum at 200 degrees C, 250 degrees C, or 300 degrees C with different time intervals from 1 to 5 h. The voltage noise PSD was measured with a bias current between 0.07 and 0.6 mu A before and after annealing. The lowest measured noise voltage PSD before annealing was on devices with Si0.053Ge0.875O0.072 and Si0.041Ge0.902O0.057 films. They were 7.42 x 10(-15) and 2.07 x 10(-14) V-2/Hz at 23 Hz, respectively. The corresponding 1/f -noise coefficients, K-f, of the devices were 3.65 x 10(-14) and 3.01 x 10(-14), respectively. The voltage noise PSD was reduced as the annealing time and temperature were increased. The lowest measured noise was 1.96 x 10(-14) V-2/Hz at the corner frequency, 12 Hz, on a device with Si0.034Ge0.899O0.067 film annealed at 300 degrees C for 4 h, before annealing the noise was 4.09 x 10(-13) V-2/Hz at 12 Hz. This corresponds to a factor of 24 reduction of noise. The testing results demonstrate that annealing at higher temperature 300 degrees C reduced the low-frequency voltage noise PSD more than that of 200 degrees C and 250 degrees C temperatures.