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A 3D stackable and bidirectional Threshold Vacuum Switching (TVS) selector using the same WO x material as the RRAM element is reported. It provides the highest reported current density of >10 8 A/cm 2 and the highest selectivity of >10 5 . Stress test at high current density indicates >10 8 cycle capability for Reset/Set operation. A mechanism based on recombination of oxygen-ions and vacancies is proposed for the observed volatile switching of TVS. Utilizing the threshold characteristics of the TVS selector, a two-step reading waveform offers potential for 3D-stackable and 4F 2 cross-point RRAM applications. I. IntroductionAs a 3D non-volatile memory technology, RRAM is attractive and much investigated in the recent decade [1-5, 10]. For future 3D-stackable 4F 2 memory array applications, a selector device with high current density and high selectivity is required. Fig. 1 [6-9] shows the current density and selectivity of various selectors reported in recent years and of this study. Driving current non-linearity is usually manipulated by back-end process changes. This paper reports a novel 3D stackable and bidirectional threshold switching with record high current density and selectivity.In this work, a CMOS compatible and 3D stackable RRAM structure with TVS selector and TMO memory is demonstrated. Contrary to reported selectors with current non-linearity manipulation, we show for the first time a novel bidirectional threshold switching. Based on threshold characteristics of TVS, suppression of sneak current by a two-step read scheme of cycle waveform offer attractive features for high-density RRAM applications.

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