Multiple slopes in the negative differential resistance region of NbOx-based threshold switches
Multiple slopes in the negative differential resistance region of NbOx-based threshold switches
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DOI：
10.1088/1361-6463/ab217a
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发表时间：
2019-08-07
影响因子：
3.4
通讯作者：
Slesazeck, Stefan
中科院分区：
文献类型：
--
作者：
Herzig, Melanie;Weiher, Martin;Slesazeck, Stefan
氧化铌器件表现出阈值切换行为，使其能够用作存储器阵列中的选择器或用作神经形态计算的本地有源器件。在非线性电路中出现的基本动态现象中，利用阈值开关器件的负微分电阻（NDR）效应的张弛振荡器中产生的振荡对于神经形态电子系统的设计具有特殊意义。这里，检查了在简单的张弛振荡器电路中出现这种振荡的必要要求以及它们对所测量的阈值开关的准静态I-V-m特性的形状的影响。在相应的实验中，发现阈值开关的准静态I-V-m特性中出现多个NDR区域，同时发生振荡。因此，观察到的“多重 NDR 现象”仅仅是由于与用于测量器件电流和电压的源测量单元 (SMU) 的工作原理相关的平均效应而产生的测量假象。在这项工作中，我们分析了张弛振荡器中振荡行为的出现如何取决于器件层堆栈的组成。通过降低氧化铌双层堆叠的亚化学计量底层中的氧含量，可以增加大电流范围内出现振荡的可能性。结果表明，这种趋势是由于阈值开关器件的热电容和热阻之间的乘积值减小而引起的。此外，改变的堆叠组成减少了可变性并改变了形成电压，这与阈值电压的改变密切相关。
Niobium oxide devices exhibit threshold switching behavior which enables their use as selectors in memory arrays or as locally active devices for neuromorphic computing. Among the basic dynamical phenomena appearing in non-linear circuits, the oscillations generated in a relaxation oscillator, which is making use of the negative differential resistance (NDR) effect of a threshold switching device, are of special significance for the design of neuromorphic electronic systems. Here, the necessary requirements for the emergence of oscillations of this kind in a simple relaxation oscillator circuit and their influence on the shape of the measured quasi-static I-V-m characteristic of the threshold switch are examined. In the corresponding experiments multiple NDR regions were found to appear in the quasi-static I-V-m characteristic of the threshold switch concurrently with the occurrence of oscillations. The observed 'multiple NDR phenomenon' is therefore merely a measurement artefact due to the averaging effect associated to the operating principles of the source measure unit (SMU) utilized to measure the device current and voltage. In this work, we analyzed how the emergence of oscillatory behavior in the relaxation oscillator depends upon the device layer stack composition. The probability of the appearance of oscillations within a large current range can be increased by decreasing the oxygen content in the sub-stoichiometric bottom layer of a niobium oxide bi-layer stack. It is shown that this trend is caused by the resulting decrease in the value of the product between thermal capacitance and thermal resistance of the threshold switching device. Furthermore, the changed stack composition reduces the variability and changes the forming voltage, which goes hand in hand with a change of the threshold voltage.