An MTJ-Based Asynchronous System With Extremely Fine-Grained Voltage Scaling.

In this work, we present an asynchronous MTJ-CMOS hybrid system with extremely fine-grained voltage scaling (EFGVS) technique. The supply voltage of the system is turned on/off by asynchronous bundled-data handshake signals. The MTJ write circuit is variation robust, self-terminated and redundant-write preventing. Besides, EFGVS and asynchronous data driven handshake enhance the timing robustness by removing the matching delay elements and reducing timing assumptions. The completion detection circuitry is also simplified. A RISC processor with proposed techniques is designed and fabricated by 55nm technology. The voltage supplies are turned on/off within tens of picoseconds. The energy for writing MTJs is 0.45pJ. The tolerance of the minimum TMR due to process variation is 75%. Sleep mode leakage power can be reduced over 10 $\times$ by powering off modules with the Break-even Time of 23.6 ns. Because of the extremely fine-grained voltage scaling, no more than 20% of the modules are powered on during the execution. [ABSTRACT FROM AUTHOR]