Campbell Kristy A, Drake Kolton T, Barney Smith Elisa H
Department of Electrical and Computer Engineering, Boise State University , Boise, ID , USA.
Front Bioeng Biotechnol. 2016 Dec 26;4:97. doi: 10.3389/fbioe.2016.00097. eCollection 2016.
Ion-conducting memristors comprised of the layered materials GeSe/SnSe/Ag are promising candidates for neuromorphic computing applications. Here, the spike-timing dependent plasticity (STDP) application is demonstrated for the first time with a single memristor type operating as a synapse over a timescale of 10 orders of magnitude, from nanoseconds through seconds. This large dynamic range allows the memristors to be useful in applications that require slow biological times, as well as fast times such as needed in neuromorphic computing, thus allowing multiple functions in one design for one memristor type-a "one size fits all" approach. This work also investigated the effects of varying the spike pulse shapes on the STDP response of the memristors. These results showed that small changes in the pre- and postsynaptic pulse shape can have a significant impact on the STDP. These results may provide circuit designers with insights into how pulse shape affects the actual memristor STDP response and aid them in the design of neuromorphic circuits and systems that can take advantage of certain features in the memristor STDP response that are programmable the pre- and postsynaptic pulse shapes. In addition, the energy requirement per memristor is approximated based on the pulse shape and timing responses. The energy requirement estimated per memristor operating on slower biological timescales (milliseconds to seconds) is larger (nanojoules range), as expected, than the faster (nanoseconds) operating times (~0.1 pJ in some cases). Lastly, the memristors responded in a similar manner under normal STDP conditions (pre- and post-spikes applied to opposite memristor terminals) as they did to the case where a waveform corresponding to the difference between pre- and post-spikes was applied to only one electrode, with the other electrode held at ground potential. By applying the difference signal to only one terminal, testing of the memristor in various applications can be achieved with a simplified test set-up, and thus be easier to accomplish in most laboratories.
由层状材料GeSe/SnSe/Ag组成的离子导电忆阻器是神经形态计算应用的有前途的候选者。在此，首次展示了尖峰时间依赖可塑性（STDP）应用，使用单一类型的忆阻器作为突触，在从纳秒到秒的10个数量级的时间尺度上运行。这种大动态范围使忆阻器可用于需要缓慢生物时间的应用，以及神经形态计算所需的快速时间，从而在一种忆阻器类型的一个设计中实现多种功能——一种“一刀切”的方法。这项工作还研究了改变尖峰脉冲形状对忆阻器STDP响应的影响。这些结果表明，突触前和突触后脉冲形状的微小变化会对STDP产生重大影响。这些结果可能为电路设计者提供有关脉冲形状如何影响实际忆阻器STDP响应的见解，并帮助他们设计能够利用忆阻器STDP响应中某些可编程的突触前和突触后脉冲形状特征的神经形态电路和系统。此外，根据脉冲形状和定时响应估算了每个忆阻器的能量需求。正如预期的那样，在较慢的生物时间尺度（毫秒到秒）上运行的每个忆阻器的能量需求估计更大（纳焦耳范围），比在较快的（纳秒）运行时间（在某些情况下约为0.1 pJ）更大。最后，忆阻器在正常STDP条件下（突触前和突触后尖峰应用于相反的忆阻器端子）的响应与将对应于突触前和突触后尖峰之间差异的波形仅应用于一个电极，另一个电极接地的情况类似。通过仅将差异信号应用于一个端子，可以使用简化的测试设置实现忆阻器在各种应用中的测试，因此在大多数实验室中更容易完成。
