在本論文中， 主要研究AlGaN/GaN高電子遷移率電晶體無閘極的結構使用於感測器應用，利用改變元件的表面能態導致二維電子氣濃度產生變化，利用此效應來感測不同的酸鹼度，以及在不同環境下元件所反映出來的相關特性，研究中發現，雖然環境中的光源會使元件產生環境雜訊，但是如果固定光源強度，當固定電流情況，照光之下電壓值會下降；進行酸鹼測量，酸鹼值由5至7的過程中，固定電流值為20毫安培測量電壓變化，在酸性環境下電壓值較鹼性來的小，與文獻中實驗相互對照，符合其中理論分析結果，酸鹼值影響是由氫原子主導，使得GaN表面二維電子氣濃度增加，相對電壓值較小，感測能力約27.78mV/pH。
另一方面，在交流量測部分，利用改變頻率觀察元件感測能力變化，加上鎖向放大器的差動放大的功能，在高頻方波的感測能力表現可以高達約17μV/pH的效果。
總而言之，製程中的保護層選用聚甲基丙烯酸甲酯這種高分子材料，具有穩定防水且保護電極的效果，利用元件特性在直流以及交流訊號中的特性曲線，加上紫外光對於元件有一定程度的影響條件下，對於開發新的元件結構與提高其感測能力有一定程度的幫助。

value of a solution under DC and AC biasing condition. For DC biasing condition, the channel resistance is found to decrease with reducing pH value under dark condition. The sensitivity is about 27.78 mV/pH when biasing the device with a constant current of 20 mA. The environmental lighting will induce parasitic effect to the measurement result. The channel resistance is observed to increase with reducing pH value of the solution when illuminated the device with a constant ultraviolet light. The effect of the ultraviolet illumination is also investigated. The pH value is also measured when biasing the device with AC current. Different types of AC signal from a pulse generator with different frequencies are injected into the devices and the signal is detected and analyzed by a lock-in amplifier. The sensitivity of the device is observed to depend on the type of AC signal and the frequency used. The maximum pH sensitivity is about 17 V/pH when biasing with square waves with a frequency of 100 KHz. In conclusion, gateless HEMT chemical sensors are fabricated and analyzed. Both DC and AC biasing characteristics are studied. The ultraviolet illumination affects the device performance and should be controlled for future device application. A detailed understanding of the AC biasing condition will help to develop new sensor capability in the near future.

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