Characterization of Inversion Tunneling Current for MOS Devices with High-k Gate Dielectrics

The inversion tunneling current of MOS devices is composed of the generation current due to interface states, the generation-recombination current due to bulk traps, and the diffusion current from back contact. The generation-recombination current due to bulk traps is proportional to the depletion width. The deep-depletion behavior is observed from C-V curves and the deep-depletion width is extracted. According to the calculated results with increments of gate voltage, depletion width and inversion tunneling current, which are designed to eliminate the effects of generation current due to interface states and diffusion current, it was found the inversion tunneling current is dominated by the generation-recombination current due to bulk traps, and two different minority carrier generation lifetimes are acquired. One is the equivalent minority carrier generation lifetime due to surface trap which is close to the interface of Si-SiO2, and the other is the minority carrier generation lifetime due to bulk trap which is far from the interface of Si-SiO2. The quality of high-k gate dielectric is related to the occurred gate voltage of deep-depletion. The accumulation tunneling current would be smaller with higher occurred gate voltage of deep-depletion.l2O3 and HfO2 gate dielectrics show better capabilities to block the inversion tunneling current than SiO2 gate dielectrics at a small gate voltage and thus have the smaller inversion tunneling current. The saturation current of SiO2 gate dielectrics increases with increasing EOT due to sub-oxide effect. Al2O3 gate dielectrics show good capabilities to block the tunneling current in the saturation region, but HfO2 gate dielectrics show bad capabilities due to the small conduction band offset of HfO2, and the saturation current keeps the same value with increasing EOT. Al2O3 gate dielectrics have the best capabilities to block the inversion tunneling current and thus have the largest saturation voltage.