Abstract
Although phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. In this work, a correlation between the rate of applied voltage and the dynamics of threshold-switching is investigated at picosecond-timescale. A distinct characteristic feature of enabling a rapid threshold-switching at a critical voltage known as the threshold voltage as validated by an instantaneous response of steep current rise from an amorphous off to on state is achieved within 250 picoseconds and this is followed by a slower current rise leading to crystallization. Also, we demonstrate that the extraordinary nature of threshold-switching dynamics in AgInSbTe cells is independent to the rate of applied voltage unlike other chalcogenide-based phase change materials exhibiting the voltage dependent transient switching characteristics. Furthermore, numerical solutions of time-dependent conduction process validate the experimental results, which reveal the electronic nature of threshold-switching. These findings of steep threshold-switching of ‘sub-50 ps delay time’, opens up a new way for achieving high-speed non-volatile memory for mainstream computing.
Highlights
In phase-change memory (PCM), information is encoded rapidly by means of switching between high-resistance amorphous and low-resistance crystalline phases owing to Joule heating caused by nano/pico-second electrical pulses
Since the delay time decreases rapidly for over voltages[14], the reported delay time value on the chalcogenide-based memory devices so far has only been in the order of 1–10 ns[5,12,14,17,18] and the switching time is limited by the response time of the experimental setup[14]
Very recently a voltage-dependent threshold-switching dynamics in sub-ns timescale is demonstrated revealing a short delay time as small as 300 ps in InSbTe material probed using an advanced custom-built programmable electrical tester[19]. Owing to these facts, achieving a faster set process is primarily hindered by the voltage dependent transient parameters and the speed of crystallization is much slower compared to that of amorphization, which is the main drawback keeping us from realizing ps-programming characteristics of PCM devices
Summary
Phase-change memory (PCM) offers promising features for a ‘universal memory’ owing to high-speed and non-volatility, achieving fast electrical switching remains a key challenge. Very recently a voltage-dependent threshold-switching dynamics in sub-ns timescale is demonstrated revealing a short delay time as small as 300 ps in InSbTe material probed using an advanced custom-built programmable electrical tester[19] Owing to these facts, achieving a faster set process is primarily hindered by the voltage dependent transient parameters and the speed of crystallization is much slower compared to that of amorphization, which is the main drawback keeping us from realizing ps-programming characteristics of PCM devices. In case of PCM, owing to threshold-switching a rapid change from its high resistance to a low resistance (from ~1 MΩ to a few 100 Ω) state causes loading and unloading of parasitic capacitances in ps, which limits realization of the actual response of the device We tackled this key issue, by using a custom-designed programmable electrical tester (PET) having a dedicated measurement line to capture ultrafast transitions[19]. An arbitrary waveform generator allows electrical pulses down to a plateau length (duration of maximum voltage between the rising and falling edge), rise and fall time (i.e. time taken to reach voltage from 10% to 90% and 90% to 10% respectively) of 1 ns having an amplitude of up to 5 V and the digital storage oscilloscope is capable of capturing electrical transients at 50 ps resolution (time duration between two successive data points at a sampling rate of 20 GSa/sec)
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