Far IR Transmission Characteristics of Silicon Nitride Films using Fourier Transform Spectroscopy

Abstract

We are fabricating amorphous Silicon (a‐Si) bolometers doped with boron with a measured NEP∼1.5×10−16 W/Hz1/2 suitable for use in millimeter and sub‐millimeter astronomy. In this paper we present the preliminary results of the absorber optimization for the a‐Si bolometers. A film of Silicon Nitride (SiN), deposited by LPCVD (Low Pressure Chemical Vapor Deposition) process at INAOE, with or without metallic coating is used as a weak thermal link to the heat sink as well as an absorber. We have measured the transmission spectrum of thin films of SiN in the range of 200 to 1000 GHz using Fourier Transform Spectroscopy (FTS) and a bolometric system with a NEP∼1.26×10−13. The transmission of thin films of SiN with a thickness of 0.4 μn has been measured at temperatures of 290 K and 4 K. The uncoated SiN films have a transmission of 80% and we expect a 50% transmission for the metallic (e.g. Titanium) coated films.