Study of SiOx-based Complementary Resistive Switching Memristor

Yao-Feng Chang (a, Yen-Ting Chen (a, Fei Xue (a, Yanzhen Wang (a, Fei Zhou (a, Burt Fowler (b and Jack C. Lee (a

a. Microelectronics Research Center, Department of Electrical and Computer Engineering,

The University of Texas at Austin, Austin, Texas 78758 USA.

b. PrivaTran, LLC, 1250 Capital of Texas Highway South, Bldg 3, Ste 400, Austin TX 78746 USA.

Phone: 512-221-9610, email: yfchang@utexas.edu

The electrical characteristics of SiOx-based complementary resistive switching (CRS) memristor have been investigated. Post-deposition annealing (PDA: 500°C 5min in O2) of TaNIS i02/n++ Si-substrate CRS memristor has been found to reduce operational variation in device characteristics, as well as improve the electrical stability during repeated switching. In this work, we have also studied the effects of sweeping polarity, operating temperature, electrode material and dimension scaling. Our experimental results not only provide additional insights into optimization of the SiOx-based CRS memory but also help in constructing a physical picture for the switching mechanism.

The schematic cross section and process flow of a SiOx-based CRS memristor are shown in Fig. l. The electroforming process was performed by ramping applied bias from OV to about 15V. A typical CRS operation with repeated cycling (30 times) for devices undergone a PDA anneal is shown in Fig. 2. The electrical stability of memory window (i.e. low resistance statel high resistance state (LRS/HRS) current ratio @ 0.2V) has been found to improve significantly for devices with PDA anneal (see Fig. 3). Also, the CRS memory window was maintained at least one order of magnitude and without degradation during cycling for each polarity sweeping. Note that the HRS current and the reset voltage values are larger in the negative reset operation than in the positive operation, but they are found to be independent with the set process polarities (Fig. 3). However, the reset current values were found to exhibit an opposite trend (Fig. 4). According to previous studies [1], the Si nano-filaments would be formed at the device edge after an electroforming process. The current-induced Joule heating energy [2] and asymmetric thermal conductivity between top TaN electrode and bottom n++ Si-substrate [3] indicate that the resistive switching occurs at the cathode rather than the anode side.

Comparing to the TaN electrode CRS memristors, the memory window of the poly-Si top electrode devices exhibit less stable CRS behavior (see Fig. 5). The temperature dependence for the TaN electrode devices suggests semiconductor-type current transport for both HRS and LRS (Fig. 5). Higher temperature would accumulate resistive switching reaction in the CRS behaviors [2]. By scaling the device area, the reset current has been reduced to the sub-1 OOuA regime (Fig. 6). The results indicate that SiOx-based CRS memristors hold good promise for the future nonvolatile memory applications.

In conclusion, CRS behaviors have been demonstrated with TaN/Si02/n ++ Si-substrate memristor structure. Post-deposition anneal (PDA) treatment has been used to improve electrical characteristics and device stability. Moreover, by detailed analysis of the switching characteristics, it has been found that resistive switching occurs at the cathode side. This could be due to asymmetric thermal dissipation with two different materials. Electrode and temperature effect indicate that TaN is a suitable electrode for the SiOx-based CRS memristor and thermal switching reaction may be responsible for CRS operation. Our results suggest that SiOx-based CRS memristors hold good promise for future resistive switching memory.

[1] J. Yao et aI., Nano Lett., vol. 10, p. 4105 (2010) [2] U. Russo et aI., IEDM Tech. Dig, p. 775, (2007). [3] E. B. Grayeli et al.,Appl. Phys. Lett. , vol. 99, p. 261906 (2011)

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