本論文為三閘極氮化鎵高電子遷移率電晶體應用於氫氣感測的研究。實驗方面，製備了800、400、200 nm，三種不同鰭寬的三閘極結構以及作為對照的平面型結構，並各別在電性以及氣體響應特性上分析。由於三閘極結構中的側壁空乏效應，使得閾值電壓會隨著鰭寬的縮小而有正偏移的趨勢，從平面型的-3.9 V，到三閘極結構鰭寬為800、400、200 nm的-3.2，-2.1，-0.8 V。同時影響到最大汲極電流密度的下降，從平面型的518.3 mA/mm，到鰭寬為800、400、200 nm的552.8，463.3，266.5 mA/mm。此外，三閘極結構的次臨界擺幅跟電流開關比等特性都有明顯的優化，足見三閘極結構對閘極控制力提升所帶來的影響。
氣體響應方面，選用鉑作為閘極電極，其表面可吸附氫氣分子進行催化反應，造成位能障下降使得汲極電流上升。透過監測汲極電流變化可判定氫氣的響應。而三閘極結構相比於平面型結構擁有了更多的表面積以利氫氣分子吸附。在攝氏兩百度，氫氣濃度為250 ppm的條件下，響應值從平面型的484 %，到三閘極結構鰭寬為800、400、200 nm的661、698、1079 %。對比於平面型結構，三閘極結構不論是在元件電性上或氣體響應上都有更出色的表現。

This thesis explored the performance of tri-gate GaN high electron mobility transistor in hydrogen detection through experiments. We fabricated three tri-gate devices with different fin widths and the reference planar device. The electrical and response characteristics were investigated. The threshold voltage shifted positively with the narrowing fin width owing to the effect of sidewall depletion in the tri-gate structure. The threshold voltages of the planar device and tri-gate devices with 800, 400, and 200 fin widths were − 3.9, −3.2, −2.1, and −0.8 V, respectively. The maximum drain current density decreased with the increase in threshold voltage. The maximum drain current densities of the planar device and tri-gate devices with 800, 400, and 200 nm fin widths were 518.3, 552.8, 463.3, and 266.5 mA/mm, respectively. The improvement of subthreshold swing and on-off ratio indicated that the gate controllability was well enhanced in the tri-gate devices.
With regard to the hydrogen response characteristics, we chose platinum as the gate electrode because its surface can capture the hydrogen molecules in air and then performed the catalytic reaction, leading to the increasing drain current with lowering barrier height. The hydrogen response characteristics were determined by governing the variation of the drain current. The tri-gate device had more surface area than the planar device, which was beneficial to the molecular adsorption. At 200 °C and 250 ppm, the sensitivity of the planar device was 484%, and the sensitivities of the tri-gate devices with 800, 400, and 200 nm were 661%, 698%, and 1079%, respectively. The tri-gate device had superior performance in electrical and response characteristics compared with the planar device.

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