D. C. Gilmer

Metal oxide resistive memory switching mechanism based on conductive filament properties

By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament (CF) features controlling TiN/HfO2/TiN resistive memory (RRAM) operations. The leakage current through the dielectric is found to be supported by the oxygen vacancies, which tend to segregate at hafnia grain boundaries. We simulate the evolution of a current path during the forming operation employing the multiphonon trap-assisted tunneling (TAT) electron transport model. The forming process is analyzed within the concept of dielectric breakdown, which exhibits much shorter characteristic times than the electroforming process conventionally employed to describe the formation of the conductive filament. The resulting conductive filament is calculated to produce a non-uniform temperature profile along its length during the reset operation, promoting preferential oxidation of the filament tip. A thin dielectric barrier resulting from the CF tip oxidation is found to control filament resistance in the high resistive state. Field-driven dielectric breakdown of this barrier during the set operation restores the filament to its initial low resistive state. These findings point to the critical importance of controlling the filament cross section during forming to achieve low power RRAM cell switching.

Resistive Switching by Voltage-Driven Ion Migration in Bipolar RRAM—Part II: Modeling

Resistive-switching memory (RRAM) based on transition metal oxides is a potential candidate for replacing Flash and dynamic random access memory in future generation nodes. Although very promising from the standpoints of scalability and technology, RRAM still has severe drawbacks in terms of understanding and modeling of the resistive-switching mechanism. This paper addresses the modeling of resistive switching in bipolar metal-oxide RRAMs. Reset and set processes are described in terms of voltage-driven ion migration within a conductive filament generated by electroforming. Ion migration is modeled by drift–diffusion equations with Arrhenius-activated diffusivity and mobility. The local temperature and field are derived from the self-consistent solution of carrier and heat conduction equations in a 3-D axis-symmetric geometry. The model accounts for set–reset characteristics, correctly describing the abrupt set and gradual reset transitions and allowing scaling projections for metal-oxide RRAM.

Resistive Switching by Voltage-Driven Ion Migration in Bipolar RRAM—Part I: Experimental Study

Resistive-switching random access memory (RRAM) based on the formation and the dissolution of a conductive filament (CF) through insulating materials, e.g., transition metal oxides, may find applications as novel memory and logic devices. Understanding the resistive-switching mechanism is essential for predicting and controlling the scaling and reliability performances of the RRAM. This paper addresses the set/reset characteristics of RRAM devices based on

Grain boundaries as preferential sites for resistive switching in the HfO2 resistive random access memory structures

\hbox{HfO}_{x}

Multiple Memory States in Resistive Switching Devices Through Controlled Size and Orientation of the Conductive Filament

. The set process is analyzed as a function of the initial high-resistance state and of the current compliance. The reset process is studied as a function of the initial low-resistance state. Finally, the intermediate set states, obtained by set at variable compliance current, and reset states, obtained by reset at variable stopping voltage, are characterized with respect to their reset voltage, allowing for a microscopic interpretation of intermediate states in terms of different filament morphologies.

Metal oxide RRAM switching mechanism based on conductive filament microscopic properties

Resistive switching (RS) phenomenon in the HfO2 dielectric has been indirectly observed at device level in previous studies using metal-insulator-metal structures, but its origin remains unclear. In this work, using the enhanced conductive atomic force microscope (ECAFM), we have been able to obtain in situ direct observation of RS with nanometric resolution. The ECAFM measurements reveal that the conductive filaments exhibiting the RS are primarily formed at the grain boundaries, which were shown exhibiting especially low breakdown voltage due to their intrinsic high density of the oxygen vacancies.

Low power operating bipolar TMO ReRAM for sub 10 nm era

Multilevel operation in resistive switching memory (RRAM) based on HfOx is demonstrated through variable sizes and orientations of the conductive filament. Memory states with the same resistance, but opposite orientation of defects, display a different response to an applied read voltage, therefore allowing an improvement of the information stored in each physical cell. The multilevel scheme allows a 50% increase (from 2 to 3 bits) of the stored information.

Analytical Modeling of Oxide-Based Bipolar Resistive Memories and Complementary Resistive Switches

By combining electrical, physical, and transport/atomistic modeling results, this study identifies critical conductive filament features controlling TiN/HfO2/TiN resistive memory operations. The forming process is found to define the filament geometry, which in turn determines the temperature profile and, consequently, the switching characteristics. The findings point to the critical importance of controlling filament dimensions during the forming process (polarity, max current/voltage, etc.).

Complementary Switching in Oxide-Based Bipolar Resistive-Switching Random Memory

The bottle neck of ReRAM (Resistive RAM) for post-NAND storage application is high operational current [1,2]. Herein, we report a method to acquire low operational currents from a hetero structure ReRAM (AlOx/TiOx). The mechanism study of the hetero structure ReRAM reveals that the AlOx layer as a tunnel barrier is critical for switching, and thus switching parameters are governed by the properties of the AlOx layer. By tuning tunnel oxide properties along with adopting 5 nm sized “Dash BE” [3], operational currents of ≤ 10 µA have been achieved from this hetero structure device.

Methodology for the statistical evaluation of the effect of random telegraph noise (RTN) on RRAM characteristics

To allow for novel memory and computing schemes based on the resistive switching memory (RRAM), physically based compact models are needed. This paper presents a new analytical model for HfO2-based RRAM, relying on a simplified description of the conductive filament (CF) in terms of its diameter and gap length. The set and reset operations are described by CF growth and gap opening, respectively, activated by the local field and temperature. The analytical model is then used to describe the switching dynamics in the complementary resistive switch (CRS), consisting of an antiserial connection of two resistive devices. The impact of the gap resistivity on the CRS characteristics is discussed, highlighting the tradeoff between off-state leakage and set/reset window.