Investigation On 2D Antimonic Phase-change Memory Materials And Devices

Phase-change random-access memory(PCRAM)is the most promising candidate as next-generation non-volatile memory,due to its excellent overall performance such as high speed,low power consumption,and high density.Neuromorphic computing devices based on PCRAM have attracted intensive attention in artificial intelligence.Being able to achieve high-accuracy in-memory computing via stable multi-state programming,presenting outstanding potential to overcome the intrinsic bottleneck of current von Neumann hierarchical computing system,i.e.,low efficiency and high energy consumption when shuttling data back and forth between processing and storage units.However traditionally commercial Ge₂Sb₂Te₅-based PCRAM exhibits strong temporal resistance drift in amorphous phase and severe fluctuation under reprogramming in the intermediate states,leading to mingling of adjacent states and decoding error,and thus obstructing high-accuracy matrix-vector multiplication in neuromorphic computing.Moreover,the abrupt resistance change under electrical field of traditional PCRAM devices during amorphization process(RESET)hinders valid simulation of the long-term depression(LTD)in biological neurons.To address the above issues,this dissertation adopted elemental antimony(Sb)as phase-change medium.We systematically explored the size effect of thermal stability and drift coefficient of amorphous phase,and verified the superior amorphous stability and extremely low drift coefficient of the 2D(two dimensional)monatomic Sb films,demonstrating their promising application in PCRAM and high possibility to precisely control its resistance states.Subsequently,this dissertation shows that PCRAM based on 2D monatomic Sb film achieved reliable multi-level states with considerably low resistance drift and small programming noise through iterative RESET.Furthermore,the Sb-based PCRAM is also capable of performing progressive RESET operations and cumulative(progressive)SET,ensuring its symmetrical emulation in biological synapses.This work thus convincingly demonstrates that PCRAM based on 2D Sb films shows bright future in high-density storage and neuromorphic computing.The primary conclusions of this dissertation are as following:1?Excellent amorphous stability and low drift of 2D Sb films.Decreasing the thickness of Sb films from 5 to 3 nm leads to the remarkable increment of crystallization temperature,crystallization activation energy,and data retention.Sb films with3 nm and 4 nm-thickness display superior thermal stability,with thousands of years in data retention at room temperature.Besides,extremely low resistance drift(with drift coefficient?=0.001)in amorphous phase has been observed for 4 nm-thick Sb film?2 hours after sample deposition,which is only one hundredth of a traditional Ge₂Sb₂Te₅ film.The above results confirm that 2D Sb film is excellent candidate for low drift PCRAM.2?2D Sb phase-change memory for multi-level and neuromorphic computing.Through geometrical shrinkage and interfacial confinement,the 4 nm-thick Sb film based PCRAM accomplishes reliable iterative RESET and cumulative SET operations simultaneously,as well as multiple intermediate resistant states because of gradually augmented amorphous-to-crystalline volume ratio,with each state exhibiting a very low drift coefficient(?0.006<?<?0.027,amorphous resistance of GST??0.11).Moreover,progressive RESET and SET is another merit of the 2D Sb-based device,which is of necessity for emulating the symmetrical responses of biological synapses.