Quantifying Temperature-Dependent Substrate Loss in GaN-on-Si RF Technology

Intrinsic limits to temperature-dependent substrate loss for GaN-on-Si technology, due to the change in resistivity of the substrate with temperature, are evaluated using an experimentally validated device simulation framework. Effect of room temperature substrate resistivity on temperature-dependent coplanar waveguide (CPW) line loss at various operating frequency bands is then presented. CPW lines for GaN-on-high-resistivity Si are shown to have a pronounced temperature dependence for temperatures above 150 °C and have lower substrate losses for frequencies above the X-band. On the other hand, GaN-on-low-resistivity Si is shown to be more temperature insensitive and has lower substrate losses than even highly resistive Si for lower operating frequencies. The effect of various CPW geometries on substrate loss is also presented to generalize the discussion. These results are expected to act as a benchmark for temperature-dependent substrate loss in GaN-on-Si RF technology.