123 research outputs found

    Theory of high performance piezotronic quantum harmonic oscillator under nonuniform strain

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    Piezotronics and piezo-phototronics are two emerging fields that involve high performance piezoelectric semiconductor devices. The nonuniform strain can create nonlinear piezopotential even in nonpiezoelectric materials such as silicon. Here, we propose theory of quantum piezotronics under nonuniform strain using a typical example of the interaction between independently trapped charges under nonlinear piezopotential. The trapped-ion motional frequency along the x direction can increase from 4 MHz to 25 MHz, and the electric-field noise can decrease by 15 times under nonuniform strain. This piezotronic harmonic oscillator based on trapping wells not only provides a good understanding of quantum piezotronics but also a guide for developing peizotronic devices for quantum computing

    UV Sensor Based on Surface Acoustic Waves in ZnO/Fused Silica

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    Zinc oxide (ZnO) thin films have been grown by radio frequency sputtering technique on fused silica substrates. Optical and morphological characteristics of as-grown ZnO samples were measured by various techniques; an X-ray diffraction spectrum showed that the films exhibited hexagonal wurtzite structure and were c-axis-oriented normal to the substrate surface. Scanning electron microscopy images showed the dense columnar structure of the ZnO layers, and light absorption measurements allowed us to estimate the penetration depth of the optical radiation in the 200 to 480 nm wavelength range and the ZnO band-gap. ZnO layers were used as a basic material for surface acoustic wave (SAW) delay lines consisting of two Al interdigitated transducers (IDTs) photolithographically implemented on the surface of the piezoelectric layer. The Rayleigh wave propagation characteristics were tested in darkness and under incident UV light illumination from the top surface of the ZnO layer and from the fused silica/ZnO interface. The sensor response, i.e., the wave velocity shift due to the acoustoelectric interaction between the photogenerated charge carriers and the electric potential associated with the acoustic wave, was measured for different UV power densities. The reversibility and repeatability of the sensor responses were assessed. The time response of the UV sensor showed a rise time and a recovery time of about 10 and 13 s, respectively, and a sensitivity of about 318 and 341 ppm/(mW/cm2) for top and bottom illumination, respectively. The ZnO/fused silica-based SAW UV sensors can be interrogated across the fused silica substrate thanks to its optical transparency in the UV range. The backlighting interrogation can find applications in harsh environments, as it prevents the sensing photoconductive layer from aggressive environmental effects or from any damage caused by cleaning the surface from dust which could deteriorate the sensor’s performance. Moreover, since the SAW sensors, by their operating principle, are suitable for wireless reading via radio signals, the ZnO/fused-silica-based sensors have the potential to be the first choice for UV sensing in harsh environments

    Impedance-matched High-overtone Bulk Acoustic Resonator

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    A high-overtone bulk acoustic resonator (HBAR), in which a piezoelectric transducer is set on an acoustic cavity, has been attracting attention in both fundamental research and RF applications due to its scalability, high frequency, and high quality factor. The acoustic impedance matching in HBARs is crucial for efficient acoustic power transfer from the piezoelectric transducer to the cavity. However, impedance mismatch remains in most HBARs due to the metal layer insertion between the piezoelectric layer and cavity substrate. In this study, we fabricated a nearly impedance-matched high-quality HBAR using an epitaxial AlN piezoelectric layer directly grown on a conductive SiC cavity substrate with no metal layer insertion. The small impedance mismatch was verified from the variation in the free spectral range (FSR), which is comparable to the best value in previously reported HBARs. The experimentally obtained FSR spectra was greatly reproduced by using the Mason model. Broadband phonon cavity modes up to the K-band (26.5 GHz) were achieved by reducing the thickness of the AlN layer from 800 to 200 nm. The high figure of merit of f×Q∼1.3×1013 Hzf\times\text{Q} \sim 1.3\times 10^{13}\ \textrm{Hz} at 10 GHz was also obtained. Our nearly impedance-matched high-quality HBAR will enable the development of RF applications, such as low-phase noise oscillators and acoustic filters, as well as research on high-frequency acoustic systems hybridized with electric, optical, and magnetic systems

    Beyond 5 GHz excitation of a ZnO-based high-overtone bulk acoustic resonator on SiC substrate

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    This work describes the fabrication and characterization of an Au/ZnO/Pt-based high-overtone bulk acoustic resonator (HBAR) on SiC substrates. We evaluate its microwave characteristics comparing with Si substrates for micro-electromechanical applications. Dielectric magnetron sputtering and an electron beam evaporator are employed to develop highly c-axis-oriented ZnO films and metal electrodes. The crystal structure and surface morphology of post-growth layers have been characterized using X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM) techniques. HBAR on SiC substrate results in multiple longitudinal bulk acoustic wave resonances up to 7 GHz, with the strongest excited resonances emerging at 5.25 GHz. The value of f.Q (Resonance frequency * Quality factor) parameter obtained using a novel Q approach method for HBAR on SiC substrate is 4.1 * 10^13 Hz which, to the best of our knowledge, is the highest among all reported values for specified ZnO-based devices

    Towards a circular economy: fabrication and characterization of biodegradable plates from sugarcane waste

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    Bagasse pulp is a promising material to produce biodegradable plates. Bagasse is the fibrous residue that remains after sugarcane stalks are crushed to extract their juice. It is a renewable resource and is widely available in many countries, making it an attractive alternative to traditional plastic plates. Recent research has shown that biodegradable plates made from Bagasse pulp have several advantages over traditional plastic plates. For example, they are more environmentally friendly because they are made from renewable resources and can be composted after use. Additionally, they are safer for human health because they do not contain harmful chemicals that can leach into food. The production process for Bagasse pulp plates is also relatively simple and cost-effective. Bagasse is first collected and then processed to remove impurities and extract the pulp. The pulp is then molded into the desired shape and dried to form a sturdy plate. Overall, biodegradable plates made from Bagasse pulp are a promising alternative to traditional plastic plates. They are environmentally friendly, safe for human health, and cost-effective to produce. As such, they have the potential to play an important role in reducing plastic waste and promoting sustainable practices. Over the years, the world was not paying strict attention to the impact of rapid growth in plastic use. As a result, uncontrollable volumes of plastic garbage have been released into the environment. Half of all plastic garbage generated worldwide is made up of packaging materials. The purpose of this article is to offer an alternative by creating bioplastic goods that can be produced in various shapes and sizes across various sectors, including food packaging, single-use tableware, and crafts. Products made from bagasse help address the issue of plastic pollution. To find the optimum option for creating bagasse-based biodegradable dinnerware in Egypt and throughout the world, researchers tested various scenarios. The findings show that bagasse pulp may replace plastics in biodegradable packaging. As a result of this value-added utilization of natural fibers, less waste and less of it ends up in landfills. The practical significance of this study is to help advance low-carbon economic solutions and to produce secure bioplastic materials that can replace Styrofoam in tableware and food packaging production

    Development of a 3-axis MEMS magnetometer based on Lorentz force

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    Dissertação de mestrado em Physics Engineering, (especialização em Devices, Microsystems and Nanotechnologies)Typical magnetometers found in the magnetic fields research are highly incompatible with the massive MEMS technology industry that has been the object of study in the past years. This aspect leads to the rapid increase in production costs and reliability reduction. Furthermore, most of the magnetometers that are adapted to this technology are highly complex and with little to no adaptation to outer-space research. In this work, a novel single-axis MEMS magnetometer based on the principle of the Lorentz force capable of reading fields in the X or Y direction is designed and simulated with the description of a fabrication method to be used. This magnetometer uses an innovative design for a current-carrying-bar that’s highly adaptable to a variety of scenarios with a low 100Ω current resistance in each of its paths. An amplitude-modulated method is approached through the use of a capacitive-readout system and an off-resonance frequency of operation to achieve the detection baseline of a 1aF capacitive variation at a 20nT magnetic field. This involves the use of various mechanisms to increase the quality factor and reduce the overall stiffness of the device to increase its displacement caused by the Lorentz force. The device is also to be operated at a 500Pa atmosphere to reduce the damping and, at the same time, increase the quality factor. A thermomechanical noise below 3 /√ with a frequency of operation at around 4977 Hz was deemed necessary to adapt the design to another previously designed single-axis MEMS magnetometer capable of reading fields in the Z direction. Various simulation and design tools are used to predetermine the best properties at which the magnetometer will be operated to its highest capabilities. Through these simulations, a 50Hz bandwidth magnetometer, required for spatial research, is achieved with a capacitance variation of 1.37aF at 20nT surpassing the initial requirements. A 1.77 /√ thermomechanical noise is obtained, well below the baseline that was defined for this work. A fabrication layout was developed with all lithography masks designed, and a microfabrication process flow was devised. The microfabrication process run was partially completed and it’s still ongoing.Os magnetómetros típicos encontrados na investigação de campos magnéticos são altamente incompatíveis com a enorme indústria da tecnologia MEMS que tem sido objeto de estudo nos últimos anos. Este aspeto leva ao rápido aumento dos custos de produção e à redução da fiabilidade. Para além disso a maioria dos magnetómetros adaptados a esta tecnologia são altamente complexos e com pouca ou nenhuma adaptação à investigação espacial. Neste trabalho, um novo magnetómetro MEMS de um único eixo baseado no princípio da força de Lorentz capaz de ler campos na direção X ou Y é concebido e simulado com a descrição de um método de fabrico a ser utilizado. Este magnetómetro utiliza um desenho inovador para uma barra condutora que é altamente adaptável a uma variedade de cenários com uma baixa resistência de 100Ω em cada um dos seus caminhos. Um método de modulação em amplitude é abordado através da utilização de um sistema de leitura capacitiva e uma frequência de operação com um desvio da ressonância para alcançar a linha de base de deteção de uma variação capacitiva de 1aF para um campo magnético de 20nT. Isto envolve a utilização de vários mecanismos para aumentar o fator de qualidade e reduzir a rigidez geral do dispositivo para aumentar o deslocamento causado pela força de Lorentz. O dispositivo deve também ser operado a uma atmosfera de 500Pa para reduzir o amortecimento e, ao mesmo tempo, aumentar o factor de qualidade. Um ruído termomecânico inferior a 3 /√ com uma frequência de operação de cerca de 4977 Hz foram consideradas necessárias para adaptar o desenho a outro magnetómetro MEMS de um eixo, previamente concebido, capaz de ler campos na direção Z. Várias ferramentas de simulação e desenho são utilizadas para pré-determinar as melhores propriedades em que o magnetómetro será operado até às suas capacidades mais elevadas. Através destas simulações, um magnetómetro de 50Hz de largura de banda, necessário para a investigação espacial, é alcançado com uma variação de capacidade de 1.37aF a 20nT, ultrapassando os requisitos iniciais. É obtido um ruído termomecânico de 1.77 /√, bem abaixo da linha de base que foi definida para este trabalho. Foi desenvolvido um esquema de fabricação com todas as máscaras litográficas concebidas, e foi concebido um fluxo de processo de microfabricação. A execução do processo de microfabricação foi parcialmente concluída e ainda está em curso.This work was framed in the scope of the Project (Link4S)ustainability - A new generation connectivity system for creation and integration of networks of objects for new sustainability paradigms [POCI-01- 0247-FEDER-046122 | LISBOA-01-0247-FEDER-046122], financed by the Operational Competitiveness and Internationalization Programmes COMPETE 2020 and LISBOA 2020, under the PORTUGAL 2020 Partnership Agreement, and through the European Structural and Investment Funds in the FEDER component

    Optical Gas Sensing: Media, Mechanisms and Applications

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    Optical gas sensing is one of the fastest developing research areas in laser spectroscopy. Continuous development of new coherent light sources operating especially in the Mid-IR spectral band (QCL—Quantum Cascade Lasers, ICL—Interband Cascade Lasers, OPO—Optical Parametric Oscillator, DFG—Difference Frequency Generation, optical frequency combs, etc.) stimulates new, sophisticated methods and technological solutions in this area. The development of clever techniques in gas detection based on new mechanisms of sensing (photoacoustic, photothermal, dispersion, etc.) supported by advanced applied electronics and huge progress in signal processing allows us to introduce more sensitive, broader-band and miniaturized optical sensors. Additionally, the substantial development of fast and sensitive photodetectors in MIR and FIR is of great support to progress in gas sensing. Recent material and technological progress in the development of hollow-core optical fibers allowing low-loss transmission of light in both Near- and Mid-IR has opened a new route for obtaining the low-volume, long optical paths that are so strongly required in laser-based gas sensors, leading to the development of a novel branch of laser-based gas detectors. This Special Issue summarizes the most recent progress in the development of optical sensors utilizing novel materials and laser-based gas sensing techniques

    Fluid compressional properties sensing at microscale using a longitudinal bulk acoustic wave transducer operated in a pulse-echo scheme

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    Altres ajuts: Acord transformatiu CRUE-CSICAcoustic devices have been widely used as smart chemical and biochemical sensors since they are sensitive to mechanical, chemical, optical or electrical perturbations on their surfaces; making them a reliable option for noninvasive detection of changes in physical properties of liquid samples for real-time applications. Here we present a longitudinal acoustic wave device for study of compressional properties of liquids in microfluidic systems, with the particularity of pulse-echo mode of operation. We have studied at a microscale the interaction between longitudinal acoustic waves and the compressional properties of liquid samples, interrogating the fluids with short pulses of ultrasound at GHz, finding a direct relationship between the magnitude of the bulk modulus or the specific acoustic impedance of liquids and the amplitude of the output voltage produced by acoustic echoes received by the aluminum nitride transducer. Analytical expressions and FEM simulations support the detection mechanism, while applications such as classification of liquids and detection of concentration change in solutions experimentally demonstrate the method. This contribution overcomes current restrictions of film acoustic resonators such as fragility of operation in liquid environments, high manufacturing cost or limitations regarding narrow microchannels; offering an alternative to applications that demand ultra-low consumption, miniaturization, versatility (it offers multi-frequency operation in 1 - 10 GHz range) and ease of readout (peak voltage)

    Entwicklung und Charakterisierung von Sprühtrocknungsprozessen zur Herstellung von β-phasigem PVDF in Partikeln und Filmen

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    Polyvinylidenfluorid (PVDF) ist ein teilkristallines Polymer, das in fünf kristallinen Phasen auftreten kann. In dieser Arbeit wurde die gezielte Herstellung der piezoelektrischen β-Phase durch Sprühtrocknungsprozesse untersucht, wobei der Bildungsmechanismus und die Maximierung des β-Phasenanteils im Fokus standen. Dazu wurden verschiedene Parameter im Sprühtrocknungsprozess, wie die Trocknungsluftmenge, die Art des Zerstäubers, die Massenbeladung, die Temperatur und die Tropfenladung, variiert. Es zeigten sich je nach Prozessbedingungen unterschiedliche Phasenzusammensetzungen des PVDFs. Bei der Sprühtrocknung mit pneumatischen Zerstäubern zeigte sich, dass PVDF bei hinreichend hohen Trocknungsraten nahezu vollständig (ca. 95 %) in der β-Phase hergestellt werden kann. Anhand der Resultate kann die Bildung des PVDFs in seinen unterschiedlichen Phasen mit der Ostwaldschen Stufenregel erklärt werden. Die Stufenregel besagt, dass die Bildung einer kristallinen Phase, zuerst in dem Zustand stattfindet, welcher dem Ursprungszustand energetisch am nächsten ist. Da die β-Phase den höchsten energetischen Zustand hat, wird sie bei schneller Verdampfung des Lösungsmittels gebildet. Bei der Zerstäubung durch Elektrospray entstehen die PVDF-Partikel in einem elektrischen Feld aus geladenen Tropfen. Der Einfluss der Ladung und des elektrischen Feldes auf die kristallinen Phasen wurden in einem modularen Sprühtrocknungsaufbau untersucht, der eine Trennung beider Effekte ermöglichte. Dabei zeigte sich, dass das elektrische Feld keinen Einfluss auf die Bildung der β-Phase hat. Dagegen spielt die Ladung der Tropfen eine wesentliche Rolle bei der Ausbildung der β-Phase. Es macht keinen Unterschied, ob die Ladung direkt beim Tropfenbildungsprozess aufgeprägt wird (z.B. im Elektrospray) oder nachträglich von außen aufgebracht wird (z.B. mittels Koronaaufladung). Offensichtlich hat die elektrische Ladung an der Tropfenoberfläche eine ordnende Wirkung auf die Elemente der PVDF-Ketten, so dass sie sich in der all-trans Konformation ausrichten, d.h. in der β-Phase. Der Effekt war sowohl mit positiver als auch mit negativer Ladung zu beobachten, wenn auch in unterschiedlicher Ausprägung. Um die Hypothese zur Bildung der β-Phase nach der Ostwaldschen Stufenregel weiter zu erhärten, wurden die Verdampfungsraten bei der Trocknung im Spray quantifiziert. Dabei wurde eine Methode verwendet, die eine hochauflösende Quarzkristall-Mikrowaage (QCM) nutzt, um die Trocknungszustände zu ermitteln, und mit einem Elektrospray-Aufbau kombiniert. Die QCM wurde dabei mit PVDF-Partikeln beschichtet. Durch Variation des Abstandes zwischen Elektrospraydüse und QCM konnten unterschiedliche Trocknungszustände auf der QCM realisiert werden. Wenn der Abstand zwischen Düse und QCM gering ist, treffen die Partikel mit einer Restfeuchte auf, ist der Abstand dagegen größer, sind die Partikel beim Auftreffen bereits getrocknet. Es zeigte sich, dass die Trocknungsrate im Spray um bis zu einem Faktor von 104 größer ist als in abgeschiedenen Filmen. Die Phasenzusammensetzung der im Spray getrockneten Partikel weist dabei fast vollständig die β-Phase auf. Bei der langsameren Filmverdampfung ist der β-Phasenanteil deutlich reduziert. Auch bei technisch interessanteren dicken PVDF-Schichten wurde die Abhängigkeit vom Trocknungszustand auf die Bildung der β-Phase beobachtet. Interessanterweise deutete sich beim Abscheideprozess auch eine Polarisation der PVDF-Schichten an, was besonders für die Aufbringung von piezoelektrischen Schichten in einem einfachen Einschritt-Verfahren von Bedeutung ist

    Influence of Materials and Design Parameters on Zinc Oxide Surface Acoustic Devices

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    This thesis presents research into Zinc Oxide (ZnO) based resonators to include Width Extensional Mode (WEM), Length Extensional Mode (LEM), and Surface Acoustic Wave (SAW) devices. The design and operation of ZnO based SAW devices are investigated further to characterize design parameters and operating modes. Their design, fabrication, and results are discussed in detail. SAW device testing in conjunction with X-Ray Diffractometry (XRD) and Atomic Force Microscopy (AFM) are utilized to characterize ZnO and its deposition parameters on a variety of different substrates and interlayers, with different deposition temperatures and annealing parameters. These substrates include silicon, silicon oxide-on-silicon, and sapphire wafers with interlayers including titanium, tungsten, and silicon oxide. Fabrication methods are discussed to explain all processing steps associated with SAW and released contour mode resonators. The SAW devices in this research test different design parameters to establish better reflector design spacing for higher frequency Sezawa wave modes. The characterization and design of ZnO based SAW devices establishes the potential for prototyping high frequency SAW designs using standard lithography techniques. These devices are desired for space-based operations for use in GPS filters, signal processing, and sensing in satellites and space vehicles
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