本論文研究主題為使用成長於矽基板之氮化鋁銦鎵/氮化鎵異質結構磊晶片製作毫米波功率電晶體，研究內容包括開發電子束微影T型閘極製程、空氣橋接製程、NH3表面處理製程以及基板對於元件的效應。此外，本研究亦測量元件之暫態與遲滯特性，觀察成長於高阻與低阻矽基板之元件的差異，並以X-射線繞射實驗分析元件特性與磊晶差排密度之關聯性。
為達到T型閘極製程高穩定性與高良率，此研究採用TDUR-P015/ Dilute ZEP-A7雙層光阻結構進行閘極足部與頭部的曝光，以改善ZEP-A7/LOR7A/ZEP-A7三層光阻結構中，頭部曝光劑量會影響足部曝光劑量，造成製程不穩定的窘境。此外，以PMGI_SF15阻劑作為空氣橋的犧牲層並搭配電鍍金的方式連接各個元件的源極，藉此達到高功率特性。
此研究中亦使用共平面波導(Coplanar Waveguide)圖形測試矽基板電阻率對於訊號的傳播損耗程度，在28 GHz頻率下，高阻基板與低阻矽基板訊號損耗分別為0.62 dB/mm與0.99 dB/mm，顯示矽基板阻值提升則有效降低毫米波段頻率的訊號損耗。然而，將成長於高阻與低阻矽基板之氮化鋁銦鎵/氮化鎵高電子遷移率電晶體磊晶片製作成閘極長度0.14 μm的元件進行分析，由去嵌化小訊號參數萃取結果顯示基板效應對於閘極寬度200 μm的元件影響不顯著，高阻與低阻基板元件之電流增益截止頻率(fT)分別為70與72 GHz，功率增益截止頻率(fmax)分別為91與93 GHz。由萃取之小訊號參數判斷，此微小差異應是由磊晶品質所造成，且觀察閘極寬度增加至800 μm的元件小訊號特性，其基板效應依然不顯著。但若取閘極寬度200 μm與800 μm於28 GHz下的MAG/MSG值，可觀察到高阻矽基板元件增益由12.35 dB降至7.14 dB，而低阻矽基板元件增益由12.66 dB降至6.16 dB，顯示低阻矽基板在閘極寬度增加時由於元件訊號損耗較為嚴重造成增益下降幅度較大。另外，藉由功率線性度量測得知高阻與低阻矽基板元件的三階截斷點輸出功率(OIP3)分別為27.8 dBm 與25.2 dBm，顯示高阻矽基板元件不僅有較低的訊號損耗，同時元件也有較好的的線性度表現。因此，基板電阻率對高頻功率性能（如最大可用增益和三階截斷點的輸出功率）具有深遠的影響，而直流與小信號特性主要取決於磊晶片質量和製程穩定性。

This thesis deals with the fabrication and characterization of AlInGaN/GaN-on-Si high electron mobility transistors (HEMTs) for millimeter wave applications. NH3 surface treatment, air-bridge process, and e-beam lithography for T-gate formation have been developed in this work. The correlation between epitaxial defects and device performance of the GaN HEMTs grown on high resistivity (HR) and low resistivity (LR) silicon substrates are also investigated.
The T-gate is formed by using a TDUR-P015/Dilute ZEP-A7 double-layer photoresist stack with head and foot exposed individually, resulting in highly stable and high yield T-gate GaN HEMTs as compared to the use of ZEP-A7/LOR7A/ZEP-A7 three-layer photoresist for the same. Additionally, PMGI_SF15 photoresist is used to fabricate the air-bridge to connect the source pads for power devices.
A systematic in-depth study has been carried out to investigate the high-frequency power performance of the devices grown on LR and HR silicon substrates. Transmission loss measurements at 28 GHz using coplanar waveguides on GaN/LR-Si and GaN/HR/Si indicate that the transmission loss is 0.99 dB/mm and 0.62 dB/mm, respectively. However, de-embedded AlInGaN/GaN HEMTs with a gate length of 0.14 μm and gate width of 200 μm fabricated on LR and HR silicon substrates exhibit almost similar small signal performance. The current gain cut-off frequency (fT) of the devices on LR-Si and HR-Si is 72 and 70 GHz, respectively. Whereas, the respective power gain cut-off frequency (fmax) is 93 and 91 GHz as extracted from the s-parameter measurements. The small differences in cut-off frequencies could be due to the variations in process parameters and/or slight differences in the epitaxial layer quality of the GaN HEMTs. It is further observed that substrate resistivity has insignificant influence on the small-signal performance for devices with different gate widths up to 800 μm. In contrast, both the substrate resistivity and the gate width substantially affect the power gain at high frequency. The MAG/MSG of GaN-on-HR-Si HEMTs measured at 28 GHz reduces from 12.35 dB to 7.14 dB as the gate width increases from 200 μm to 800 μm. In contrast, the MAG/MSG of the devices grown on LR-Si reduces from 12.66 dB to 6.16 dB for the same change in gate width. Besides, the output power third-order intercept point (OIP3) of the devices on HR-Si and LR-Si measured at 6 GHz is 27.8 dBm and 25.2 dBm, respectively. This might also result from the effect of substrate resistivity. In conclusion, substrate resistivity has profound effects on high frequency power performance, whereas, the DC and small signal performance mostly depend on epitaxial quality and device fabrication process.

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