Highly Sensitivity AlGaN/GaN HEMTs Sensorsusing lock-in amplification technique

• Main Authors: Po-LinFang, 方柏霖
• Other Authors: Yun-Chorng Chang
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/45430885461911181545

碩士 === 國立成功大學 === 光電科學與工程研究所 === 98 === 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.