Write Current Self-Configuration Scheme for MRAM Yield Improvement

Abstract

Magnetic random access memory (MRAM) is an emerging nonvolatile memory, which is widely studied for its high speed, high density, small cell size, and almost unlimited endurance. However, for deep-submicrometer process technologies, significant variation in the MRAM cells' operating condition results in write failures in cells and reduces the production yield. Memory designers have to characterize failed MRAM chips to find a suitable current level for reconfiguring their write current, which is time consuming. In this paper, we propose an efficient operating-current search method and the corresponding built-in circuit for toggle MRAM, which can rapidly find the minimal operating current. With the built-in search circuit, an MRAM chip can dynamically configure its write current through few tester channels. The resulting chip works correctly and consumes lower power. Production yield, thus, can be increased while the test cost is greatly reduced. We also present a generator of the circuit, which determines the circuit parameters according to the memory specifications and user requirements, and automatically generates the corresponding modules.Index Terms-Built-in self-test (BIST), characterization, memory testing, magnetic random access memory (MRAM), yield enhancement.