摘要
本論文以AlGaN/GaN異質結構所組成的高電子遷移率電晶體元件(High electron mobility transistor，HEMTs)作為化學感測器的應用。當感測區與各種不同的化學環境，元件汲極-源極間的輸出的瞬向電流的數值產生明顯的增減。化學物質的特性使感測區表面電位產生變化，改變了異質結構接面的二維電子氣體(two- dimensional electron gas，2DEG)通道的濃度，同時也改變了汲極-源極間的電阻值。
AlGaN/GaN異質結構HEMTs元件對光源的靈敏度很高，在暗室中與UV光的照射的環境，元件在固定電壓時輸出的電流值有顯著的差異。固定DC電壓2.2V量測pH5-pH9變化的酸鹼溶液，元件有20mA/pH的變化量，感測能力的極限可以偵測到0.034pH的改變。而固定AC電壓以function generator輸出4.4V，50Hz，可以量測到元件感測區會有15mV/pH的變化量，感測能力的極限可以偵測到0.006pH更細微的pH值改變。
為了測試HEMTs元件是否能進行生物感測，利用微流體通道結合HEMTs並導入鎖像放大器的量測。APTES的NH2基會與FITC 的異硫氫酸根離子產生鍵結反應，當感測區表面的APTES分子附著FITC螢光染劑前後有著9mV的改變。

Abstract
In this dissertation, applications of AlGaN/GaN high-electron-mobility transistors (HEMTs) as chemical sensors are investigated. The drain-source current is very sensitive to the chemical environment of the exposed gate region for a gateless HEMT. The change of the surface states at the gate regions affects the two-dimensional electron gas (2DEG) channel, which also changes the drain-source resistivity. The pH sensitivity of the device was measured to be 20 mA/pH when DC biasing was 2.2 V. The minimum detectable sensitivity is estimated to be 0.034 pH. It was also discovered that ultraviolet illumination affects the pH sensitivity and the measurements should be kept in dark condition to avoid this parasite effect. The pH sensitivity when biasing under AC condition was also studied. With the help from the lock-in amplifier, the device was able to distinguish 0.006 pH changes for the solution. The sensitivity was measured to be 15 mA/pH when AC biasing the device with 4.4 V. Square waves with a frequency of 50 Hz were used the excitation pulses.
In order to prepare the devices for precision bimolecule detections, the devices were integrated with a microfluidic system. Fluorescein isothiocyanate (FITC) molecules were used as the model molecules to develop a suitable detection system. The exposed gate region was first treated with (3-aminopropyl)-triethoxysilane (APTES) to obtain a amine-terminated surface. The subsequent flowing of FITC-containing solution triggered a 9 mV changes under AC biasing conditions.
HEMT sensors developed in this study were ready for future biodetection applications. Future developments of the device by reducing size the gate region will possibly increase the sensitivity. By collaborating with biologists, this HEMT sensors will have bright future in the field of biodetection and chemical detections.

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