本論文以閘極長度為0.25 μm之氮化鎵高速電子遷移率電晶體製程技術，進行相關的設計應用與研究。依照背向通孔佈局的差異，元件可分成兩種型式:外部源極通孔(outside source via)及獨立源極通孔(individual source via)電晶體。針對兩種電晶體的直流與脈衝動態量測的結果進行分析與討論，直流量測涵蓋電晶體本身以及其蕭特基閘極二極體的導通和崩潰特性。兩個元件導通的特性表現不同，原因可能來自於背向通孔的佈局位置和通孔周圍的應力大小。此外，通孔接地後形成的背部場效板則使主動區內的電場分布不再集中於閘極邊緣，有助於改善崩潰特性。利用脈衝動態量測元件，研究常溫與變溫的電流崩塌機制，其中電流崩塌比率與臨界電壓偏移量在不同工作偏壓之下有不同的變化。 其次是應用於5G通訊系統頻段之3.5 GHz功率放大器的研製，包括class-AB及Doherty功率放大器。class-AB放大器是由單級電晶體與輸入、輸出匹配組成的電路架構，預計輸出功率將有40 dBm，而實際量測僅34.5 dBm，功率附加效益為25.1 %。Doherty功率放大器輸出端設計低品質因數的電路實現大頻寬，並使用集總電路取代傳輸線節省面積。量測結果雖然不如典型的Doherty放大器，在其飽和及功率回退處呈現最大效率，不過頻帶之內的增益並沒有太大的改變。;The design applications and research are presented in this thesis with 0.25 μm GaN HEMT technology. The devices can be divided into two types depending on the difference in the backside via layouts. One is called an outside backside via (OSV) transistor; the other is an individual backside via (ISV) transistor. First, the DC and pulse dynamic measurement results of both devices are discussed. The conduction and breakdown characteristics of the transistor and its Schottky gate diode are included in the DC measurement. Variation in conduction characteristic is thought to be possibly caused by the location of backside via and its induced stress. The electric field in active region is no longer converge at the edge of gate because of backside field plate formed by backvia grounding. Therefore, the breakdown characteristic is improved in the ISV device. A pulse measurement is performed in order to study the mechanism of current collapse in various temperatures. The change in the current collapse ratio and threshold voltage shift are observed under different quiescent biases. In the second part of this thesis, power amplifiers operated in 3.5 GHz for 5G communcication system are discussed, including a class-AB power amplifier and a Doherty power amplifier. The class-AB power amplifier is consisted of a single transistor and input/output matching networks with an estimated output power of 40 dBm. However, the output power is measured only 34.5 dBm and PAE is 25.1 %. As for Doherty power amplifier, the low-Q output circuit is designed to obtain a wide bandwidth. In addition, the transmission line is replaced with lumped circuit to reduce the size of a chip. Although the maximum efficiency at its saturated output and power back-off does not appear in the measured result as a typical one, there is no considerable change in power gain within the band.
