Current path optimized structure for high drain current density and high gate-turn-on voltage enhancement mode heterostructure field effect transistors

We developed a new type of enhancement-mode (E-mode) heterostructure field effect transistors (FETs) which provide single-voltage operation of power amplifiers in portable phone handsets. Gate leakage current paths were optimized, and a high gate-turn-on voltage and a high drain current density were obtained at the same time. This allows a 50% increase of the drain current by shortening the gate-to-source length without increasing the gate leakage current. We applied this technique to completely E-mode FETs (Vth>0.3 V). A power added efficiency as high as 70.6% has been achieved for an output power of 33 dBm under a Vds of 3.5 V at 850 MHz.