electron charge and h is the Planck constant. [6] Electronic switches with atomicsized functional building blocks are the main driving force of modern nanotechnology. The design of atomic dimensional memory devices is limited by the lithographic bottleneck. Nevertheless, the origin of atomic contact in nanoscale architectures is being investigated. [7] The conductive bridge RAM device with quantized conductance (QC) effect proposed by Terebe et al., [8] was based on the fabrication of a gap-type Pt/ nano-gap/Ag 2 S/Ag structure. A small operating voltage of ±600 mV can switch the device between the "OFF" and "ON" states. When a device changes its resistance from high to low, it is usually known as "set"; the reverse change is known as "reset". The QC effect is suitable to realize multiple levels in devices and has been studied in both electrochemical metallization type [9][10][11][12][13][14] and valance change memory type [15,16] gap-less RRAM. In most cases, switching is the after-effect of a stress dependent virginity breakdown, which can consolidate the CF for switching operations. Because the behavior of the CF of conductive bridge RAM is considered to be an example of atomic-switching, further discussion is mainly focused on conductive bridge RAM type devices. Higher initial stress injects more cations into the switching oxide layer that results in poor control over the reset process, resulting in abrupt state transition, and atomic conductance instability. [9][10][11][12][13][14] In another approach, single-atom memory has been proposed for mechanically controllable break junctions (MCBJs), [17] which are a kind of electronic device formed by two knife-edged metal wires placed with a nanometer sized gap, as shown in Figure 1a. MCBJs are well known as atomic or single molecular junction, and have even been investigated to in the context of control of quantum interferences in graphene. [18,19] In an MCBJ, when the two wires are curved, broadening the gap, the contact is broken, and the reverse order experiences an atomic-contact at the break junction. Break junctions are a possible approach to the fabrication of atomic switches. However, in reality, for an electronic device, such design is burdensome due to exorbitant lithographic processes. It is possible to prepare a break junction by electrically controlling the ion migration process in conductive bridge RAM devices, as the switching mechanism is driven by the formation of metallic wire like CF. Although the concept of QC in conductive bridge RAM has been investigated for over a decade, precise and reliable atomic-level control Atomic-level control of conductance in a Cu/Ti/HfO 2 /TiN-based electrically controllable break junction (ECBJ) is demonstrated. The ECBJ is designed through sophisticated stack engineering and refined electrical operation. Control over bias-induced ion migration is the key to forming the ECBJ. Precise atomic-level control is accomplished with an optimized high temperature forming (OHTF) scheme. OHTF-controlled single-atomic switch...