Integration of Bulk Piezoelectric Materials into Microsystems.

Bulk piezoelectric ceramics, compared to deposited piezoelectric thin-films, provide greater electromechanical coupling and charge capacity, which are highly desirable in many MEMS applications. In this thesis, a technology platform is developed for wafer-level integration of bulk piezoelectric substrates on silicon, with a final film thickness of 5-100μm. The characterized processes include reliable low-temperature (200˚C) AuIn diffusion bonding and parylene bonding of bulk-PZT on silicon, wafer-level lapping of bulk-PZT with high-uniformity (±0.5μm), and low-damage micro-machining of PZT films via dicing-saw patterning, laser ablation, and wet-etching. Preservation of ferroelectric and piezoelectric properties is confirmed with hysteresis and piezo-response measurements. The introduced technology offers higher material quality and unique advantages in fabrication flexibility over existing piezoelectric film deposition methods. In order to confirm the preserved bulk properties in the final film, diaphragm and cantilever beam actuators operating in the transverse-mode are designed, fabricated and tested. The diaphragm structure and electrode shapes/sizes are optimized for maximum deflection through finite-element simulations. During tests of fabricated devices, greater than 12μmPP displacement is obtained by actuation of a 1mm2 diaphragm at 111kHz with <7mW power consumption. The close match between test data and simulation results suggests that the piezoelectric properties of bulk-PZT5A are mostly preserved without any necessity of repolarization. Three generations of resonant vibration energy harvesters are designed, simulated and fabricated to demonstrate the competitive performance of the new fabrication process over traditional piezoelectric deposition systems. An unpackaged PZT/Si unimorph harvester with 27mm3 active device volume produces up to 205μW at 1.5g/154Hz. The prototypes have achieved the highest figure-of-merits (normalized-power-density × bandwidth) amongst previously reported inertial energy harvesters. The fabricated energy harvester is utilized to create an autonomous energy generation platform in 0.3cm3 by system-level integration of a 50-80% efficient power management IC, which incorporates a supply-independent bias circuitry, an active diode for low-dropout rectification, a bias-flip system for higher efficiency, and a trickle battery charger. The overall system does not require a pre-charged battery, and has power consumption of <1μW in active-mode (measured) and <5pA in sleep-mode (simulated). Under 1g vibration at 155Hz, a 70mF ultra-capacitor is charged from 0V to 1.85V in 50 minutes.Ph.D.Electrical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/1/aktakka_3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/2/aktakka_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91479/3/aktakka_1.pd

Materials jetting for advanced optoelectronic interconnect: technologies and application

This report covers the work carried out on Teaching Company Scheme No. 2275 "Materials Jetting for Advanced Interconnect" between February 1998 and February 2000. The project was conducted at the Harlow laboratories of Nortel Networks with the support of the Department of Manufacturing Engineering of Loughborough University. Technical direction and supervision has been provided by Mr Paul Conway, Reader, at Loughborough University, Professor Ken Snowdon and Mr Chris Tanner of Nortel Networks. The aim of the project was to produce and deposit minute and precise volumes of a range of materials, such as metallic alloys, glasses and polymers, onto a variety of substrates commonly used in the electronics and optoelectronics fields. The technology, which is analogous to ink-jet printing, firstly had to be refined to accommodate higher processing temperatures of up to 350°C. The ultimate project deliverable was to produce a specification for jetting equipment suited towards volume manufacturing. [Continues.

Volume-conservative modeling of structures manufactured by molten drop-on-drop deposition

An improved analytic model to accurately determine the geometry of structures manufactured by molten drop-on-drop deposition is presented. This deposition mode allows quasi-spherical deposited droplets to be achieved and precise control over the geometry of the final manufactured structures. The model exactly conserves the volume of the deposited material and matches the solidification contact angle between consecutive deposited droplets, providing a precise geometrical description of the manufactured structures. The proposed model is validated using results of experiments performed with several materials for the deposited droplets and substrate, and droplet radii ranging from 40 to 800 m. A good degree of agreement was found between theoretical and experimental results. A comparison with the well-established Gao&Sonin model shows that the proposed model represents a major improvement, and may be of great practical interest in industrial applications.The authors gratefully acknowledge the joint support of the Spanish Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación and FEDER through projects DPI2017-87826-C2-1-P and DPI2017-87826-C2-2-P, and the Spanish Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (MCIN/ AEI/ 10.13039/501100011033) through projects PID2020-120100GB-C21 and PID2020-120100GB-C22

Peripheral soldering of flip chip joints on passive RFID tags

Flip chip is the main component of a RFID tag. It is used in billions each year in electronic packaging industries because of its small size, high performance and reliability as well as low cost. They are used in microprocessors, cell phones, watches and automobiles. RFID tags are applied to or incorporated into a product, animal, or person for identification and tracking using radio waves. Some tags can be read from several meters away or even beyond the line of sight of the reader. Passive RFID tags are the most common type in use that employ external power source to transmit signals. Joining chips by laser beam welding have wide advantages over other methods of joining, but they are seen limited to transparent substrates. However, connecting solder bumps with anisotropic conductive adhesives (ACA) produces majority of the joints. A high percentage of them fail in couple of months, particularly when exposed to vibration. In the present work, failure of RFID tags under dynamic loading or vibration was studied; as it was identified as one of the key issue to explore. Earlier investigators focused more on joining chip to the bump, but less on its assembly, i.e., attaching to the substrate. Either of the joints, between chip and bump or between antenna and bump can fail. However, the latter is more vulnerable to failure. Antenna is attached to substrate, relatively fixed when subjected to oscillation. It is the flip chip not the antenna moves during vibration. So, the joint with antenna suffers higher stresses. In addition to this, the strength of the bonding agent i.e., ACA also much smaller compared to the metallic bond at the other end of the bump. Natural frequency of RFID tags was calculated both analytically and numerically, found to be in kilohertz range, high enough to cause resonance. Experimental investigations were also carried out to determine the same. However, the test results for frequency were seen to be in hundred hertz range, common to some applications. It was recognized that the adhesive material, commonly used for joining chips, was primarily accountable for their failures. Since components to which the RFID tags are attached to experience low frequency vibration, chip joints fail as they face resonance during oscillation. Adhesives having much lower modulus than metals are used for attaching bumps to the substrate antennas, and thus mostly responsible for this reduction in natural frequency. Poor adhesive bonding strength at the interface and possible rise in temperature were attributed to failures under vibration. In order to overcome the early failure of RFID tag joints, Peripheral Soldering, an alternative chip joining method was devised. Peripheral Soldering would replace the traditional adhesive joining by bonding the peripheral surface of the bump to the substrate antenna. Instead of joining solder bump directly to the antenna, holes are to be drilled through antenna and substrate. S-bond material, a less familiar but more compatible with aluminum and copper, would be poured in liquid form through the holes on the chip pad. However, substrates compatible to high temperature are to be used; otherwise temperature control would be necessary to avoid damage to substrate. This S-bond would form metallic joints between chip and antenna. Having higher strength and better adhesion property, S-bond material provides better bonding capability. The strength of a chip joined by Peripheral Soldering was determined by analytical, numerical and experimental studies. Strength results were then compared to those of ACA. For a pad size of 60 micron on a 0.5 mm square chip, the new chip joints with Sbond provide an average strength of 0.233N analytically. Numerical results using finite element analysis in ANSYS 11.0 were about 1% less than the closed form solutions. Whereas, ACA connected joints show the maximum strength of 0.113N analytically and 0.1N numerically. Both the estimates indicate Peripheral Soldering is more than twice stronger than adhesive joints. Experimental investigation was carried out to find the strength attained with S-bond by joining similar surfaces as those of chip pad and antenna, but in larger scale due to limitation in facilities. Results obtained were moderated to incorporate the effect of size. Findings authenticate earlier predictions of superior strengths with S-bond. A comparison with ACA strength, extracted from previous investigations, further indicates that S-bond joints are more than 10 times stronger. Having higher bonding strength than in ACA joints, Peripheral Soldering would provide better reliability of the chip connections, i.e., RFID tags. The benefits attained would pay off complexities involved in tweaking

Technological Integration in Printed Electronics

Conventional electronics requires the use of numerous deposition techniques (e.g. chemical vapor deposition, physical vapor deposition, and photolithography) with demanding conditions like ultra-high vacuum, elevated temperature and clean room facilities. In the last decades, printed electronics (PE) has proved the use of standard printing techniques to develop electronic devices with new features such as, large area fabrication, mechanical flexibility, environmental friendliness and—potentially—cost effectiveness. This kind of devices is especially interesting for the popular concept of the Internet of Things (IoT), in which the number of employed electronic devices increases massively. Because of this trend, the cost and environmental impact are gradually becoming a substantial issue. One of the main technological barriers to overcome for PE to be a real competitor in this context, however, is the integration of these non-conventional techniques between each other and the embedding of these devices in standard electronics. This chapter summarizes the advances made in this direction, focusing on the use of different techniques in one process flow and the integration of printed electronics with conventional systems

Digital fabrication of optical elements through inkjet printing of direct photocurable hybrid inks

La tecnología de impresión inkjet permite eyección controlada de gotas de tinta de volumen definido y su posicionamiento preciso en un sustrato. Esta tecnología, entre otras virtudes, ofrece una gran flexibilidad para la preparación de estructuras en superficies gracias a su carácter digital, siendo además un proceso fácilmente escalable a nivel industrial, distinguiéndose en estos aspectos de otras técnicas comúnmente utilizadas como, por ejemplo, la fotolitografía. Ya es posible, de hecho, encontrar la tecnología inkjet en aplicaciones de fabricación masiva como la impresión de cartelería o de elementos decorativos. Más allá de la impresión de texto y trabajos gráficos, la capacidad de depositar una gran variedad de materiales de manera digital en forma de recubrimientos homogéneos y patrones en superficies ha despertado gran interés para la preparación de superficies y dispositivos funcionales. Pese a ello, la penetración del inkjet en entornos industriales para la implementación de este tipo de aplicaciones es todavía muy limitada. Entre otras cosas, esto se debe a que los materiales a depositar requieren unas propiedades muy exigentes para poder ser eyectados en condiciones óptimas por los cabezales de impresión, lo que limita la disponibilidad de fluidos compatibles con esta tecnología. Por ello, se hace preciso una adaptación de la viscosidad de los fluidos para poder ser impresos sin que ello reduzca su estabilidad a lo largo de su vida útil ni se vea penalizada la funcionalidad de los depósitos finales, que han de cumplir unos requerimientos específicos, generalmente muy exigentes, para cada aplicación. Por ejemplo, en aplicaciones de micro-óptica u óptica integrada suele ser necesario que los materiales finales tengan buena transparencia y propiedades ópticas adecuadas como alto índice de refracción o luminiscencia según el caso de uso y que estas propiedades no se vean mermadas por el uso o el paso del tiempo.En este ámbito concreto de las aplicaciones de micro-óptica u óptica integrada, se encuentran en la literatura diversas aproximaciones para el desarrollo de tintas inkjet con las que implementar guías de luz o microlentes. Una de las más prometedoras consiste en la preparación de tintas basadas en materiales híbridos orgánico-inorgánicos que ofrecen una gran flexibilidad para funcionalizar el material gracias a su componente orgánica, a la vez que presentan gran resistencia mecánica y química debido a la red inorgánica. Típicamente, se lleva a cabo la hidrólisis y condensación de un organosilano y se añade un disolvente para ajustar la viscosidad de modo que la formulación sea eyectable. Una vez depositada se elimina el disolvente y se cura la parte orgánica. La necesidad de eliminar el disolvente añade complejidad al proceso. Por otro lado, los procesos de hidrólisis y condensación previos a la impresión del fluido suelen penalizar la estabilidad de las tintas. Asimismo, también es frecuente la combinación del inkjet con el uso de tecnologías adicionales como la fotolitografía para el acondicionamiento de la superficie, previo a la impresión, o procesos térmicos para la posterior fijación de la tinta en el sustrato. Si bien se ha demostrado en la literatura el desarrollo de depósitos y dispositivos de buena calidad óptica con estos materiales híbridos, la falta de estabilidad de las tintas y la complejidad de los procesos envueltos para implementar estos dispositivos ópticos limitan la integración de la tecnología inkjet a nivel industrial en estos ámbitos de aplicación.Buscando superar estas limitaciones, este trabajo se ha centrado en el desarrollo de tintas funcionales y la implementación con ellas, mediante impresión por tecnología inkjet, de elementos de micro-óptica y óptica integrada. Para ello, más allá de la formulación de tintas funcionales, se ha trabajado en la definición y optimización de todo el proceso, abordando desde la preparación de la superficie hasta el proceso de impresión y fijación de la tinta al sustrato. Con esto, se ha perseguido conseguir depósitos funcionales mediante un proceso económico y viable en un entorno industrial.Para ello, las tintas desarrolladas se han basado en precursores híbridos orgánico-inorgánicos comerciales y ampliamente empleados en la literatura. De manera distintiva, con el fin de mejorar la estabilidad de las tintas y controlar los procesos de impresión y fijación, se ha perseguido que las tintas desarrolladas no empleen disolventes y sea posible el curado simultáneo de ambas redes (orgánica e inorgánica) únicamente mediante la exposición a luz UV tras el proceso de impresión. Para ello se han incorporado en las formulaciones fotogeneradores de ácido. Además, se han incluido en las tintas los aditivos necesarios para implementar las funcionalidades deseadas y controlar su viscosidad y tensión superficial, lo que permite una adecuada eyección y mojado de las superficies, así como unas prestaciones satisfactorias para las aplicaciones perseguidas.Siguiendo esta directriz, a lo largo de esta tesis se han desarrollado diferentes tintas inkjet, libres de disolventes y de curado directo. La primera de ellas, una tinta modelo eyectable sobre la cual se han incorporado posteriormente las funcionalidades deseadas. Así, se ha preparado otra tinta que resulta en depósitos de un elevado índice de refracción que ha permitido, por un lado, la fabricación de guías de luz planares cuando se imprime como un depósito homogéneo y, por otro lado, la preparación de microlentes cuando la tinta se imprime como gotas aisladas con geometrías controladas. Finalmente, también se han formulado dos tintas luminiscentes que permiten la preparación de elementos emisores de luz.Además del diseño y formulación de las tintas, se han diseñado y optimizado los procesos que intervienen en la preparación de los depósitos con el fin de desarrollar un sistema integral viable a nivel industrial. Por un lado, se han desarrollado diferentes protocolos de preparación de superficies con el fin de controlar la mojabilidad de estas y conseguir, desde gotas aisladas con geometrías controladas y patrones de gotas, hasta líneas continuas o depósitos homogéneos. Por otro lado, el propio proceso de impresión también ha sido optimizado, ajustando la configuración correspondiente para eyectar cada una de las tintas en las condiciones deseadas. Por último, como se ha remarcado anteriormente, el proceso de fijación de la tinta sobre el sustrato también ha sido llevado a cabo exclusivamente por activación mediante luz actínica.Para poner en valor la funcionalidad de las tintas y los procesos desarrollados, se han diseñado y preparado diferentes sistemas demostradores de casos de uso en micro-óptica y óptica integrada. Por ejemplo, como se ha mencionado con anterioridad, se ha llevado a cabo la impresión de guías de luz planares sobre diferentes sustratos, incluso flexibles, patrones de microlentes con geometrías controladas y un sensor óptico de temperatura planar con indicadores luminiscentes.<br /

Green Energy and Environment

Energy is a vital element in sustaining our modern society but the future of energy is volatile, uncertain, complex, and ambiguous; especially when facing a continuous drive to ensure a sustained and equitable access as well as mounting pressures to reduce its emissions. Traditional approaches in developing energy technologies have always been in isolation with distinct and unique contexts. However, we cannot afford to work in silos any longer. Future energy systems and their relationship with the society and the environment will have to be conceived, designed, developed, commissioned, and operated alongside and within contemporary geo-political, ethical, and socio-economic contexts. This has posed an unprecedented volatility, uncertainty, complexity, and ambiguity (VUCA), where systemic and holistic approaches are often warranted. This book aims to focus on the VUCA of addressing the future of energy and environment by considering contemporary issues and insights from diverse contexts, viewed as a system, and anchored upon emerging and smart energy technologies

Flexible and Stretchable Electronics

Flexible and stretchable electronics are receiving tremendous attention as future electronics due to their flexibility and light weight, especially as applications in wearable electronics. Flexible electronics are usually fabricated on heat sensitive flexible substrates such as plastic, fabric or even paper, while stretchable electronics are usually fabricated from an elastomeric substrate to survive large deformation in their practical application. Therefore, successful fabrication of flexible electronics needs low temperature processable novel materials and a particular processing development because traditional materials and processes are not compatible with flexible/stretchable electronics. Huge technical challenges and opportunities surround these dramatic changes from the perspective of new material design and processing, new fabrication techniques, large deformation mechanics, new application development and so on. Here, we invited talented researchers to join us in this new vital field that holds the potential to reshape our future life, by contributing their words of wisdom from their particular perspective