| Popis: |
Oxide based RRAM memories are considered as potential candidates to replace floating gate memory devices [1-2] due to their proven low power operation , high switching speed [3] and compatibility with conventional CMOS back-end-of-line process. The working principle relies on the reversible change of the oxide layer’s resistance between two levels namely HRS (High Resistance State) and LRS (Low Resistance State). This resistance change has been widely attributed to the creation/reconstruction and rupture of a localized or multiple conductive filaments (CF) in the oxide layer. Various companies [4] and research laboratories [5] have adopted the HfOx solution as the active oxide layer that casts the memory effect. However, the process of the CF creation responsible for resistive switching and the oxide layer degradation are yet to be fully explored. In this paper we use first principles calculations to investigate Frenkel-Pair formation (FP) in HfO2 that play an important role in the CF creation. Depending on the electrode nature, its work function and reactivity with oxygen, we bring more insight into the FP formation leading to CF creation and device reliability. We show that oxygen active electrodes with low work function, like Ti, improve device reliability. Finally, endurance tests on a memory cell with Ti as top electrode were performed to assess cycling stability. Endurance up to 108 cycles, with optimized set conditions has been demonstrated. [1] H. Akinaga and H. Shima, Proc. IEEE, vol. 98, p. 2237, 2010.[2] V. Sriraman et al., IPCSIT, vol. 32, p.101, 2012 [3] B. Govoreanu et al., IEDM Tech. Dig., pp. 729-732, 2011 [4] Ch. Walczyk et al., J. Vac. Sci. Technol. B 29, 01AD02 (2011) [5] Y.S.Chen et al., IEDM Tech. Dig,pp. 31.3.1 - 31.3.4,2011. |
