藉氮化鋁鈍化層與表面處理改善氮化鎵高電子遷移率電晶體 直流與高頻特性之研究

Abstract

氮化鎵高電子遷移率電晶體具有高崩潰電壓、高電子遷移率與低導通電阻特性，廣泛應用在高功率、高頻率上。然而電流驟降的現象影響著元件特性，多數文獻中證明鈍化層能解決電流驟降的現象。 本研究利用氮化鋁當作鈍化層材料來改善元件電流驟降的現象，並建立標準化元件製程。從文獻得知，氮化鋁和氮化矽兩種材料，氮化鋁有較大的能隙，可有效阻擋電子漏電到介面，使原本導致形成虛擬閘極影響電性能有效改善。從電性量測結果來和氮化矽鈍化層元件比較，結果顯示使用氮化鋁鈍化層的元件具有較好抑制電流崩潰現象，且在高頻特性方面，也有較高的電流截止頻率和最大功率增益頻率，透過小訊號等效電路模型來萃取本質電容的變化，發現氮化鋁有較小的本質電容值。另外本研究在沉積氮化鋁前，浸泡不同的化學溶液做處裡，降低表面平坦度和表面鎵氧鍵結，進而提升元件特性。

AlGaN/GaN HEMTs have high electron mobility, high saturation velocity and high breakdown, comparing with other electron device. AlGaN/GaN HEMTs have been wide applications for high frequency and high power densities. However, their performance is limited by current collapse. The surface passivation layer has shown remarkable improvement in reducing the current collapse effect. Compared with those of SiNx, AlN thin film has a larger band-gap (6.2 eV), which can suppress traps to surface. DC and pulse IV measurement results are used to compare with AlGaN/GaN HEMTs with SiNx passivation layer .The results indicated that AlGaN/GaN HEMTs with AlN passivation layer, larger current-gain cutoff frequency (fT) and maximum oscillation frequency (fmax). Beside, small signal equivalent circuits are used to extract variation of intrinsic capacitance. AlGaN/GaN HEMTs with AlN passivation layer has small intrinsic capacitances. Complementary, the wet chemical treatments of AlGaN surface prior to deposition AlN passivation layer can reduce surface roughness and the presence of dangling bond (Ga-O). It can improve the device performance.