Three-Path SiGe BiCMOS LNA on Thinned Silicon Substrate for IoT Applications

This paper reports on a design methodology and measurement results of a fully integrated low noise amplifier (LNA) on a thinned substrate for Internet of Things (IoT) applications. Several key RF performance parameters of the LNA with different substrate thickness are evaluated through full-wave electromagnetic (EM) simulations. The proposed LNA operating at 5.5 GHz is fabricated in a cost-effective 0.25 μm SiGe BiCMOS technology (IHP process SGB25V; ft = 75 GHz). The Si chip is thinned to ~38 μm in order to be embedded seamlessly into a flexible foil system. The small-signal gain of the LNA, measured on the chuck is 14.32 dB before thinning. The measured center frequency on the thin silicon (thickness of 38 μm) is shifted about 700 MHz towards higher frequencies compared to the thick silicon due to the image mirror currents within the conducting material at the backside of the chip. The measured noise figure (NF) with the thick and thin substrate on the conducting material is around 3.36 dB at 5.5 GHz and 3.74 dB at 6.3 GHz, respectively.