Small- and large-signal performance up to 175°C of low-cost porous silicon substrate for RF applications


This paper focuses on the comparison of the RF performances of various advanced trap-rich (TR) siliconon-insulator (SOI) and porous silicon (PSi) substrates. The PSi substrates are produced by electroporisification starting either from cheap standard resistivity (10 Q·cm) silicon (PSi-S) or from the most widespread highly doped milliohm-centimeter Si wafers (PSi-M). Through small-signal RF measurements, it is shown that TR-enhanced high-resistivity silicon and both types of PSi are acceptable for RF applications, showing high effective resistivities and low RF substrate losses. What is more the substrate effective permittivity is decreased in the PSi substrates providing higher coupling isolation at high frequencies. Furthermore, large-signal harmonic distortion measurements reveal very strong linearity for both PSi substrates, with PSi-S achieving 50-dB improvement over the already highly linear TR substrate. Finally, RF characterization was carried out over temperature from 25 °C to 175 °C. While the performances of TR and PSi-M substrate rapidly deteriorate above 120 °C, the cost-effective PSi-S substrate maintains high performance all the way up to 175 °C, allowing it a wider range of potential applications.