Gate dielectric material influence on DC behavior of MO(I)SHEMT devices operating up to 150 °C

In this work, the DC behavior of AlGaN/GaN Metal-Insulator-Semiconductor high electron mobility transistors (MO(I)SHEMTs) with two different gate dielectrics (Al₂O₃ and Si₃N₄) is analyzed through the experimental comparison of their basic and analog parameters. The transistors with Si₃N₄ insulator are more closely related to the normally-off devices (less negative threshold voltage) and less affected by the short channel effects (better DIBL behavior). Although the devices with Si₃N₄ layer presented a double conduction, that results in anomalous transconductance behavior, it is more suitable for analog applications since the Al₂O₃ devices suffer large self-heating. The very high gate leakage of Si₃N₄ MISHEMT degrades the subthreshold regime, which decreases the transistor efficiency at weak inversion. On the other hand, the devices with Si₃N₄ insulator present relatively large Early voltage and consequently high intrinsic voltage gain in strong inversion, reaching 84 V/V (38.5 dB). Even at high temperatures the intrinsic voltage gain is practically the same, degrading only 1.5 dB from 25 °C to 150 °C for a long channel device.