[论文解读] Resistance switching devices based on amorphous insulator-metal thin films

Xiang Yang|arXiv (Cornell University)|Dec 5, 2014

Advanced Memory and Neural Computing参考文献 126被引用 7

一句话总结

本论文提出了一种基于非晶态绝缘体-金属薄膜的新型非易失性电阻开关随机存取存储器（RRAM），其中在双极电压控制下，电子捕获/释放可调节电子局域化长度和电阻率。关键贡献在于实现了稳定、均匀且可扩展的RRAM，具备亚皮秒级开关速度、长期记忆保持能力以及低功耗运行，该成果已在掺铂或铬的Si3N4薄膜中得到验证，并进一步拓展至多种氧化物和氮化物材料。

ABSTRACT

Nanometallic devices based on amorphous insulator-metal thin films are developed to provide a novel non-volatile resistance-switching random-access memory (RRAM). In these devices, data recording is controlled by a bipolar voltage, which tunes electron localization length, thus resistivity, through electron trapping/detrapping. The low-resistance state is a metallic state while the high-resistance state is an insulating state, as established by conductivity studies from 2K to 300K. The material is exemplified by a Si3N4 thin film with randomly dispersed Pt or Cr. It has been extended to other materials, spanning a large library of oxide and nitride insulator films, dispersed with transition and main-group metal atoms. Nanometallic RRAMs have superior properties that set them apart from other RRAMs. The critical switching voltage is independent of the film thickness/device area/temperature/switching speed. Trapped electrons are relaxed by electron-phonon interaction, adding stability which enables long-term memory retention. As electron-phonon interaction is mechanically altered, trapped electron can be destabilized, and sub-picosecond switching has been demonstrated using an electromagnetically generated stress pulse. AC impedance spectroscopy confirms the resistance state is spatially uniform, providing a capacitance that linearly scales with area and inversely scales with thickness. The spatial uniformity is also manifested in outstanding uniformity of switching properties. Device degradation, due to moisture, electrode oxidation and dielectrophoresis, is minimal when dense thin films are used or when a hermetic seal is provided. The potential for low power operation, multi-bit storage and complementary stacking have been demonstrated in various RRAM configurations.

研究动机与目标

• 开发一种基于非晶态绝缘体-金属薄膜的新一类非易失性电阻开关存储器（RRAM）。
• 通过被捕获电子的电子-声子弛豫实现稳定、长期的记忆保持。
• 通过电机械诱导的应力脉冲实现超快开关。
• 通过致密且气密密封的薄膜实现空间均匀性与可扩展性。
• 在RRAM结构中实现低功耗运行、多比特存储以及互补堆叠。

提出的方法

• 采用具有随机分散Pt或Cr纳米颗粒的非晶态Si3N4薄膜作为电阻开关介质。
• 利用双极电压脉冲控制电子捕获/释放，从而调节电子局域化长度和电阻率。
• 应用交流阻抗谱以确认电阻状态的空间均匀性，并验证电容与面积成正比、与厚度成反比的线性关系。
• 利用电子-声子相互作用稳定被捕获电子，从而实现长期记忆保持。
• 借助电磁感应产生的应力脉冲使被捕获电子失稳，实现亚皮秒级开关。
• 通过致密薄膜沉积或气密密封技术，最大限度减少水分、电极氧化及介电电泳引起的退化。

实验结果

研究问题

• RQ1 非晶态绝缘体-金属薄膜能否实现稳定、非易失性电阻开关并具备长期保持能力？
• RQ2 电子-声子相互作用如何影响电阻开关机制中被捕获电子的稳定性？
• RQ3 能否通过调控被捕获电子的机械应力实现亚皮秒级开关？
• RQ4 电阻状态在器件上的空间均匀性如何？其与器件尺寸的关系如何？
• RQ5 开关行为能否与薄膜厚度、器件面积、温度及开关速度解耦？

主要发现

• 临界开关电压与薄膜厚度、器件面积、温度及开关速度无关，表明具有鲁棒性和可扩展性。
• 通过电磁感应产生的应力脉冲使被捕获电子失稳，已实现亚皮秒级开关。
• 交流阻抗谱证实电阻状态具有空间均匀性，电容与面积成正比、与厚度成反比。
• 由于被捕获电子的电子-声子弛豫，记忆保持能力长期稳定，漏电流极低。
• 当采用致密薄膜或气密密封时，器件退化极小，显著提升了可靠性。
• RRAM表现出低功耗运行、多比特存储能力，且与互补堆叠结构兼容。