高頻高功率應用之氮化鎵系列半導體

Abstract

氮化鎵系列材料為新世代半導體之星，其應用範圍涵蓋高頻元件、功率電子元件、以及光電元件。本論文即針對氮化鎵材料的高頻與高功率應用所做之研究。首先是機械張應力對氮化鋁鎵/氮化鎵高電子遷移率電晶體之效應的研究，研究發現機械張應力能使元件產生額外的通道電子，進而改變通道飽和電流特性，此現象同時取決於電子通道的方向；另外，張應力能使元件的脈衝電流特性變差，這表示張應力透過增加壓電極性使元件表面產生更多電子能井，這些額外的表面能井侷限住更多電子，使通道瞬間電流受到抑制。論文第二部分成功驗證了氮化鋁鎵/氮化鎵高電子遷移率電晶體在30GHz下依舊保有優良的低雜訊特性，當該元件偏壓在閘極為-3V與汲極為10V時，其30GHz的最低雜訊值為1.6dB且元件的增益值為5dB，在現今文獻中，此項成果是第一篇將氮化鎵元件低雜訊特性提升至30GHz之國際期刊。論文第三部分結合氟離子電漿與金氧半閘極結構技術，成功製作出具備高閘極起始電壓的增強型氮化鋁鎵/氮化鎵電晶體。透過16nm的氧化鋁閘極氧化層，使閘極起始電壓提升至5.1V，同時，該元件依舊保有高電流密度500mA/mm，此成果是第一篇將閘極起始電壓提升至超過5V並能同時具備高電流密度之國際期刊。

GaN-based semiconductors are promising candidates for RF high frequency wireless, power electronics, and optoelectronics applications. This thesis focuses GaN-based High Electron Mobility Transistors (HEMTs) for high frequency and high power application. First of all, the characteristics of unpassivated AlGaN/GaN HEMTs under uniaxial tensile strain were investigated. Mechanical stress can produce additional charges resulting in the change of HEMT channel current. This phenomenon depends on gate orientation, and may be the result of the piezoelectric effect and changes in electron mobility due to the applied uniaxial stress. Additionally, results show that tensile strain reduces the transient current, which is likely due to the additional donor-like surface states created through the piezoelectric effect. Secondly, a 100-nm gate-recessed n-GaN/AlGaN/GaN HEMT with low noise properties at 30 GHz is demonstrated. The recessed GaN HEMT exhibits a low ohmic-contact resistance of 0.28□□•mm, and a low gate leakage current of 0.9 μA/mm when biased at VGS = −3 V and VDS = 10 V. At the same bias point, a minimum noise figure of 1.6 dB at 30 GHz and an associated gain of 5dB are achieved. To the best of our knowledge, this is the first and the best noise performance reported at 30 GHz for gate-recessed AlGaN/GaN HEMTs. Finally, a normally-off operation AlGaN/GaN HEMT with high threshold voltage is developed utilizing a Fluorine-based treatment technique combined with a metal-oxide-semiconductor gate architecture. Threshold voltage as high as 5.1 V was achieved using a 16-nm-thick Al2O3 gate oxide film. Additionally, the device performed a drain current density of 500 mA/mm and a peak transconductance of 100 mS/mm. These performances are comparable to the conventional normally-on devices.