Resistive Switching Device Technology Based on Silicon Oxide for Improved ON–OFF Ratio—Part II: Select Devices

Abstract

The cross-point architecture for memory arrays is widely considered as one of the most attractive solutions for storage and memory circuits thanks to simplicity, scalability, small cell size, and consequently high density and low cost. Cost-scalable vertical 3-D cross-point architectures, in particular, offer the opportunity to challenge Flash memory with comparable density and cost. To develop scalable cross-point arrays, however, select devices with sufficient ON-OFF ratio, current capability, and endurance must be available. This paper presents a select device technology based on volatile resistive switching withCu and Ag top electrode and silicon oxide (SiO x ) switching materials. The select device displays ultrahigh resistance window and good current capability exceeding 2 MAcm −2 . Retention study shows a stochastic voltage-dependent ON-OFF transition time in the 10 µs-1 ms range, which needs to be further optimized for fast memory operation in storage class memory arrays. Index Terms-Conductive bridge RAM (CBRAM), cross-point array, select device, silicon oxide, storage class memory, volatile switching. I. INTRODUCTIONC ROSS-POINT arrays represent a promising architecture to compete with Flash memories in terms of density and bit cost. In a cross-point array, every memory element is located at the intersection between a row and a column electrode wire, therefore achieving a minimum device size of 4F 2 , where F is the minimum lithographic feature. Cross-point arrays were proposed for resistive switching (RS) memory (RRAM) [1]-[3] and phase change memory (PCM) [4], [5], both benefitting from a relatively large resistance window and

Volatile Resistive Switching Memory Based on Ag Ion Drift/Diffusion—Part II: Compact Modeling

“…Fig. 6(a) shows the measured and calculated switching voltages, namely, V T+ , V H+ , V T− and V H− , as a function of I C [27]. The calculation results agree with the experimental data in the broad range from 0.1 to 80 μA.…”

“…DC Characteristics Fig. 5(a) shows the structure of the volatile RRAM with Ag/SiO x /C stack and a select transistor to control the maximum current, namely I C [27]. The thickness of the dielectric layer was L = 5nm.…”

“…Also note that, due to the asymmetric device structure shown in Fig. 5(a), switching voltages are typically smaller for negative voltage than for positive voltage [27]. To describe this effect, different values of E bulk and α were used in the model as summarized in Table I.…”

Switching Kinetics Control of W‐Based ReRAM Cells in Transient Operation by Interface Engineering

“…For the (Pt/HfO 2 /W) Set (cycle in Figure a), a positive voltage of 2.8 V is required, while for the Reset operation, the memory switches from LRS to HRS showing two intermediate steps at −0.9 and −1.5 V with a high overshoot current. Reset current overshoot is caused due to the large value of the V Set that makes the fast current rising (in range of few μs) before the current limiting tool can overcome the voltage drop across the circuits . Moreover, this device tends to show high current fluctuation through the Set operation before the abrupt Set occurs.…”

Stochastic Memory Devices for Security and Computing

“…The stochastic behavior of t D is a consequence of the ion migration in RRAM being dependent on the local microstructure and atomistic migration of ions. [132] In this type of devices, the Ag migration from the TE results in the formation of an unstable CF, which decays soon after the set transition with a retention time ranging from few µs to few ms. [133][134][135][136] The volatile behavior is the result of the large diffusivity of Ag combined with the mechanical compressive stress in the dielectric layer [137] and the tendency to minimize the surface to volume ratio of the CF. This can be explained by the set transition being a thermally activated process to overcome an energy barrier E A which controls the time constant according to the Arrhenius law τ = τ 0 exp (E A /kT), where τ 0 is a constant, k is the Boltzmann constant, and T is the local temperature.…”