Proton exchange reactions in SiO_x-based resistive switching memory: Review and insights from impedance spectroscopy

In this work, the AC admittance and conductance of non-polar SiO_x-based resistive switching memory devices is measured as a function of temperature to investigate charge transport and potential switching mechanisms. After electroforming using a forward/backward voltage scan, devices were measured over the frequency range of 1 k–1 MHz and the temperature range of 200–400 K. For temperature (T) > 300 K, AC conductance follows σ(ω) = Aω^s, where s is linearly dependent on temperature and close to, but less than, unity. For T < 300 K, σ(ω) is almost temperature-independent with s ∼ 1. A classical hopping model and AC impedance spectroscopy measurements are found to provide reasonable explanations of the experimental data. Defect concentration is estimated to be 1–5 × 10¹⁹ cm⁻³ and independent of device resistive state when modeling charge transport using a polaron hopping characteristic. The energy barrier to electron hopping is estimated to change from 0.1 eV to 0.6 eV and the average hopping distance varies from 1 nm to 6 nm when the device is switched between low- and high-resistance states, respectively. Device switching mechanisms are modeled by simple proton exchange reactions that both activate and deactivate the defects involved in change transport. The impedance spectroscopy results supporting hole-like polaron hopping and the values obtained for the physical parameters provide additional insights into the fundamental mechanisms of SiO_x-based resistive memory. Uniform switching performance with robust high temperature reliability and fast operating speed demonstrate good potential for future nonvolatile memory applications.