Electrical Properties Of Ferroelectric Tunnel Junctions Based On The Different Thickness BaTiO₃Films

Ferroelectric tunnel junctions (FTJs) is composed of two metal electrodessandwiched with an ultrathin ferroelectric barrier inside. According to the differentpolarization direction, FTJs can have different tunneling electrical contactresistance to realize nondestructive read of stored information. However, how torealize the ultra-thin ferroelectric tunnel junctions is always many scholars to solvethe problem. Meanwhile, in addition to the nature of the ferroelectric material itself,Electrode materials and the strength of the interface coupling effect betweenferroelectric materials has important effects on electrically induced resistance.The Thomas-Fermi block length difference of two electrodes is larger, thehigher electric resistance effect. Therefore, in this article, Single-crystalline0.7wt%Nb-doped SrTiO3is chosen as the semiconductor substrate. The BaTiO3ferroelectric film was prepared by pulsed laser deposition (PLD). By polarization ofBaTiO3to Nb: SrTiO3charge control interface change the barrier height and widthto improve TER values and explore the ferroelectric device function parameters oftunnel junctions. The main research works are summarized as follows:First, the structure of Nb:SrTiO3/BaTiO3/Pt with a20nm thick BaTiO3wasdeposited by PLD and Magnetron Sputtering. Whereafter, the tunnel junctions wasprepared by Ultraviolet Lithography. Because of the Nd:SrTiO3is n-typesemiconductor. When the ferroelectric polarization of BaTiO3points to Nd:SrTiO3,a large amount of negative bound charges will emerge in Nd:SrTiO3interface,leading to the reduce on height and the width of the barrier. However, as thepolarization is reversed, pointing to Pt, a large amount of positive bound chargeswill emerge in Pt interface. Therefore,the height and the width of the barrier will beincreased. Thus, Tunneling electrical resistance value can reach10000%.Second, the Nd:SrTiO3/BaTiO3/Pt tunnel junctions with a3nm thick BaTiO3has been deposited on Nd:SrTiO3substrates by PLD. Through the tunnel junctionsR-V curve test show that the resistance of the tunnel junctions has asymmetrichysteresis curve under different voltage polarization. Namely, the tunnel junctionshas nonvolatile resistance transformation characteristics. By the retention propertymeasurements, there is no significant reduction in the resistance contrast within10000s.These suggest the Pt/BTO/Nd:SrTiO3FTJs is good reproducibility anduniformity.Third, the Nd:SrTiO3/BaTiO3/SrRuO3tunnel junctions has been producted andresearched the electrical characteristic of the tunnel junctions. Because of BaTiO3 different polarization direction on the Nd:SrTiO3interface to improve, making thestructure also has a high electrical resistance change effect. But, due to the shieldingcharge difference between Nd:SrTiO3to SrRuO3and Nd:SrTiO3to Pt, so that theNd:SrTiO3/BaTiO3/SrRuO3tunnel junction resistance effect is small.In summary, we have fabricated ultrathin ferroelectric tunnel junctions. Thetransport property of ferroelectric tunnel junctions with different electrode materialswas studied. We found that the strength of the interface effect between electrodepotential and iron base has a strong influence on tunnel junctions resistance. Thegreater the difference of two electrode resistivity, tunnel junctions of electricalresistance change effect more apparent.