Ascoli Alon, Demirkol Ahmet S, Tetzlaff Ronald, Slesazeck Stefan, Mikolajick Thomas, Chua Leon O
Faculty of Electrical and Computer Engineering, Institute of Circuits and Systems, Technische Universität Dresden, Dresden, Germany.
Department of Microelectronics, Brno University of Technology, Brno, Czechia.
Front Neurosci. 2021 Apr 20;15:651452. doi: 10.3389/fnins.2021.651452. eCollection 2021.
Local activity is the capability of a system to amplify infinitesimal fluctuations in energy. Complex phenomena, including the generation of action potentials in neuronal axon membranes, may never emerge in an open system unless some of its constitutive elements operate in a locally active regime. As a result, the recent discovery of solid-state volatile memory devices, which, biased through appropriate DC sources, may enter a local activity domain, and, most importantly, the associated stable yet excitable sub-domain, referred to as edge of chaos, which is where the seed of complexity is actually planted, is of great appeal to the neuromorphic engineering community. This paper applies fundamentals from the theory of local activity to an accurate model of a niobium oxide volatile resistance switching memory to derive the conditions necessary to bias the device in the local activity regime. This allows to partition the entire design parameter space into three domains, where the threshold switch is locally passive (LP), locally active but unstable, and both locally active and stable, respectively. The final part of the article is devoted to point out the extent by which the response of the volatile memristor to quasi-static excitations may differ from its dynamics under DC stress. Reporting experimental measurements, which validate the theoretical predictions, this work clearly demonstrates how invaluable is non-linear system theory for the acquirement of a comprehensive picture of the dynamics of highly non-linear devices, which is an essential prerequisite for a conscious and systematic approach to the design of robust neuromorphic electronics. Given that, as recently proved, the potassium and sodium ion channels in biological axon membranes are locally active memristors, the physical realization of novel artificial neural networks, capable to reproduce the functionalities of the human brain more closely than state-of-the-art purely CMOS hardware architectures, should not leave aside the adoption of resistance switching memories, which, under the appropriate provision of energy, are capable to amplify the small signal, such as the niobium dioxide micro-scale device from NaMLab, chosen as object of theoretical and experimental study in this work.
局部活性是系统放大能量中微小波动的能力。包括神经元轴突膜中动作电位产生在内的复杂现象，在开放系统中可能永远不会出现，除非其某些组成元素在局部活性状态下运行。因此，最近发现的固态挥发性存储器件，通过适当的直流电源偏置时，可能进入局部活性域，而且最重要的是，进入相关的稳定但可激发的子域，即所谓的混沌边缘，这里实际上是复杂性的种子所在之处，这对神经形态工程学界极具吸引力。本文将局部活性理论的基本原理应用于氧化铌挥发性电阻开关存储器的精确模型，以推导使器件处于局部活性状态所需的条件。这使得可以将整个设计参数空间划分为三个域，其中阈值开关分别处于局部无源（LP）、局部有源但不稳定以及局部有源且稳定的状态。文章的最后一部分致力于指出挥发性忆阻器对准静态激励的响应与其在直流应力下的动态特性可能存在的差异程度。通过报告验证理论预测的实验测量结果，这项工作清楚地表明了非线性系统理论对于全面了解高度非线性器件动态特性是多么宝贵，而这是有意识且系统地设计稳健神经形态电子器件的必要前提。鉴于最近已证明生物轴突膜中的钾离子和钠离子通道是局部活性忆阻器，新型人工神经网络的物理实现若要比当前最先进的纯CMOS硬件架构更紧密地再现人类大脑的功能，就不应忽视采用电阻开关存储器，在适当的能量供应下，这种存储器能够放大小信号，比如本工作中作为理论和实验研究对象的来自NaMLab的二氧化铌微尺度器件。
