Study On Preparation And Performance Control Of GeTe-based Ovonic Threshold Switch

Three-dimensional phase change memory(3D PCM)uses a multi-layer cross-stack structure to maintain the excellent storage performance while doubling the storage density,which has attracted much attention in the industry.However,with the increase in the size of the array,the leakage current flowing through other cells adjacent to the memory cell being operated is getting larger and larger,which will cause serious misreading,misoperation,and increased power consumption.Traditional three-terminal addressing devices(such as MOS)are not suitable for three-dimensional stacking.Therefore,two-terminal addressing devices need to be developed—selectors and phase-change memory cells are integrated to suppress leakage current.Ovonic Threshold Switch(OTS)selector stands out due to its good integration with phase change memory cells,and has become a hotspot of current selector research.However,the currently used Ge Se-based OTS(such as As Te Ge Si N)selector still have problems such as too small selectivity,excessive switching voltages,and complicated material systems.To this end,this paper proposes a GeTe-based OTS selector with simple components and excellent performance,and studies its working mechanism in conjunction with software simulation.The main results obtained are as follows:(1)The preparation technology of the self-heating structure OTS selector is studied.The key process parameters such as thin film deposition,UV lithography,and electron beam lithography were optimized.Designed and implemented a highly reliable self-heating device structure and process flow,laying a solid foundation for the subsequent regulation of the parameters of the OTS selector.(2)Reveals the changing rule of GeTe-based OTS selector performance.The effects of key factors such as the feature size,material thickness,Te content,and electrode material on threshold voltage,switching ratio,off current,and leakage current were systematically studied.The integration requirements of different memory cells can be adjusted and screened.(3)A new C-GeTe-based OTS selector that can meet the needs of 3D PCM integration is realized through C doping.This selector has extremely low off current(from 35 n A to 2.4n A),high switching ratio(4.2×10~4),high turn-on speed(<10 ns),good cycle performance(10~7 times),and excellent drive Capability(impulse response current up to 2?3 m A),excellent comprehensive performance,can meet the integration requirements of 3D PCM.Combining software simulation and P-F model,it is found that the excellent comprehensive performance of C-GeTe-based OTS selector mainly comes from the energy barrier between the higher conduction band and quasi-Fermi level caused by doping.