Integrated Radiometer at 240 GHz With SiGe MMIC Detector and GRIN Silicon Lens

We describe an integrated radiometer at 240 GHz consisting of a direct detection MMIC fabricated in BiCMOS SiGe and a silicon gradient refractive index (GRIN) lens. The planar GRIN lens enables placing the MMIC with an on-chip dipole antenna directly on the GRIN lens in the focal point of the lens. We describe, how this method of integration can be extended to larger detector arrays while presenting results of a single pixel in this article. The direct detection MMIC includes an on-chip dipole antenna, a low-noise amplifier (LNA), and a diode detector. The radiometer bandwidth (BW) is 38 GHz, defined by the monolithic microwave integrated circuit (MMIC). The GRIN lens is fabricated in high-resistivity silicon and has a gain of 12.2 dBi at 240 GHz with an on-chip feed antenna. The integrated radiometer achieves noise-equivalent temperature difference (NETD) of 0.5 K/Hz1/2. The radiometer with external chopping is stable up to an integration time of 100 s, as demonstrated by the Allan variance measurement, where an NETD of 0.03 K with 100-s integration time is measured.