Low-Frequency Noise and Passive Imaging With 670 GHz HEMT Low-Noise Amplifiers

We combine newly developed InP HEMT amplifiers operating at 670 GHz with a zero-bias diode (ZBD) in order to investigate limits on passive imaging performance possible with fully uncooled, direct-detection technology. Noise-equivalent temperature difference (NETD) values under 2 K are found for reference conditions (30 Hz modulation). However, noise spectra continue to fall approximately as 1/f out to “knee” frequencies of several hundred hertz (Hz) and spectral densities of ~ 0.12 K/Hz
^1/2
for the current, somewhat gain-starved, amplifiers. The amplifier alone contributes 0.043 K/Hz
^1/2
. These results indicate that modest-sized, rapidly scanned arrays should provide real-time, passive imaging-desired for standoff security screening and other applications-with the same image quality as cryogenic bolometer arrays.