An Energy-Efficient Normally Off Microcontroller With 880-nW Standby Power, 1 Clock System Backup, and 4.69- $\mu$ s Wakeup Featuring 60-nm CAAC-IGZO FETs

This letter presents a microcontroller unit (MCU) that employs a
c
-axis aligned crystalline indium-gallium-zinc oxide semiconductor FET (CAAC-IGZO FET) with an extremely low off-state current below the zepto-ampere (10
^-21
A) level. This MCU based on IGZO-FETs has logic circuits and memory macros that can retain data even when the power supply is turned off, and internal voltage regulators that store the reference voltage. A prototype chip has been fabricated with a monolithic process that combines an IGZO process (embedded in BEOL) and an Si CMOS process; the chip has a standby power of 880 nW, a system backup time of 21 ns with 44 fJ/bit, and a wakeup time of 4.69 μs. The fabricated chip has demonstrated that the highly energy-efficient normally off computing that establishes low-power operations in Internet of Things and edge AI computing can be achieved with IGZO technology.