磁性隨機存取記憶體 (MRAM) 因為其讀寫速度迅速、具非揮發性、易於與半導體製程整合等優點，一直 被視為是未來舉足輕重的記憶體。本文將詳細介紹：從早期的藉由磁場運作類型、近期剛開始商業化生產 的自旋轉移力矩 (STT) 運作型，一直到自旋軌道力矩 (SOT) 型，MRAM 運作模式也從間接地由電流給予 磁場，轉變為直接給予非常短暫的脈衝就可以讀寫運作，達到快速讀寫的目標。本文也會著墨於 SOT 型 MRAM 的一些運作挑戰，及其逐漸地被克服的解決方案。

Magnetic random access memory (MRAM) has been regarded as an important memory because of its fast readwrite operation, non-volatility and capability of integration to current semiconductor process. In this article, we will go through different operating mechanisms of MRAM: toggle-mode type, recent spin-transfer torque (STT) type and spin-orbit torque (SOT) type. The operating mechanism changes from applying magnetic fi eld to only a single, fast pulse, and thus accomplishes the fast read-write process. This article will also describe about the challenges of SOT, and corresponding solutions.