and rupture of the metallic conducting filament (CF) composed of active metal atoms, typically Ag and Cu, are responsible for the resistance switching. Unlike other resistive switching devices, the active metal constitutes one of the electrodes which is critically involved in the redox reaction of CF formation and rupture in ECM devices. According to the conventional ECM theory, the cations generated from the anode (active metal) migrate through the solid electrolyte layer when a positive bias is applied to the active metal electrode. The migrated metal cations receive electrons at the cathode (inert metal)/electrolyte interface, and are reduced to metal atoms forming the growing CF. After a series of reduction processes, metallic CF(s) is (are) formed, and current flows through them, thus, the device resistance state becomes a low resistance state (LRS), which corresponds to set switching. When the bias polarity is reversed, a reverse reaction occurs, and the device turns back to a high resistance state (HRS), which is most probably mediated by the oxidation of the metal atoms at the filament tip near the active metal electrode. This corresponds to reset switching. In this conventional ECM model based on the redox reaction of active metal atoms, the idea that a conical-shaped filament grows from the cathode/ electrolyte interface toward the active electrode (anode) and that ECM devices show bipolar resistive switching (BRS) has been widely accepted. [6,7] However, counterarguments against the conventional ECM filament forming theory, covering not only the reset polarity but also the filament geometry, have been discovered in recent years. [8,9] These studies revealed that the filament growth can be extensively influenced by the detailed material parameters, such as the type of electrolyte materials as well as the cation/electron mobility and its redox rate. [9][10][11][12][13] With the aid of in situ transmission electron microscopy (TEM) and conductive atomic force microscopy techniques, real-time image of growth and rupture of conducting filament have been reported. [14,15] These factors contribute not only to the initiation location of the filament growth but also to the consequent shape of the grown filament. In addition, studies objecting to the incumbent ECM reset mechanism theory have been reported recently. According to the conventional ECM theory, due to its redox reaction based characteristics, only bipolarThe electrochemical metallization (ECM) cell is a feasible contender for high density resistance switching random access memory or neuromorphic devices. This work elucidates the detailed switching model based on the Cu conducting filament (CF) configuration and the interplay between the Joule heating and electric field effects in the Pt/TiO 2 /Cu ECM cell, which can explain the switching behaviors both in accordance and discordance with the conventional ECM theory. The Cu CF configuration is varied from the conventional conical one for a small compliance current (I cc , ≈1 mA) to the hourglass or eve...