We further explore the origin of this phenomenon by PF-01367338 in vivo employing a random circuit breaker (RCB) network model
[9, 12]. We show that ReRAM devices that have the same initial resistance would attain distinct initial filament distributions, which would finally result in very dissimilar resistive switching dynamics even when programmed with the same pulse schemes. Methods Fabrication of TiO2-based active cells In this study, we employed the following fabrication process flow. Firstly, 200-nm-thick SiO2 was thermally grown on a 4-in. silicon wafer. Then, e-gun evaporation was employed to deposit 5-nm Ti and 30-nm Pt that serve as adhesion and bottom electrode (BE) layers, respectively. The stoichiometric TiO2-based layer with a total thickness of 31 nm was then deposited by RF magnetron sputtering at 300 W and with an Argon gas flow of 30 sccm. Subsequently, a 30-nm-thick Pt top electrode (TE) film was deposited by e-gun evaporation. Optical lithography and lift-off process were adopted to define the patterns of each layer. The design allows having Pt/TiO2/Pt ReRAM structures in crossbars and stand-alone configurations. In this manuscript, the tested devices possess a stand-alone crossbar MK-1775 mw configuration with an active area QNZ concentration of 5 × 5 μm2. Electrical measurements Electrical measurements for active cells
on wafer were performed utilizing a low-noise Keithley 4200 semiconductor characteristic system (Keithley Instruments Inc., Cleveland, OH, USA) combined with a semi-automatic probe station (Wentworth AVT 702, Wentworth Laboratories, Inc., Brookfield,
CT, USA). During measurements, the programming voltage bias was applied to the TE, while keeping the BE grounded. The unipolar enough I-V characteristics were firstly attained via sweeping potentials from 0 to 5 V in steps of 0.1 V and then back to 0 V. To capture the switching dynamics of devices, a series of programming (5 V) pulses were applied across the active cells followed by a 0.5-V pulse to read the resistance values. The width durations for programming and evaluating pulses were set to 10 and 1 μs, respectively. In addition, the compliance current was set to 1 mA to avoid any hard breakdown of the devices. Modeling and simulations The active core of ReRAM was modeled with a two-dimensional 20 × 20 random circuit breaker (RCB) network. Within the network, the stoichiometric TiO2 was represented by high-valued resistors (8 MΩ), while the conductive TiO2-x was modeled by low-valued resistors (1 KΩ). To capture the simulated evolution of resistive state, a constant 0.5 V was applied to render the formation and rupture of filaments within the network. The RCB network was established on Matlab R2012b and then created in a PSPICE circuit. In each simulation cycle, Candence PSPICE 16.5 was called from Matlab to simulate the network with results being collected and analyzed utilizing Matlab.