藉由步進式偏壓量測評估高功率氮化鎵金屬絕緣層半導體高電子遷移率電晶體之穩定性研究

Abstract

本研究旨於藉由加速性步進式偏壓的實驗方法，去評估氮化鎵金屬-絕緣層-半導體高電子遷移率電晶體的穩定性。首先，我們使用一般常見的固定式偏壓方法，實驗在通道截止狀態與閘極負偏壓條件。然後，我們改善過去文獻中的步進式偏壓量測，可以同時監控施加偏壓下的漏電流、臨界電壓以及動態導通電阻的變化。我們利用改善過後的步進式偏壓量測，實驗在通道截止狀態、閘極負偏壓條件以及基板負偏壓條件下，分別評估元件實際的操作情況、閘極氧化層能承受偏壓的程度以及磊晶層對於元件的影響。最後，我們比較上述的兩種方法，觀察到步進式偏壓能看到固定式偏壓看不到的現象。針對此現象，我們實驗不同溫度下的通道截止狀態，並計算其活化能大小。經由活化能的計算，我們找出此現象可能來自於磊晶的淺層缺陷。此外，施加偏壓下的基板漏電流隨著溫度的上升可能源自於氮缺陷以及鎵與氧的混合物。

By means of an accelerated step-stress methodology, the stability of GaN MIS-HEMTs was evaluated. We first studied the off-state stress condition and the reverse gate bias condition by using the constant stress measurement. Then, we utilized the step-stress measurement to monitor the stress leakage current, threshold voltage and on-resistance variation. The measurements were made under : (1) the off-state step-stress condition to study the real operation of devices. (2) the reverse gate step-stress condition to study the capability and endurance of the films below the gate. (3) the back-gating step-stress condition to study the influence of the epitaxial layer. Comparing the two methodologies, we found an interesting phenomenon under off-state step-stress condition. Based on the evaluation of the activation energy, the shallow traps are responsible for the phenomenon. In addition, the increase of the bulk leakage current is due to the traps of the complexes of gallium vacancies and oxygen or/and nitrogen vacancies.