利用中性粒子束蝕刻製作掘入式閘極增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體於高頻高功率上的應用

Abstract

增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體近年來被廣泛研究。掘入式閘極是製作增強型元件的常見方法，因為它能降低短通道效應及增加閘極控制通道的能力。然而，一般用於製作掘入式閘極的感應耦合電漿反應離子蝕刻會導致電漿損傷，如粗糙的界面、紊亂的化學鍵與在氮化鋁鎵表面形成各式類型的缺陷，例如：氮空缺等等。因此，我們引入新穎的低損傷中性粒子束蝕刻技術來解決此問題，透過在電漿與樣品載台間使用具有高深寬比孔徑的碳板，能有效地使電漿中的離子中性化及阻擋紫外線輻射。 使用低損傷中性粒子束蝕刻技術製作的掘入式閘極增強型氮化鋁鎵/氮化鎵高電子遷移率電晶體具有優異的電性表現，包含1.65 A/mm的最大汲極電流、653 mS/mm的峰值外部轉導、0.06 V的臨界電壓、183 GHz的電流增益截止頻率、191 GHz的最大震盪頻率，以及在54 GHz下，擁有2.56 dB的最小雜訊指數與5.61 dB的相關增益。此外，在38 GHz，可獲得2.7 W/mm的最大輸出功率、20.9 ％的峰值功率轉換效率與9.4 dB的線性增益。如此優異的特性證實在毫米波應用中採用低損傷中性粒子束蝕刻製作氮化鎵元件具有極大的潛力。

Enhancement-mode AlGaN/GaN high electron mobility transistors (HEMTs) have been extensively studied in recent years. The gate recess is a common method to realize the e-mode operation because it can suppress short-channel effect and enhance the gate controllability. However, the conventional inductively coupled plasma reactive ion etching (ICP-RIE) which is used to perform the gate recess will induce plasma damage such as interface roughness, disorder of chemical bonds and formation of various types of defect complexes including nitrogen-vacancy-related defects at the AlGaN surface. Therefore, the novel damage-free neutral beam etch (NBE) technique is introduced to solve this problem through completely eliminating ion charges and UV photons from plasma using a carbon plate with high aspect ratio apertures between the plasma and the sample stage. The gate-recessed enhancement-mode AlGaN/GaN HEMT device fabricated using the damage-free neutral beam etching (NBE) method exhibited superior electrical performances, including a maximum drain current density (IDS,max) of 1.65 A/mm, a peak extrinsic transconductance (gm) of 653 mS/mm, a threshold voltage (Vth) of 0.06 V, a current-gain cutoff frequency (fT) of 183 GHz, a maximum oscillation frequency (fMAX) of 191 GHz, and a minimum noise figure (NFmin) of 2.56 dB with an associated gain (GAS) of 5.61 dB at 54 GHz. In addition, at 38 GHz, a maximum output power (Pout) of 2.7 W/mm, a peak power-added efficiency (PAE) of 20.9 %, and a linear gain of 9.4 dB were obtained. Such superior characteristics confirm the inherent advantages of adopting the damage-free NBE process in fabricating GaN devices for millimeter-wave applications.