Research On The Preparation And Storage Performance Of Metal/ferroelectric/semiconductor Ferroelectric Tunnel Junction

As a new emerging memory technology,ferroelectric tunnel junctions（FTJs）have attracted great attention recently due to the advantages of non-volatile data storage and non-destructivereadout.Adoptingsemiconductorasthebottomelectrode,metal/ferroelectric/semiconductor（MFS）-type FTJs have been proven to be effective to enhance the tunneling electroresistance（TER）given that the Schottky barrier in the semiconducting electrode can be effectively modulated in both width and height by the polarization reversal in the ferroelectric barrier.We adopt Pulsed Laser Deposition（PLD）to prepare the MFS-type FTJ devices with Pt/BaTi O₃/Nb:SrTiO₃ stacking structure and then carry out systematic investigation on the electroresistance performance by engineering the Schottky barrier through varing the Ba TiO₃thickness and the Nb doping concentration.The Schottky barrier profiles at the BaTiO₃/Nb:SrTiO₃interfaces are analyzed by transport and capacitance measurements.When the BaTiO₃ barrier is 4 unit cells（u.c.）in thickness and the Nb concentration is 0.1 wt%,we achieve the maximum TER ratio of¹0⁷ at room temperature,which is comparable to the ON/OFF current ratio of the mainstream Flash memories,indicating great potential of the MFS tunneling devices in the memory applications.As memory cells in integrated circuits,the devices are always working above room temperature due to the unavoidable self-heating effect.Thermal stability is an importance perfomance character for the FTJ devices.We therefore study temperature-dependent TER of the Pt/BaTiO₃/Nb:SrTiO₃ FTJs,from 300 up to 513 K.Although the TER perfomance degrades with increasing temperature,the Pt/Ba TiO₃/Nb:SrTiO₃ device can maintain a high ON/OFF ratio of³×10⁵ at 383 K（higher than the work temperature of semiconductor memories,³58 K）and exhibit the typical hysteresis characteristics in resistance-voltage loops up to 513 K.These results indicate excellent high-temperature endurance of the MFS-FTJs.The reduction of the TER perproties are studied with the development of the transport and the capacitance characterics,associated with the decrease of polarization in the Ba TiO₃ barrier with increasing temperature.In addition,the two terminal architecture of the FTJs makes the integration of these devices into the passive crossbar memory arrays possible.The FTJ devices therefore can achieve ultrahigh density of data storage with the simple and efficient circuit structure of crossbar arrays.However,sneak leakage is an inherent problem of the passive crossbar arrays.The complementary resistive switch（CRS）concept has been proposed to suppress the sneak current as the binary"0"and"1"storage states have similar resistance values close to the high resistance state of conventional resistive cells.But the CRS scheme also introduces a new problem of destructive readout since the complementing storage states cannot be distinguished with each other due to the resistor-like symmetric current-voltage character.Note that the MFS FTJs have typical rectifying characteristics in transport,we propose a new CRS device by connecting two Pt/Ba TiO₃/Nb:SrTiO₃ elements antiseriesly.In the Pt/BaTiO₃/Nb:SrTiO₃ CRSes,the two complementing states exhibit rectifying current-voltage curves with opposite rectification direction,enabling the non-destructive readout.Besides,the sneak current are significantly limited in the MFS-type CRS devices and,correspondingly,the maximum scaling size of crossbar array is enhanced by above two orders of magnitude.