Memory Devices Based On Two-dimensional Materials

Since the discovery of graphene,two-dimensional（2D）materials have attracted extensive interest.Deep investigation is underway in basic science research and technology applications.Monolayer molybdenum disulfide（MoS2）is a typical example of 2D materials.Because of its atomic thickness,excellent electrical performance,good flexibility,etc.,a wide range of new technology applications can be realized,such as low power devices,flexible/transparent devices.In this paper,we demonstrate some memory device applications based on two-dimensional materials,including non-volatile memories based on MoS2 and h-BN heterostructures,memristors based on quasi-two-dimensional metal oxides,and short-channel devices.1.We first studied a new-type floating gate nonvolatile memory based on molybdenum disulfide.Using dry transfer technology,we have realized boron nitride/molybdenum disulfide/boron nitride heterostructure.The device uses a double-gate structure with a conductive channel between the double gates.Due to the coupling between the top gate（floating gate）and the bottom gate（control gate）,we can use small operating voltage for electron tunneling thicker dielectric layer.When removing operating voltage,electrons are more difficult to tunnel out of the floating gate,which enhances the data retention of the device.At the same time,monolayer molybdenum disulfide is used as the channel material.The off-state current of the device is on the order of 10^-13 A,which can reduce the power consumption of the device.This new structure provides a new way for future memory applications.2.Memristor based on quasi-two-dimensional gallium dioxide.In this paper,we have prepared an ultra-thin quasi-two-dimensional metal oxide（gallium oxide）film by squeegee methods.The thickness of the film is between 1 nm and 4 nm.In addition,using PC（Propylene Carbonate）as sacrificial laye,the PC stamp technology has been developed to transfer the film to any substrate.Using this quasi-two-dimensional gallium oxide as the intermediate dielectric layer,graphene as the bottom electrode and silver as the top electrode,we have constructed a memristor.Based on the thin film memristor,the functional bionics of synapses have been realized,including short-term memory to long-term memory transition,spike-rate dependent plasticity and spike timing-dependent plasticity.3.We have constructed an ultra-short channel device.We used hydrogen plasma to etch the graphene grain boundaries and obtained a sub-10 nm gap.When molybdenum disulfide is stacked on the graphene,the graphene on both sides of the gap is used as electrodes,and the effective channel length of the monolayer molybdenum disulfide is controlled by this gap.The device still has good performance when the channel is below10 nm.The device exhibits good switching characteristics with a switching ratio of approximately 10⁶ and a mobility of 30 cm²V^-1S^-1.This demonstrates that using a two-dimensional material to construct a field effect transistor can effectively reduce the characteristic lengthλof the device and reduce the influence of the short channel effect on the device.This opens up the possibility of ultra-short-channel devices based on two-dimensional materials in the future.