A symmetric GaAs MESFET structure with a lightly doped deep drain for linear amplifiers operating with a single low-voltage supply

An improved symmetric GaAs MESFET structure with a lightly doped deep source/drain is proposed for application to power amplifiers in mobile communication terminals. With lightly doped deep drain, the impact ionization falls as the electron current expands and the current density decreases. Thus, the breakdown voltage rises, while a high transconductance and low parasitic resistance are maintained, Furthermore, the symmetric structure suits for mass production because of its fabrication process without mask alignment precision. This structure was fabricated using the WNx/W self-aligned gate process, and DC and RF characteristics were evaluated. The power-added efficiency was 37% at an adjacent channel leakage power of -55 dBc for pi/4-shift QPSK modulated input signals at 1.9 GHz with a single positive supply voltage of 3 V. The efficiency was also high at a lower supply voltage: 34% at 1.2 V.