Emulation of spike-timing dependent plasticity in nano-scale phase change memory

The spike-timing dependent plasticity (STDP) of biological synapses, which is known to be a function of the formulated Hebbian learning rule of human cognition, learning and memory abilities, was emulated with two-phase change memory (2-PCM) cells built with 39 nm technology. For this, we designed a novel time-modulated voltage (TMV) scheme for changing the conductance of 2-PCM cells, that could produce both long-term potentiation (LTP) and long-term depression (LTD) by applying variable (decreasing/increasing) pulse voltages according to the sign and magnitude in time interval between pre- and post-spikes. Since such schemes can be easily modified to have a variety of pulse shapes and time intervals between pulses, it is expected to be a proper scheme for designing diverse synaptic connection abilities. In addition, the small form factor and low energy consumption of 2-PCM make them comparable to biological synapses, which makes phase change memory a promising candidate for electronic synapses in large-scale neuromorphic system applications.