Instability in In0.7Ga0.3As Quantum-Well MOSFETs with Single-Layer Al2O3 and Bi-Layer Al2O3/HfO2 Gate Stacks Caused by Charge Trapping under Positive Bias Temperature (PBT) Stress

The instability of transistor characteristics caused by charge trapping under positive bias temperature (PBT) stress in In0.7Ga0.3As metal oxide semiconductor field-effect transistors (MOSFETs) with single-layer Al2O3 and bi-layer Al2O3/HfO2 gate stacks was investigated. The equivalent field across the multi-gate stacks was compared with a single layer used to compare the instability of electrical characteristics. The observed threshold voltage degradation (ΔVT) was consistent with the phenomenon of fast transient trapping of injected electrons at pre-existing shallow defects in the high-κ dielectric of HfO2, in which this charging was recovered by applying a relaxation voltage. Excluding the fast-transient charging components, the power law exponent (n), with respect to the time-dependent threshold voltage degradation, ranged from 0.3 to 0.35 for both single-layer Al2O3 and bi-layer Al2O3/HfO2 gate stacks. This long-term (slow) VT shift, which was strongly correlated with transconductance (Gm) degradation, was attributed to significant charge trapping in the border trap or/and defect sites within the high-κ dielectric.