Advanced Si-based substrates for RF passive integration: Comparison between local porous Si layer technology and trap-rich high resistivity Si

• A comparison is made of the RF dielectric properties of porous Si and trap-rich HR-Si.
• Porous Si layers locally grown on Si show superior RF substrate properties than trap-rich HR-Si.
• Porous Si dielectric properties include reduced substrate losses and lower harmonic distortion.
• The tailored lower permittivity of porous Si makes it appropriate for crosstalk reduction.
• Better performance inductors were demonstrated on porous Si compared to trap-rich HR Si.

In this work, two novel RF substrate technologies are compared, namely local porous Si RF substrate technology and high resistivity Si with a trap-rich layer on top (trap-rich HR-Si). Using standard Si processing, identical co-planar waveguide transmission lines and test inductors were fabricated on the above two substrates, as well as on quartz and on standard p-type Si. Broadband electrical characterization in the frequency range from 40 MHz to 40 GHz revealed that porous Si substrate provides much higher effective resistivity and lower dielectric constant than trap-rich HR-Si, actually comparable with quartz substrate values. Lower dielectric constant leads to drastic reduction of crosstalk and provides design options for higher characteristic impedance devices. Higher effective substrate resistivity leads to lower attenuation losses and reduced non-linearities, as well as better quality factor for both transmission lines and inductors. Porous Si, which is CMOS-compatible and cost-efficient, demonstrates state-of-the-art RF performances comparable with quartz substrate.