An Embedded Nonvolatile SRAM in Logic CMOS Process

There is an increasing demand for nonvolatile memory (NVM) due to the rapid growth of IoT devices that need to operate with a tight power budget. These devices often have low activity rates and most of the time are in standby mode, resulting in a high leakage energy consumption. To reduce the leakage energy, the supply power can be turned off, but beforedoing so, data need to be stored in an NVM. Also, many IoT devices are battery-operated or powered wirelessly and can see fluctuations in their supply power. Therefore their critical data need to be stored before a power-loss event. However, the conventional NVMs such as EEPROM and FLASH are not logic CMOS compatible in terms of technology node andoperating voltages. They also require extra fabrication steps, which increases the cost for IoT devices that use small memories. Additionally, most NVMs are not embedded with logic. Embedding memory with the logic improves the memory access time and energy. It also increases data security by eliminating interface ports that are vulnerable to sidechannelattacks and malicious activities. Furthermore, embedding nonvolatile memories (eNVM) with logic enables novel architectures, such as in-SRAM nonvolatile weight storage for compute-in-memory (nvCIM). In the past, researchers have proposed various eNVMs, such as RRAM, PCM, and STT-RAM [1]. However, these solutions require significant changes to the manufacturing process making it challenging to integrate them into modern SoCs. Therefore, there is a need for an eNVM that can be fabricated in a standard logic CMOS process.This dissertation presents the first on-chip demonstration of an embedded Nonvolatile SRAM (eNVSRAM) in the standard CMOS logic process. We propose an 8T eNVSRAM architecture and present experimental results of a chip that was taped-out in GlobalFoundries 22FDX technology. In addition to eNVSRAM, I present a few other projects that I have worked on during my PhD studies. These include a nonvolatile circuit tuning technique used to modify the frequency of a ring oscillator, a supply-fluctuation resilient SRAM, and a low-power ASIC chip for detecting heart-rate and missing beats.