Low Power RRAM with Improved HRS/LRS Uniformity through Efficient Filament Control Using CVS Forming

Resistance change memory (RRAM) based on transition metal oxides (TMO), whose operation is based on the change in resistivity of a conductive filament in the oxide material, has attracted a lot of attention in recent years due to its promise of high density, speed, and retention. However, achieving a low power operation and high device-to-device uniformity of the cell resistance states are the major challenges for practical applications of the RRAM technology. While some progress has been made on the understanding of the switching mechanism of TMO memory devices [1], lack of precise control over the filament formation, perceived to be a random process, which inturn introduces randomness into the switching characteristics ofthis class of devices, complicates further progress. This studydemonstrates a forming methodology, which addresses the abovediscussed issues by performing a forming operation under theconstant voltage stress (CVS) condition at lower voltages ratherthan by the conventionally used fast voltage ramp method. Thisapproach is shown to lower the reset current, increase resistivityof the low and high resistive states (LRS, HRS) and improvedevice to device uniformity in the HfO2-based RRAM devices.