Memristors using solution-based IGZO nanoparticles

Solution-based indium-gallium-zinc oldde (IGZO) nanoparticles deposited by spin coating have been investigated as a resistive switching layer in metal-insulator-metal structures for nonvolatile memory applications. Optimized devices show a bipolar resistive switching behavior, low programming voltages of +/- 1 V, on/off ratios higher than 10, high endurance, and a retention time of up to 104 s. The better performing devices were achieved with annealing temperatures of 200 degrees C and using asymmetric electrode materials of titanium and silver. The physics behind the improved switching properties of the devices is discussed in terms of the oxygen deficiency of IGZO. Temperature analysis of the conductance states revealed a nonmetallic filamentary conduction. The presented devices are potential candidates for the integration of memory functionality into low-cost System-on-Panel technology.National Funds through FCT - Portuguese Foundation for Science and Technology [UID/CTM/50025/2013, SFRH/BDP/99136/2013]; FEDER [POCI-01-0145-FEDER-007688]info:eu-repo/semantics/publishedVersio

RESISTIVE SWITCHING CHARACTERISTICS OF NANOSTRUCTURED AND SOLUTION-PROCESSED COMPLEX OXIDE ASSEMBLIES

Miniaturization of conventional nonvolatile (NVM) memory devices is rapidly approaching the physical limitations of the constituent materials. An emerging random access memory (RAM), nanoscale resistive RAM (RRAM), has the potential to replace conventional nonvolatile memory and could foster novel type of computing due to its fast switching speed, high scalability, and low power consumption. RRAM, or memristors, represent a class of two terminal devices comprising an insulating layer, such as a metal oxide, sandwiched between two terminal electrodes that exhibits two or more distinct resistance states that depend on the history of the applied bias. While the sudden resistance reduction into a conductive state in metal oxide insulators has been known for almost 50 years, the fundamental resistive switching mechanism is a complex phenomenon that is still long-debated, complex process. Further improvements to existing memristor performance require a complete understanding of memristive properties under various operation conditions. Additional technical issues also remain, such as the development of facile, low-cost fabrication methods as an alternative to expensive, ultra-high vacuum (UHV) deposition methods. This collection of work explores resistive switching within metal oxide-based memristive material assemblies by analyzing the fundamental physical insulating material properties. Chapter 3 aims to translate the utility and simplicity of the highly ordered anodic aluminum oxide (AAO) template structure to complex, yet more functional (memristive) materials. Functional oxides possessing ordered, scalable nanoporous arrays and nanocapacitor arrays over a large area is of interest to both the fields of next-generation electronics and energy storing/harvesting devices. Here their switching performance will be evaluated using conductive atomic force microscopy (C-AFM). Chapter 4 demonstrates a convective self-assembly fabrication method that effectively enables the synthesis of a low-cost solution processed memristor comprising binary oxide and perovskite ABO3 nanocrystals of varying diameter. Chapter 5 systematically compares the influence of inter-nanoparticle distance on the threshold switching SET voltage of hafnium oxide (HfO2) memristors. Utilizing shorter phosphonic acid ligands with higher binding affinity on the nanocrystal surface enabled a record-low SET voltage to be achieved. Chapter 6 extends the scope to the fine tuning of solution processed memristors with two types of perovskites nanocrystals. The primary advantage of nanocrystal memristors is the ability to draw from additional degrees of freedom by tuning the constituent nanocrystal material properties. Recent advancement of solution phase techniques enables a high degree of controllability over the nanocrystal size and structure. Thus, this work found in this dissertation aims to understand and decouple the effects of the geometric size and substitutional nanocrystal parameters on resistive switching

Solution-based IGZO nanoparticles memristor

This work aims to characterize Indium-Gallium-Zinc-Oxide nanoparticles (IGZOnp) as a resistive switching matrix in metal-insulator-metal (MIM) structures for memristor application. IGZOnp was produced by low cost solution-based process and deposited by spin-coating technique. Several top and bottom electrodes combinations, including IZO, Pt, Au, Ti, Ag were investigated to evaluate memory performance, yield and switching properties. The effect of ambient and annealing temperature using 350 ºC and 200 ºC was also analysed in order to get more insight into resistive switching mechanism. The Ag/IGZOnp/Ti memristor structure annealed at 200 ºC exhibits the best results with a large yield. The device shows a self-compliant bipolar resistive switching behavior. The switching event is achieved by the set/reset voltages of -1 V/+1 V respectively with an operating window of 10, and it can be programmed for more than 100 endurance cycles. The retention time of on and off-states is up to 104 s. The obtained results suggest that Ag/IGZOnp/Ti structure could be applied in system on a panel (SoP) as a viable device

Oxide Memristive Devices

Resistive switching in metal oxide materials has recently renewed the interest of many researchers due to the many application in non-volatile memory and neuromorphic computing. A memristor or a memristive device in general, is a device behaving as nonlinear resistor with memory which depends on the amount of charges that passes through it. A novel idea of combining the physical resistive switching phenomenon and the circuit-theoretic formalism of memristors was proposed in 2008. The physical mechanism on how resistive switching occurs is still under debate. A physical understanding of the switching phenomenon is of much importance in order to tailor specific properties for memory applications. To investigate the resistive switching in oxide materials, memristive devices were fabricated starting from materials processing: low-pressure chemical vapor deposition of ZnO nanowires (NWs), low-temperature atomic layer deposition (ALD) of TiO2 thin films and micro-pulse ALD of Fe2O3 thin films. The distinct geometry of ZnO NWs makes it possible to investigate the effect of the electrode material, surface states and compliance to the memristive properties. A simpler method of fabricating TiO2-based devices was explored using low-temperature atomic layer deposition. This approach is very promising for device application using photoresist and polymeric substrates without thermal degradation during and after device fabrication. ALD of pure phase Fe2O3 thin films was demonstrated using cyclic micro-pulses. Based on the performance of the fabricated devices, the oxide materials under this study have promising properties for the next-generation memory devices