Sensitivity improvements in uncooled microbolometer FPAs

Raytheon IRCOE has developed a family of uncooled, microbolometer FPAs. These FPAs have been designed to address commercial and high-performance military applications. The SE-151 is a high-sensitivity 320 x 240 FPA with 50 um pixels. The SE-151 FPA has been fabricated with several microbolometer pixel designs that allow optimization of either sensitivity or response time. Noise equivalent temperature difference (NETD) values as low as 8.6 mK have been measured for the SE-151 FPAs with f/1 optics. NETD values less than 25 mK have been measured for FPAs with thermal time constants of approximately 18 msec. The SB-151 FPAs have been integrated into a variety of prototype sensors including the Raytheon Long-wavelength Staring Sensor (LWSS). The LWSS is a low-power, lightweight sensor that has achieved excellent sensitivity and imagery with E/2.1 optics. The LWSS was characterized by the US Army's NVESD in August 1998. NVESD measured NETD values in agreement with the Raytheon data. The NVESD evaluation also demonstrated outstanding MRT and spatial noise characteristics. Raytheon IRCOE has also initiated production of the microbolometer FPAs for commercial applications. The AE-189 is a 320 x 240 FPA that was developed for use in a commercial radiometer imager - the ExplorIR. Over 1000 qualified FPAs have been produced on this project. The pixel operability of the production radiometer FPAs (AE-189) is typically greater than 99.9%. The responsivity nonuniformity is typically less than 4% (sigma/mean) and the average f/l NETD is less than 90 mK. Raytheon is also developing a 320 x 240 FPA (SB-212) with 25 um pixels. The microbolometer pixels for the SB-212 are fabricated using a novel micromachining process. This approach allows the thermal isolation and optical fill-factor to be comparable to that achieved with conventional 50 um pixels. The SBRC-212 FPA has achieved outstanding f/1 NETD values of less than 50 mK.