Improvement of DC and RF Characteristics of AlGaN/GaN High Electron Mobility Transistors by Thermally Annealed Ni/Pt/Au Schottky Gate

Abstract

A thermally annealed Ni/Pt/Au metal structure was employed as the gate contacts of AlGaN/GaN high electron mobility transistors (HEMTs), and their DC and RF performances were investigated. This gate structure markedly improved the Schottky characteristics such as the Schottky barrier height and leakage current. Regarding the DC characteristics, the maximum drain current and off-state breakdown voltage were increased from 0.78 A/mm (V g=1 V) to 0.90 A/mm (V g=3 V) due to the improved applicability of the gate voltage and from 108 V to 178 V, respectively, by annealing the gate metals. In addition, a reduction of the transconductance was not observed. Furthermore, even after the deposition of SiN x passivation film, the off-state breakdown voltage remained at a relatively high value of 120 V. Regarding the RF characteristics, the cut-off frequency and maximum oscillation frequency were also improved from 10.3 GHz to 13.5 GHz and from 27.5 GHz to 35.1 GHz, respectively, by annealing the gate metals whose gate length was 1 µm.

Enhancement of both direct-current and microwave characteristics of AlGaN∕GaN high-electron-mobility transistors by furnace annealing

“…The annealing effects of Schottky diodes and devices were studied. [6][7][8][9] Furnace annealing effects of Ti, Ni, and Pd Schottky contacts on AlGaN were systematically investigated. 6 The rapid thermal annealing ͑RTA͒ effects were studied on Ti/ Pt/ Au metal-gate AlGaN / GaN HEMTs and the results showed enhancement of cut-off frequency ͑f T ͒ and maximum oscillation frequency ͑f max ͒ without increase of extrinsic transconductance ͑g m max ͒.…”

“…6 The rapid thermal annealing ͑RTA͒ effects were studied on Ti/ Pt/ Au metal-gate AlGaN / GaN HEMTs and the results showed enhancement of cut-off frequency ͑f T ͒ and maximum oscillation frequency ͑f max ͒ without increase of extrinsic transconductance ͑g m max ͒. 7 Other report showed the reduction in drain current density ͑I D max ͒ with enhanced breakdown voltage ͑BV͒ by postgate annealing. 8 However, no direct correlation has been observed between the direct-current ͑dc͒ and small signal performances of AlGaN / GaN HEMTs before and after annealing.…”

“…8 However, no direct correlation has been observed between the direct-current ͑dc͒ and small signal performances of AlGaN / GaN HEMTs before and after annealing. [7][8][9] Recently, postgate annealing at 500°C was used for the demonstration of enhancement-mode AlGaN / GaN HEMTs. 9 Except the positive shift in threshold voltage ͑V th ͒ by postgate annealing, no enhancement of microwave properties 9 and g m max ͑Refs.…”

Fabrication of enhancement‐mode AlxGa1–xN/GaN junction heterostructure field‐effect transistors with p‐type GaN gate contact

“…Recently, it has been widely reported that high-temperature, high-power and high-frequency devices using GaN and related materials have been successfully operated [3][4][5][6][7][8][9][10]. Nowadays, depletion-mode Al x Ga 1-x N/GaN HFETs have already been commercialized.…”

Ion implantation doping for AlGaN/GaN HEMTs

“…After removing the SiN cap layer in a HF solution, the source/drain ohmic contacts were formed by electron-beam evaporation of Ti/Al and annealing at 600 °C for 2 min in a nitrogen atmosphere [9]. Following the device isolation, the Schottky gate was formed [10]. The typical HEMT dimensions used in this work are as follows: gate length = 1 µm; source-drain distance = 4 µm; and gate width = 100 µm.…”