High Aspect-ratio Biomimetic Hair-like Microstructure Arrays for MEMS Multi-Transducer Platform

Many emerging applications of sensing microsystems in health care, environment, security and transportation systems require improved sensitivity and selectivity, redundancy, robustness, increased dynamic range, as well as small size, low power and low cost. Providing all of these features in a system consisting of one sensor is not practical or possible. Micro electro mechanical microsystems (MEMS) that combine a large sensor array with signal processing circuits could provide these features. To build such multi-transducer microsystems we get inspiration from “hair”, a structure frequently used in nature. Hair is a simple yet elegant structure that offers many attractive features such as large length to cross-sectional area ratio, large exposed surface area, ability to include different sensing materials, and ability to interact with surrounding media in sophisticated ways. In this thesis, we have developed a microfabrication technology to build 3D biomimetic hair structures for MEMS multi-transducer platform. Direct integration with CMOS will enable signal processing of dense arrays of 100s or 1000s of MEMS transducers within a small chip area. We have developed a new device structure that mimics biological hair. It includes a vertical spring, a proof-mass atop the spring, and high aspect-ratio narrow electrostatic gaps to adjacent electrodes for sensing and actuation. Based on this structure, we have developed three generations of 3D high aspect-ratio, small-footprint, low-noise accelerometers. Arrays of both high-sensitivity capacitive and threshold accelerometers are designed and tested, and they demonstrate extended full-scale detection range and frequency bandwidth. The first-generation capacitive hair accelerometer arrays are based on Silicon-on-Glass (SOG) process utilizing 500 µm thick silicon, achieving a highest sensor density of ~100 sensors/mm2 connected in parallel. Minimum capacitive gap is 5 μm with device height of 400 μm and spring length of 300 μm. A custom-designed Bosch deep-reactive-etching (DRIE) process is developed to etch ultra-deep (> 500 µm) ultra-high aspect-ratio (UHAR) features (AR > 40) with straight sidewalls and reduced undercut across a wide range of feature sizes. A two-gap dry-release process is developed for the second-generation capacitive hair accelerometers. Due to the large device height at full wafer thickness of 1 mm and UHAR capacitive transduction gaps at 2 µm that extend > 200 µm, the accelerometer achieves sub-µg resolution (< 1µg/√Hz) and high sensitivity (1pF/g/mm2), having an area smaller than any previous precision accelerometers with similar performance. Each sensor chip consists of devices with various design parameter to cover a wide range. Bonding with metal interlayers at < 400 °C allows direct integration of these devices on top of CMOS circuits. The third-generation digital threshold hair accelerometer takes advantage of large aspect-ratio of the hair structure and UHAR DRIE structures to provide low noise (< 600 ng/√Hz per mm2 footprint proof-mass due to small contact area) and low power threshold acceleration detection. 16-element (4-bit) and 32-element (5-bit) arrays of threshold devices (total chip area being < 1 cm2) with evenly-spaced threshold gap dimensions from 1 µm to 4 µm as well as with hair spring cross-sectional area from 102 µm to 302 µm are designed to suit specific g-ranges from < 100 mg to 50 g. This hair sensor and sensor array technology is suited for forming MEMS transducer arrays with circuits, including high performance IMUs as well as miniaturized detectors and actuators that require high temporal and spatial resolution, analogous to high-density CMOS imagers.PHDElectrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/143975/1/yemin_1.pd

MEMS Accelerometers

Micro-electro-mechanical system (MEMS) devices are widely used for inertia, pressure, and ultrasound sensing applications. Research on integrated MEMS technology has undergone extensive development driven by the requirements of a compact footprint, low cost, and increased functionality. Accelerometers are among the most widely used sensors implemented in MEMS technology. MEMS accelerometers are showing a growing presence in almost all industries ranging from automotive to medical. A traditional MEMS accelerometer employs a proof mass suspended to springs, which displaces in response to an external acceleration. A single proof mass can be used for one- or multi-axis sensing. A variety of transduction mechanisms have been used to detect the displacement. They include capacitive, piezoelectric, thermal, tunneling, and optical mechanisms. Capacitive accelerometers are widely used due to their DC measurement interface, thermal stability, reliability, and low cost. However, they are sensitive to electromagnetic field interferences and have poor performance for high-end applications (e.g., precise attitude control for the satellite). Over the past three decades, steady progress has been made in the area of optical accelerometers for high-performance and high-sensitivity applications but several challenges are still to be tackled by researchers and engineers to fully realize opto-mechanical accelerometers, such as chip-scale integration, scaling, low bandwidth, etc

Design, fabrication, characterization and reliability study of CMOS-MEMS Lorentz-Force magnetometers

Tesi en modalitat de compendi de publicacionsToday, the most common form of mass-production semiconductor device fabrication is Complementary Metal-Oxide Semiconductor (CMOS) technology. The dedicated Integrated Circuit (IC) interfaces of commercial sensors are manufactured using this technology. The sensing elements are generally implemented using Micro-Electro-Mechanical-Systems (MEMS), which need to be manufactured using specialized micro-machining processes. Finally, the CMOS circuitry and the MEMS should ideally be combined in a single package. For some applications, integration of CMOS electronics and MEMS devices on a single chip (CMOS-MEMS) has the potential of reducing fabrication costs, size, parasitics and power consumption, compared to other integration approaches. Remarkably, a CMOS-MEMS device may be built with the back-end-of-line (BEOL) layers of the CMOS process. But, despite its advantages, this particular approach has proven to be very challenging given the current lack of commercial products in the market. The main objective of this Thesis is to prove that a high-performance MEMS, sealed and packaged in a standard package, may be accurately modeled and manufactured using the BEOL layers of a CMOS process in a reliable way. To attain this, the first highly reliable novel CMOS-MEMS Lorentz Force Magnetometer (LFM) was successfully designed, modeled, manufactured, characterized and subjected to several reliability tests, obtaining a comparable or superior performance to the typical solid-state magnetometers used in current smartphones. A novel technique to avoid magnetic offsets, the main drawback of LFMs, was presented and its performance confirmed experimentally. Initially, the issues encountered in the manufacturing process of MEMS using the BEOL layers of the CMOS process were discouraging. Vapor HF release of MEMS structures using the BEOL of CMOS wafers resulted in undesirable damaging effects that may lead to the conclusion that this manufacturing approach is not feasible. However, design techniques and workarounds for dealing with the observed issues were devised, tested and implemented in the design of the LFM presented in this Thesis, showing a clear path to successfully fabricate different MEMS devices using the BEOL.Hoy en día, la forma más común de producción en masa es una tecnología llamada Complementary Metal-Oxide Semiconductor (CMOS). La interfaz de los circuitos integrados (IC) de sensores comerciales se fabrica usando, precisamente, esta tecnología. Actualmente es común que los sensores se implementen usando Sistemas Micro-Electro-Mecánicos (MEMS), que necesitan ser fabricados usando procesos especiales de micro-mecanizado. En un último paso, la circuitería CMOS y el MEMS se combinan en un único elemento, llamado package. En algunas aplicaciones, la integración de la electrónica CMOS y los dispositivos MEMS en un único chip (CMOS-MEMS) alberga el potencial de reducir los costes de fabricación, el tamaño, los parásitos y el consumo, al compararla con otras formas de integración. Resulta notable que un dispositivo CMOS-MEMS pueda ser construido con las capas del back-end-of-line (BEOL) de un proceso CMOS. Pero, a pesar de sus ventajas, este enfoque ha demostrado ser un gran desafío como demuestra la falta de productos comerciales en el mercado. El objetivo principal de esta Tesis es probar que un MEMS de altas prestaciones, sellado y empaquetado en un encapsulado estándar, puede ser correctamente modelado y fabricado de una manera fiable usando las capas del BEOL de un proceso CMOS. Para probar esto mismo, el primer magnetómetro CMOS-MEMS de fuerza de Lorentz (LFM) fue exitosamente diseñado, modelado, fabricado, caracterizado y sometido a varias pruebas de fiabilidad, obteniendo un rendimiento comparable o superior al de los típicos magnetómetros de estado sólido, los cuales son usados en móviles actuales. Cabe destacar que en esta Tesis se presenta una novedosa técnica con la que se evitan offsets magnéticos, el mayor inconveniente de los magnetómetros de fuerza Lorentz. Su efectividad fue confirmada experimentalmente. En los inicios, los problemas asociados al proceso de fabricación de MEMS usando las capas BEOL de obleas CMOS resultaba desalentador. Liberar estructuras MEMS hechas con obleas CMOS con vapor de HF producía efectos no deseados que bien podrían llevar a la conclusión de que este enfoque de fabricación no es viable. Sin embargo, se idearon y probaron técnicas de diseño especiales y soluciones ad-hoc para contrarrestar estos efectos no deseados. Se implementaron en el diseño del magnetómetro de Lorentz presentado en esta Tesis, arrojando excelentes resultados, lo cual despeja el camino hacia la fabricación de diferentes dispositivos MEMS usando las capas BEOL.Postprint (published version

All Source Sensor Integration Using an Extended Kalman Filter

The global positioning system (GPS) has become an ubiquitous source for navigation in the modern age, especially since the removal of selective availability at the beginning of this century. The utility of the GPS is unmatched, however GPS is not available in all environments. Heavy reliance on GPS for navigation makes the warfighter increasingly vulnerability as modern warfare continues to evolve. This research provides a method for incorporating measurements from a massive variety of sensors to mitigate GPS dependence. The result is the integration of sensor sets that encompass those examined in recent literature as well as some custom navigation devices. A full-state extended Kalman filter is developed and implemented, accommodating the requirements of the varied sensor sets and scenarios. Some 19 types of sensors are used in multiple quantities including inertial measurement units, single cameras and stereo pairs, 2D and 3D laser scanners, altimeters, 3-axis magnetometers, heading sensors, inclinometers, a stop sign sensor, an odometer, a step sensor, a ranging device, a signal of opportunity sensor, global navigation satellite system sensors, an air data computer, and radio frequency identification devices. Simulation data for all sensors was generated to test filter performance. Additionally, real data was collected and processed from an aircraft, ground vehicles, and a pedestrian. Measurement equations are developed to relate sensor measurements to the navigation states. Each sensor measurement is incorporated into the filter using the Kalman filter measurement update equations. Measurement types are segregated based on whether they observe instantaneous or accumulated state information. Accumulated state measurements are incorporated using delayed-state update equations. All other measurements are incorporated using the numerically robust UD update equations

Enhanced Piezoelectric Performance of Printed PZT Films on Low Temperature Substrates

Since piezoelectric effect was discovered in 1880, it has been widely used in micro-actuators, sensors, and energy harvesters. Lead Zirconate Titanate (PZT) is a commonly used piezoelectric material due to the high piezoelectric response. The basic PZT film fabrication process includes deposition, sintering, and poling. However, due to the high sintering temperature (\u3e 800 °C) of PZT, only high melting point material can be served as the substrate. Otherwise, complex film transfer approach is needed to achieve flexible and foldable PZT devices. The exploration is accordingly necessary to realize direct fabrication of PZT films on low melting point substrates without affecting the piezoelectric performance. In order to lower the PZT film sintering temperature, in this work, the effect of the powder size and sintering aid on the sintering temperature was studied. A maskless, CAD driven, non-contact direct printing system, aerosol jet printer, was used to deposit PZT thick films on the substrate. This technique allows creating features without masking and etching processes that are generally required for realizing designed features via conventional deposition approaches. Broadband, sub-millisecond, high intensity flash pulses were used to sinter the PZT films. The role of all sintering parameters was investigated to regulate the sintering quality of the PZT thick films. The photonically sintered films showed much lower substrate temperature increase mainly due to the extremely short pulse duration and temperature gradient through the film thickness. The superior piezoelectric property to thermally sintered group was also obtained. This process significantly shortens the processing duration and dramatically expands the possible substrate materials. It accordingly opens the possibility of processing PZT film directly on low melting point materials. A PZT energy harvester based on this process was directly fabricated on the polyethylene terephthalate (PET) substrate to demonstrate the capability. The relation between the load and the generated power was investigated to obtain the highest output power. Up to 0.1 μW was generated from this flexible energy harvester when connected with 10 MΩ resistive load. Photonic sintering of PZT film also creates the opportunity of processing poling during sintering. Different combinations of the sintering and poling techniques were studied. It was observed that the best piezoelectric property was obtained while performing poling during photonic sintering. Consequently, a new method of printing, sintering, and poling of micro-scaled PZT films was demonstrated in this work resulting in high performance films. This process provides the capability of realizing PZT devices on low temperature substrate, facilitates the fabrication of flexible piezoelectric devices, and enhances the piezoelectric property

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Optimisation of vibration monitoring nodes in wireless sensor networks

This PhD research focuses on developing a wireless vibration condition monitoring (CM) node which allows an optimal implementation of advanced signal processing algorithms. Obviously, such a node should meet additional yet practical requirements including high robustness and low investments in achieving predictive maintenance. There are a number of wireless protocols which can be utilised to establish a wireless sensor network (WSN). Protocols like WiFi HaLow, Bluetooth low energy (BLE), ZigBee and Thread are more suitable for long-term non-critical CM battery powered nodes as they provide inherent merits like low cost, self-organising network, and low power consumption. WirelessHART and ISA100.11a provide more reliable and robust performance but their solutions are usually more expensive, thus they are more suitable for strict industrial control applications. Distributed computation can utilise the limited bandwidth of wireless network and battery life of sensor nodes more wisely. Hence it is becoming increasingly popular in wireless CM with the fast development of electronics and wireless technologies in recent years. Therefore, distributed computation is the primary focus of this research in order to develop an advanced sensor node for realising wireless networks which allow high-performance CM at minimal network traffic and economic cost. On this basis, a ZigBee-based vibration monitoring node is designed for the evaluation of embedding signal processing algorithms. A state-of-the-art Cortex-M4F processor is employed as the core processor on the wireless sensor node, which has been optimised for implementing complex signal processing algorithms at low power consumption. Meanwhile, an envelope analysis is focused on as the main intelligent technique embedded on the node due to the envelope analysis being the most effective and general method to characterise impulsive and modulating signatures. Such signatures can commonly be found on faulty signals generated by key machinery components, such as bearings, gears, turbines, and valves. Through a preliminary optimisation in implementing envelope analysis based on fast Fourier transform (FFT), an envelope spectrum of 2048 points is successfully achieved on a processor with a memory usage of 32 kB. Experimental results show that the simulated bearing faults can be clearly identified from the calculated envelope spectrum. Meanwhile, the data throughput requirement is reduced by more than 95% in comparison with the raw data transmission. To optimise the performance of the vibration monitoring node, three main techniques have been developed and validated: 1) A new data processing scheme is developed by combining three subsequent processing techniques: down-sampling, data frame overlapping and cascading. On this basis, a frequency resolution of 0.61 Hz in the envelope spectrum is achieved on the same processor. 2) The optimal band-pass filter for envelope analysis is selected by a scheme, in which the complicated fast kurtogram is implemented on the host computer for selecting optimal band-pass filter and real-time envelope analysis on the wireless sensor for extracting bearing fault features. Moreover, a frequency band of 16 kHz is analysed, which allows features to be extracted in a wide frequency band, covering a wide category of industrial applications. 3) Two new analysis methods: short-time RMS and spectral correlation algorithms are proposed for bearing fault diagnosis. They can significantly reduce the CPU usage, being over two times less and consequently much lower power consumptio

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators

NEMS by sidewall transfer lithography

A batch fabrication process for nano-electro-mechanical systems (NEMS) based on sidewall transfer lithography (STL) is developed and demonstrated. The STL is used to form nanoscale flexible silicon suspensions entirely by conventional lithography. A two-step process is designed for single-layer STL to fabricate simple electrothermal actuators, while a three-step process is designed to allow nanoscale features intersecting with each other for more complicated device lay-outs. Fabricated nanoscale features has a minimum in-plane width of approx. 100nm and a high aspect ratio of 50 : 1. Combined structures with microscale and nanoscale parts are transferred together into silicon by deep reactive etching (DRIE). Suspensions are achieved either by plasma undercut or HF vapour etch based on BSOI. The STL processes are used to form nanoscale suspensions while conventional lithography is used to form localised microscale features such as anchors. A wide variety of demonstrator devices have been fabricated with high feature quality. Analytic models have been developed to compare with experimental characterization and finite element analysis (FEA) predictions. Lattice structures fabricated by multi-layer STL have also be investigated as a novel type of mechanical metamaterial. Thus, the process could allow low-cost and mass parallel fabrication of future NEMS with a wider range of potential applications.Open Acces

Advanced Nanoelectromechanical Systems for Next Generation Energy Harvesting

The ever-increasing desire to produce portable, mobile and self-powered wireless micro-/nano systems (MNSs) with extended lifetimes has lead to the significant advancement in the area of mechanical energy harvesting over the last few years and it has been possible not only because has nanotechnology evolved as a powerful tool for the manipulation of matter on an atomic, molecular, and supramolecular scale, but also different micro-/nano fabrication techniques have enabled researchers and scientists to create, visualize, analyse and manipulate nano-structures, as well as to probe their nano-chemistry, nano-mechanics and other properties within the systems. The dissertation first discusses briefly about energy harvesting technologies for self-powered MNSs, for example a wireless aircraft structural health monitoring (SHM) system, with a particular focus on piezoelectric nanogenerators (PENG) and triboelectric nanogenerators (TENG) as they are the most promising approaches for converting ambient tiny mechanical energy into electrical energy efficiently and effectively and then it analyzes the theoretical and experimental methodologies for efficient energy harvesting using PENG, TENG and hybrid devices. The piezoelectric property intertwined with the semiconducting behaviour of different ZnO nanostructures has made them ideal candidate for piezoelectric energy harvesting, also intensive and state-of-the-art research has been going on to enhance the performance of the PENG devices based on 1D and 2D ZnO nanostructures. In this work, a high performance and consolidated PENG device based on the integration of ZnO nanowires and nanoplates on the same substrate has been demonstrated, that produces an output electrical power of 8.4 µW/cm2 at the matched load of 10MΩ that manifests their ability for powering up different MNSs. Since hybrid nanogenerators (HNG) integrate different types of harvesters in a single unit, where several energy sources can be leveraged either simultaneously or individually, in the next part of this work, a HNG device integrating PENG and TENG components has been designed, fabricated and characterized where PENG and TENG parts mutually enhance the performance of each other resulting an instantaneous peak power density of 1.864mW/cm2 and subsequently the device has been used to charge several commercial capacitors to corroborate their potential for aircraft SHM applications. Moreover, the hybrid device exhibits strong potential for wearable electronics as it can harvest energy from human walking and normal hand movements. However, successful implementation of self-powered electronics, such as a wireless aircraft SHM depends not only on the performance of individual parts but also on components integration within the system, where each device/system node within the network consists of a low-power microcontroller unit, high-performance data-processing/storage units, a wireless signal transceiver, ultrasensitive sensors based on a micro-/nano electro-mechanical system, and most importantly the embedded powering units. This dissertation aims to deepen the understanding of the different energy harvesting methods utilizing the knowledge of nanoscale phenomena and nanofabrication tools along with the associated prospects and challenges and thus, this research in the field of energy harvesting using advanced nano electro-mechanical systems could have a substantial impact on many areas, ranging from the fundamental study of new nanomaterial properties and different effects in nanostructures to diverse applications