Fabrication of Microbolometer Arrays Based on Polymorphous Silicon-Germanium

This work reports the development of arrays of infrared sensors (microbolometers) using a hydrogenated polymorphous silicon-germanium alloy (pm-Si_xGe_1-x:H). Basically, polymorphous semiconductors consist of an amorphous semiconductor matrix with embedded nanocrystals of about 2-3 nm. The pm-Si_xGe_1-x:H alloy studied has a high temperature coefficient of resistance (TCR) of 4.08%/K and conductivity of 1.5 × 10^-5 S∙cm^-1. Deposition of thermosensing film was made by plasma-enhanced chemical vapor deposition (PECVD) at 200 °C, while the area of the devices is 50 × 50 μm² with a fill factor of 81%. Finally, an array of 19 × 20 microbolometers was packaged for electrical characterization. Voltage responsivity values were obtained in the range of 4 × 10⁴ V/W and detectivity around 2 × 10⁷ cm∙Hz^1/2/W with a polarization current of 70 μA at a chopper frequency of 30 Hz. A minimum value of 2 × 10^-10 W/Hz^1/2 noise equivalent power was obtained at room temperature. In addition, it was found that all the tested devices responded to incident infrared radiation, proving that the structure and mechanical stability are excellent.