An Error-Free 64KB ReRAM-Based nvSRAM Integrated to a Microcontroller Unit Supporting Real-Time Program Storage and Restoration

Nonvolatile SRAM (nvSRAM), which integrates the nonvolatile elements with SRAM using a direct bit-to-bit connection has raised much attention in the past few years, owing to its fast parallel data transfer and fast power-on/off speed. However, few nvSRAM macros have been silicon verified to be enacted through the power-failure event. On the other hand, the capacity of fabricated nvSRAM macro is small (~ Kbit) to date, inhibiting its practical application. This study presents a novel ReRAM-based nvSRAM bitcell with improved reliability and scalability. A 64KB nvSRAM macro was designed and integrated into a 32-bit microcontroller unit (MCU). The chip was fabricated using HfOx-based BEOL ReRAM and a 130nm CMOS technology. To pursue fast storage, a write-without-verify scheme is adopted to program ReRAM, measurement results show that the raw bit error rate between the power outages is < 0.1% for the full macro under such constraint. Cryptography and machine learning applications are successfully performed on the MCU system. For the first time, with the help of correction techniques, we achieved an error-free nvSRAM macro that is reliable enough to store/restore programs and demonstrated a real-time robotic control system empowered by the nvSRAM. The proposed nvSRAM macro has the largest capacity to date.