Electrochemical metallization memories—fundamentals, applications, prospects

Abstract

This review focuses on electrochemical metallization memory cells (ECM), highlighting their advantages as the next generation memories. In a brief introduction, the basic switching mechanism of ECM cells is described and the historical development is sketched. In a second part, the full spectra of materials and material combinations used for memory device prototypes and for dedicated studies are presented. In a third part, the specific thermodynamics and kinetics of nanosized electrochemical cells are described. The overlapping of the space charge layers is found to be most relevant for the cell properties at rest. The major factors determining the functionality of the ECM cells are the electrode reaction and the transport kinetics. Depending on electrode and/or electrolyte material electron transfer, electro-crystallization or slow diffusion under strong electric fields can be rate determining. In the fourth part, the major device characteristics of ECM cells are explained. Emphasis is placed on switching speed, forming and SET/RESET voltage, R(ON) to R(OFF) ratio, endurance and retention, and scaling potentials. In the last part, circuit design aspects of ECM arrays are discussed, including the pros and cons of active and passive arrays. In the case of passive arrays, the fundamental sneak path problem is described and as well as a possible solution by two anti-serial (complementary) interconnected resistive switches per cell. Furthermore, the prospects of ECM with regard to further scalability and the ability for multi-bit data storage are addressed.

Mechanism for resistive switching in chalcogenide-based electrochemical metallization memory cells

“…It has been reported that compared to the central area of the Cu electrode, the margin of the Cu electrode is apt to be oxidized to Cu(OH) 2 in air. 45 Therefore, the bulges are likely dominated by Cu(OH) 2 which is difficult to be removed by adhesive tape compared to Cu. We can thus conclude that only a single complete Cu filament forms after the Electroforming operation for Cu/ZnS/Pt ECM cells.…”

“…1,2 The ECM cell consists of an insulator layer sandwiched between two electrodes, in which one is made from an electrochemically active electrode (AE) metal, such as Ag or Cu, and the other is a counter electrode (CE), such as Pt, Ir, W, or Ag. 3,4 Till now, a large number of ECM cells have been reported, employing various insulating materials such as chalcogenides, [5][6][7][8][9][10][11][12][13] oxides, [14][15][16][17][18][19][20][21][22][23][24] amorphous Si (Refs.…”

Reliable current changes with selectivity ratio above 109 observed in lightly doped zinc oxide films

“…[1][2][3] Among them, ReRAM has been extensively studied because of its non-volatile memory characteristics owing to its excellent retention, endurance and high on/off current ratio. [4][5][6][7] Furthermore, ReRAM has a simple two-terminal structure, fast switching speed and low power consumption with excellent scalability. ReRAM cells have been integrated into cross-point arrays (4F 2 ) to obtain an area-efficient structure for non-volatile memory applications.…”

Rate-limiting processes in the fast SET operation of a gapless-type Cu-Ta2O5 atomic switch

“…4. 2,7,16 The subsequent reformation and dissolution of the metal filament take place at the same location on the Pt electrode. This situation is quite similar to that observed for a gap-type atomic switch, in which a metal bridge is formed between the tip of a scanning tunneling microscope (STM) and a sample.…”

“…6 Because it is constructed by electrochemical deposition and dissolution of a metal on an inert electrode, this type of cell is also referred to as an electrochemical metallization (ECM) cell. 7 It has been demonstrated that the oxide-based atomic switches exhibit an effect analogous to the long-term potentiation of biological synapses, suggesting their potential for use in neural computing systems. 8 Among the various properties of a RRAM operation, switching speed is one of the most important.…”