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 Si
_x
Ge
_y
O
_1-x-y
uncooled infrared microbolometers with four different compositions. The noise reduction was achieved by passivating Si
_x
Ge
_y
O
_1-x-y
with Si
₃
N
₄
layers and by annealing the devices in vacuum at 200 °C, 250 °C, or 300 °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 μA before and after annealing. The lowest measured noise voltage PSD before annealing was on devices with Si
_0.053
Ge
_0.875
O
_0.072
and Si
_0.041
Ge
_0.902
O
_0.057
films. They were 7.42 × 10
^-15
and 2.07 × 10
^-14
V
²
/Hz at 23 Hz, respectively. The corresponding 1/f-noise coefficients, Kf , of the devices were 3.65 × 10
^-14
and 3.01 × 10
^-14
, respectively. The voltage noise PSD was reduced as the annealing time and temperature were increased. The lowest measured noise was 1.96 × 10
^-14
V
²
/Hz at the corner frequency, 12 Hz, on a device with Si
_0.034
Ge
_0.899
O
_0.067
film annealed at 300 °C for 4 h, before annealing the noise was 4.09 × 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 °C reduced the low-frequency voltage noise PSD more than that of 200 °C and 250 °C temperatures.