Description:
Nano-ionic resistive memory devices are of significant interest as a high density storage-class memory, and well as in neuromorphic accelerator computing. For both of these applications, a key challenge is cycle to cycle (temporal) and device to device write variability. Highly uniform films with evenly distributed concentrations of oxygen vacancies are desired for this purpose. The switchable resistive properties of these resistive memory devices have been typically fabricated from sub-stoichiometric tantalum pentoxide using reactive sputtering of Tantalum metal with a mixture of Argon and Oxygen, which does not result in a highly uniform film. Alternatively, by using annealed stoichiometric atomic layer deposited films combined with a reducing metal layer a more uniform film is obtained, but the oxygen vacancy distribution cannot be precisely controlled. Using Ion Assisted Deposition (IAD), we have successfully made memristor devices with a significant improvement in yield and a significant reduction in device performance variability. The IAD deposition approach involves e-beam evaporation of tantalum metal with a reactive beam of argon and oxygen ions impinging upon the growing film. Using this technique, the oxide formation occurs at the substrate resulting in better control over film stoichiometry. IAD is a popular technique for the deposition of oxide thin films in the optical coating industry, but this is the first known usage of this technique for stoichiometry control of ReRAM thin films. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. Figure 1