氮化鎵材料因為具有快速的電子飽和速度與高崩潰電場，使得氮化鎵元件非常適合製作低串聯電組與高崩潰電壓的元件，主要應用在商業化 RF power amplification 和 HV power switching中。但氮化鋁鎵/氮化鎵在磊晶過程中會產生一些缺陷，這些缺陷會造成電流崩塌現象，對電晶體做為切換開關或是不同頻率操作下，是非常嚴重的問題。本論文將利用商業製程元件進行一系列元件的電流崩塌現象測量分析，並進一步深入討論缺陷所在跟元件特性關聯。 本論文選用穩懋半導體且其閘極長度為0.25 µm的HEMT元件進行研究。建立等校電路模型以萃取小訊號參數，並以動態量測方法經過關閉狀態後進入開啟狀態，觀察發生電流崩塌時小訊號參數變化，可以發現到其中源極電阻(Rs)、閘極與汲極間電容(CGD) 等內部元件參數在偏壓後有顯著的變化。 最後除了進行不同溫度下的小訊號參數測試研究外，進一步討論電流崩塌跟溫度的關聯性。還設計了在高溫下(150°C)進行熱儲存(Thermal Storage)，改變熱儲存之時間以觀察元件電性的改變。 ;GaN based devices are suitable candidates of low on resistance and high breakdown device because of high electron velocity and breakdown field in GaN materials. The major applications include RF power amplifiers and power switching. However, there is a serious current collapse problem when transistor operated as a switch in high frequencies. The main cause is due to epitaxial layer quality, which effects in AlGaN/GaN and buffer layers act like traps which traps carriers and results in current collapse leading to a great impact on the DC and RF characteristics. This study analyzes device current collapse phenomenon using commercial GaN HEMT in small-signal model and gate-lag/drain-lag measurement. In small signal equivalent circuit modeling, extracted values of intrinsic elements in leaner and saturation regions were compared after different high-voltage off-state biases. The significant change in the intrinsic elements after high-voltage off-state biases are channel resistance (Rds) and gate-drain capacitance (Cgd), which may attribute to the GaN channel and buffer layers. Besides, small signal equivalent circuit model after high-voltage off-state was investigated under different temperatures. Gate-lag and drain-lag were measured at different temperatures to study the trapping effect. Because of temperature effect, trapping effect is alleviated at higher temperature thus current collapse is less severe. . Finally, a thermal storage was carried out on GaN HEMTs at 150 C under room temperature ambient. No degradation was found after 55 hours storage.
