BIST-Supported Cryogenic Write Trimming With In-MRAM Computing Case Study

In the processor-memory separated von-Neumann computation paradigm, the “memory-wall” effect becomes critical due to large access latency and tremendous amount of data movement. In this work, we pursue cryogenic temperature based memory design and focus on spin-transfer-torque magnetoresistive random access memory (STT-MRAM) at 77-Kelvin (achieved with low-cost liquid nitrogen). Cryogenic compact model and its related cryogenic bit-cell are investigated, based on 77 K experiment data of magnetic tunnel junction (MTJ) and CMOS transistor. Compared with the simulated room temperature results, 70% reduction of sensing latency can be obtained at 0.7 V supply voltage, whereas writing latency and yield performance are significantly degraded. In order to overcome the above drawbacks, a novel joint trimming system is proposed including a build-in-self-test (BIST) block and a string of multi-stage level shifters (LS). A case study is executed with in-MRAM computing (IMC). Results show that cryogenic IMC with write trimming provides performance improvements of 33% on average, and concurrently reduces memory energy consumption by 70% on average. The proposed 77 K cryogenic design method can be further applied to other energy constrained applications.