The Resistive Memory Device And Technology Research

Memories play important roles in semiconductor market.With the population of mobile electrical device,the non-volatile memory is getting more and more important in the total memory market.Currently, Flash is dominant in memory area,with 90%market share.As the scaling of semiconductor technology,Flash memory encounters more and more bottlenecks,e.g.,the thickness of floating gate can not be decreased infinitely.According to some reports,the limitation of Flash technology would be at 32 nm node or so.Moreover,other shortcoming such as low programming speed,high operating voltage etc,also limit the application of Flash,which forces people to search more excellent technology for next generation non-volatile memory.Recently,resistance type memories are attracted great attention for their high density and low cost.Many materials with switching characteristics were discovered,e.g. chalcogenides,doped SrZrO₃,PbZrTiO₃,Pr_1-xCa_xMnO₃,binary metal oxide and organic materials.The resistance type memories based on chalcogenides are also called phase change memory(PCM),which has great advantages on speed,endurance,retention,cell size and multi-level storage.It is one of the most promising candidates for next generation non-volatile memory. The most commonly used material in PCM is GeSbTe,which can transit between amorphous state and crystalline state,corresponding to high and low resistance state.Currently,the main problem preventing PCM from application is the large RESET current.There are mainly two ways to reduce the RESET current.One approach is doping in commonly used GST material or searching new phase change materials.The other one is reducing cell size.The first part of this thesis is mainly focused on design and fabrication of 3D nano device of phase change memory.By using spacer pattern technology,the cross-section area of electrode is defined by the height of step and film thickness,which is totally independent of lithographic technology.By using this method,sub-100 nm sized memory array are successfully fabricated with no need of advanced lithographic equipment.The manufacturing cost is greatly reduced.Metal oxides based resistance type memories are also called resistive switching memory(Resistive Random Access Memory,RRAM).Binary metal oxide(such as Nb₂O₅,A1₂O₃,Ta₂O₅,Ti_xO,Ni_xO,Cu_xO,etc.)are attracted great attention,because of their simple structure and composition.Among them, Cu_xO has more advantages,because Cu is widely used in modern semiconductor manufacturing and the fabrication of a Cu_xO memory cell is perfectly compatible with standard Cu interconnect processes.The second part of this thesis is mainly focused on Cu_xO resistive switching memory.Take RIE method for Cu_xO preparation and investigate the critical characteristics of devices,such as forming voltage,endurance and retention,etc.And then raise a switching model of local conductive formation and rupture near the interface between Cu_xO and top electrode based on experiment data.Finally,the integration solution based on damascene Cu interconnect process is put forwards,which further lays foundation for producing high density,low cost and high reliable Cu_xO based RRAM.