Band-to-Band Tunneling Based Unified RAM (URAM) for Low Power Embedded Applications

Abstract

In this article, we have reported a tunnel field-effect transistor (TFET) based unified random access memory (T-URAM), integrating nonvolatile memory (NVM) and single transistor (1T) DRAM into a single TFET device. Unlike previously published URAMs, the proposed T-URAM utilizes band-to-band tunneling (BTBT) conduction for programming both NVM and 1T DRAM. This approach offers two main advantages: low supply voltage requirements and disturbance-free NVM operation. Additionally, T-URAM ensures interference-free memory operation through separate gates for NVM and 1T DRAM. Simulations show that T-URAM requires 1.5× to 4.5× less supply voltage compared to existing URAMs. At 358 K, the retention time (RT) of T-URAM in 1T DRAM mode is 500 ms, which is $\sim$ 62.5× and $\sim$ 7.8× higher than the buried n-well bulk FinFET URAM and ITRS prediction, respectively. For NVM mode, the RT at a gate length of 50 nm matches that of previously reported URAMs. The sense margin of T-URAM in 1T DRAM mode at 358 K is about 1.9 $\mu$ A/ $\mu$ m, which is roughly 7.6× higher than TFT-based URAM. We also propose a 2x2 crossbar memory array implementation using T-URAM. These findings pave the way for designing low-power, multi-purpose embedded memory for future applications.