Electro-Optical Characterization of Amorphous Germanium-Tin (Ge1-XSnx) Microbolometer

Abstract

Abstract The utilization of amorphous germanium-tin (Ge1 − xSnx) semiconducting thin films as temperature sensing layers in microbolometers was recently presented and patented. The work in this paper started by extending the latest study to acquire better characteristics of the Sn concentrations % for microbolometer applications. In this work, Ge1-xSnx thin films with various Sn concentrations %, x, where 0.31 ≤ x ≤ 0.48 we sputter deposited. Elemental composition was evaluated using Energy Dispersive X-ray (EDX) spectroscopy. Surface morphology was evaluated using Atomic Force Microscopy (AFM) revealing average roughness values between ~ 0.2–0.8 nm. Sheet resistance versus temperature measurements was performed and analyzed revealing temperature coefficients of resistances, TCRs, ranging from − 3.11%/K to -2.52%/K for x ranging from 0.31 to 0.40. The Ge1-xSnx thin film was found to depart the semiconducting behavior at 0.40 < x ≤ 0.48. Empirical relationships are derived relating resistivity, TCR, and Sn concentration % for amorphous Ge1-xSnx thin films. One of the films with 31% Sn concentration (Ge0.69Sn0.31) was used to fabricate 10×10 µm2 microbolometer prototypes using electron-beam lithography and liftoff techniques and the microbolometer is fabricated on top of oxidized silicon substrates with no air gap between them. The noise behavior and the maximum detected signal of the fabricated microbolometer were measured. The signal-to-noise ratio, voltage responsivity, and noise equivalent power values of the prototypes were calculated. Finally, the expected performance of the microbolometer when fabricated in an air bridge is calculated.