Ferroelectric‐Gated HfZrO2/AlGaN/GaN High‐Electron‐Mobility Transistors with Regrown Contacts for Radio Frequency and Millimeter‐Wave Switch Applications

Emerging millimeter‐wave wireless communication systems require high‐performance radio frequency switches to support advanced functionality such as frequency agility, circuit reconfigurability, and beamforming. Ferroelectric (FE)‐gated AlGaN/GaN high‐electron‐mobility transistors (HEMTs) (FeHEMTs) are developed and demonstrated as a technology option for this important role. AlGaN/GaN HEMT heterostructures grown by metal‐organic chemical vapor deposition are augmented with a FE gate stack comprising atomic layer deposition‐grown HfZrO2. In addition, highly doped regrown source and drain Ohmic contacts are integrated into an improved fabrication process flow. This improved process leads to contact resistances of 0.105 Ω mm and a reduction in switch on‐resistance as compared to prior reports, as well as drain current densities of 1 A mm−1and measured ft= 54 GHz for gate lengths of 0.1 μm. The improved contact and gate length scaling makes FeHEMTs a promising candidate for mm‐wave switch applications achieving a reported switch figure of merit of fCO= 1.55 THz. The advent of nontraditional thin‐film ferroelectric (FE) materials with improved polarization retention such as HfZrO2has served to extend the application space for many transistor technologies. Herein, FE HfZrO2in GaN‐based radio frequency (RF)‐optimized transistors to facilitate new applications are studied. Specifically, by implementing a FE gate‐stack, the performance augmentation at high frequencies is particularly useful for RF switch applications.