Study On The Phase Transition Characteristics Of Two-dimensional MoTe₂ Material

Phase change random access memory(PCRAM)is considered to be one of the most promising next-generation mainstream non-volatile memories as the only memory that works based on the Joule thermal effect.However,the storage performance of traditional chalcogenide phase change materials will drop sharply when the size shrinks to a few nanometers.Two-dimensional transition metal dichalcogenides(TMDs)have a phase transition behavior similar to that of chalcogenide phase change materials,and can work in ultra-small sizes,and are expected to make breakthroughs in the development of ultra-high density PCRAM.However,due to the complicated phase change behavior induced by the temperature field of two-dimensional TMDs,there is still no systematic study on the mechanism of thermally induced phase change.In particular,there are still great challenges to realize the reversible and non-volatile phase transition of two-dimensional TMDs through the current Joule heating effect.There is no experiment to confirm that two-dimensional TMDs can realize the information storage function similar to PCRAM.This paper takes the two-dimensional MoTe₂ with the lowest phase change barrier in TMDs as an example.Studies the thermally induced phase change behavior in depth,and to prepare and test PCRAM devices based on 2D MoTe₂.The thesis firstly conducted a systematic study on the phase change behavior and phase change mechanism of molybdenum ditelluride(MoTe₂)under the action of the thermal field.The variable temperature Raman test was used to study the reversible phase transition behavior of MoTe₂ under the action of the thermal field.It was found that the Raman peak of the 1T'phase will appear in 2H-MoTe₂ at high temperature,and this structure can be maintained after cooling.The prepared 1T'phase samples will also be partially transformed into 2H phase after high temperature annealing,this phase transition is related to the cooling rate.It is confirmed that MoTe₂ can undergo a reversible transformation of 2H phase and 1T'phase under an appropriate temperature field,and both can remain stable at room temperature.Further,the resistance-temperature(R-T)test was used to study the electrical property changes caused by the phase transition in 2H-MoTe₂ under the action of thermal field.The resistance changes caused by the sample structure changes during the heating process were observed.After cooling,the resistance is 1-3 orders of magnitude lower than the initial resistance.Based on this,the phase transition mechanism of MoTe₂ at high temperature is discussed and an atomic displacement model of phase transition is proposed.This reversible phase transition adjusted by temperature makes it applicable to PCRAM.Finally,the contact characteristics of the material and the electrode were optimized,and a unit device based on the Au/MoTe₂/Au vertical structure was prepared.The device electrical test successfully achieved reversible transition that high resistance state(HRS)to low resistance state(LRS)at a low voltage,and LRS to HRS at a high voltage.Based on the atomic displacement model,the resistance-state transition behavior of this TMDs-based PCRAM device is analyzed.