Monolithically integrated enhancement/depletion-mode AlGaN/GaN HEMTs SRAM unit and voltage level shifter using fluorine plasma treatment^*

A GaN-based E/D mode direct-couple logic 6 transistors SRAM unit and a voltage level shifter were designed and fabricated. E-mode and D-mode AlGaN/GaN HEMTs were integrated in one wafer using fluorine plasma treatment and using a moderate AlGaN barrier layer heterojunction structure. The 6 transistors SRAM unit consists of two symmetrical E/D mode inverters and two E-mode switch HEMTs. The output low and high voltage of the SRAM unit are 0.95 and 0.07 V at a voltage supply of 1 V. The voltage level shifter lowers the supply voltage using four Ni-AlGaN Schottky diodes in a series at a positive supply voltage of 6 V and a negative supply voltage of −6 V. By controlling the states of inverter modules of the level shifter in turn, the level shifter offers two channel voltage outputs of −0.5 and −5 V. The flip voltage of the level shifter is 0.76 V. Both the SRAM unit and voltage shifter operate correctly, demonstrating the promising potential for GaN-based E/D mode digital and analog integrated circuits. Several considerations are proposed to avoid the influence of threshold voltage degradation of D-mode and E-mode HEMT on the operation of the circuit.