Critical design issues for high-power GaN/AlGaN anti-serial Schottky varactor frequency triplers

In this paper the importance of a new design variable for high power anti-serial Schottky varactors, the aluminum composition of the AlGaN barrier layer, is demonstrated. AlGaN/GaN varactors containing either (1) a high-doped/low-doped GaN region or (2) just a low doped GaN region have been compared demonstrating that the selection of the device structure also depends on the amplitude of the input signal being tripled in frequency. Stronger susceptance modulation is exhibited in AlGaN/GaN ASVs made from Ga-face polar material compared to N-face polar material. Results indicate choosing the proper aluminum composition results in 27% conversion efficiency with an input signal of 5GHz and over 7% conversion efficiency with an input signal of 60GHz along with optimization trends. With input voltage amplitudes over 10V an AlGaN/GaN structure with 15% Al provides greater conversion efficiency than one with 5% Al. Power absorbed in the varactor also increases as aluminum percent increases affecting reliability and power transfer. Results of a GaN ASV performing as a frequency tripler for fundamental frequencies up to 110GHz indicate an advantage to using an AlGaN/GaN epi-structure over only a GaN epi-structure.