Fabrication and Linearity Analysis of Field-Plated AlGaN/GaN High Electron Mobility Transistors for Microwave Applications
|摘要:||本論文最主要是研究含閘極電場板之氮化鋁鎵/氮化鎵高電子遷移率電晶體製作及線性度分析，雙通道訊號及寬頻分碼多工存取訊號將用作線性度分析之依據。相較於一般高電子遷移率電晶體，閘極電場板之高電子遷移率電晶體的擁有較高的崩潰電壓160伏。此外，閘極電場板之高電子遷移率電晶體偏壓在30伏時，在頻率2 GHz下，亦有較高的功率25.4 dBm，其效率為43%。當偏壓在30伏，電流為15 mA/mm時，其2 GHz下的三階互調失真及鄰近通道功率溢出分別為-27.1 dBc及-33.8 dBc。量測的結果顯示當元件操作於較高的輸出時，閘極電場板之高電子遷移率電晶體的線性度較一般佳，故適合用於為高功率操作。
當氮化鋁鎵/氮化鎵高電子遷移率電晶體的閘極線寬為0.5微米時，閘極總長100微米的元件之直流飽和電流密度為823 mA/mm，最大電導值為225 mS/mm。截止頻率和最大振盪頻率分別為33和57GHz。該元件偏壓在30伏時，其功率輸出為27 dBm，線性增益為21.2 dB，效率為50%。
在本研究中，閘極總長為1.2和2.4厘米之氮化鋁鎵/氮化鎵高電子遷移率電晶體偏壓在30伏時，總功率輸出分別為31.34 dBm (1.36W)及34.38 dBm (3.74W)。功率密度分別為1.13及1.14 W/mm，其功率密度遠小於閘極總長100微米元件的4.3 W/mm。主要是由於大尺寸元件因散熱不良，而使得元件的功率輸出大為下降。|
A field-plated (FP) AlGaN/GaN high electron mobility transistor (HEMT) was fabricated. Investigations on the linearity characteristics were performed through two-tone and wide band code division multiple access (WCDMA) modulated excitations. The FP-HEMT exhibited an improved breakdown voltage of 160 V compared with that of the conventional HEMT. Additionally, a higher output power of 25.4 dBm with 43% power added efficiency at a 30 V drain bias at 2 GHz was achieved. When biased at 30 V and 15 mA/mm current density, the third-order intermodulation (IMD3) level was measured to be -27.1 dBc (at P1dB) and the adjacent channel power rejection (ACPR) was -33.8 dBc (at P1dB) under WCDMA modulation at 2 GHz. Measurement results revealed that the field-plated structure improved the linearity performance over the conventional structure at high output power levels even beyond P1dB. 0.5×100 μm2 AlGaN/GaN HEMT has a drain saturation current density of 823 mA/mm and and maximum transconductance of 225 mS/mm. The cut-off frequency and maximum oscillating frequency are 33 and 57 GHz. The device has output power of 27 dBm with power added efficiency of 50%, and the linear gain was 21.2 dB. The output power of 1.2 mm and 2.4 mm AlGaN/GaN HEMTs demonstrated, respectively, 31.34 dBm (1.27 W) and 34.38 dBm (2.74 W) of output power when biased at a drain voltage of 30 V. The power densities of 1.2 mm and 2.4 mm large periphery devices were 1.13 and 1.14 W/mm which were lower than 4.3 W/mm of 100 μm AlGaN/GaN HEMT. This implies that self-heating problem affected the large periphery devices and degraded their power performance.