Resonate and Fire Neuron with Fixed Magnetic Skyrmions

In the brain, the membrane potential of many neurons oscillates in a subthreshold damped fashion and fire when excited by an input frequency that nearly equals their eigen frequency. In this work, we investigate theoretically the artificial implementation of such "resonate-and-fire" neurons by utilizing the magnetization dynamics of a fixed magnetic skyrmion in the free layer of a magnetic tunnel junction (MTJ). To realize firing of this nanomagnetic implementation of an artificial neuron, we propose to employ voltage control of magnetic anisotropy or voltage generated strain as an input (spike or sinusoidal) signal, which modulates the perpendicular magnetic anisotropy (PMA). This results in continual expansion and shrinking (i.e. breathing) of a skyrmion core that mimics the subthreshold oscillation. Any subsequent input pulse having an interval close to the breathing period or a sinusoidal input close to the eigen frequency drives the magnetization dynamics of the fixed skyrmion in a resonant manner. The time varying electrical resistance of the MTJ layer due to this resonant oscillation of the skyrmion core is used to drive a Complementary Metal Oxide Semiconductor (CMOS) buffer circuit, which produces spike outputs. By rigorous micromagnetic simulation, we investigate the interspike timing dependence and response to different excitatory and inhibitory incoming input pulses. Finally, we show that such resonate and fire neurons have potential application in coupled nanomagnetic oscillator based associative memory arrays

Energy Efficient Spintronic Device for Neuromorphic Computation

Future computing will require significant development in new computing device paradigms. This is motivated by CMOS devices reaching their technological limits, the need for non-Von Neumann architectures as well as the energy constraints of wearable technologies and embedded processors. The first device proposal, an energy-efficient voltage-controlled domain wall device for implementing an artificial neuron and synapse is analyzed using micromagnetic modeling. By controlling the domain wall motion utilizing spin transfer or spin orbit torques in association with voltage generated strain control of perpendicular magnetic anisotropy in the presence of Dzyaloshinskii-Moriya interaction (DMI), different positions of the domain wall are realized in the free layer of a magnetic tunnel junction to program different synaptic weights. Additionally, an artificial neuron can be realized by combining this DW device with a CMOS buffer. The second neuromorphic device proposal is inspired by the brain. Membrane potential of many neurons oscillate in a subthreshold damped fashion and fire when excited by an input frequency that nearly equals their Eigen frequency. We investigate theoretical implementation of such “resonate-and-fire” neurons by utilizing the magnetization dynamics of a fixed magnetic skyrmion based free layer of a magnetic tunnel junction (MTJ). Voltage control of magnetic anisotropy or voltage generated strain results in expansion and shrinking of a skyrmion core that mimics the subthreshold oscillation. Finally, we show that such resonate and fire neurons have potential application in coupled nanomagnetic oscillator based associative memory arrays

Perovskite Materials for Resistive Random Access Memories

Resistive random access memory (RRAM) utilizes the resistive switching behavior to store information. Compared to charge-based memory devices, the merits of RRAM devices include multi-bit capability, smaller cell size, and energy per bit (~fJ/bit). In this chapter, we review different perovskite material-based resistive random access memories (RRAMs). We first introduce the history of RRAM development and operational mechanism of conduction, followed by a review of two types of materials with perovskite crystal structure. One is conventional perovskite oxides (PCMO, a-LCMO, etc.), and the other is perovskite halides (organic-inorganic hybrid perovskites and inorganic perovskites) that have recently emerged as novel materials in optoelectronic fields. Our goal is to give a comprehensive review of perovskite-based RRAM materials that can be used for neuromorphic computing and to help further ongoing development in the field

Thulium-Doped Fiber As Gain Medium And Saturable Absorber For Pulsed Fiber Laser

The study focuses on developing and demonstrating fiber laser applications using newly developed thulium-doped fiber (TDF). TDF functions as two different devices in this study. Firstly, TDF is use as gain medium to increase gain significantly at 2 μm wavelength. It specifically functions at that region due to pumped thulium ions reaction force an emission at 2 μm region. The energy transition of 3F4→3H6 can be obtained by pumping TDF with 802 nm and 1552 nm source. Secondly, TDF is use as passive saturable absorber. Passive saturable absorber works to generate self-starting pulse. This happen when TDF absorb lights that going through it until accumulated energy reached saturation level. At saturation level, accumulated energy will discharge and forcing pulse to occur. Instead of TDF, carbon nanotubes (CNT) are also used as saturable absorber in generating pulse. Pulse, or commonly known as ultra-fast pulse are divided into two; Q-switched pulse and mode-locked pulse. Q-switched pulse is a short, high energy pulse from a laser modulating through the intracavity losses and the quality (Q) factor of the ring laser. The microsecond pulse usually occurs in kHz frequency. High pulse energy will force the frequency of the pulse to increase, while the pulses become thinner. Mode-locked pulse is an ultra-short pulses from laser cavity with duration of nanosecond to femtosecond. Due to some circumstances, mode-locked pulse can only appears in a very low power laser cavity. As a result, no stimulated emission will occur since loss is higher than the power. In most cases, mode-locked pulse has a fixed frequency and pulse width depending on the cavity, even the power is changed

Ultra-energy-efficient Silicon Photonic Modulators Driven by Transparent Conductive Oxides

Silicon photonics has become the most promising platform for future large-scale optical interconnect and optical computing systems due to its inherent CMOS compatibility, which brings exclusive advantages in bandwidth density, energy efficiency, and cost effectiveness. Parallel optical interconnects based on photonic integrated circuits (PICs) have the capacity to meet the high bandwidth density requirement of parallel computing systems, however, are facing the same challenge in energy efficiency and bandwidth limit as their electrical counterparts because the margin shrinks unfavorably for shorter distance optical interconnects. Unprecedented requirement in energy efficiency has been outlined, which poses tremendous challenges to existing PIC devices, even to the state-of-the-arts silicon photonics. In recent years, transparent conductive oxides (TCOs) have emerged as increasingly favorable tunable materials for active photonic devices. TCOs exhibit a large refractive index tunability on the order of unity, which enables unique epsilon-near-zero (ENZ) light confinement and significant enhancement in light-matter interaction. These intriguing optical properties offer us the potential to expand the functionality and improve the device performance of the silicon photonics platform. This dissertation presents design and demonstration of novel active photonic devices driven by TCOs on silicon photonics platform, with a focus on achieving ultra-energy-efficient silicon photonic modulator. Three types of photonic devices are investigated. Firstly, an electrically tunable plasmonic subwavelength grating based on a metallic subwavelength slit array coupled with a Si/SiO2/ITO MOS capacitor is designed and demonstrated. We show that large modulation depth can be achieved for both transmission and reflection modes through modifying the electron concentration within 0.5 nm thick TCO accumulation layer. In the second part, we develop a novel device platform of TCO-gated silicon micro-resonators. A Si-TCO photonic crystal (PC) nanocavity modulator is designed and demonstrated. We achieve extreme large wavelength tuning of 250 pm/V, single digit femto-joule per bit energy efficiency, and 2.2 GHz operation bandwidth with a deep sub-λ ultra-small modulation volume. We also propose a strategy to improve bandwidth to over 23GHz and reduce energy consumption to atto-joule per bit level. Besides, TCO-gated microring resonators are investigated for two applications. We design and demonstrate a tunable microring filter with an unprecedented wavelength tuning of 271 pm/V, a large electrical tuning range of 2 nm, and a negligible static energy consumption, which can be used for wavelength division multiplex (WDM) application. A TCO-gated microring modulator is also designed, which can potentially achieve a large operation bandwidth over 50GHz. Lastly, a sub-micron, sub-pico-second, femto-joule level all-optical switch (AOS) using hybrid plasmonic-silicon waveguides driven by high mobility TCOs is proposed. By defining a comprehensive metric using the product of device size, switching energy and switching time, the proposed device shows superior performance than any existing on-chip AOS device. In addition to the device research, we systematically analyze the energy efficiency and bandwidth limit of resonator-based silicon photonic modulators from three fundamental perspectives: free carrier dispersion strength of the active materials, Purcell factors of the resonators, and electrical configuration of the capacitors. The analysis lays the theoretical foundation and identifies possible routes for achieving atto-joule per bit energy efficiency and approaching the bandwidth limit of silicon photonic modulators. In summary, TCOs could play an important role in the development of future photonics technology, which provide a CMOS compatible solution to overcome the intrinsic weak E-O effect of the silicon photonics platform, lead to unprecedented reduction in energy consumption, increasing bandwidth, as well as enable novel functionalities. Future researches should include, but not limited to, optimizing the design and fabrication of TCO-driven modulators to reduce series resistance and increasing overlapping factor, integrating TCO-driven devices with photonics foundry fabricated PICs, and developing of high mobility TCOs

A walk on the frontier of energy electronics with power ultra-wide bandgap oxides and ultra-thin neuromorphic 2D materials

Altres ajuts: the ICN2 is funded also by the CERCA programme / Generalitat de CatalunyaUltra-wide bandgap (UWBG) semiconductors and ultra-thin two-dimensional materials (2D) are at the very frontier of the electronics for energy management or energy electronics. A new generation of UWBG semiconductors will open new territories for higher power rated power electronics and deeper ultraviolet optoelectronics. Gallium oxide - GaO(4.5-4.9 eV), has recently emerged as a suitable platform for extending the limits which are set by conventional (-3 eV) WBG e.g. SiC and GaN and transparent conductive oxides (TCO) e.g. In2O3, ZnO, SnO2. Besides, GaO, the first efficient oxide semiconductor for energy electronics, is opening the door to many more semiconductor oxides (indeed, the largest family of UWBGs) to be investigated. Among these new power electronic materials, ZnGa2O4 (-5 eV) enables bipolar energy electronics, based on a spinel chemistry, for the first time. In the lower power rating end, power consumption also is also a main issue for modern computers and supercomputers. With the predicted end of the Moores law, the memory wall and the heat wall, new electronics materials and new computing paradigms are required to balance the big data (information) and energy requirements, just as the human brain does. Atomically thin 2D-materials, and the rich associated material systems (e.g. graphene (metal), MoS2 (semiconductor) and h-BN (insulator)), have also attracted a lot of attention recently for beyond-silicon neuromorphic computing with record ultra-low power consumption. Thus, energy nanoelectronics based on UWBG and 2D materials are simultaneously extending the current frontiers of electronics and addressing the issue of electricity consumption, a central theme in the actions against climate chang

Laser Machining by short and ultrashort pulses, state of the art and new opportunities in the age of the photons

An overview is given of the applications of short and ultrashort lasers in material processing. Shorter pulses reduce heat-affected damage of the material and opens new ways for nanometer accuracy. Even forty years after the development of the laser there is a lot of effort in developing new and better performing lasers. The driving force is higher accuracy at reasonable cost, which is realised by compact systems delivering short laser pulses of high beam quality. Another trend is the shift towards shorter wavelengths, which are better absorbed by the material and which allows smaller feature sizes to be produced. Examples of new products, which became possible by this technique, are given. The trends in miniaturization as predicted by Moore and Taniguchi are expected to continue over the next decade too thanks to short and ultrashort laser machining techniques. After the age of steam and the age of electricity we have entered the age of photons now