Integrated interface electronics for capacitive MEMS inertial sensors

This thesis is composed of 13 publications and an overview of the research topic, which also summarizes the work. The research presented in this thesis concentrates on integrated circuits for the realization of interface electronics for capacitive MEMS (micro-electro-mechanical system) inertial sensors, i.e. accelerometers and gyroscopes. The research focuses on circuit techniques for capacitive detection and actuation and on high-voltage and clock generation within the sensor interface. Characteristics of capacitive accelerometers and gyroscopes and the electronic circuits for accessing the capacitive information in open- and closed-loop configurations are introduced in the thesis. One part of the experimental work, an accelerometer, is realized as a continuous-time closed-loop sensor, and is capable of achieving sub-micro-g resolution. The interface electronics is implemented in a 0.7-µm high-voltage technology. It consists of a force feedback loop, clock generation circuits, and a digitizer. Another part of the experimental work, an analog 2-axis gyroscope, is optimized not only for noise, but predominantly for low power consumption and a small chip area. The implementation includes a pseudo-continuous-time sense readout, analog continuous-time drive loop, phase-locked loop (PLL) for clock generation, and high-voltage circuits for electrostatic excitation and high-voltage detection. The interface is implemented in a 0.35-µm high-voltage technology within an active area of 2.5 mm². The gyroscope achieves a spot noise of 0.015 °/s/√H̅z̅ for the x-axis and 0.041 °/s/√H̅z̅ for the y-axis. Coherent demodulation and discrete-time signal processing are often an important part of the sensors and also typical examples that require clock signals. Thus, clock generation within the sensor interfaces is also reviewed. The related experimental work includes two integrated charge pump PLLs, which are optimized for compact realization but also considered with regard to their noise performance. Finally, this thesis discusses fully integrated high-voltage generation, which allows a higher electrostatic force and signal current in capacitive sensors. Open- and closed-loop Dickson charge pumps and high-voltage amplifiers have been realized fully on-chip, with the focus being on optimizing the chip area and on generating precise spurious free high-voltage signals up to 27 V

The development of a field-portable MEMS gravimeter

Gravimetry is a technique that has existed since the 17th and 18th century and involves the measurement of the acceleration due to gravity. The technique can be used to measure changes in density below the ground where conventional methods cannot. This is because gravity cannot be shielded, and therefore, can always be measured. It has many useful applications, particularly in surveying for oil, gas and minerals but can also be used to detect the precursors to volcanic eruptions and earthquakes, the density contrast of buried walls for archaeology and the detection of subsurface voids. Typically, however, gravimeters can cost in excess of ￡70k and weight over 8 kg. This cost and weight has prohibited some applications of gravimeters where either many of the devices would be required or if weight was prohibitive. In the winter of 2014, an important step forward to a lightweight, low-cost and portable MEMS gravimeter was made. This was the first time that a MEMS based gravimeter had measured the Earth Tides as reported by R. P. Middlemiss et al. The device, however, still required a large array of electronics and vacuum equipment which made it impossible to be able to be taken into the field. Clearly, if the device was to ever become a disruptive technology within the gravimeter industry, significant effort would be required to obtain a device with sufficient sensitivity that was also portable. This thesis highlights the work that was required to bring the MEMS that was a lab-bound device, and make successful measurements of the change in acceleration due to gravity in the field. In this thesis, a miniaturised MEMS gravimeter is presented with an RMS of 13 μGal when averaged to 1000 s, a factor three better than the original set-up from R. P. Middlemiss et al. The system went from a set-up with the approximate dimensions of a typical fridge freezer(including the array of electronic equipment) to a portable platform of dimensions 30cm wide by 30 cm deep by 15 cm high. The platform used a small steel cube as a vacuum container for the device, three micrometer legs for precision levelling, batteries and a custom electronics board. This custom electronics board was designed, tested and improved during the course of this thesis. The board was controlled by a microcontroller from Microchip (the dsPIC33EP512MU810) and is shown to be capable of a large amount of digital filtering that was required for this application, including the use of a decimator and digital based lock-in amplifier. The board measured displacements, temperatures (which were also controlled) and tilts, all of which the microcontroller digitally filtered and down sampled so that they could be sent to a computer for data logging

NASA SBIR abstracts of 1992, phase 1 projects

The objectives of 346 projects placed under contract by the Small Business Innovation Research (SBIR) program of the National Aeronautics and Space Administration (NASA) are described. These projects were selected competitively from among proposals submitted to NASA in response to the 1992 SBIR Program Solicitation. The basic document consists of edited, non-proprietary abstracts of the winning proposals submitted by small businesses. The abstracts are presented under the 15 technical topics within which Phase 1 proposals were solicited. Each project was assigned a sequential identifying number from 001 to 346, in order of its appearance in the body of the report. Appendixes to provide additional information about the SBIR program and permit cross-reference of the 1992 Phase 1 projects by company name, location by state, principal investigator, NASA Field Center responsible for management of each project, and NASA contract number are included

Label-free and Multi-parametric Monitoring of Cell-based Assays with Substrate-embedded Sensors

Various approaches have been pursued on the basis of electrochemical or piezoelectric transducers, particularly of the quartz crystal microbalance (QCM), to monitor non-invasively and in real-time cellular states and reactions with substrate-embedded sensors. On the one hand, these comprised the technical development of piezoelectric sensors with multiple read-out spots and the integration of additional non-invasive (electro- and optochemical) sensor technologies on the QCM surface. On the other hand, a variety of studies and cell-based assays (CBAs) have been performed in order to test the sensor performances and to gain a deeper understanding of the sensors’ readout parameters with respect to their information content about the biophysical properties and the metabolic behavior of cells. Fig. 7–1 presents an overview of the different projects on the basis of QCM sensor disks presented in this thesis. In the first project (Fig. 7–1 A) a novel electrode layout was designed on the basis of commercial 5 MHz AT-cut quartz disks to implement two independent readout spots on the QCM surface. This also comprised the construction of new measurement chambers for the electrical actuation and sensing of quartz oscillations. These two-electrode QCM sensors (2ElQ) are also referred to as multichannel QCM (MQCM). The developed MQCM sensor spots on one quartz disk exhibited a strong interference, even though they were operated sequentially, which is in contrast to the results of previous theoretical calculations. The resonances could be successfully decoupled by coating half of the quartz surface and one sensor spot, respectively, with a thin and rigid film of photoresist. This quartz loading with mass caused a shift in the resonance spectra of the coated resonator to lower frequencies and efficient decoupling. The operation of the decoupled MQCM sensors demonstrated both, a sensitive and equal change in the oscillation characteristics of the two resonators upon loading of the quartz with medium. The Q-factor was not significantly different for the two resonators, qualifying the MQCM for its application in CBAs. Building on the preceding development of the double-electrode quartz disks, a novel electrode layout has been realized at the sensor surface, which enables the complementary electrochemical (impedance spectroscopical) characterization of the substrate-liquid interface in addition to its mechanical characterization by the piezoelectric transducers (Fig. 7–1 B). This layout was achieved by removing a small area of the insulating photoresist on the coated electrode in the photolithographic process. By this, a coplanar electrode arrangement of a small working electrode and a bigger counter electrode was created. This sensor combination on the basis of the MQCM is an improvement of the so-called 2nd generation QCM to what we call the 3rd generation QCM, and which is also referred to as QCM-ECIS. Various electrode layouts, varying in size and number of the working electrode(s), were fundamentally characterized microscopically and by profilometry regarding the geometrical properties and by means of impedance spectroscopy with respect to the sensing performances in QCM- and ECIS-mode. An optimal electrode layout was identified and defined as standard for subsequent applications in CBAs. In both QCM- and ECIS studies of cell-covered sensor surfaces significant changes in the characteristic sensing parameters with respect to the cell-free electrodes are measurable. In addition to the measurement of absolute signal changes, the transducer technologies of QCM and ECIS also enable to monitor the kinetic changes of the readout parameters with high temporal resolution. This allows to use the dual sensors for monitoring and analyzing the states of adherent cell cultures in any kind of assay, label-free, non-invasively, and in real-time. Mechanical (QCM-mode) and the dielectric (ECIS-mode) characteristics of cell adhesion were simultaneously measured for two different cell lines (MDCK II and NRK), with high reproducibility for each. The total and kinetic parameter changes in both sensing modes distinguished clearly and were specific for the cell lines under test. The signals from both QCM-mode and ECIS-mode recordings also reported on significant impacts of the presence/ absence of bivalent cations (Ca2+, Mg2+) on the attachment and spreading kinetics and behavior of MDCK II cells. Aside from cell adhesion studies, the cytomechanical and cell morphological reactions towards various stimuli were monitored and analyzed by QCM-ECIS in a multitude of cellular assays: systematic softening and stiffening of cells (using agents for disassembling the actin cytoskeleton and cross-linking protein structures, respectively), intracellular stimulation (using a second messenger analogue), as well as electrical manipulation (electroporation (ELPO) and wounding) of cell layers (applying invasive voltage pulses). The applicability of electrical actuation and the subsequent non-invasive, time-resolved, and dual sensing with the electrodes of the QCM-ECIS substrates has been successfully demonstrated. The monitoring of CBAs with the dual QCM-ECIS sensor chips developed in this thesis provides not only a multiplication of the information gain due to the complementarity of QCM and ECIS readout parameters. The simultaneous, time-resolved measurements also enable the kinetic correlation of the sensor signals in novel 2 D and 3 D diagrams, which offers the hitherto unprecedented opportunity for a more detailed view and analysis of the coherence or consecutiveness of mechanical and morphological/ dielectric changes of a cell layer under study. A third research project focused on the combination of optical-chemical sensors (OCS) with the piezoelectric (QCM) sensor technology. For this purpose, the quartz crystal surface was coated with a polymer film with embedded phosphorescent indicator dye for the target analyte. The luminescence properties were measured by means of fluorescence (phosphorescence) lifetime imaging (FLIM). By using a temperature-sensitive paint (TSP), an increase in temperature on the sensor surface upon high-amplitude oscillations was monitored and imaged this way in one project (Fig. 7–1 C). Based on this experimentally determined local heating on the QCM surface and the thereby generated temperature gradient in the liquid above the resonator, a thermophoretic convection in the fluid has been simulated. Theoretical considerations showed that the convection profile in the measurement vessel counteracts and even largely prevents the sedimentation of cells onto the sensor surface. It is suggested that the effect of thermophoresis is crucial especially in studies of biomolecular interactions on QCM surfaces at elevated shear amplitudes and driving voltages, respectively, which however has not been considered in literature to date. The phosphorescence quenching capability of oxygen was utilized in a second imaging project to monitor and image the local concentration and distribution of oxygen on the growth substrate of cells by means of a so-called pressure(/oxygen)-sensitive paint (PSP) (Fig. 7–1 D). A home-made experimental setup was constructed for sensor calibration and the imaging of subcellular oxygen, consisting of a FLIM setup coupled to an upright microscope and a temperature- and oxygen-controlled calibration and measurement chamber suitable for cellular applications. The cytocompatible sensor films have been characterized under various test conditions (in air, under medium, at different temperatures) regarding their sensitivity and response characteristics to different oxygen partial pressures. The oxygen consumption of cells adherently grown on the sensor film was successfully monitored and imaged by this setup. The time-resolved measurements demonstrated a significantly faster consumption of oxygen of a cell layer stimulated with a respiration chain decoupler compared to an unstimulated control cell layer. Taken together, various technical improvements of piezoelectric sensors (QCM) have been realized (MQCM, QCM-ECIS, ELPO-QCM-ECIS, QCM-OCS), which provide a significant information gain in cell-based applications. The sensors developed enable the high-content screening (HCS) of adherent cell lines in a wide range of assay formats and provide complementary physico-chemical information for obtaining a more complete picture of the state of cells and their reactions in contact to diverse stimuli. All sensor techniques share the characteristics of time-resolved, label-free, and non-invasive monitoring. This allows to disclose and analyze even the kinetics, delayed effects, recoveries, and fluctuations of physicochemical alterations of a studied cell layer, in addition to the absolute parameter changes, which is a valuable improvement compared to classical endpoint assays. The approach of combined, independent sensor systems also provides the novel possibility to bring parameters obtained by the different readout technologies from one cell layer in a temporal correlation, by which new insights into physiological relationships are possible

Technology 2004, Vol. 2

Proceedings from symposia of the Technology 2004 Conference, November 8-10, 1994, Washington, DC. Volume 2 features papers on computers and software, virtual reality simulation, environmental technology, video and imaging, medical technology and life sciences, robotics and artificial intelligence, and electronics

Applications and Experiences of Quality Control

The rich palette of topics set out in this book provides a sufficiently broad overview of the developments in the field of quality control. By providing detailed information on various aspects of quality control, this book can serve as a basis for starting interdisciplinary cooperation, which has increasingly become an integral part of scientific and applied research