| With the advent of the era of big data,the performance of storage faces severe challenges,such as storage density,storage speed,and energy consumption.Traditional dynamic random-access memory cannot satisfy the requirement due to its limitation of volatile and power-consumable data storage.The only way to meet the challenges of big data is finding new types of memory.Phase change memory and all-photonic memory based on phase change material are considered to be the most likely memories for achieving ultra-high-density storage,high storage efficiency,and low power consumption.However,there are still exist some problems in phase change memory and all-photonic memory based on phase change materials:(1)For phase change memory,resistance drift is still one of the problems that hinder its development.First,there is still disagreement concerning the understanding of resistance drift,and the microscopic origin of resistance drift remains vague.Second,the?_R of phase-change films is reported to be about 0.050~0.130,far greater than the ideal value of 0.010.There has not yet been an effective way to reduce the resistance drift in phase-change films.(2)For the all-photonic memory,it can overcome the von Neumann bottleneck in computers,by avoiding the conversion between electric and optical signals to greatly increase the storage rate.However current waveguides have large footprints and studies have shown that footprint can be reduced by reducing the laser wavelength.Unfortunately,the phase change material has a relatively large extinction coefficient in the ultraviolet-visible band,which results in high energy loss.It is required to find a phase change material with a relatively low extinction coefficient to reduce the footprints.Present researches show that doping is one of the effective means to change the extinction coefficient of phase change materials,but how to reduce the extinction coefficient and the underlying mechanism of phase change materials in the ultraviolet-visible range has not yet been studied.To solve the problems above,we conducted the following two aspects of research by combining experimental and theoretical calculations:(1)Study on the physical mechanism and the way to reduce the resistance drift of GST thin film.We find that,for the first time,resistance drift originates from change in electron binding energy induced by structural relaxation and is proportional to the reciprocal of dielectric coefficient according to hydrogen-like model.On this basis,we propose to reduce resistance drift by increasing thermal stability of dielectric coefficient.Two series of experiments prove the effectiveness of our new strategy.The resistance drift exponent of phase-change films is significantly reduced to 0.023 by using our strategy,which is lower by half than the best result(0.050)reported previously.This study reveals the quantitative relationship between the resistance drift and the dielectric constant and proposes a new idea for suppressing the resistance drift,which is of great significance for finding a phase change material with high stability and high storage density.(2)Study aimed at reducing the extinction coefficient and underlying mechanism.The results show that the extinction coefficient of the Ge-Sb-Te films gradually decreases with the vacancy concentration decreases.This is attributed to the lower vacancy concentration,the greater the degree of disorder,which causes the decreasing and increasing of A and C of the Lorentz oscillator.This in turn causes the electronic structure of the film to change.And the extinction coefficient of the Ge-Sb-Te phase change films first decreases and then increases with the increase of nitrogen doping content.This is because moderate amount of nitrogen doping changes the disorder of the thin film and causes the change of the amplitude A of the Lorentz oscillator,which affects the electronic structure of the thin film. |
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