A MEMS Dual Vertical Electrometer and Electric Field-Mill

Presented is the first iteration of a Microelectromechanical System (MEMS) dual vertical electrometer and electric field-mill (EFM). The device uses a resonating structure as a variable capacitor that converts the presence of a charge or field into an electric signal. Previous MEMS electrometers are lateral electrometers with laterally spaced electrodes that resonate tangentially with respect to each other. Vertical electrometers, as the name suggests, have vertically spaced electrodes that resonate transversely with respect to each other. The non-tangential movement reduces damping in the system. Both types demonstrate comparable performance, but the vertical electrometer does so at a fraction of the size. In addition, vertical electrometers can efficiently operate as an electric field sensor. The electric field sensor simulations did not compare as well to other MEMS electric field sensors. However, the dual nature of this device makes it appealing. These devices can be used in missiles and satellites to monitor charge buildup in electronic components and the atmosphere [11]. Future iterations can improve these devices and give way to inexpensive, high-resolution electrostatic charge and field sensors

Towards a high bias voltage MEMS filter using electrostatic levitation

Traditional MEMS filters use a comb drive structure that suffers from the pull- in instability, which places a significant limitation on the achievable signal-to- noise ration of the sensor. Because the output signal from a capacitive sensor is linearly related to the applied voltage, it is desirable to use a capacitive sensor that can withstand large voltages upwards of 100V. However, the pull-in instability causes high voltages to destroy the device and a trade-off between performance and reliability must be made. Electrostatic levitation, which works by pulling electrodes apart instead of together, eliminates the pull-in instability and allows for very high voltages to be applied without damaging or destroying the sensor/actuator. This study theoretically and experimentally demonstrates that a filter based on electrostatic levitation eliminates the voltage limitation of the capacitive sensor, which has historically hampered the performance of the filter. A model of the filter is derived and validated with experimental data. Voltages up to 100V are applied without damaging the filter

Design of an Integrated Electrostatic Atomic Force Microscope

The need for investigation and characterization of physical, chemical and structural properties of material surfaces at the micro and nano scales led to the invention of Atomic Force Microscopy (AFM) in 1986 as a successor to the well-known Scanning Tunneling Microscopy (STM) to overcome the main shortcoming of STM, which worked only on conducting or semiconducting materials. In fact, the idea of AFM is predicated on the measurement of inter-atomic interaction forces between the molecules of a sharp stylus at the end of a silicon probe and the molecules of a specimen, when the tip comes to close proximity (less than $100$nm) of the sample. It detects the height of the probe hovering above the specimen surface by measuring the tip deflection, or the amplitude and frequency of its vibration. In each case (mode), the interaction forces between the sharp tip and the specimen govern the measured parameter which is detected optically by a laser beam reflected of the probe back side. A piezoelectric actuator drives the probe vibrations and Z-axis motions. Optical detection and piezoelectric actuation contribute significantly to the price and complexity of traditional AFM systems. In this research effort, we use electrostatic actuation and capacitive motion detection of off-shelf AFM probes via electrodes printed on a Printed Circuit Board (PCB), thereby eliminating the optical and piezoelectric components of traditional AFMs, drastically reducing its cost, size and complexity as well as enabling new AFM operating modes. Two configurations for the probe-electrode system were modeled, simulated and demonstrated experimentally. The actuation voltage contains DC and AC components while the actuation frequency is set close to the probe natural frequency. Model and experimental results show that the DC component controls the operating point (static gap between the electrode and the probe) and the AC component controls the sensitivity of the AFM. The detector output current is first amplified using a low-noise transimpedance amplifier. Next, a lock-in amplifier measures the magnitude and phase of the current at the second harmonic of the actuation frequency which is directly related to the tip-sample separation. This detection method overcomes the effect of large parasitic capacitance. It enables us to sketch two-dimensional maps of the current's magnitude or phase representing the specimen's topography. To improve sensitivity, the static distance between the probe\textquoteright s tip and the specimen was set to operate the AFM in intermittent (tapping) mode. A nano-stage was developed for this purpose. It allows us to raster scan the specimen surface. In future work, automatic closed-loop feedback control should be deployed to manage the height of the AFM tip over the specimen. A resonant drive and detection scheme should also be used to miniaturize the footprint of the AFM system to a few centimeters

Hardware and Methods for Scaling Up Quantum Information Experiments

Quantum computation promises to solve presently intractable problems, with hopes of yielding solutions to pressing issues to society. Despite this, current machines are limited to tens of qubits. The field is in a state of continuous scaling, with groups around the world working on all aspects of this problem. The work of this thesis aims to contribute to this effort. It is motivated by the goal of increasing both the speed and bandwidth of experiments conducted within our laboratory. Low-loss radio-frequency multiplexers were characterised at cryogenic temperatures, with some shown to operate at below 7mK. The Analog Devices ADG904 was one of these, and its insertion loss was measured at <0.5dB up to 2GHz. Their heat load was measured, and it was found that a switching speed of 10 MHz with an RF signal power of -30dB dissipates 43uW. Installing these switches yields a benefit over installing extra cabling in our cryostat for a switching speed of up to 2MHz and RF power of -30dBm. A switch matrix was prototyped for cryogenic operation, enabling re-routing of wiring inside a cryostat with a minimally increased thermal load. This could be used to significantly increase the scale of high frequency experiments. This switch has also been embedded within a calibration routine, facilitating measurement of a specific feature of interest at millikelvin temperatures. As the field of quantum engineering scales, such measurements will be crucial to close the loop, providing feedback to fabrication and semiconductor growth efforts. Finally, a rapid-turnaround test rig has been developed which has 32 high frequency and 100 DC lines, enabling tests of significant scale in liquid helium. This reduces the time per experiment at 4.2 K to hours rather than days, enabling tests such as thermal cycling, as well as the evaluation of on-chip structures or active electronics and classical computing hardware; which are all necessary elements of any solid state quantum computing architecture

Design and investigation of microelectromechanical (MEMS) varactors

Three surface micromachined all-metal electrostatically driven varactors were designed, fabricated, and tested at low frequency (10 kHz) in the presented work. Capacity ratios of 1.65, 3.29, and 4.36 were measured. Main problems with possible solutions were discussed. Ways to improve the capacity ratios were proposed

Multimodal Wearable Sensors for Human-Machine Interfaces

Certain areas of the body, such as the hands, eyes and organs of speech production, provide high-bandwidth information channels from the conscious mind to the outside world. The objective of this research was to develop an innovative wearable sensor device that records signals from these areas more conveniently than has previously been possible, so that they can be harnessed for communication. A novel bioelectrical and biomechanical sensing device, the wearable endogenous biosignal sensor (WEBS), was developed and tested in various communication and clinical measurement applications. One ground-breaking feature of the WEBS system is that it digitises biopotentials almost at the point of measurement. Its electrode connects directly to a high-resolution analog-to-digital converter. A second major advance is that, unlike previous active biopotential electrodes, the WEBS electrode connects to a shared data bus, allowing a large or small number of them to work together with relatively few physical interconnections. Another unique feature is its ability to switch dynamically between recording and signal source modes. An accelerometer within the device captures real-time information about its physical movement, not only facilitating the measurement of biomechanical signals of interest, but also allowing motion artefacts in the bioelectrical signal to be detected. Each of these innovative features has potentially far-reaching implications in biopotential measurement, both in clinical recording and in other applications. Weighing under 0.45 g and being remarkably low-cost, the WEBS is ideally suited for integration into disposable electrodes. Several such devices can be combined to form an inexpensive digital body sensor network, with shorter set-up time than conventional equipment, more flexible topology, and fewer physical interconnections. One phase of this study evaluated areas of the body as communication channels. The throat was selected for detailed study since it yields a range of voluntarily controllable signals, including laryngeal vibrations and gross movements associated with vocal tract articulation. A WEBS device recorded these signals and several novel methods of human-to-machine communication were demonstrated. To evaluate the performance of the WEBS system, recordings were validated against a high-end biopotential recording system for a number of biopotential signal types. To demonstrate an application for use by a clinician, the WEBS system was used to record 12‑lead electrocardiogram with augmented mechanical movement information

An Implantable Microsystem for Autonomous Intraocular Pressure Monitoring .

Glaucoma, a leading cause of blindness worldwide, is a disease in which the pressure within the eye is too high for the eye to tolerate and must be reduced in order to slow or prevent damage to the optic nerve. Conventional methods for monitoring eye pressure are normally only used in the physician’s office and rely on indirect measurement methods, leading to inaccuracies. Furthermore, intraocular pressure can vary throughout the day and also depends on activity. An autonomous implantable microsystem capable of monitoring intraocular pressure with minimal patient intervention would provide useful information to the clinician in the management of glaucoma. This dissertation studies the feasibility of an integrated microsystem for autonomously measuring intraocular pressure. Small size ensures minimal impact on the patient, preventing the device from entering the field of view and simplifying implantation. Integrated haptics aid surgical implantation and minimize trauma while allowing the implant to be removed if needed. A touch-mode capacitive pressure sensor, fabricated using the dissolved wafer process, transduces intraocular pressure into capacitance with a linear response and a sensitivity of 26 fF/mmHg. A new fabrication technique has been developed to embed vertical interconnects within a glass package containing the pressure sensor, a microbattery, readout circuitry, and an antenna. This enables the vertical stacking of these components and very efficient use of limited volume. The 1.5 mm x 2 mm x 0.5 mm transparent parylene-coated glass package enables solar cells to be placed on the circuit chip for power generation, trickle charging an on-board microbattery formed using standard cleanroom materials and a non-toxic electrolyte. Flooded-cell tests verified the electrochemistry and achieved a current capacity of 8 µAh/mm2. A simple integrated readout circuit consuming 35 pW in the idle mode implemented a finite-state machine and used an optical wakeup trigger to further reduce power. The microsystem has also been demonstrated with a microprocessor to autonomously gather and store data, reading it out on demand. Finally, a pulse-based ultrawideband wireless transmission technique is proposed using non-resonant antennas. The all-digital transmitter is expected to consume much less power than conventional encoded wireless transmitters and eliminates complex circuitry.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89809/1/rhaque_1.pd

Untersuchungen zur Messung elektrischer Spannungen mit mikroelektromechanischen Bauelementen

Die vorliegende Arbeit beschäftigt sich mit der Analyse, dem Entwurf, der Fertigung und der Charakterisierung von mikroelektromechanischen Sensoren zur Messung elektrischer Spannungen basierend auf dem Effekt der elektrostatischen Anziehung. Als Ergebnis wurden zwei völlig unterschiedliche Sensorentwürfe realisiert, die das Potenzial haben, elektrische Wechselspannungen mit Frequenzen bis zu 1 GHz mit einem Messfehler kleiner als 10 ppm zu bestimmen. Zunächst wurde eine umfassende Betrachtung des Stands der Technik vorgenommen. Es wurden die klassischen Verfahren zur Messung von Hochfrequenzspannungen vorgestellt und daraus der Anwendungsbereich der mikromechanischen Sensoren auf Frequenzen bis 1 GHz abgeleitet. Die typischen Effektivwerte in der HF-Messtechnik bewegen sich im Bereich von unter 1 V mit einer Anforderung an die Auflösung von 1 μV über weite Frequenzbereiche. Die etablierten Verfahren zur Spannungsmessung basieren auf der Dissipation der Leistung an ohmschen Widerständen, deren Erwärmung, und dem hochpräzisen Messen der Temperatur über Thermoelemente. Im Bereich der elektrostatischen Messtechnik für elektrische Spannungen wurde die Brücke geschlagen von den Anfängen des 20. Jahrhunderts mit feinwerktechnisch aufgebauten Elektrometern bis zu heutigen mikromechanischen hergestellten Effektivwertsensoren. Aufgrund der erreichbaren Plattengeometrien waren die frühen Elektrometer hauptsächlich für die Messungen von hohen Spannungen und Frequenzen bis maximal 1 MHz geeignet. Das Aufkommen der Mikrotechnik erlaubte, den Plattenabstand stark zu verringern und damit die Empfindlichkeit der Sensoren im niedrigen Spannungsbereich zu erhöhen. Durch die Reduzierung der Gesamtabmessungen sind sie für die Einkopplung hoher Frequenzen besser geeignet und durch die kleinere bewegte Masse unempfindlicher gegenüber äußeren Einflüssen. Es wurde gezeigt, dass es vielversprechende Ansätze und Realisierungen, sowohl in der Bulk-, als auch in der Oberflächenmikromechanik gibt, auf die in dieser Arbeit aufgebaut werden konnte. In Kapitel 3 wurde anschließend die zugrundeliegende Theorie für die elektrostatische Messung von Effektivwerten zusammenfassend dargestellt. Dabei wurde die Bedeutung der Pull-In-Spannung als Kenngröße der Systeme herausgestellt. Diese bestimmt nicht nur den maximalen Spannungsbereich, sondern darüber hinaus auch die erreichbare Auflösung. Es wurde gezeigt, dass sich damit sowohl für den translatorischen als auch den rotatorischen Fall geeignete Systeme im Rahmen der Vorgaben der Mikrotechnik entwickeln lassen. Dabei ist es wichtig, das Gesamtsystem zu betrachten, insbesondere die verfügbare Technik, um die Position der Platte zu bestimmen. Dies kann entweder durch optisches Abtasten der Entfernung oder durch Messen der Kapazität durch einen zweiten Satz von Elektroden geschehen. Die notwendige Positionsgenauigkeit für eine hohe Auflösung wurde untersucht und festgestellt, dass eine Auflösung von 10−4 h0 bzw. 10−3 C0 für eine Genauigkeit besser 1 ppm in der Nähe der Pull-In-Spannung ausreichend ist. Methoden zum Erweitern des Messbereichs durch Überlagern derWechsel- mit einer Gleichspannung wurden vorgestellt. Basierend auf diesen Erkenntnissen wurden Sensoren entwickelt und optimiert, die das Spektrum der Herstellungstechnik und die theoretischen Möglichkeiten weitestgehend abdecken. In Abschnitt 4.2 ist der Aufbau eines rotatorischen Sensors aus Bulk-Silizium beschrieben. Die Entwicklung des Batchprozesses eröffnet die Möglichkeit zur gleichzeitigen homogenen Fertigung einer Vielzahl von Sensoren. Die kritischsten Schritte bei der Herstellung sind das anodische Bonden und das trockenchemische Strukturieren der Aktoren für hohe Aspektverhältnisse an den Torsionsbalken, die zu einer geringen Federsteifigkeit führen. Die Balken haben einen rechteckigen Querschnitt und besitzen eine Breite von nur 40 μm auf 8 mm Länge. Die Elektroden haben einen Abstand von 10 - 20 μm auf einer Fläche von 5 x 5 mm2. Damit wurden erfolgreich Sensoren gefertigt, die bei Gleich- und bei Wechselspannungen mit einer Frequenz von bis zu 20 MHz eine Kapazitätsänderung von mehr als 4 aF/μV erreichen. Abschnitt 4.3 zeigt den Entwurf, die Herstellung und die Charakterisierung von Sensoren, die im Gegensatz sowohl auf einem anderen Bewegungsprinzip als auch auf einer anderen mikromechanischen Herstellungstechnologie beruhen. Die Kombination von Dünnschicht-Oberflächenmikromechanik mit Methoden der Galvanotechnik erlaubt die Herstellung von bis zu 2 x 2 mm2 großen Aktoren, die in nur 1,5 μm Höhe über den anderen Elektroden schweben. Damit können die Pull-In-Spannungen bis zu 1 V abgesenkt werden. Die Verwendung von Kupfer als alleiniges Elektrodenmaterial in Kombination mit Glaswafern als reiner Träger, der ohne Probleme durch ein Hochfrequenzsubstrat ersetzt werden könnte, ermöglicht es Sensoren herzustellen, die noch bei 1 GHz eine Kapazitätsänderung von 0,1 aF/μV erreichen. Damit sind mit aktueller Messtechnik Spannungsänderungen auf 10 ppm genau nachweisbar