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中国物理学会期刊

具有经验学习特性的忆阻器模型分析

CSTR: 32037.14.aps.68.20190808

Analysis of memristor model with learning-experience behavior

CSTR: 32037.14.aps.68.20190808
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  • 类似人类记忆的短期、长期记忆现象在不同材料忆阻器的实验研究中有过多次报道. 在多篇这类忆阻器的研究文献中还报道了经验学习特性: “学习-遗忘-再学习”实验中, 短期记忆遗忘后再次学习, 记忆恢复的速度明显比初次学习的记忆形成速度更快. 本文对这类忆阻器已有数学模型在“学习-遗忘-再学习”实验中的特性给出进一步分析. 仅考虑短期、长期记忆现象的忆阻模型在该实验中表现为较快速再次学习特性, 再次学习的记忆恢复速度较快主要是由于脉冲间隔期间的遗忘速度比初次学习时更慢. 考虑经验学习特性的忆阻模型在再学习阶段的记忆恢复速度更快主要是因为脉冲作用时的记忆增速更快, 同时仍然存在脉冲间隔期间的遗忘速度减慢. 与经验学习特性相关的状态变量的物理意义可利用连通两电极的导电通道的周围区域在不同外加电压作用下的变化来给出解释.

     

    The behavior of transition from short-term memory (STM) to long-term memory (LTM) has been observed and reported in the experimental studies of memristors fabricated by different materials. This kind of memristor in this paper is named STM→LTM memristor. In some of these experimental researches, the learning-experience behavior observed in the " learning-forgetting-relearning” experiment is also reported. When the memristor is restimulated by pulses after forgetting the STM, its memory will quickly return to the highest state that has been reached before the forgetting period, and the memory recovery during the relearning period is obviously faster than the memory formation in the first learning process. In this paper, the behavior of the existing STM→LTM memristor model in the " learning-forgetting-relearning” experiment is further discussed. If wmax, the upper bound of the memory level, is a constant with a value of 1, the STM→LTM memristor model exhibits no learning-experience behavior, and this model shows a faster relearning behavior in the " learning-forgetting-relearning” experiment. The relearning process is faster because the memory forgetting during pulse-to-pulse interval in the relearning process is slower than that in the first learning process. In the STM→LTM memristor model with learning-experience behavior, wmax is redesigned as a state variable in 0,1, and its value will be influenced by the applied voltage. The memory formation in the first learning process is relatively slow because wmax limits the memory formation speed when the pulse is applied. After the forgetting process, the limitation of wmax on the pulse-induced memory formation is less obvious, so the memory of the device increases at a faster speed during the memory recovery of the relearning process. In this case, the forgetting speed still becomes slower after each pulse has been applied. If the pulse-induced wmax increase is so fast that wmax will quickly increase to its upper bound after a few pulses have been applied in the first learning process, and the learning-experience behavior is similar to the faster relearning behavior when wmax = 1. In most of experimental research papers about the STM→LTM memristor, the change of the memristance can be explained by the formation and annihilation of the conductive channel between two electrodes of a memristor. During a certain period of time, the ions (or vacancies), which can be used to form the conductive channel, are only those that are around the conductive channel, which indicates that there should be an upper bound for the size of the conductive channel within this time period. The area in which ions (or vacancies) can be used to form the conductive channel is called the surrounding area of the conductive channel. In the model, wmax can be understood as the size of the conductive channel’s surrounding area, and it describes the upper bound of the width of the conductive channel.

     

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