Interface Circuits for Microsensor Integrated Systems

ca. 200 words; this text will present the book in all promotional forms (e.g. flyers). Please describe the book in straightforward and consumer-friendly terms. [Recent advances in sensing technologies, especially those for Microsensor Integrated Systems, have led to several new commercial applications. Among these, low voltage and low power circuit architectures have gained growing attention, being suitable for portable long battery life devices. The aim is to improve the performances of actual interface circuits and systems, both in terms of voltage mode and current mode, in order to overcome the potential problems due to technology scaling and different technology integrations. Related problems, especially those concerning parasitics, lead to a severe interface design attention, especially concerning the analog front-end and novel and smart architecture must be explored and tested, both at simulation and prototype level. Moreover, the growing demand for autonomous systems gets even harder the interface design due to the need of energy-aware cost-effective circuit interfaces integrating, where possible, energy harvesting solutions. The objective of this Special Issue is to explore the potential solutions to overcome actual limitations in sensor interface circuits and systems, especially those for low voltage and low power Microsensor Integrated Systems. The present Special Issue aims to present and highlight the advances and the latest novel and emergent results on this topic, showing best practices, implementations and applications. The Guest Editors invite to submit original research contributions dealing with sensor interfacing related to this specific topic. Additionally, application oriented and review papers are encouraged.

Thin-Film AlN-on-Silicon Resonant Gyroscopes: Design, Fabrication, and Eigenmode Operation

Resonant MEMS gyroscopes have been rapidly adopted in various consumer, industrial, and automotive applications thanks to the significant improvements in their performance over the past decade. The current efforts in enhancing the performance of high-precision resonant gyroscopes are mainly focused on two seemingly contradictory metrics, larger bandwidth and lower noise level, to push the technology towards navigation applications. The key enabling factor for the realization of low-noise high-bandwidth resonant gyroscopes is the utilization of a strong electromechanical transducer at high frequencies. Thin-film piezoelectric-on-silicon technology provides a very efficient transduction mechanism suitable for implementation of bulk-mode resonant gyroscopes without the need for submicron capacitive gaps or large DC polarization voltages. More importantly, in-air operation of piezoelectric devices at moderate Q values allows for the cointegration of mode-matched gyroscopes and accelerometers on a common substrate for inertial measurement units. This work presents the design, fabrication, characterization, and method of mode matching of piezoelectric-on-silicon resonant gyroscopes. The degenerate in-plane flexural vibration mode shapes of the resonating structure are demonstrated to have a strong gyroscopic coupling as well as a large piezoelectric transduction coefficient. Eigenmode operation of resonant gyroscopes is introduced as the modal alignment technique for the piezoelectric devices independently of the transduction mechanism. Controlled displacement feedback is also employed as the frequency matching technique to accomplish complete mode matching of the piezoelectric gyroscopes.Ph.D

Design of a MEMS-based 52 MHz oscillator

Mechanical resonators are widely applied in time-keeping and frequency reference applications. Mechanical resonators are preferred over electrical resonators because of their high Q. In the $4.1 billion (2008) timing market, quartz crystals are still ubiquitous in electronic equipment. Quartz crystals show excellent performance in terms of stability (shortterm and long-term), power handling, and temperature drift. MEMS resonators are investigated as a potential alternative to the bulky quartz crystals, which cannot be integrated with IC technology. MEMS offer advantages in terms of size, cost price, and system integration. Efforts over recent years have shown that MEMS resonators are able to meet the high performance standards set by quartz. Critical success factors are high Q-factor, low temperature drift, low phase noise, and low power. This PhD thesis addresses the feasibility of scaling MEMS resonators/oscillators to frequencies above 10 MHz. The main deliverable is a 52 MHz MEMS-based oscillator. The MEMS resonators at NXP are processed on 8-inch silicon-on-insulator (SOI) wafers, with a SOI layer thickness of 1.5 µm and a buried oxide layer thickness of 1 µm. The strategic choice for thin SOI substrates has been made for two reasons. First, MEMS processing in thin silicon layers can be done with standard CMOS processing tools. The silicon dioxide layer serves as a sacrificial layer. Second, identical substrates are used for the Advanced Bipolar CMOS DMOS (ABCD) IC-processes. This class of processes can handle high voltages (ABCD2 up to 120V). The high voltage capability is suitable for the transduction of the mechanical resonator. Both MEMS and IC are processed on a similar substrate, since the strategic aim is to integrate the MEMS structure with the IC-process in the long run. Frequency scaling is investigated for both the capacitive and the piezoresistive MEMS resonator. MEMS resonators have been successfully tested from 13 MHz to over 400 MHz. This is achieved by decreasing the size of the resonator with a factor 32. We show that the thin SOI layer and the decreasing size of the resonator increase the effective impedance of the capacitive resonator at higher frequencies. For the piezoresistive resonator, we show that this readout principle is insensitive to geometrical scaling and layer thickness. Therefore, the piezoresistive readout is preferred at high frequencies. The effective impedance can be kept low, at the expense of higher power consumption. Frequency accuracy can be improved by decreasing the initial frequency spread and the temperature drift of the MEMS resonator. The main source of initial frequency spread is geometrical offset, due to the non-perfect pattern transfer from mask layout to SOI. A FEM tool has been developed in Comsol Multiphysics to obtain compensated layouts. The resonance frequency of these designs is first-order compensated for geometric offset. The FEM tool is used to obtain compensated resonators of various designs. We show empirically that the compensation by design is effective on a 52 MHz square plate design. For the compensated design, frequency spread measurements over a complete wafer show that there are other systematic sources of frequency spread. The resonance frequency of the silicon MEMS resonator drifts about –30 ppm/K. This is due to the Young’s modulus of silicon that depends on temperature. We have investigated two compensation methods. The first is passive compensation by coating the silicon resonator with a silicon dioxide skin. The Young’s modulus of silicon dioxide has a positive temperature drift. Measurements on globally oxidized structures show that the right oxide thickness reduces the linear temperature drift of the resonator to zero. A second method uses an oven-control principle. The temperature of the resonator is fixed, independent of the ambient temperature. A demo of this principle has been designed with a piezoresistive resonator in which the dc readout current through the resonator is used to control the temperature of the resonator. With both concepts, more than a factor 10 reduction in temperature drift is achieved. To demonstrate the feasibility of high-frequency oscillators, a MEMS-based 56 MHz oscillator has been designed for which a piezoresistive dogbone resonator is used. The amplifier has been designed in the ABCD2 IC-process. The MEMS oscillator consumes 6.1 mW and exhibits a phase noise of –102 dBc/Hz at 1 kHz offset from the carrier and a floor of –113 dBc/Hz. This demonstrates feasibility of the piezoresistive MEMS oscillator for lowpower, low-noise applications. Summarizing, this PhD thesis work as part of the MEMSXO project at NXP demonstrates a MEMS oscillator concept based on the piezoresistive resonator in thin SOI. It shows that by compensated designs for geometric offset and oven-control to reduce temperature drift, a frequency accuracy can be achieved that can compete with the performance of crystal oscillators. In a benchmark with MEMS competitors the concept shows the lowest phase noise, making it the most suited concept for wireless applications

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 implementation of a mobile sensor system for human posture tracking

De reconstructie van menselijke houding en het traceren van bewegingen kan in vele toepassingen worden gebruikt. Van animatie waar de bewegingen van acteurs kunnen gekoppeld worden aan een digitaal personage, tot revalidatie waar artsen na biomechanische analyse snel accurate diagnoses kunnen stellen. De snelle evolutie in de ontwikkeling van microsensoren en de opkomst van draadloze sensornetwerken hebben ertoe geleid dat draadloze nodes met verschillende sensoren hiervoor kunnen worden gebruikt. Door de informatie van deze sensoren te combineren is het immers mogelijk om absolute oriëntatie te berekenen. Eens deze informatie van elk lichaamsdeel bekend is, kan de volledige houding gereconstrueerd worden. In dit onderzoek werd een inertieel traceringssysteem ontwikkeld waarbij, in tegenstelling tot commerciële oplossingen, geen gyroscopen werden gebruikt. De sensor nodes worden enkel voorzien van accelerometers en magnetometers. Computer software implementeert het traceringssalgoritme en visualiseert de gereconstrueerde menselijke houding. Ingebedde software bepaalt dan weer de werking van de nodes en implementeert een draadloos protocol op maat dat toelaat om de informatie van verschillende nodes te ontvangen. De werking van het volledige systeem werd gevalideerd aan de hand van experimenten waarbij de houding van een persoon werd gevolgd.Human posture reconstruction and motion tracking is of interest for many different applications. From animation where captured motion sequences from actors can be mapped to a digital character in order to obtain a realistic visualization, to revalidation, where biomechanical analysis enables physicians to determine which exercises should be executed for a better and faster recovery. The combination of the increasingly fast evolution in the development of micromachined and the rise of wireless sensor networks as a distributed solution has allowed inertial sensors to become a fast emerging technology for orientation tracking. Sensor nodes equipped with accelerometers, magnetometers and gyroscopes supply three dimensional readings that can be used to determine driftfree absolute orientation. By approximating the human body by a set of rigid structures interconnected by joints, posture reconstruction is made possible when each of the individual bodyparts is equipped with a sensor node. In this work, an inertial tracking system was developed where, contrast to commercial applications, no gyroscopes were included. The sensor nodes were only equipped with accelerometers and magnetometers. Computer software implements the tracking algorithm and visualizes the reconstructed human posture. Embedded software determines the functionality of the nodes and implements a fully custom wireless protocol that allows to receive information from several nodes. The functionality of the entire system was validated by conducting full body tracking experiments

The 2nd International Electronic Conference on Applied Sciences

This book is focused on the works presented at the 2nd International Electronic Conference on Applied Sciences, organized by Applied Sciences from 15 to 31 October 2021 on the MDPI Sciforum platform. Two decades have passed since the start of the 21st century. The development of sciences and technologies is growing ever faster today than in the previous century. The field of science is expanding, and the structure of science is becoming ever richer. Because of this expansion and fine structure growth, researchers may lose themselves in the deep forest of the ever-increasing frontiers and sub-fields being created. This international conference on the Applied Sciences was started to help scientists conduct their own research into the growth of these frontiers by breaking down barriers and connecting the many sub-fields to cut through this vast forest. These functions will allow researchers to see these frontiers and their surrounding (or quite distant) fields and sub-fields, and give them the opportunity to incubate and develop their knowledge even further with the aid of this multi-dimensional network