33.1 A 16nm 32Mb Embedded STT-MRAM with a 6ns Read-Access Time, a 1M-Cycle Write Endurance, 20-Year Retention at 150°C and MTJ-OTP Solutions for Magnetic Immunity

Embedded non-volatile memory (eNVM) is an essential element for microcontrollers (MCUs) used in automotive applications. As the automotive market transitions to greater electrification and autonomy, we are seeing MCU growth in the car: including integration to simplify system design, an electrical and electronic (E/E) architectural evolution to domain/zone control, and over-the-air (OTA) updates beyond 128Mb eNVM densities. To support this transition technology nodes are migrating from 55/40nm to 28/16nm. In addition, traditional charge-based embedded Flash will be replaced by Back-end-of-line (BEOL) memories: such as STT-MRAM [1]–[3], PCRAM [4], and RRAM. Of these candidates, STT-MRAM is the most promising solution for automotive applications due to its high-temperature data retention, high write endurance, and fast write speed. However, STT-MRAM still faces several challenges from the inherent properties of magnetic tunnel junctions (MTJs) and the side effects of process integration: such as array-level variability and magnetic-field interference (MFI). In this work, several design solutions are proposed to overcome these challenges: (1) a novel merged-local-reference scheme is used to overcome the array-edge effect on the MTJs; (2) write bias segment trimming is used to mitigate the near-far effect for better write endurance; (3) an MTJ-based one-time programmable (OTP) is used to preserve critical data during the wafer-level chip-scale packaging (WLCSP) process (360°C, 3hr), and; (4) a novel sensing-reference scheme is used so that this MTJ-OTP is immune to external-magnetic-field interference. A 32-Mb STT-MRAM test chip based on these proposed solutions is successfully fabricated in a 16nm FinFET CMOS process, Measured results confirm its excellent performance and manufacturability for next generation automotive MCU application.