We report a 3-D-stackable 1S1R passive cross-point resistive random access memory (RRAM). The sneak (leakage) current challenge in the cross-point RRAM integration has been overcome utilizing a field-assisted superlinear threshold selector. The selector offers high selectivity of >10 7 , sharp switching slope of <5 mV/decade, ability to tune the threshold voltage, stable operation at 125°C, and endurance of >10 11 . Furthermore, we demonstrate 1S1R integration in which the selectorsubthreshold current is <10 pA while offering >10 2 memory ON/ OFF ratio and >10 6 selectivity during cycling. Combined with self-current-controlled RRAM, the 1S1R enables high-density and high-performance memory applications.Index Terms-1S1R, cross-point memory, resistive random access memory (RRAM), select device, selectivity, sneak path.

Starting with the 4ϫ4 Luttinger-Kohn Hamiltonian, we develop a scattering-matrix approach to study coherent hole transport through the valence-band energy profile across the emitter-base junction of typical abrupt and graded Pnp heterojunction bipolar transistors. The tunneling and reflection coefficients of heavy and light holes are calculated for the upper and lower 2ϫ2 Hamiltonians obtained through a unitary transform of the 4ϫ4 Luttinger-Kohn Hamiltonian. The probability for a transition from heavy ͑light͒ to light ͑heavy͒ hole while tunneling across the emitter-base junction is calculated as a function of the value of the wave vector parallel to the emitter-base heterointerface for both abrupt and graded heterojunctions. For holes injected from the emitter into the base, the probability of heavy-to light-hole conversion is shown to be quite different when calculated with the upper and lower Hamiltonians. On the other hand, the probability of light-to heavy-hole conversion is nearly the same for the upper and lower Hamiltonians. The energy dependence of the heavy-and light-hole tunneling coefficients is shown to be quite different from those calculated using a parabolic-band model, in which the effects of mixing and anisotropy in the valence band are neglected.

Organic bistable memory devices were fabricated by embedding a thin layer of molybdenum trioxide (MoO) between two tris-(8-hydroxyquinoline)aluminum (Alq) layers. The device exhibited excellent switching characteristics with an ON/OFF current ratio of 1.15 × 10 at a read voltage of 1 V. The device showed repeatable write-erase capability and good stability in both the conductance states. These conductance states are non-volatile in nature and can be obtained by applying appropriate voltage pulses. The effect of MoO layer thickness and its location in the Alq matrix on characteristics of the memory device was investigated. The field emission scanning electron microscopy (FE-SEM) images of the MoO layer revealed the presence of isolated nanoparticles. Based on the experimental results, a mechanism has been proposed for explaining the conductance switching of fabricated devices.

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