We show that the main mechanism for the dc voltage or dc current induced insulator-metal transition in vanadium dioxide VO(2) is due to local Joule heating and not a purely electronic effect. This "tour de force" experiment was accomplished by using the fluorescence spectra of rare-earth doped micron sized particles as local temperature sensors. As the insulator-metal transition is induced by a dc voltage or dc current, the local temperature reaches the transition temperature indicating that Joule heating plays a predominant role. This has critical implications for the understanding of the dc voltage or dc current induced insulator-metal transition and has a direct impact on applications which use dc voltage or dc current to externally drive the transition.

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This tutorial describes challenges and possible avenues for the implementation of the components of a solid-state system, which emulates a biological brain. The tutorial is devoted mostly to a charge-based (i.e. electric controlled) implementation using transition metal oxides materials, which exhibit unique properties that emulate key functionalities needed for this application. In the Introduction, we compare the main differences between a conventional computational machine, based on the Turing-von Neumann paradigm, to a Neuromorphic machine, which tries to emulate important functionalities of a biological brain. We also describe the main electrical properties of biological systems, which would be useful to implement in a charge-based system. In Chapter II, we describe the main components of a possible solid-state implementation. In Chapter III, we describe a variety of Resistive Switching phenomena, which may serve as the functional basis for the implementation of key devices for Neuromorphic computing. In Chapter IV we describe why transition metal oxides, are promising materials for future Neuromorphic machines. Theoretical models describing different resistive switching mechanisms are discussed in Chapter V while existing implementations are described in Chapter VI. Chapter VII presents applications to practical problems. We list in Chapter VIII important basic research challenges and open issues. We discuss issues related to specific implementations, novel materials, devices and phenomena. The development of reliable, fault tolerant, energy efficient devices, their scaling and integration into a Neuromorphic computer may bring us closer to the development of a machine that rivals the brain.

The metal insulator transition of nano-scaled V O2 devices is drastically different from the smooth transport curves generally reported. The temperature driven transition occurs through a series of resistance jumps ranging over 2 decades in amplitude, indicating that the transition is caused by avalanches. We find a power law distribution of the jump amplitudes, demonstrating an inherent property of the V O2 films. We report a surprising relation between jump amplitude and device size. A percolation model captures the general transport behavior, but cannot account for the statistical behavior.PACS numbers: 71.30.+h, 72.80.Ga, 64.60.Ht,64.60.an There are many systems in nature that have a transition from one state to another which is driven by an external force, where the transition is not continuous, but rather through a series of avalanches. These systems are diverse as is the driving force and the measurement technique used to observe them. Examples include: Barkhausen noise in ferromagnets [1,2], acoustic emission in martensitic transition [3,4], magnetocaloric effect in giant magnetocaloric alloys [5], sharp magnetization steps or sharp resistance steps in manganites [6,7] and capillary condensation of He in nanoporous material [8].In general an external parameter modifies the free energy of the two phases, which provides the driving force for the system. The nature of the avalanches provides much information about the system at hand. One can learn about the types of interaction, the role of fluctuations, existence of self organized criticality and the universal features of the transitions which transcend the specific physical system [4,9,10,11].Several of these systems are characterized by phase separation during the transition. This implies that the transition occurs through a series of avalanches transforming portions of the system from one phase to the other [12,13,14]. One such system, which has received much attention, is Vanadium Oxide (V O 2 ). V O 2 undergoes a first order metal insulator transition (MIT) of over 4 orders of magnitude at ∼ 340 K. The transition is from a high temperature metallic rutile phase to a low temperature insulating monoclinic phase, and can be driven by temperature, light irradiation or pressure [15]. Avalanches may be expected in this system for multiple reasons; it has a first order phase transition, there is a state of phase separation between metallic and insulating regions along the transition [16,17]; and ultra fast measurements reveal a phase transition in separated domains of the system with a transition time on the order of a few picoseconds [18,19]. In this paper we report the first observation of multiple avalanches across the temperature driven MIT in V O 2 .Generally, in order to identify an avalanche, the sensitivity of measurement has to be greater than the magnitude change of the relevant parameter, and the measurement frequency faster than the avalanche frequency [2,3,20]. For resistance measurements in V O 2 this implies that the size of the device has ...