Pulse width and height modulation for multi-level resistance in bi-layer TaOx based RRAM

Mutli-level switching in resistive memory devices enables a wide range of computational paradigms, including neuromorphic and cognitive computing. To this end, we have developed a bilayer tantalum oxide based resistive random access memory device using Hf as the oxygen exchange layer. Multiple, discrete resistance levels were achieved by modulating the RESET pulse width and height, ranging from 2 k Omega to several M Omega. For a fixed pulse height, OFF state resistance was found to increase gradually with the increase in the pulse width, whereas for a fixed pulse width, the increase in the pulse height resulted in drastic changes in resistance. Resistive switching in these devices transitioned from Schottky emission in the OFF state to tunneling based conduction in the ON state, based on I-V curve fitting and temperature dependent current measurements. These devices also demonstrated endurance of more than 10(8) cycles with a satisfactory R-off/R-on ratio and retention greater than 10(4) s. Published by AIP Publishing.