3-Path SiGe BiCMOS power amplifier on thinned substrate for IoT applications

This paper reports a transformer-based integrated class-A Differential Power Amplifier (DPA) for the Internet of Things (IoT) applications. The proposed 5-6 GHz fully integrated differential PA is fabricated in a cost-effective 95 GHz-fmax, 0.25 μm SiGe BiCMOS technology (IHP process SGB25V). The amplifier utilizes a thin Si chip with a thickness of 45 μm in order to be embedded into flexible electronic foil systems. Several key RF performance parameters of the DPA with different substrate thicknesses are evaluated at the wafer level. The measurement results indicate that the DPA shows no significant S-parameters degradation due to the thickness differences. The measured gain center frequency is shifted about 300 MHz towards higher frequencies after thinning because of the image mirror currents within the conducting material at the backside of the chip. The DPA achieves 10.65 dB and 9.7 dB small-signal gain at 5.5 GHz before and after thinning, respectively. The PA delivers an output power of +9 dBm before and +8.1 dBm after thinning process at Pin = −1.3 dBm. The simulated 1 dB compression point occurs at +10.76 dBm output power with a PAE of 15%.