Switching in metal-oxide-metal devices has been studied since the late 1960s. A number of mechanisms have been identified to explain the change in resistance in such structures, including the formation of metallic filaments which bridge the insulating layer and provide a low resistance pathway between the electrodes. The low power “cationic” switching of copper-silica-metal devices, where the metal is a relatively inert conductor (e.g., tungsten), has gained attention in recent times as these materials are already present in the back-end-of-line (BEOL) of integrated circuits, making device integration simpler and less expensive than in the case of more “exotic” resistive switching systems. This technology is a variant of programmable metallization cell (PMC) or conductive-bridging random access memory (CBRAM). The switching mechanism involves the transport of copper ions in the oxide and their subsequent reduction to form the conducting metallic pathway. The oxidizable electrode provides ions into the reaction environment to maintain the supply of copper for the growing filament. The switching process is bipolar, in that a bias opposite to that used for writing is required to reverse the filament formation process to return the device to its high resistance state. The copper-silica-metal structures exhibit similar switching characteristics to previously-commercialized devices based on higher chalcogenide glasses, albeit at somewhat lower switching speed for the same programming voltage, while possessing inherently greater CMOS compatibility. Devices have been fabricated using either physical vapor deposition (PVD) or chemical vapor deposition (CVD) of the silica under conditions that allow the film to have a slightly lower density than a typical deposited oxide to promote ion transport and facilitate filament formation. A forming step is required to form a switchable region in the oxide and following this, sub-µs switching at low voltage and current is readily attainable.

In this talk we will report on the operational characteristics of these copper-silica-metal devices and the effect of different processing approaches on individual structures as well as crossbar arrays. We will also show the results of impedance spectroscopy analysis as they pertain to the physical structure of the devices. The applications of this technology range from active and passive non-volatile memories to neuromorphic elements and physical unclonable functions (PUFs) for physical and cyber security and these uses will be highlighted in the talk.