Noise Reduction of Amorphous SixGeyO1–x–yThin Films for Uncooled Microbolometers by Si3N4Passivation and Annealing in Vacuum

Abstract

This paper presents the fabrication and reduction of noise voltage power spectral density (PSD) of Si x Ge y O1– x – y uncooled infrared microbolometers with four different compositions. The noise reduction was achieved by passivating Si x Ge y O1– x – y with Si3N4 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 $0.6~\mathrm {\mu }\text{A}$ 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 $7.42\times 10^{-15}$ and $2.07\times 10^{-14}~\text{V}^{2}$ /Hz at 23 Hz, respectively. The corresponding 1/ ${f}$ -noise coefficients, $\textit{K}_{f}$ , of the devices were $3.65\times 10^{-14}$ and $3.01\times 10^{-14}$ , respectively. The voltage noise PSD was reduced as the annealing time and temperature were increased. The lowest measured noise was $1.96\times 10^{-14}~\text{V}^{2}$ /Hz at the corner frequency, 12 Hz, on a device with Si0.034Ge0.899O0.067 film annealed at 300 °C for 4 h, before annealing the noise was $4.09\times 10^{-13}~\text{V}^{2}$ /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.