**3. Interface-type switching**

The interface type switching is usually of uniform nature and shows area scalable characteristics. ReRAMs devices utilizing metal oxides (initially semiconductor or conductor) are frequently governed by interface type switching phenomena. Such a resistive switching behavior is primarily observed at the metal oxide and electrode interface. In this context, Baikalov *et al*. [1] investigate the resistance behavior of theperovskite oxide based memory devices. It has been demonstrated that an applied electric field significantly modifies the value of contact resistance measured among perovskite oxide and metal electrode. In order to understand the interface type resistive switching, many groups of researchers have given effort to establish different models for switching mechanism. These models are framed using ionic point defects (oxygen vacancies) and their drifted movement or electromigration within the metal oxide materials [1–5]. Some of the models are based on the formation of charge carrier i.e. electrons and/or holes trapping at defect sites [6] and observation of Mott transitions taking place at the interfaces [7, 8]**.** In the case of ReRAMs, low resistance value (in the range of kΩ) as well as the extended retention behavior (in the range of years) are realized in terms of models based on the modification of atomic or ionic configurations. Therefore, ionic and electronic mechanisms are used to examine the resistive switching characteristics and its origin at microscopic level. For ReRAMs, the interface type resistive switching is primarily predicted to dominant if the resistance of device scales with area. Therefore, Nb-doped SrTiO3 is governed by interface type switching whereas filament based resistive switching prevails in NiO based memory cells [9, 10].

In case of valence change memory (VCM) devices, the resistive-switching phenomenon is understood by the chemical reactions and events taking place near or at the interface of metal electrode and oxide. While characterizing such VCM devices through spectroscopic techniques, the interface related switching behavior is investigated after averaging the area which essentially eliminates the need of any optical arrangements for focusing and/or magnification. The predefined interface dependent switching helps to designate the localized resistive switching phenomenon ascribed to CFs. Due to such interface i.e. thin oxide layer developed between insulator oxide and reactive metal electrode, the external stimuli driven electrochemical modification of interface considerably affects the performance of device. It is known that devices fabricated with reactive electrodes and insulating oxide materials show redox type reactions inducing movement of oxygen towards metal electrode (**Table 1**).


#### **Table 1.**

*Comparison of different parameters for interfacial type RS devices.*
