Development of a compact wireless SAW Pirani vacuum microsensor with extended range and sensitivity

Vakuumsensoren haben nach wie vor einen begrenzten Messbereich und erfordern eine aufwendige Verkabelung sowie eine komplexe Integration in Vakuumkammern. Ein kompakter Sensor, der in der Lage ist, den Erfassungsbereich zwischen Hochvakuum und Atmosphärendruck zu erweitern und dabei drahtlos zu arbeiten, ist äußerst wünschenswert. Der Schwerpunkt dieser Arbeit liegt auf dem Entwurf, der Simulation, der Herstellung und der experimentellen Validierung eines drahtlosen kompakten Vakuum-Mikrosensors mit erweiterter Reichweite und Empfindlichkeit. Zunächst wurde ein neuer Sensor unter Verwendung vorhandener und neu entwickelter Komponenten entworfen. Zweitens wurden die Sensorkomponenten simuliert, um ihre Parameter zu optimieren. Drittens wurde ein Prototyp unter Verwendung der verfügbaren Mikrobearbeitungs- und Halbleitertechnologien hergestellt und montiert. Viertens wurde der Prototyp unter Umgebungs- und Vakuumbedingungen charakterisiert, um seine Leistungen zu validieren. Für das Wandlerprinzip wurden zwei Techniken kombiniert, nämlich Pirani-Sensorik und akustische Oberflächenwellen. Das Design der Sensorkomponenten bestand aus vier Einheiten: Sensoreinheit, Heizeinheit, Abfrageeinheit und Gehäuse. Alle Einheiten wurden in einen kompakten Würfel eingebaut. Einige Komponenten wurden neu entwickelt, während andere gekauft, modifiziert und dann miteinander verbunden wurden. Die Sensoreinheit besteht aus einem neuen Chip mit verbesserter Sensorleistung dank eines optimierten Verhältnisses von Oberfläche zu Volumen. Die Heizeinheit wurde aus zwei induktiv gekoppelten Spulen und der zugehörigen Konditionierungselektronik zusammengesetzt. Die Abfrageeinheit wurde mit einer Mikro-Patch-Antenne hergestellt. Ein würfelförmiges Polymergehäuse wurde entwickelt, um alle Komponenten in einer Vakuumkammer unterzubringen. Zweitens wurde die Simulation des Verhaltens der Sensorkomponenten behandelt. Die für die Druckmessung verantwortliche Wärmeübertragung des Sensorchips wurde vom Hochvakuum bis zum Atmosphärendruck untersucht, um seine Abmessungen zu optimieren. Die Verwendung eines hängenden Lithium-Niobat-Chips mit Y-Z-Schnitt und einem TCF von 94 ppm/K führte zu einer verbesserten Leistung in einem Messbereich zwischen \num{d-4}~Pa und \num{e5}~Pa. Die elektronische Kopplung der Heizspulen wurde ebenfalls simuliert, um die Leistungsübertragung und den Kopplungsabstand zu optimieren. Der dritte Teil betrifft die Herstellungs- und Montageschritte des Prototyps unter Verwendung der verfügbaren Halbleitertechnologien und -ausrüstung. Ein SAW Chip wurde mit einer 100~nm dicken Goldschicht an der Unterseite gesputtert, um den Heizwiderstand zu bilden, und mit Hilfe von Drahtbonding elektrisch mit dem Rest des Sensors verbunden. Es wurde eine Leiterplatte vorbereitet, die die Heiz- und Sensoreinheit enthält. Ein kubisches Gehäusewurde aus PTFE hergestellt. Viertens wurden die Sensorkomponenten zunächst separat charakterisiert, um ihre Leistungen zu überprüfen, und dann zusammen unter Umgebungsbedingungen. Später wurde der Sensor im Vakuum integriert, und es wurde ein druckabhängiges Verhalten des Sensorchips beobachtet. Die Relevanz eines drahtlosen Übertragungsverfahrens wurde den herkömmlichen drahtgebundenen Methoden gegenübergestellt. Die Ergebnisse der experimentellen Arbeiten außerhalb und innerhalb des Vakuums zeigten die Machbarkeit und Relevanz des neuen Konzepts

Design and Simulation of a Wireless SAW-Pirani Sensor with Extended Range and Sensitivity

Pressure is a critical parameter for a large number of industrial processes. The vacuum industry relies on accurate pressure measurement and control. A new compact wireless vacuum sensor was designed and simulated and is presented in this publication. The sensor combines the Pirani principle and Surface Acoustic Waves, and it extends the vacuum sensed range to between 10-4 Pa and 105 Pa all along a complete wireless operation. A thermal analysis was performed based on gas kinetic theory, aiming to optimize the thermal conductivity and the Knudsen regime of the device. Theoretical analysis and simulation allowed designing the structure of the sensor and its dimensions to ensure the highest sensitivity through the whole sensing range and to build a model that simulates the behavior of the sensor under vacuum. A completely new design and a model simulating the behavior of the sensor from high vacuum to atmospheric pressure were established

Nanoelectromechanical Sensors based on Suspended 2D Materials

The unique properties and atomic thickness of two-dimensional (2D) materials enable smaller and better nanoelectromechanical sensors with novel functionalities. During the last decade, many studies have successfully shown the feasibility of using suspended membranes of 2D materials in pressure sensors, microphones, accelerometers, and mass and gas sensors. In this review, we explain the different sensing concepts and give an overview of the relevant material properties, fabrication routes, and device operation principles. Finally, we discuss sensor readout and integration methods and provide comparisons against the state of the art to show both the challenges and promises of 2D material-based nanoelectromechanical sensing.Comment: Review pape

Investigating polymer optical fibre Bragg grating technology for freeze drying applications

Pharmaceuticals and biologics that are unstable in aqueous form but liable to thermal degradation are generally freeze dried or lyophilised to extend their shelf life. Primary drying is the most expensive and longest stage of the freeze drying process, prompting extensive research to reduce production costs and increase productivity. This work investigated current commercially available technologies used to detect sublimation of water vapour and determine the end of primary drying time. The investigation identified the potential cost benefits of using polymer optical fibre Bragg gratings (POFBGs), as non-invasive sensors that monitor batch sublimation of water vapour during primary drying. The thesis initially discusses the fabrication of POFBG sensors, the protocols and housing structure developed to protect the sensors in this extreme environment. This was achieved by studying the behaviour of custom-built anemometers, temperature data loggers and sensors that detect changes in gas composition. The next stage involved the characterisation of PMMA and TOPAS POFBGs to changes in temperature and pressure within the chamber. This provided information on the sensitivity of the sensors to these parameters at dry sub-atmospheric pressures. The studies revealed red shifts in the Bragg wavelengths as temperature decreased from an inlet shelf temperature of 20oC to -20oC and temperature drifts from radiative heat effects. The pressure studies revealed non-linear Bragg wavelength sensitivity within the region of 200μbar to 2500μbar, several orders of magnitude greater than reported within literature in high pressure chambers. The POFBGs were exposed to water vapour subliming from samples of water, mannitol and native collagen, which were frozen and attached to the access port or placed onto the shelf and freeze dried. The studies reveal the potential for POFBG technology to be used to detect sublimation and end of primary drying, with future work focusing on modifications to the design and temperature compensation technique

Integration of electronic and optical techniques in the design and fabrication of pressure sensors

Since the introduction of micro-electro-mechanical systems fabrication methods, piezoresistive pressure sensors have become the more popular pressure transducers. They dominate pressure sensor commercialization due to their high performance, stability and repeatability. However, increasing demand for harsh environment sensing devices has made sensors based on Fabry-Perot interferometry the more promising optical pressure sensors due to their high degree of sensitivity, small size, high temperature performance, versatility, and improved immunity to environmental noise and interference. The work presented in this dissertation comprises the design, fabrication, and testing of sensors that fuse these two pressure sensing technologies into one integrated unit. A key innovation is introduction of a silicon diaphragm with a center rigid body (or boss), denoted as an embossed diaphragm, that acts as the sensing element for both the electronic and optical parts of the sensor. Physical principles of piezoresistivity and Fabry-Perot interferometry were applied in designing an integrated sensor and in determining analytic models for the respective electronic and optical outputs. Several test pressure sensors were produced and their performance was evaluated by collecting response and noise data. Diaphragm deflection under applied pressure was detected electronically using the principle of piezoresistivity and optically using Fabry-Perot interferometry. The electronic part of the sensor contained four p-type silicon piezoresistors that were set into the diaphragm. They were connected in a Wheatstone bridge configuration for detecting strain-dependent changes in resistance induced by diaphragm deflection. In the optical part of the sensor, an optical cavity was formed between the embossed surface of the diaphragm and the end face of a single mode optical fiber. An infrared laser operating at 1.55 was used for optical excitation. Deflection of the diaphragm, which causes the length of the optical cavity to change, was detected by Fabry-Perot interference in the reflected light. Data collected on several sensors fabricated for this dissertation were shown to validate the theoretical models. In particular, the principle of operation of a Fabry-Perot interferometer as a mechanism for pressure sensing was demonstrated. The physical characteristics and behavior of the embossed diaphragm facilitated the integration of the electronic and optical approaches because the embossed diaphragm remained flat under diaphragm deflection. Consequently, it made the electronic sensor respond more linearly to applied pressure. Further, it eliminated a fundamental deficiency of previous applications of Fabry-Perot methods, which suffered from non-parallelism between the two cavity surfaces (diaphragm and fiber), owing to diaphragm curvature after pressure was applied. It also permitted the sensor to be less sensitive to lateral misalignment during the fabrication process and considerably reduced back pressure, which otherwise reduced the sensitivity of the sensor. As an integrated sensor, it offered two independent outputs in one sensor and therefore the capability for measurements of: (a) static and dynamic pressures simultaneously, and (b) two different physical quantities such as temperature and pressure

A Low-Cost Short-Distance Thermal Conduction Pressure Sensor

A low-cost thermal pressure sensor based on short-distance thermal conduction and used in atmospheric pressure range has been explored. This simple device consists of a heater made of a polysilicon resistor, a heat sink made by the silicon substrate and a tiny air gap between them. With innovative ideas and simple processes, the gap can be made in the order of nanometers inexpensively, which significantly increases the measurement range of the sensor. Devices capable of measuring 700kPa (7atm) or more have been fabricated with a 3-mask, 3pm and CMOS compatible process. The device can be made as small as 50x50pm2, less than the size of a standard bonding pad. The simple process and low cost associated with these devices could make commercial adaptation promising

A new SiC/HfB2 based micro hotplate for metal oxide gassensors

Abstract Solzbacher, Florian A new SiC/HfB2 based modular concept of micro hotplates for metal oxide gassensors Im Rahmen dieser Arbeit wurde ein neuer SiC/HfB2-basierter Mikroheizer mit niedrigster Leistungsaufnahme für die Anwendung in Metalloxid-Gassensoren entwickelt und demonstriert. Erstmals wurden Siliziumkarbid (SiC) und Hafniumdiborid (HfB2) als Werkstoffe für einen Mikroheizer eingesetzt. Durch geringe Modifikation der Herstellungsprozesse lässt sich der Heizer so variieren, dass der Einsatz sowohl für den automobilen Anwendungsbereich (12V- 24V) als auch für tragbare Geräte (1V-2V) für eine Vielzahl unterschiedlicher Messgase möglich ist. Es ist der erste Mikroheizer für Gassensoren überhaupt, der den Batteriebetrieb bei nur 1-2 V erlaubt. Der modulare Fertigungsansatz ermöglicht die Reduzierung der Entwicklungs- und Fertigungskosten für die unterschiedlichen Anwendungsbereiche. Aus der Marktentwicklung in der Sensorik, den industriellen Anforderungen und den zu den Metalloxid-Gassensoren im Wettbewerb stehenden alternativen Technologien ergeben sich das Anforderungsprofil des Sensors. Die Wahl der Materialien spielt eine Schlüsselrolle für die Heizereigenschaften. Der Mikroheizer besteht aus einer 1 (m dicken, an 150 (m langen und 10 bis 40 (m breiten Stegen aufgehängten Membran mit Außenmaßen von 100 (m x 100 (m. Alternativ kommen eine HfB2 - Dünnfilm-Widerstandsheizung oder ein dotierter SiC-Heizer zum Einsatz. Mit Leistungsaufnahmen von 32 mW werden Temperaturen von 600°C erreicht, was einer Effizienz von ca. 19 K/mW entspricht. Die verwendeten hexagonalen Strukturen ermöglichen dichtes Packen der Sensoren in Arrays bei hoher mechanischer Stabilität. Erste NO2 Sensoren mit gassensitiver In2O3 Schicht konnten gezeigt werden.A new SiC/HfB2-based micro hotplate with ultra low power consumption for the application in metal oxide micro gas sensors is developed and demonstrated. For the first time, silicon carbide (SiC) and Hafniumdiboride (HfB2) are used as materials for a micro hotplate structure. Using only slight modifications of the fabrication process, the device can be used either for automotive applications with operating voltages of 12V-24V or for battery operated handheld detectors with operating voltages of 1V-2V for a variety of different gases. It is the first micro hotplate device ever designed to work for low battery voltages of 1V-2V. The modular approach towards the processing allows easy modification for a variety of application fields and thus also reduces market entrance barriers. Based on the market development of micro sensors, the industrial requirements, and competing metal oxide gas sensors using alternative technologies, technical specifications for the hotplate as well as the state of the art's limits are determined. The new material choice plays a key role in the device properties. The micro hotplate consists of a 100 ?m x 100 ?m membrane supported by thin beams of 1 ?m thickness, 150 ?m length and 10 to 40 ?m width. Alternatively, an HfB2 ? thin film resistive heater or a doped SiC heater are used. Temperatures of 600°C are achieved using a power consumption of only 32 mW resulting in a thermal heater efficiency of ~19 K/mW. The hexagonal geometry allows close packing of the hotplates in array structures with high mechanical strength. NO2 sensors with gas sensitive In2O3 layer are presented

Technology Development Roadmap: A Technology Development Roadmap for a Future Gravitational Wave Mission

Humankind will detect the first gravitational wave (GW) signals from the Universe in the current decade using ground-based detectors. But the richest trove of astrophysical information lies at lower frequencies in the spectrum only accessible from space. Signals are expected from merging massive black holes throughout cosmic history, from compact stellar remnants orbiting central galactic engines from thousands of close contact binary systems in the Milky Way, and possibly from exotic sources, some not yet imagined. These signals carry essential information not available from electromagnetic observations, and which can be extracted with extraordinary accuracy. For 20 years, NASA, the European Space Agency (ESA), and an international research community have put considerable effort into developing concepts and technologies for a GW mission. Both the 2000 and 2010 decadal surveys endorsed the science and mission concept of the Laser Interferometer Space Antenna (LISA). A partnership of the two agencies defined and analyzed the concept for a decade. The agencies partnered on LISA Pathfinder (LPF), and ESA-led technology demonstration mission, now preparing for a 2015 launch. Extensive technology development has been carried out on the ground. Currently, the evolved Laser Interferometer Space Antenna (eLISA) concept, a LISA-like concept with only two measurement arms, is competing for ESA's L2 opportunity. NASA's Astrophysics Division seeks to be a junior partner if eLISA is selected. If eLISA is not selected, then a LISA-like mission will be a strong contender in the 2020 decadal survey. This Technology Development Roadmap (TDR) builds on the LISA concept development, the LPF technology development, and the U.S. and European ground-based technology development. The eLISA architecture and the architecture of the Mid-sized Space-based Gravitational-wave Observatory (SGO Mid)-a competitive design with three measurement arms from the recent design study for a NASA-led mission after 2020-both use the same technologies. Further, NASA participation in an ESA-led mission would likely augment the eLISA architecture with a third arm to become the SGO Mid architecture. For these reasons, this TDR for a future GW mission applies to both designs and both programmatic paths forward. It is adaptable to the different timelines and roles for an ESA-led or a NASA-led mission, and it is adaptable to available resources. Based on a mature understanding of the interaction between technology and risk, the authors of this TDR have chosen a set of objectives that are more expansive than is usual. The objectives for this roadmap are: (1) reduce technical and development risks and costs; (2) understand and, where possible, relieve system requirements and consequences; (3) increase technical insight into critical technologies; and (4) validate the design at the subsystem level. The emphasis on these objectives, particularly the latter two, is driven by outstanding programmatic decisions, namely whether a future GW mission is ESA-led or NASA-led, and availability of resources. The relative emphasis is best understood in the context of prioritization

NASA Tech Briefs, October 2010

Topics covered include: Hybrid Architecture Active Wavefront Sensing and Control; Carbon-Nanotube-Based Chemical Gas Sensor; Aerogel-Positronium Technology for the Detection of Small Quantities of Organic and/or Toxic Materials; Graphene-Based Reversible Nano-Switch/Sensor Schottky Diode; Inductive Non-Contact Position Sensor; High-Temperature Surface-Acoustic-Wave Transducer; Grid-Sphere Electrodes for Contact with Ionospheric Plasma; Enabling IP Header Compression in COTS Routers via Frame Relay on a Simplex Link; Ka-Band SiGe Receiver Front-End MMIC for Transponder Applications; Robust Optimization Design Algorithm for High-Frequency TWTs; Optimal and Local Connectivity Between Neuron and Synapse Array in the Quantum Dot/Silicon Brain; Method and Circuit for In-Situ Health Monitoring of Solar Cells in Space; BGen: A UML Behavior Network Generator Tool; Platform for Post-Processing Waveform-Based NDE; Electrochemical Hydrogen Peroxide Generator; Fabrication of Single, Vertically Aligned Carbon Nanotubes in 3D Nanoscale Architectures; Process to Create High-Fidelity Lunar Dust Simulants; Lithium-Ion Electrolytes Containing Phosphorous-Based, Flame-Retardant Additives; InGaP Heterojunction Barrier Solar Cells; Straight-Pore Microfilter with Efficient Regeneration; Determining Shear Stress Distribution in a Laminate; Self-Adjusting Liquid Injectors for Combustors; Handling Qualities Prediction of an F-16XL-Based Reduced Sonic Boom Aircraft; Tele-Robotic ATHLETE Controller for Kinematics - TRACK; Three-Wheel Brush-Wheel Sampler; Heterodyne Interferometer Angle Metrology; Aligning Astronomical Telescopes via Identification of Stars; Generation of Optical Combs in a WGM Resonator from a Bichromatic Pump; Large-Format AlGaN PIN Photodiode Arrays for UV Images; Fiber-Coupled Planar Light-Wave Circuit for Seed Laser Control in High Spectral Resolution Lidar Systems; On Calculating the Zero-Gravity Surface Figure of a Mirror; Optical Modification of Casimir Forces for Improved Function of Micro- and Nano-Scale Devices; Analysis, Simulation, and Verification of Knowledge-Based, Rule-Based, and Expert Systems; Core and Off-Core Processes in Systems Engineering; Digital Reconstruction Supporting Investigation of Mishaps; and Template Matching Approach to Signal Prediction

Graphene/P(VDF-TrFE) Heterojunction Based Wearable Sensors with Integrated Piezoelectric Energy Harvester

Graphene, with its outstanding material properties, including high carrier mobility, atomically thin nature, and ability to tolerate mechanical deformation related strain up to 20% before breaking, make it very attractive for developing highly sensitive and conformable strain/pressure sensor for wearable electronics. Unfortunately, graphene by itself is not piezoresistive, so developing a strain sensor utilizing just graphene is challenging. Fortunately, graphene synthesized on Cu foil can be transferred to arbitrary substrates (preserving its high quality), including flexible polymer substrates, which will allow the overall flexibility and conformability of the sensing element, to be maintained. Furthermore, a graphene/polymer based sensor devices can be easily patterned into an array over dimensions reaching several feet, taking advantage of large area synthesis of graphene, which will make the ultimate sensor very inexpensive. If a piezo-electric polymer, such as P(VDF-TrFE), is chosen to form a heterojunction with graphene, it will strongly affect the carrier density in graphene, due to the fixed charge developing on its surface under strain or pressure. Taking advantage of the high carrier mobility in graphene, such a charge change can result in very high sensitivity to pressure and strain. Hence, these features, coupled with the flexible nature of the device and ease of fabrication, make it a very attractive candidate for use in the growing wearable technology market, especially biomedical applications and smart health monitoring system as well as virtual reality sensors. In this dissertation, various unique properties of graphene and P(VDF-TrFE), and their current applications and trends are discussed in chapter 1. Additionally, synthesis of graphene and P(VDF-TrFE) and their characterizations by various techniques are investigated in chapter 2. Based on piezoelectric property of P(VDF-TrFE), a highly flexible energy harvesters on PDMS as well as PET substrates have been developed and demonstrated their performances in chapter 3. As follow-up research, graphene/P(VDF-TrFE) heterojunction based wearable sensors with integrated piezoelectric energy harvester on flexible substrates have also been fabricated and demonstrated for practical wearable application in chapter 4. Finally, major findings and future directions of the project are discussed in chapter 5