Reliable current changes with selectivity ratio above 109 observed in lightly doped zinc oxide films

Low-power operation of semiconductor devices is crucial for energy conservation. In particular, energy-efficient devices are essential in portable electronic devices to allow for extended use with a limited power supply. However, unnecessary currents always exist in semiconductor devices, even when the device is in its off state. To solve this problem, it is necessary to use switch devices that can turn active devices on and off effectively. For this purpose, high on/off current selectivity with ultra-low off-current and high on-current is required. Here, we report a novel switch behavior with over 109 selectivity, a high on-current density of 1 MA cm-2, an ultra-low off-current density of 1 mA cm-2, excellent thermal stability up to 250 °C and abrupt turn-on with 5 mV per decade in solution-processed silver-doped zinc oxide thin films. The selection behavior is attributed to light doping of silver ions in zinc oxide films during electrochemical deposition to generate atomic-scale narrow conduction paths, which can be formed and ruptured at low voltages. Device simulation showed that the new selector devices may be used in ultra-high-density memory devices to provide excellent operation margins and extremely low power consumption. A resistive switch device with a billion-fold difference between its conductive ‘on’ and insulating ‘off’ states has been developed. Next-generation memory cells that use differences in on/off current ratios to store information have low power requirements and can be stacked into three-dimensional arrays. But these devices can suffer from current leaking from nominally off cells. Now, Jang-Sik Lee from the Pohang University of Science and Technology in Korea and co-workers have used silver-doped zinc oxide thin films to diminish this effect. Fabricated by solution-processing precursors into nanoscale holes on a silicon wafer, these cells contain a dilute fraction of silver ions that form conductive filaments in the on state. The silver threads, however, break up into atomic constituents when the off state is accessed – a change that drops leakage current to insignificant, femtoamp levels. The novel switching behavior is observed in solution-processed silver-doped zinc oxide thin films. This switch exhibited high on-current density of 1 MA cm-2, ultra-low off-current of 100 fA, excellent thermal stability up to 250 °C, abrupt turn-on with 5 mV per decade and a high on/off ratio of 109. This study demonstrates that the switch devices can be applicable for selectors in ultra-high-density cross-point memory devices with excellent operation margin and extremely low power consumption.