Study On The Growth And Resistive Switching Property Of H-BN

Two-dimensional(2D)materials have anisotropic physical properties because the transport of electrons and phonons is restricted to a 2D plane.Most kinds of 2D materials can be peeled off from their corresponding bulk materials,and when the thickness is thinning to a few or one single atomic layer,their unique physical properties emerged.2D materials with unique properties have aroused widespread interest in both academia and industry.Research groups in various fields have carried out in-depth investigations on 2D materials ranging from the earliest discovered graphene to hexagonal boron nitride(h-BN),transition metal sulfides(TMDs),black phosphorene(BP),and silicene and so on.So far,the CVD technology for the synthesis of large-area 2D materials with low defect density and high continuity has been proved highly repeatable and thus is the mainstream 2D material preparation scheme in most laboratories in the field.By optimizing the CVD process,the morphology of the synthesizing film can be well-tuned.The introduction of a small amount of oxygen during the h-BN growth process effectively reduce the nucleation density and accelerate crystal growth,thereby greatly increasing the domain size and improving the film quality.Electrical analysis in our experiments suggests that,as the substrate of graphene conductive channels,oxygen-assisted CVD-grown h-BN films has better dielectric properties than SiO2,which is manifested in the graphene's carrier mobility increased by approximately 3 times.The reason is that the h-BN film can effectively shield the charge scattering center introduced by the contact oxide and offer an atomically flat surface.In conclusion,the shielding effect and charge capture inhibition of h-BN preserve the excellent electrical properties of graphene.The h-BN behaves as one of the most promising resistive switching material because of its electrical insulating property,chemical stability,high thermal conductivity,and mechanical flexibility.The semiconductor industry has been looking for non-volatile storage techniques with high speed,low power consumption,and easy to achieve high-density 3D integration to combine the respective technical advantages of dynamic random access memory and Flash.Resistive random access memory(RRAM)has the characteristics of both nonvolatile and high-speed access,but it also requires improving the entire resistive switching(RS)performance for a given device and reducing the variation of RS performance.We fabricated h-BN RRAMs based on oxygen-assisted CVD-grown multilayer h-BN films.These devices exhibit high RS performance with low variabilities,such as good endurance,long retention,small Off current,low set voltage(<2 V)and large current On/Off ratio(108).The statistical analysis of the RS performance of RRAM devices shows that the oxygen-assisted CVD-grown h-BN film behaves significantly better than that of the oxygen-free grown samples,which benefits from a flatter and cleaner surface with higher crystalline quality.In addition,in the non-volatile h-BN RRAMs,we have achieved nonpolar RS in these devices.The achievement of nonpolar RS in h-BN RRAMs implies that besides the Coulomb force that drives charged ions to migrate along the electric field,non-directional effects like Joule heating should play an essential role in the rupture of conductive filaments.This is of great significance for understanding the RS mechanism of RRAMs based on h-BN and other 2D materials.For the practical purpose of 3D integration,the nonpolar RS behavior has the potential to reduce the peripheral circuit complexity,and increase information storage density.The RS performance of devices was characterized by applying bias to the electrode.The long-term resistive-state retention(>90 days)of both HRS and LRS suggests the non-volatile RS characteristics.Moreover,manual DC switching for?103 cycles with an average window over five orders of magnitude at ambient conditions was demonstrated.More endurance cycles are expected because no significant device degradation was observed after performing over 1200 manual DC sweeps.In summary,although the challenges of device stability and RS performance of 2D-material based RRAMs remains,it is highly possible to improve the entire RS performance and achieve mass production of 2D-material RRAMs in the future.This dissertation content starts with chemical vapor deposition(CVD)technology and introduces my research that includes the controllable synthesis of large-area high-quality h-BN thin films and their applications in transistors and resistive random access memories.In conclusion,we study on the growth and resistive switching property of h-BN.