利用氧化鋁/氧化氮堆疊當介電層的方式製作出可改善起始電壓穩定性的增強型氮化鎵金屬-絕緣體-半導體高電子遷移率電晶體

Abstract

氮化鋁鎵/氮化鎵增強型高電子遷移率電晶體近幾年來廣受注目。既往研究中常以氧化鋁當介電層以改善電性。但許多文獻中已經證實氧化鋁/氮化鋁鎵的界面會產生高密度的界面能阱，導致載子被侷限在能阱中而導致起始電壓向正方向偏移。除此之外，目前還沒有一個確切方法可穩定地製造出高起始電壓元件,並可避免元件因雜訊而開關的不正常行為。 本研究提出氧化鋁/氧化氮堆疊當介電層的方式製作出可改善起始電壓穩定性的增強型金屬-絕緣體-半導體高電子遷移率電晶體，並建立其標準化製程。與利用單層氧化鋁當介電層的元件比較，本實驗成果除了擁有穩定的起始電壓外，而且能有較高的起始電壓，因而能減少雜訊所致的不正常開關情況。本實驗以傳統的增強型高電子遷移率電晶體進行蝕刻製之參數測試，以建立元件最佳化製成。此元件擁有325 mA/mm 的通道電流，55 mS/mm 之互導係數，4.2V的高起始電壓，超過800V之崩潰電壓，及非常低的起始電壓偏移率(65 mV)。由於以上電性表現證實能應用於功率開關元件。

AlGaN/GaN enhancement-mode(E-mode) high electron mobility transistors (HEMTs) has been extensively studied in recent years. Aluminum oxide (Al2O3) is a common gate insulator to improve the electrical characteristics of AlGaN/GaN HEMTs. However, there is high density of interface states at Al2O3/AlGaN interface, leads to the charges trapping and positive shift of threshold voltage(Vth). At present, there is still no solution to fabricate the HEMTs with high Vth so as to overcome the mis-operation in high voltage operations. In this thesis, gate recess technique is used to fabricate the E-mode Al2O3/AlN AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT). Such a device structure exhibited high Vth stability as revealed by C-V and pulse measurement in comparison with the Al2O3 E-mode MIS-HEMT. Additionally, this structure achieved very high Vth ( > 3 V ) to avoid the mis-operation of the device. Conventional E-mode HEMT was used for process parameter evaluation to identify the optimum etching process condition, so as to establish the standard recessed E-mode MIS-HEMT fabrication process. The device demonstrated channel current = 325mA/mm , transconductance = 55 mS/mm , Vth = 4.2V, andbreakdown voltage = 800V, respectively. Furthermore, the device shows small △VTH of about 65 mV. Above data indicate that such a device structure is promising for power switching applications.