The Electro-resistive Effect Of The Ferroelectric Tunnel Junction And The Influence Of The Thickness Of The Ferroelectric Layer On The Tunneling Mechanism

With the rapid progress of integrated circuit technology and two-dimensional material processing technology,the characteristic size of traditional semiconductor devices has been reduced to nanometer scale.Especially in the industry represented by international large-scale manufacturers such as TSMC?Taiwan Semiconductor Manufacturing Company?,mature application of 7 nm technology has begun and wafer production has been achieved.However,with the further reduction of device feature size,the non-ideal effects such as quantum tunneling caused by physical limits have brought a lot of difficulties to the industry,especially in the field of memory.It has become a consensus in the industry to find alternatives to traditional silicon materials for meeting the requirements of smaller device size,higher integration density and more stable performance.Ferroelectrics,as a kind of potential substitutes,have attracted more attention due to the hysteresis loops.Based on this background,the ferroelectric tunnel junctions with BaTiO₃ as ferroelectric functional layer,LaNiO₃ and SrRuO₃ as bottom electrodes are studied in this paper.We have fabricated epitaxial thin films with smooth surface,clear interface and good phase formation by pulsed laser deposition technology.Different functional layers are stacked to form ferroelectric tunnel junction devices.After X-ray diffraction,atomic force microscopy,piezoelectric force microscopy characterization and electrical performance testing,we have obtained stable and reproducible ferroelectric tunnel junction devices with ON/OFF ratio up to 10³.In addition,the effect of ferroelectric layer thickness on the performance of tunnel junction devices was studied in detail.The thickness of the films was measured by X-ray reflection and the growth rate of different materials under certain technological conditions was calculated,so as to control the film thickness and prepare a series of tunnel junction samples with different ferroelectric layer thickness.The macroscopic electrical properties of tunnel junctions with different thicknesses are tested by using the resistance measurement system built by Keithley 2400 source meters.Quantitative tunneling currents are obtained by using MATLAB and other fitting tools.It is concluded that the proportion of FN tunneling and thermally-activated thermionic injection is closely related to the switching performance of devices,and TER effect increases gradually with the increase of thickness.Based on theoretical analysis and data fitting,the conversions of transport mechanism of different thickness are obtained.Finally,we studied the weakening of the retention performance by the built-in barrier in the ferroelectric tunnel junction.Polarization instability and ferroelectric fatigue are mainly attributed to the built-in potential field in the ultra-thin ferroelectric layer,which stabilizes one direction polarization but inhibits the other direction.According to using Ag as the top electrode,the performance of maintaining and reversing is improved obviously,and the problem of polarization instability and the influence of ferroelectric fatigue on device life is solved.