Resistive switching and data reliability of epitaxial (Ba,Sr)TiO3 thin films

Abstract

We report on resistive switching of capacitor-like SrRuO 3 /Ba 0.7 Sr 0.3 TiO 3 / Pt thin films epitaxially grown on SrTiO 3 substrates. We observe a weak but stable hysteresis in the current-voltage curve. By applying short voltage pulses, a high or low resistive state as well as intermediate states can be addressed even at room temperature. We demonstrate a multiple-branch hysteresis curve corresponding to multilevel switching modus revealing different subloops for different write voltages. Furthermore reliability issues such as cycling endurance and data retention are presented. 10 Here, different resistance levels could be addressed by a variation of length and amplitude of the programming voltage pulse. There is still some debate about the physical mechanisms of the resistance change and about the key experimental parameters. Mechanisms under discussion are ͑i͒ trapping/detrapping effects and charge transfer processes via donor and acceptor levels ͑Cr 3+ /Cr 4+ ͒, 10,13 ͑ii͒ a Mott metal-insulator transition, 14 ͑iii͒ formation of local current domains, 12 ͑iv͒ redox processes of extended defects, 15 and ͑v͒ conductivity changes due to a reversal of a local spontaneous polarization. 16 Polarization changes might not be stringently of ferroelectric nature, but might also be due to defect dipoles, e.g., formed by acceptor/oxygen vacancy defect associates. 17 In our present work, we investigate resistive switching of 0.2% chromium-doped Ba 0.7 Sr 0.3 TiO 3 ͑BST͒ capacitorlike thin films of around 40 nm thickness at RT. We investigate in detail multibranch type I͑V͒ curves, which have not been reported for perovskites dielectrics so far. We will present detailed measurements of the multilevel switching and focus on reliability issues such as cycling endurance and data retention.SrRuO 3 ͑SRO͒ bottom electrodes of 100 nm thickness and BST layer of 40 nm thickness are grown in situ epitaxially on single crystalline ͑100͒ oriented SrTiO 3 ͑STO͒ substrates. The films are deposited by pulsed laser ablation while maintaining a substrate temperatur of 700°C and an oxygen base pressure of 0.25 mbar. The epitaxial growth of the bilayers is confirmed by x-ray diffraction measurements ͓Phil-ips PW 3020 ͑Cu K␣͔͒. Pt top electrodes are deposited by sputtering and patterned by optical lithography and a lift-off process to areas of 0.09 mm 2 down to 100 m 2 . The bottom electrode is contacted after removing the BST film from the sample edge by wet chemical etching. A postannealing step in oxygen is performed at 700°C for 5 min. The currentvoltage characteristics are measured with a Keithley 2410 source meter. To protect samples from damages due to high currents a current compliance is used. All samples reveal low initial resistances so that a high voltage treatment prior to quasistatic I͑V͒ characterization or pulse measurements to convert the sample from an insulating state into a low conductive state as described in Ref. 11 for SrTiO 3 single crystals ͑"forming process"͒ is not required here. The stable switching behavior r...

Nonvolatile resistive switching in graphene oxide thin films

“…Most materials, for example, NiO, TiO 2 , ZnO, CuO, and SrTiO 3 etc. Do et al, 2008;Chang et al, 2008;Fujiwara et al, 2008;Oligschlaeger et al, 2006), have already been reported to be in need of Forming process. It is necessary to find some solutions to overcome this difficulty.…”

Impact of the electroforming process on the device stability of epitaxial Fe-doped SrTiO3 resistive switching cells

“…Unlike to samples with a low initial resistance which typically do not need a stressing dc-forming treatment, 25,26 the investigated devices with Pt electrodes require an electroforming step to set the sample to a low resistance state.…”

“…In addition, the drift can be avoided by the use of samples with thinner films which typically need only a short or no forming process. 10,25,26 Furthermore, it has to be mentioned that only small resistance drifts were observed for devices which were subsequently switched after the forming treatment to the HRS or LRS, respectively ͑not shown here͒. This can be understood by regarding the oxygen gradients induced by the two different processes ͑electroforming and resistive switching͒.…”

Improved endurance behavior of resistive switching in (Ba,Sr)TiO3 thin films with W top electrode

“…However, the W/BST/SRO device uniformity is greatly improved and all 40 measured pads show stable resistive switching, which is much higher than the devices with Pt top electrodes, about 58% and 40% as reported previously. 9 The R off / R on of the W/BST/SRO device, readout at 0.5 V, remains about 6 for 1000 cycles, while the R off / R on of the Pt/BST/SRO device already decreases from about 6 to 1.3 after 100 cycles. and LRS and the memory window is closed after 2000 cycles ͓Fig.…”

“…[7][8][9] Several models have been proposed to explain the mechanism. [10][11][12] Even though the exact microscopic mechanisms are still under controversial discussion, there exists a general agreement that the migration of oxygen ions under an applied electric field plays a key role.…”