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 10 9 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-highdensity memory devices to provide excellent operation margins and extremely low power consumption.

Flexible threshold switch devices are essential for low‐power and high‐speed semiconductor devices. Especially, bidirectional threshold switch has been regarded as the ideal switching device for ultrahigh‐density crosspoint memory devices. Here, a flexible Pt/Ag‐doped ZnO/Pt switch on the flexible plastic substrate synthesized by electrochemical bottom‐up deposition is introduced. The flexible switch has bidirectional threshold switching behavior with ultralow off‐current, high selectivity (≈107), and super‐steep threshold slope. The bidirectional threshold switching behavior is related to migration of silver ions to form Ag filament. This device shows stable electrical properties, endures constant voltage stress, and retains good reliability under mechanical stress. It is believed that this study would open up new possibilities for high‐density flexible memory devices by introducing flexible novel bidirectional, high‐performance switching devices for emerging flexible electronics.

The bottom-up approach using self-assembled materials/processes is thought to be a promising solution for next-generation device fabrication, but it is often found to be not feasible for use in real device fabrication. Here, we report a feasible and versatile way to fabricate high-density, nanoscale memory devices by direct bottom-up filling of memory elements. An ordered array of metal/oxide/metal (copper/copper oxide/copper) nanodots was synthesized with a uniform size and thickness defined by self-organized nanotemplate mask by sequential electrochemical deposition (ECD) of each layer. The fabricated memory devices showed bipolar resistive switching behaviors confirmed by conductive atomic force microscopy. This study demonstrates that ECD with bottom-up growth has great potential to fabricate high-density nanoelectronic devices beyond the scaling limit of top-down device fabrication processes.

A facile and versatile scheme is demonstrated to fabricate nanoscale resistive switching memory devices that exhibit reliable bipolar switching behavior. A solution process is used to synthesize the copper oxide layer into 250-nm via-holes that had been patterned in Si wafers. Direct bottom-up filling of copper oxide can facilitate fabrication of nanoscale memory devices without using vacuum deposition and etching processes. In addition, all materials and processes are CMOS compatible, and especially, the devices can be fabricated at room temperature. Nanoscale memory devices synthesized on wafers having 250-nm via-holes showed reproducible resistive switching programmable memory characteristics with reasonable endurance and data retention properties. This integration strategy provides a solution to overcome the scaling limit of current memory device fabrication methods.

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