InP/GaAsSb DHBTs Fabricated in a Low-Temperature Teflon Planarization Process

We demonstrate InP/GaAsSb/InP double heterojunction bipolar transistors (HBTs) fabricated in a low-temperature planarization process based on a spin-on Teflon amorphous fluoropolymer interlevel dielectric with ε_r = 1.9 and a low dissipation factor. Devices with 0.3-μm-wide emitters show excellent junction characteristics, cutoff frequencies f_T = 362 GHz and f_MAX = 450 GHz, a peak current gain β = 28, and a common-emitter breakdown voltage BV_CEO = 5.1 V. Teflon is seen to be an advantageous alternative to common benzocyclobutene and polyimide planarization dielectrics. A side-by-side comparison of devices fabricated in Teflon and airbridge processes shows nearly identical performances. The present approach is equally applicable to GaAs- and GaInAs-based HEMT and HBT technologies.