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

Abstract

In this work, the results of our detailed investigations on the electroforming procedure in Pt/SrTi0.99Fe0.01O3/SrTi0.99Nb0.01O3 [Pt/STO(Fe)/Nb:STO] metal-insulator-metal (MIM)-devices and its impact on the performance of resistive switching memory devices are presented. Questions about the exact location of the modifications triggered by the electroforming procedure within the investigated MIM-devices will be addressed. From a technological point of view, the thermal stability of formed devices becomes important. An increase in the device resistances during retention measurements has been observed indicating the presence of internal redistribution effects. These may result from an oxygen vacancy gradient induced by the forming process. However, these internal relaxation effects will not end up in the unformed state. Annealing experiments under defined atmospheric conditions allowed distinguishing between internal and external rediffusion effects. We found that SrTiO3 starts to interact with the surrounding atmosphere at moderate temperatures. The occurring external reoxidation effect set the device back to its initial (unformed) state. As a result, the investigated MIM-structures can no longer be regarded as closed systems and presented the large implication on the retention of such devices. The experimental findings are supported by calculations of the penetration depth of oxygen ions/vacancies in SrTiO3.

Enhanced carrier density in Nb-doped SrTiO3 thermoelectrics

“…1-3 Strontium titanate (SrTiO 3 ; STO) is one of the most widely used cubic perovskite oxides, owing to its chemically and compositionally stable structure and small lattice mismatch with other perovskite oxides. [4][5][6] It finds a wide range of applications in non-volatile resistive switching memories, 7,8 field effect transistors, 9 and memory storage devices. 10 The electronic structure of STO as obtained by reflectivity measurements reveals a band insulator with a bandgap of 3.2 eV at room temperature.…”

Probing the oxygen vacancy distribution in resistive switching Fe-SrTiO3 metal-insulator-metal-structures by micro-x ray absorption near-edge structure

“…1,2 The key role of oxygen nonstoichiometry and oxygen-deficient oxide-phases as the underlying mechanism of the resistance change has been recognized for many different oxide systems (e.g., TiO 2 , 3,4 Ta 2 O 5 , 5 SrTiO 3 . 6 It is becoming widely accepted that the resistance switching process in SrTiO 3 is related to the movement of oxygen vacancies and the associated electron doping. The mechanism of electroforming in Pt/Fe: SrTiO 3 /Nb:SrTiO 3 metal-insulator-metal (MIM) structures suggested by Menke et al 6 proposes the local bypassing of the interfacial Schottky-type barrier by oxygen-deficient filaments forming along extended defects.…”

“…6 It is becoming widely accepted that the resistance switching process in SrTiO 3 is related to the movement of oxygen vacancies and the associated electron doping. The mechanism of electroforming in Pt/Fe: SrTiO 3 /Nb:SrTiO 3 metal-insulator-metal (MIM) structures suggested by Menke et al 6 proposes the local bypassing of the interfacial Schottky-type barrier by oxygen-deficient filaments forming along extended defects. It is assumed that the films are already oxygen deficient after deposition.…”

Band alignment at memristive metal-oxide interfaces investigated by hard x-ray photoemission spectroscopy

“…While using a noble metal electrode (such as Pt) results in a high initial resistance that needs to be irreversibly lowered to enable resistive switching (called electroforming) [12], the use of a reactive electrode (e.g., Ti) can remove the need for electroforming through a chemical reduction of the oxide [8,13]. Concomitantly to the chemical reduction, the electronic properties of an insulating oxide and especially of the metal/oxide interface can be strongly influenced by the creation of point defects as localized electronic states, or self-doping via shallow donor states close to the conduction band [14][15][16].…”