| dc.description.abstract | The electrical characteristics of AlGaN/GaN high-electron mobility transistors with the different layouts of the second gate are designed and investigated. First, Silvaco TCAD is used to simulate and investigate the electrical characteristics. The experimental study of devices include two parts, (1) device performance with dual gates structure; (2) device performance with the same size of the ohmic contact but varying the second gate length to adjust the 2DEG channel width. DC and high frequency measurements of different structural devices under the different temperatures conditions are measured and analyzed. In the first part, device with dual gates provide the larger depletion region under the gate metal, which can improve the leakage current ID, off and result in Vth shift. In addition, applying a bias voltage of 0 V to the second gate can make the electric field become uniform between gate and drain. Moreover, the temperature coefficients of the Vth, gm, max, ID, ID, off, and Ron at different temperatures conditions are performed and calculated. The values of thermal impedance are divided into low power range and high power range. Regardless of low and high power range, dual gates structure with floating second gate shows better thermal impedance. So the second gate structure could contribute to thermal dissipation.
In the second part, devices with the same ohmic contact size (Wsource) but using the second gate length to adjust the 2DEG channel width is designed and characterized. The 2DEG channel width is designed to 3/4 Wsource, 1/2 Wsource and 1/4 Wsource. There are two structures: (Ⅰ) gate and second gate are connected, (Ⅱ) second gate is floating. With the reduction of the 2DEG channel width, the gm, max and ID show an increase trend. The leakage current also shows an increase trend. But the S.S and Ron are improved. The measurement results agree well with the simulation results of Silvaco TCAD DC characteristics. The thermal impedance decreases as the channel width is reduced. Therefore, changing the width of the channel could contribute to thermal dissipation of the device. | en_US |