Area-efficient LUT circuit design based on asymmetry of MTJ's current switching for a nonvolatile FPGA

A compact lookup table (LUT) circuit using spin transfer-torque magnetic tunnel junction (STT-MTJ) devices combined with MOS transistors is proposed for a standby-power-free field-programmable gate array (FPGA). Since STT-MTJ devices essentially have an asymmetric characteristic in switching currents, one of two write-control transistors can be implemented with a small feature size, while the width of the other one is still large. By sharing the large size of write-control transistor, almost all the transistor size in the proposed LUT circuit becomes small. In fact, the effective silicon area of the proposed write-control transistors for a 6-input LUT circuit is reduced to 68 % in comparison with that of a conventional nonvolatile LUT circuit without applying the asymmetric transistor sizing.