$D$ -Band Total Power Radiometer Performance Optimization in an SiGe HBT Technology

A D-band SiGe HBT total power radiometer is reported with a peak responsivity of 28 MV/W, a noise equivalent power (NEP) of 14-18 fW/Hz^1/2, and a temperature resolution better than 0.35 K for an integration time of 3.125 ms. The 1/f noise corner of the radiometer is lower than 200 Hz. Fabricated in a developmental technology with 270-GHz f_T and 330-GHz/max, it includes a five-stage low-noise amplifier (LNA) with 4-7-GHz bandwidth and over 35 dB of gain centered at 165 GHz, along with a square-law detector with an NEP below 6 pW/Hz^1/2 up to 170 GHz. An average system noise temperature of 1645 K is obtained using the Y-factor method and a noise bandwidth of 10 GHz calculated from the measured S21(f) characteristics of the radiometer. The reduced 1/f noise corner frequency in the presence of the amplifier, compared to that of the detector, appears to indicate that, unlike in III-V radiometers, LNA gain fluctuations are not a problem in SiGe HBT radiometers. The circuit consumes 95 mW and occupies 765 × 490 μm². Wafer mapping of the radiometer sensitivity and of the amplifier gain was performed across different process splits. The mapping results demonstrate that the radiometer can be employed as a relatively simple and area-efficient transistor noise-measure monitor, useful in SiGe HBT vertical profile optimization.