Transition of short-term to long-term memory of Cu/TaOx/CNT conductive bridge random access memory for neuromorphic engineering

This work presents the resistive switching characteristics of the TaO_x-based conductive-bridge random-access memory (CBRAM) for neuromorphic engineering. Controlling the Cu filament inside the TaO_x film allows the device to operate as both volatile and nonvolatile memory. For volatile switching induced by a lower compliance current (I_cc), a threshold switching operation is observed. Upon completion of the set process, the retention and current decay were observed, suggesting that the device has the potential for short-term memory applications. Increasing I_cc enables the CBRAM to act as a memory-switching device, as confirmed by the lengthy retention time of up to 10⁴ s. Additionally, short-term memory (STM) and long-term memory (LTM) of the device were demonstrated by time-dependent memory decay, where the various magnitude differences of the time-dependent operations. STM was identified by applying two identical pulses to the device to mimic the paired-pulse facilitation (PPF) of the neural system. Furthermore, long-term potentiation and depression were accomplished via consequent identical pulse stimuli under different switching modes to demonstrate stable LTM properties.