Design of Synchronous MRAM Circuits for Local-Field-Switching MTJ

Abstract

Magnetoresistive Random Access Memory(MRAM)는 자성체(magneto-resistan ce material)를 storage element로 사용하는 메모리이다. MRAM은 비휘발성, high density, low supply voltage, low power consumption 등의 장점을 가지고 있어, 현재 많이 사용되고 있는 DRAM(Dynamic RAM), SRAM(Static RAM), Flash Memory 등의 단점을 보완할 차세대 메모리로서 그 연구가 활발히 진행되고 있다. 하지만 write 동작을 할 때 memory array에서 cell의 selectivity가 어렵다는 단점을 갖고 있다. 이 점을 해결하기 위해 여러 가지 cell 구조와 write 방법이 연구되고 있는데 최근에 LFS(Local Field Switching)를 이용한 새로운 MTJ 구조가 제안되고 있다. 본 논문에서는 LFS를 이용한 새로운 MTJ 구조를 사용하여 page mode로 동작하는 synchronous MRAM을 설계하였다.;The development of MRAM technology has faced many challenges. These include achieving adequate write switching and obtaining adequate read margin to support reliable operation. These days, some solutions are proposed. And one of the solutions is LFS(Local Field Switching) which is switching the spin valve of MTJ free layer by the orientation of the current passing through the MTJ material. We design synchronous MRAM circuits for LFS. 256bit synchronous MRAM is designed using 0.18um technology, and it shows reliable read and write operation at 100MHz. The memory include write driver which makes a change the orientation of the current passing through the MTJ cell according to the data input. And the memory include a current mode sense amplifier and mid-point reference cell block. And we also design the emulation cell in order to verify the correct functioning of the memory in only CMOS process.