Changing Resistance By Control Of Barrier In Ferroelectric Tunnel Junctions

Ferroelectric materials have attracted extensive research by scientific researchers because of their excellent ferroelectricity and piezoelectric properties.Ferroelectric tunnel junctions with ultra-thin ferroelectric materials as barriers have become the one of the most hot research field of ferroelectric material devices in the past decade because of their low energy consumption?non-volatile reading or writing and easy integration with other electronic components.The logic identification and service life at work are pivotal problems in commercial application of ferroelectric tunnel junctions.Therefore,how to improve the high-low resistance ratio(OFF/ON)of ferroelectric tunnel junctions has been the main aspect in the study of ferroelectric tunnel junctions.In this paper,the ferroelectric tunnel junctions,which based on barium titanate(BaTi O₃,BTO)ferroelectric film and different electrode materials were prepared by pulsed laser deposition(PLD)and magnetron sputtering.We not only systematic research the impact of barrier on the resistive characteristics and OFF/ON ratio in the ferroelectric tunnel junctions by measuring the electrical performance of ferroelectric tunnel junctions,but also characterized the device performance of the ferroelectric tunnel junctions.The main contents are as follow:1.Two different top electrode ferroelectric tunnel junctions with structure of Pt/BTO(5 nm)/SRO and Ni/BTO were prepared on a(001)oriented single crystal barium titanate(STO)substrate by PLD and magnetron sputtering.Compare the difference in the OFF/ON ratios of the two tunnel junctions and obtain an OFF/ON ratio of more than 1000in the Ni/BTO/SRO tunnel junction.The improvement of the OFF/ON ratio of the Ni/BTO/SRO ferroelectric tunnel junction is attributed to the Ni oxidation at the Ni/BTO interface through comparing the barrier height fitting results by the direct tunneling model with the XPS measurement results.2.Select STO and BTO as the dielectric layer and ferroelectric barrier respectively,and transform the thickness of STO and the relative position of BTO with 2nm thickness to prepare Pt/STO(xnm)/BTO/SRO and Pt/BTO/STO(xnm)/SRO(x=0.8,1.3,1.8)composite barrier ferroelectric tunnel junction with different structures.The barrier model was obtained by fitting the I-V curve of each ferroelectric tunnel junctions via the direct tunneling model.Comparing the different structures of the ferroelectric tunnel junctions barrier model indicates that the average barrier height corresponding to the high resistance state is the main cause of the difference in OFF/ON ratio.An OFF/ON ratio of approximately 2000 was obtained in the best-structured composite barrier ferroelectric tunnel junction.In addition,the ferroelectric tunnel junctions have good device life and more big OFF/ON ratio.3.A Pt/BTO/NSTO semiconductor ferroelectric tunnel junction with 5 nm BTO barrier and diameter of 100 um Pt top electrodes was constructed by PLD and magnetron sputtering deposition and further research the memristive properties and electron transport mechanisms in this semiconductor ferroelectric tunnel junctions.The electrons pass through the barrier by a direct tunneling manner when the junction is in a low-impedance state.When the tunnel junction gradually changes from low resistance to high resistance under the action of external voltage,the electronics transport mechanism changes from direct tunneling to Schottky thermal emission due to the extra Schottky barrier formed at the BTO/NSRO interface.Apart from the above,an OFF/ON ratio of more than 10,000 and good device characteristics are obtained in this semiconductor ferroelectric tunnel junction.