High-Voltage Amorphous InGaZnO TFT With Al 2 O 3 High- $k$ Dielectric for Low-Temperature Monolithic 3-D Integration

On-chip high-voltage (HV) power management integrated circuits would deliver smaller form factor, lower system cost, higher power efficiency, and suppressed noise in system-on-chip designs. A reliable HV amorphous-indium–gallium–zinc–oxide (a-IGZO) thin-film transistor (TFT) technology has been presented for potential applications of monolithic 3-D integration on CMOS. By using a process temperature below 200 °C, the instability of positive- and negative-bias stresses can be carefully minimized. The HV a-IGZO TFT with an Al 2 O 3 high-k gate dielectric possesses a high breakdown voltage exceeding 45 V, a high saturation mobility of 11.3 cm 2 /Vs, and a large ON-/OFF-current ratio of $10^{9}$ . The long-term reliability study projects that the device can be operated at 20 V for ten years without catastrophic dielectric breakdown while maintaining sufficient ON-current.