The Self-directed Channel Memristor: Operational Dependence on the Metal-Chalcogenide Layer

Comparison of the Electrical Response of Cu and Ag Ion-Conducting SDC Memristors Over the Temperature Range 6 K to 300 K

“…Self-directed channel (SDC) memristors are a type of chalcogenide-based electrochemical metallization (ECM) device [1,2,3,4,5,6,7] in which it is posited that re-usable and irreversible ion-transport channels are formed within the active chalcogenide layer during the first write operation [6,7]. The persistence of these channels, even after the device is cycled between high and low resistance states, is considered the largest factor responsible for consistent SDC device state switching [6].…”

“…The persistence of these channels, even after the device is cycled between high and low resistance states, is considered the largest factor responsible for consistent SDC device state switching [6]. ECM devices of many different material types, ranging from oxides, to chalcogenides, typically using Ag or Cu as the ion source, are lauded as having the highest likelihood for success in next generation non-volatile memory, neuromorphic computing, and space applications where a robust, radiation hardened, and temperature tolerant device is desirable [1,2,3,4,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Investigation of ECM device operational theory is ongoing since device improvement and good application-based device design requires a closer understanding of how the devices work.…”

“…First, the description of “GeSe-based CBRAM” is currently associated with a doped solid solution GeSe-Ag system [25,28,30]. The SDC does not contain a doped solid solution; the device does not require Ag doping, nor allow doping [7]. Unlike the GeSe-Ag CBRAM device, the SDC device structure contains material layers meant to store metal ions (the SnSe layer or other metal-chalcogenide layer—see [7] for experimental data and a discussion of the effects of the metal on SDC operation) and to facilitate fast switching; these are not present in the GeSe-Ag solid solution-based device.…”

“…Third, and most importantly, it is a working hypothesis that the SDC operation requires a separate metal chalcogenide layer and an amorphous active layer, such as Ge 2 Se 3 , which contains thermodynamically unstable homopolar bonds (such as the Ge-Ge bonds that are present in the SDC device Ge 2 Se 3 active layer). Channel formation then occurs through an irreversible chemical reaction between the device material layers upon the first programming event [7,35]; the combination of these layers will reactively generate permanent channels, i.e., Ag or Cu ion transport routes, through the SDC device Ge 2 Se 3 active layer via a chemical reaction preferentially with the Ge-Ge bond sites. Once the channel is formed, it is permanent under similar operating conditions, with the device state change depending on Ag or Cu ion movement within the established channel.…”

“…The formed channels assist the device in fast and consistent switching since it allows formation and storage of oxidizable metal ions instead of overcrowding and saturating the active glass layer. The desired morphology of the SnSe layer is thus one that is disordered, with a large surface area for Ag or Cu (and their ions) to react with SnSe [7].…”