Abstract
Magnetic Random Access Memory (MRAM) is a non-volatile memory which is widely researched because of its high speed, high density, small cell size, and almost unlimited endurance. There are many types of MRAM. The toggle MRAM is the most popular one because it solves the half-select problem and has a large operating region distribution. It is operated by applying the operating current including the write word line current (IWWL) and the bit line current (IBL). For deep-submicron process technologies, the variation among the MRAM cells’ operating regions is significant. The operating region shift problem results in the write failure to cells under the operating current of specification and reduces the production yield. In tradition, we characterize the failed MRAM chips to search for the suitable operating current for them. However, the conventional characterization method is inflexible and time-consuming. In this thesis, we propose an operating current search method and design the corresponding built-in circuit, Current Selector, for toggle MRAM, which can rapidly find the customized operating current for each chip. Compared to the conventional characterization method, the proposed search method is 10 to 30 times faster while the built-in Current Selector circuit costs little area overhead (0.01% for a 16 Mb MRAM). With the built-in Current Selector, we can dynamically reconfigure the operating current of the MRAM chip for improving its reliability and increasing its life-time. Meanwhile, those chips failing to write under the operating current of specification can be identified and possibly corrected, and consequently the yield is improved.