Cu Atom Switch With Steep Time-to-ON-State Versus Switching Voltage Using Cu Ionization Control

To break the tradeoff relationship between fast and low-voltage programming of a Cu atom switch, the effect of the composition in the AlTi oxide buffer layer placed on a Cu electrode is investigated. To improve the voltage dependence of time-to-ON-state, namely, switching slope (SS), the Cu ionization rate is increased by changing the composition ratio of the AlTi oxide buffer. An Al_0.5Ti_0.5O_y buffer leads to an extremely steep SS of 56 mV/decade by eliminating metallic Al residue on the Cu electrode. This buffer enables fast (10 ns) and low-voltage (~2 V) programming, as demonstrated in a 1-Mbit array. Cycle endurance (> 10³ cycles) with a high ON/OFF resistance ratio (>10⁴) was also confirmed. The steep SS technology is indispensable for conducting bridges used in a low-power nonvolatile field-programmable gate array.