Record 9nm half-pitch functional Transition-Metal-Oxide based Resistive Random Access Memory (TMO-RRAM) cell and the lowest reported 1A programming current (I prog , both Set and Reset) have been achieved with thermally oxidized sub-stoichiometric WO x and Nano Injection Lithography (NIL) technique [1]. The unexpectedly low programming current at 9nm diameter has been examined in-depth, it offers potential for scaling low power non-volatile memory. This small device shows Reset/Set resistance ratio around 10, stability during read operation, and good data-retention. A switching mechanism based on oxygen-ion dynamics can account for the observed device characteristics as discussed in this work.
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.
By using sidewall electrode technology, both record small functional TiO 2 selection device (1 × 5 nm 2 ) and HfO 2 based RRAM device (1 × 3 nm 2 ) were for the first time successfully demonstrated in this work, improving the understanding of the switching mechanism in an ultra-small, functional resistive random access memory (RRAM) device. The tunneling based low temperature back-end selection devices show high driving current density of > 10 MA/cm 2 and selectivity of > 10 3 . The pulse driven cycle endurance of sub-5nm selection device and RRAM device reaches 10 6 and 10 3 , respectively. Well controlled TiO 2 barrier produced with conformal plasma oxidation exhibits tight uniformity. The 1 × 3 nm 2 RRAM device exhibited an excellent performance, featuring a large on/off verified window (>100), and reasonable reliability (stress time > 10 3 s). Furthermore, the 1 × 3 nm 2 RRAM device exhibited distinctive unipolar behavior when a high voltage and rapid switching operation (7 V, 50 ns) were applied. We also study on double oxide layer device and propose a physical mechanism picture to compare with previous study. This technology demonstrates the potential of future atomicscale memories.
A sidewall electrode technology was successfully developed for the first time in this study, improving the understanding of the working mechanism in an ultra small, functional HfO 2 -based resistive random access memory (RRAM) device (< 1 × 3 nm 2 ). This technology exhibits potential for application in atomic-scale memories. The 1 × 3 nm 2 RRAM device exhibited an excellent performance, featuring a high endurance of more than 10 4 cycles, a large on/off verified window (>100), and reasonable reliability (stress time > 10 3 s, 2 × 10 4 h at 250 ℃). Furthermore, the 1 × 3 nm 2 RRAM device exhibited distinctive unipolar behavior when a high voltage and rapid switching operation (7 V, 50 ns) were applied, and a switching mechanism model is proposed.
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