Studies On The Resistive Switching Characteristics Of La-based High-k Materials

After decades of rapid development,microelectronics technology has encountered many technical bottlenecks.In order to solve these problems,new materials,new structures,new devices or other new methods are constantly proposed and studied,which promotes the continuous development of semiconductor technology.Nowadays,traditional Flash memory,is also facing the bottleneck of scaling down due to its physical limitation,which makes it unable to meet the requirements of future memories.A new type of emerging memory,resistive random access memory?RRAM?,which has many advantages,such as simple structure,high scalability,fast read/write speed,excellent reliability,multi-value storage,low power consumption and great CMOS process compatibility,has attracted considerable attentions.It is worth noting that the traditional high-k materials?i.e.HfO₂,ZrO₂,etc.?have become the most commonly used dielectric materials in RRAM research,because of their mature technology,precise control of components or impurities,stable performance and good compatibility with CMOS technology.Among all the high-k materials,lanthanum oxides?La₂O₃?,lanthanum-aluminium oxides?LaAlO₃?or La-based stack structures?i.e.Al₂O₃/La₂O₃?are considered to be one of the most novel high-k dielectrics for their outstanding properties,which have attracted much attentions in the application of gate dielectrics.However,few researches have focused on the effects of resistive switching characteristics on La-based RRAM devices.In order to supplement the insufficiency of this aspect of research,the La-based RRAMs are prepared and studied in this dissertation.The main contents and achievements are as follows:1.The oxygen vacancy driven conductive filament La-based RRAM,which based on Ti/LaAlO₃/Pt structure was prepared.Later,the switching characteristics,such as stable and clean bipolar RS behavior,good cycling endurance?>10²?,fine retention ability?>10⁴s?,suitable ON/OFF ratio?>10²?,and small dispersion?<0.25V?were obtained by electrical measurement.The analysis of mechanism proved that the space charge limited current?SCLC?is the main conduction mechanism,and the resistive switching behavior of Ti/LaAlO₃/Pt RRAM is believed to be originated from the formation and dissolution of the conductive filaments?CFs?,which is composed of oxygen vacancies.2.The metal conductive filament Cu/LaAlO₃/Pt RRAM was prepared,and its electrical characteristics and resistive switching mechanism,i.e.I-V characteristic,cycling endurance,dispersion characteristic and conduction mechanism were emphatically studied.The results shown that the Cu/LaAlO₃/Pt RRAM is a typical metal conductive filament type RRAM,which could be attributed to the formation and rupture of Cu nano wires in the LaAlO₃ film.Compared with Ti/LaAlO₃/Pt RRAM,Cu/LaAlO₃/Pt RRAM had a much larger ON/OFF ratio?the maximum value can be up to 10⁶?.However,the large voltage or resistance dispersions indicated that the stability of Cu/LaAlO₃/Pt RRAM is poor,resulting in only about 100 of the actual memory window.3.In order to have a better understanding of La-based RRAM,the effects of stack structure,annealing treatment or different bottom electrodes on the resistive switching characteristics of La-based RRAM were studied,respectively.It was found that the switching characteristics of LaAlO₃ are better than that of Al₂O₃/La₂O₃ stack structure,even both of them have the same La/Al component ratio.And the annealing treatment is harmful to the oxygen vacancy driven conductive filament La-based RRAM,but has little effect on the metal conductive filament La-based RRAM.Although the device with heavily doped N⁺Si as bottom electrode still has some resistive switching characteristics,its performance seems very unstable.4.A metal doped method was used in metal conductive filament Cu/LaAlO₃/Pt RRAM to improve the poor stability and serious parameter dispersions.Thus,the Cu nano-crystals was embedded in the LaAlO₃ film to form Cu/LaAlO₃:Cu-NCs/Pt devices.Evident resistive switching characteristics improvements,such as lower forming voltage,higher on/off ratio and better electrical uniformity,were corroborated by the I-V measurement results after doping treatment.Further studies revealed that the resistive switching mechanism of Cu/LaAlO₃:Cu-NCs/Pt devices can be attributed to the formation and rupture of Cu conductive filaments,which is close related to the SCLC mechanism and Joule heating effect.