Identification of RF Harmonic Distortion on Si Substrates and its Reduction Using a Trap-Rich Layer

Harmonic distortion (HD) is measured arising from coplanar waveguide structures on various substrates at 900 MHz, and significant distortion for silicon substrates is demonstrated for the first time. For an input power of +35 dBm, 2^nd harmonic power of -47 dBm and 3^rd of -57 dBm are measured for a thru calibration structure on oxidized high-resistivity silicon (HRS) substrates, and 2^nd harmonic of -23 and 3^rd of -20 dBm for a longer line on a thinner oxide. These levels are high compared to a full cellular transmit switch product specification of -45 and -40 dBm for 2^nd and 3^rd harmonics, respectively, at similar power levels. The contribution of the silicon substrate to high harmonic levels is investigated experimentally, and an efficient technological solution based on the introduction of a trap-rich layer is demonstrated.