Improved electrical performance and thermal stability of HfO2 / Al2 O3 bilayer over HfO2 gate dielectric AlGaN/GaN MIS-HFETs

Abstract

AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with a HfO2 / Al2 O3 bilayer gate dielectric have been fabricated, characterized, and compared with HfO2 gate dielectric MIS-HFETs. Physical and electrical characterizations have revealed the enhanced properties of the HfO2 / Al2 O3 bilayer dielectric over that of the single HfO2 layer. As a result, the fabricated HfO2 / Al 2 O3 MIS-HFETs exhibit better electrical performance and thermal stability than the HfO2 transistors. The maximum drain current of the HfO2 / Al2 O3 MIS-HFETs has increased by ∼8.5%, while the off-state drain current has reduced by nearly 1 order of magnitude than that of the HfO2 MIS-HFETs. After the thermal stress at elevated temperatures (400 and 500°C) for a prolonged duration up to 500 min, the irreversible device performance degradation, including drain current, peak transconductance, threshold voltage, and gate leakage current for the HfO2 / Al2 O3 MIS-HFETs, is substantially less than that for the HfO2 MIS-HFETs. A longer lifetime of ∼4× 106 h at 150°C has also been estimated for the former, compared to that of the latter of ∼2× 105 h. © 2010 The Electrochemical Society.