利用3d 過渡金屬提升異質結構之自旋軌道矩轉換效率

Abstract

隨著近年來摩爾定律已經發展到盡頭，儘管有修正的摩爾定律版本，但是仍須一些特殊的技術來支持。這時，次世代記憶體越來越受到重視以及獲得許多認可。其中，最有名的磁阻式隨機存取記憶體具有非揮發性、能量消耗較低的特性因此備受矚目，其中以自旋軌道矩式磁阻式隨機存取記憶體(SOT-MRAM) 的表現最為優異，包含了快速寫入、高耐久度以及低寫入電流的特性使它具備良好的競爭力。

利用合金供給自旋電流可以有效提升類阻尼自旋軌道矩效率。然而所使用的金屬成本都不低，這對於未來在量產磁阻式隨機存取記憶體會是一大難題。因此在本篇論文，會使用相對便宜以及自然界含量高的鎢、鈷、鈦金屬來製作合金以及多層膜，其中包含了鎢鈷合金、鎢鈷多層膜、鎢鈦多層膜。我們利用這些合金或多層膜當作自旋電流供給方並進行量測，發現在類阻尼自旋軌道矩效率擁有卓越的表現；而多層膜也擁有很小的翻轉電流，進而在較低的電壓下也能進行翻轉，避免造成元件的擊穿現象。本篇期望能帶給自旋軌道矩式磁阻式隨機存取記憶體一點啟發。

As we approach the end of the Moore’s Law, the significance of next generation memories has become increasingly prominent in recent years. Among these, Magnetoresistive Random Access Memory (MRAM) has emerged as a promising nonvolatile memory, with spin-orbit torque MRAM (SOT-MRAM) being competitive. The SOT-MRAM possesses several desirable properties, such as high writing speed, high endurance, and low writing current. Furthermore, considering the environmental and economic concerns, a SOT-MRAM should exhibit high damping-like efficiency (ξDL), excellent thermal stability, and low power consumption.

Alloys are regarded as a promising substitution of heavy metal (HM) layer for future advancements, as they provide enhancements in both spin Hall angle (θSH) and ξDL while maintaining a moderate resistivity. Numerous experimental studies conducted by different research groups have confirmed the enhancements in θSH and ξDL achieved through the use of different alloys. However, the composition of these alloys can be costly, posing challenges for mass production.

In this thesis, we explore the utilization of not only alloys but also multilayers as the HM layer. WCo alloy, WCo multilayer, WTi multilayer demonstrate enhancement in ξDL. Moreover, both multilayers possess extremely low switching currents, which effectively contributes to reducing the applied voltages across the devices.