Multi Pre-Spike Synaptic Characteristics of InSbTe phase change memory
- Multi Pre-Spike Synaptic Characteristics of InSbTe phase change memory
- 김용태; 최민호; 안진호
- Issue Date
- The 14th Non-Volatile Memory Technology Symposium (NVMTS 2014)
- Recently, phase change memory (PCM) can be used for bio inspired electronic synapses as PCM mimics synaptic neurons by interconnecting pre and post PCM synaptic neurons [1-2]. Conventionally, GeSbTe (GST) PCM synapses are programmed to full, partial sets, and fully reset state by set/reset pulse trains and gradual changes in cell resistance are caused by the phase changing of GST. However, the GST synapses have some disadvantages in programming width and speed. In work, to improve the switching speed and multi-step programming of synaptic functions the memristive characteristics of nano size InSbTe (IST) chalcogenide matrix has been investigated with neuronal spiking behavior. Particularly, multi-step programming will be very useful for parallel computations . Fig. 1 shows a schematic array fabricated with IST synaptic cells. The size of a conical IST cell is 50nm and TiN bottom electrode is applied with the pre-spike pulse and post/potential spike is derived from the top Cr electrode. EDX analysis indicates that a nano pillar consists of IST. Threshold switch of IST cell device is as low as a fourth of the GST synapses. To trigger the threshold spiking, 10 different sets of consecutive pulses are used with varying amplitudes from 0.1 to 1 V with a 0.1 V step. Fig. 2 shows that the IST cell resistance are sequentially and multi-step wisely changed and the switching speed is as fast as 50 ns, which is 2.5 times faster than that of the GST with the same programming pulses. As a result, Spike-timing dependent plasticity (STDP) forms in 500-ns time window, which is in agreement with biological synapse.
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