由於傳統氮化鋁鎵/氮化鎵高電子遷移率電晶體通道中存在著極化效應所產生的二維電子氣，使得元件多為空乏型電晶體，這會造成元件額外的功率消耗且電路設計上需要正負偏壓來操作。因此，我們需要增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體來降低功率消耗及簡化電路上的設計。在本實驗中，我們使用閘極掘入的方法來增加閘極對通道的控制能力並提升元件的臨界電壓。此外，傳統蕭特基閘極常產生過大的閘極漏電流，導致元件效能不彰。所以在本實驗中，我們也應用了低成本、製程簡易的液相沉積法來沉積閘極介電層，藉以降低閘極漏電流並進一步提升崩潰電壓。
我們成功的利用自我對準閘極掘入製程研製增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體，並使用液相沉積之二氧化鈦做為閘極介電層。元件最大電流密度可達到412 mA/mm，最大轉換電導值從88 mS/mm增加到159 mS/mm，臨界電壓為0.12V，次臨界擺幅為131 mV/dec，閘極漏電流和崩潰電壓也分別增加到2.73×10-7 A/mm和96 V。而元件的截止頻率和最大震盪頻率分別為6.25GHz 和8.5GHz。

Due to the existent two-dimensional electron gas (2DEG) induced by strong polarization in the channel, conventional AlGaN/GaN high electron mobility transistor (HEMT) usually operates in depletion mode (D-mode). That will cause additional power loss and need to design circuits with negative bias and positive bias. Therefore, enhancement mode (E-mode) AlGaN/GaN HEMT is required to reduce power consumption and simplify the design of driving circuits. In this work, gate recess technique was used to improve the control of gate and increase the threshold voltage. Furthermore, Schottky gate in AlGaN/GaN HEMTs suffer from high gate leakage current which decrease the devices performance. So a low cost and less complex liquid-phase deposited (LPD) process was utilized to deposit the gate insulator, which can reduce gate leakage current and enhance breakdown voltage.
Enhancement mode AlGaN/GaN MOSHEMT with LPD-TiO2 using self-aligned gate-recessed process was fabricated. The maximum drain current density reaches about 412 mA/mm. The maximum transconductance increases from 88 mS/mm to 159 mS/mm. The threshold voltage is 0.12V and the subthreshold swing slope is 131 mV/dec. The gate leakage current and the breakdown voltage are also enhance to 2.73×10-7 A/mm and 96 V, respectively. The cut off frequency (fT) and maximum oscillation frequency (fmax) cab be increased to 6.25 GHz and 8.5 GHz, respectively.

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