Universal memory, which combines the high-speed performance of present-day static random access memory (SRAM) [1] with the non-volatility of Flash [1] must realize several goals such as low operating current, size scalability, and compatibility with mass production to become a feasible memory alternative. The best approach towards the goal of high density is to utilize stackable structures with a crossbar geometry, [2] and to achieve low-temperature fabrication [3] while still retaining a selective switch (transistor or diode) as the data storage element. Thus for high-density applications, crossbar structures are ideal, whereas for non-volatility, resistance-change materials show the best promise. In order to realize the fabrication of universal memory elements, it is imperative to develop a class of materials and structures that combine robust processibility, strong scalability, and rapid programming speed with non-volatility and low power consumption. In our work, we have focused on defining just the storage node portion of the devices, which utilize the resistance change within the film to store information via two different stable resistance states. Here, we have attempted to determine the properties of such structures and to study the mechanisms behind resistance RAM (RRAM) storage. Our Ti-doped (0.1 wt %) NiO samples deposited at room temperature show favorable node characteristics such as the lowest write current reported thus far for a unipolar switching resistance-change-based device (ca. 10 lA). In addition, the programming speed is comparable to the write time of SRAM (10 ns). By combining this node element with an appropriate select switch, such as a high-performance diode, a threshold device, or a two-terminal non-ohmic device, it becomes possible to fabricate high-density universal memory. Indeed, the fabrication of universal memory as the next generation of non-volatile memory is the logical goal for research in this field. In comparison to Flash and dynamic RAM (DRAM), which are the current industry standards, next generation memories must combine the non-volatility of Flash with the high-speed performance of SRAM.[1] Several emerging non-volatile memory architectures have been investigated in order to fabricate materials that fit these specifications. [1,[4][5][6] For example, phase-change RAM (PRAM) [7] utilizes resistance switching accompanied by full or partial phase changes in chalcogenide materials induced by electrical pulses as a method for storing information. Recently, much effort has been devoted to investigations of magnetic race-track memory, a new concept in magnetic non-volatile memory involving the storage of information in the domain walls of materials. [8,9] Also, RRAM [3,[10][11][12][13][14][15][16][17][18] has been studied as a possible candidate for new memory storage devices. RRAM is based on either transition metal oxides that exhibit unipolar switching properties [10][11][12] or perovskite materials displaying bipolar switching properties; [13][14][15] essentially, this is...

Stackable select devices such as the oxide p-n junction diode and the Schottky diode (one-way switch) have been proposed for non-volatile unipolar resistive switching devices; however, bidirectional select devices (or two-way switch) need to be developed for bipolar resistive switching devices. Here we report on a fully stackable switching device that solves several problems including current density, temperature stability, cycling endurance and cycle distribution. We demonstrate that the threshold switching device based on As-Ge-Te-Si material significantly improves cycling endurance performance by reactive nitrogen deposition and nitrogen plasma hardening. Formation of the thin Si 3 N 4 glass layer by the plasma treatment retards tellurium diffusion during cycling. Scalability of threshold switching devices is measured down to 30 nm scale with extremely fast switching speed of B2 ns.

We report a physical model for multilevel switching in oxide-based bipolar resistive memory (ReRAM). To confirm the validity of the model, we conduct experiments with tantalum-oxide-based ReRAM of which multi-resistance levels are obtained by reset voltage modifications. It is also noticeable that, in addition to multilevel switching capability, the ReRAM exhibits extremely different switching timescales, i.e. of the order of 10(-7) s to 10(0) s, with regard to reset voltages of only a few volts difference which can be well explained by our model. It is demonstrated that with this simple model, multilevel switching behavior in oxide bipolar ReRAM can be described not only qualitatively but also quantitatively.

The integration of electronically active oxide components onto silicon circuits represents an innovative approach to improving the functionality of novel devices. Like most semiconductor devices, complementary-metal-oxide-semiconductor image sensors (CISs) have physical limitations when progressively scaled down to extremely small dimensions. In this paper, we propose a novel hybrid CIS architecture that is based on the combination of nanometer-scale amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) and a conventional Si photo diode (PD). With this approach, we aim to overcome the loss of quantum efficiency and image quality due to the continuous miniaturization of PDs. Specifically, the a-IGZO TFT with 180 nm gate length is probed to exhibit remarkable performance including low 1/f noise and high output gain, despite fabrication temperatures as low as 200 °C. In particular, excellent device performance is achieved using a double-layer gate dielectric (Al₂O₃/SiO₂) combined with a trapezoidal active region formed by a tailored etching process. A self-aligned top gate structure is adopted to ensure low parasitic capacitance. Lastly, three-dimensional (3D) process simulation tools are employed to optimize the four-pixel CIS structure. The results demonstrate how our stacked hybrid device could be the starting point for new device strategies in image sensor architectures. Furthermore, we expect the proposed approach to be applicable to a wide range of micro- and nanoelectronic devices and systems.

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