Performance Characterization of Infrared Detectors Based on Polymorphous Silicon‐Germanium (pm‐SixGe1−x:H) Thin Films Deposited at Low Temperature

Abstract

In this work, the fabrication of infrared detectors (uncooled microbolometers) using surface micromachining techniques is presented. The thermo‐sensing film used in the devices is polymorphous silicon‐germanium (pm‐SixGe1−x:H) produced by low frequency plasma‐enhanced chemical vapor deposition (PECVD) at low temperature (200 °C). Polymorphous semiconductors basically are amorphous semiconductors with embedded nanocrystals (of diameter of about 2–5 nm), which are formed during the film deposition. The presence of nanocrystals impacts on the properties of the material by reducing the density of states (defects) and improving the stability of the films. For infrared detectors those materials present important properties such as high temperature coefficient of resistance (TCR = −4.7% K−1), long‐term stability, low deposition temperature, and silicon CMOS compatibility. Test structures with size of 50 × 50 μm2 and different thermal isolation designs are characterized under IR radiation (0.7–20 μm) in a frequency range of 5–100 Hz. From voltage responsivity and noise measurements, the specific detectivity is calculated achieving values of 1 × 108 cm Hz1/2 W−1 and thermal response time of 8–9 ms under 150 nA bias current. The above characteristics make those devices very suitable for the development of infrared focal plane arrays (IRFPAs).