Doctor of Philosophy

dissertationMicroelectromechanical systems (MEMS) resonators on Si have the potential to replace the discrete passive components in a power converter. The main intention of this dissertation is to present a ring-shaped aluminum nitride (AlN) piezoelectric microreson

CMOS indoor light energy harvesting system for wireless sensing applications

Dissertação para obtenção do Grau de Doutor em Engenharia Electrotécnica e de ComputadoresThis research thesis presents a micro-power light energy harvesting system for indoor environments. Light energy is collected by amorphous silicon photovoltaic (a-Si:H PV) cells, processed by a switched-capacitor (SC) voltage doubler circuit with maximum power point tracking (MPPT), and finally stored in a large capacitor. The MPPT Fractional Open Circuit Voltage (VOC) technique is implemented by an asynchronous state machine (ASM) that creates and, dynamically, adjusts the clock frequency of the step-up SC circuit, matching the input impedance of the SC circuit to the maximum power point (MPP) condition of the PV cells. The ASM has a separate local power supply to make it robust against load variations. In order to reduce the area occupied by the SC circuit, while maintaining an acceptable efficiency value, the SC circuit uses MOSFET capacitors with a charge reusing scheme for the bottom plate parasitic capacitors. The circuit occupies an area of 0.31 mm2 in a 130 nm CMOS technology. The system was designed in order to work under realistic indoor light intensities. Experimental results show that the proposed system, using PV cells with an area of 14 cm2, is capable of starting-up from a 0 V condition, with an irradiance of only 0.32 W/m2. After starting-up, the system requires an irradiance of only 0.18 W/m2 (18 mW/cm2) to remain in operation. The ASM circuit can operate correctly using a local power supply voltage of 453 mV, dissipating only 0.085 mW. These values are, to the best of the authors’ knowledge, the lowest reported in the literature. The maximum efficiency of the SC converter is 70.3% for an input power of 48 mW, which is comparable with reported values from circuits operating at similar power levels.Portuguese Foundation for Science and Technology (FCT/MCTES), under project PEst-OE/EEI/UI0066/2011, and to the CTS multiannual funding, through the PIDDAC Program funds. I am also very grateful for the grant SFRH/PROTEC/67683/2010, financially supported by the IPL – Instituto Politécnico de Lisboa

Nagy megbízhatóságú integrált mikro- és nanorendszerek új tesztelési és vizsgálati módszerei, különös tekintettel az ambient intelligence kihívásaira = New design verification and examination principles and methods for high reliability integrated micro-nano-systems with special attention to the challenges of ambient intelligence

A kutatás eredményeit mintegy 15 új publikációban fejtettük ki részletesen. Az elért eredményekben a következőkben foglalhatók össze: - Kutató és fejlesztő munkát végeztünk energiaforrással egybeintegrált érzékelők fejlesztése területén. - Kutató és fejlesztő munkákat végeztünk MEMS struktúrákba építhető tesztelő és öntesztelő struktúrák kifejlesztésére. Ezt a munkát a PATENT kiválósági hálózat nemzetközi projekt keretében különböző ad-hoc konzorciumokatban nemzetközi kooperációban végeztük. - Jelentős lépést értünk el a MEMS tokozások megbízhatósági vizsgálatában a termikus tranziens mérési módszer alkalmazásával. A kifejlesztett módszer több nemzetközi publikációban mutattuk be és a munka eredményeiből PhD disszertáció is készült. - Igen jelentős eredményeket értünk el a termikus anyagparaméterek pontosabb meghatározása területén. A témával foglalkozó publikációnkat az IEEE CPMT Best Paper díj adományozásával értékelte. - Jelentős eredményeket értünk el a mikrocsatornás hűtőszerkezetek hűtési tulajdonságainak minősítése területén. Az elért eredményeket 5 különböző nemzetközi kooperációban készült cikkben mutattuk be. | The research results are presented in detail in about 15 new publications. The achieved results can be summarized as follows: - Research and development work was accomplished in order to realize energy sources and sensors on the same chip. - Research and development work was carried out in order to develop new test and self test structures for the characterizations of MEMS systems. This work was done in the Framework of the PATENT Network of Excellence in different ad-hoc consortia. - Significant results were achieved in the field of reliability testing methods of MEMS packaging and MEMS etching with the help of the application of thermal transient testing. The newly developed methodology was presented in several international publications and it forms the basis of one PhD Thesis work. - Significant results have been achieved in the more accurate measurement of thermal material parameters. A publication dealing with this subject was given the IEEE CPMT Best Paper Award in 2006. - Significant results have been achieved in the qualification of the cooling properties of microchannel coolers. The results have been presented in 5 papers made in international cooperation

A Flexible, Highly Integrated, Low Power pH Readout

Medical devices are widely employed in everyday life as wearable and implantable technologies make more and more technological breakthroughs. Implantable biosensors can be implanted into the human body for monitoring of relevant physiological parameters, such as pH value, glucose, lactate, CO2 [carbon dioxide], etc. For these applications the implantable unit needs a whole functional set of blocks such as micro- or nano-sensors, sensor signal processing and data generation units, wireless data transmitters etc., which require a well-designed implantable unit.Microelectronics technology with biosensors has caused more and more interest from both academic and industrial areas. With the advancement of microelectronics and microfabrication, it makes possible to fabricate a complete solution on an integrated chip with miniaturized size and low power consumption.This work presents a monolithic pH measurement system with power conditioning system for supply power derived from harvested energy. The proposed system includes a low-power, high linearity pH readout circuits with wide pH values (0-14) and a power conditioning unit based on low drop-out (LDO) voltage regulator. The readout circuit provides square-wave output with frequency being highly linear corresponding to the input pH values. To overcome the process variations, a simple calibration method is employed in the design which makes the output frequency stay constant over process, supply voltage and temperature variations. The prototype circuit is designed and fabricated in a standard 0.13-μm [micro-meter] CMOS process and shows good linearity to cover the entire pH value range from 0-14 while the voltage regulator provides a stable supply voltage for the system

Low-Voltage Bulk-Driven Amplifier Design and Its Application in Implantable Biomedical Sensors

The powering unit usually represents a significant component of the implantable biomedical sensor system since the integrated circuits (ICs) inside for monitoring different physiological functions consume a great amount of power. One method to reduce the volume of the powering unit is to minimize the power supply voltage of the entire system. On the other hand, with the development of the deep sub-micron CMOS technologies, the minimum channel length for a single transistor has been scaled down aggressively which facilitates the reduction of the chip area as well. Unfortunately, as an inevitable part of analytic systems, analog circuits such as the potentiostat are not amenable to either low-voltage operations or short channel transistor scheme. To date, several proposed low-voltage design techniques have not been adopted by mainstream analog circuits for reasons such as insufficient transconductance, limited dynamic range, etc. Operational amplifiers (OpAmps) are the most fundamental circuit blocks among all analog circuits. They are also employed extensively inside the implantable biosensor systems. This work first aims to develop a general purpose high performance low-voltage low-power OpAmp. The proposed OpAmp adopts the bulk-driven low-voltage design technique. An innovative low-voltage bulk-driven amplifier with enhanced effective transconductance is developed in an n-well digital CMOS process operating under 1-V power supply. The proposed circuit employs auxiliary bulk-driven input differential pairs to achieve the input transconductance comparable with the traditional gate-driven amplifiers, without consuming a large amount of current. The prototype measurement results show significant improvements in the open loop gain (AO) and the unity-gain bandwidth (UGBW) compared to other works. A 1-V potentiostat circuit for an implantable electrochemical sensor is then proposed by employing this bulk-driven amplifier. To the best of the author’s knowledge, this circuit represents the first reported low-voltage potentiostat system. This 1-V potentiostat possesses high linearity which is comparable or even better than the conventional potentiostat designs thanks to this transconductance enhanced bulk-driven amplifier. The current consumption of the overall potentiostat is maintained around 22 microampere. The area for the core layout of the integrated circuit chip is 0.13 mm2 for a 0.35 micrometer process

Radio frequency energy harvesting for autonomous systems

A thesis submitted to the University of Bedfordshire in partial fulfilment of the requirements for the degree of Doctor of PhilosophyRadio Frequency Energy Harvesting (RFEH) is a technology which enables wireless power delivery to multiple devices from a single energy source. The main components of this technology are the antenna and the rectifying circuitry that converts the RF signal into DC power. The devices which are using Radio Frequency (RF) power may be integrated into Wireless Sensor Networks (WSN), Radio Frequency Identification (RFID), biomedical implants, Internet of Things (IoT), Unmanned Aerial Vehicles (UAVs), smart meters, telemetry systems and may even be used to charge mobile phones. Aside from autonomous systems such as WSNs and RFID, the multi-billion portable electronics market – from GSM phones to MP3 players – would be an attractive application for RF energy harvesting if the power requirements are met. To investigate the potential for ambient RFEH, several RF site surveys were conducted around London. Using the results from these surveys, various harvesters were designed and tested for different frequency bands from the RF sources with the highest power density within the Medium Wave (MW), ultra- and super-high (UHF and SHF) frequency spectrum. Prototypes were fabricated and tested for each of the bands and proved that a large urban area around Brookmans park radio centre is suitable location for harvesting ambient RF energy. Although the RFEH offers very good efficiency performance, if a single antenna is considered, the maximum power delivered is generally not enough to power all the elements of an autonomous system. In this thesis we present techniques for optimising the power efficiency of the RFEH device under demanding conditions such as ultra-low power densities, arbitrary polarisation and diverse load impedances. Subsequently, an energy harvesting ferrite rod rectenna is designed to power up a wireless sensor and its transmitter, generating dedicated Medium Wave (MW) signals in an indoor environment. Harvested power management, application scenarios and practical results are also presented

NASA Tech Briefs Index, 1977, volume 2, numbers 1-4

Announcements of new technology derived from the research and development activities of NASA are presented. Abstracts, and indexes for subject, personal author, originating center, and Tech Brief number are presented for 1977

Energy Harvesting and Remote Powering for Implantable Biosensors

The paper reviews some popular techniques to harvest energy for implantable biosensors. For each technique, the advantages and drawbacks are discussed. Emphasis is placed to the inductive links, able to deliver power wirelessly through the biological tissues and to enable a bidirectional data communication with the implanted sensors. Finally, high frequency inductive links are described, focusing also on the power absorbed by the tissues

Towards Single-Chip Nano-Systems

Important scientific discoveries are being propelled by the advent of nano-scale sensors that capture weak signals from their environment and pass them to complex instrumentation interface circuits for signal detection and processing. The highlight of this research is to investigate fabrication technologies to integrate such precision equipment with nano-sensors on a single complementary metal oxide semiconductor (CMOS) chip. In this context, several demonstration vehicles are proposed. First, an integration technology suitable for a fully integrated flexible microelectrode array has been proposed. A microelectrode array containing a single temperature sensor has been characterized and the versatility under dry/wet, and relaxed/strained conditions has been verified. On-chip instrumentation amplifier has been utilized to improve the temperature sensitivity of the device. While the flexibility of the array has been confirmed by laminating it on a fixed single cell, future experiments are necessary to confirm application of this device for live cell and tissue measurements. The proposed array can potentially attach itself to the pulsating surface of a single living cell or a network of cells to detect their vital signs

Compact Micro scale Multi- Source (Solar and Thermal) Energy harvesting IC with regulated Multi load Power Management scheme

Power is required for all man-made systems to work and perform their corresponding activi-ties.Generation of power in large scale is carried out from power grids and supplied to systems that need high power whereas systems requiring less power are supplied from batteries. Batteries need to be replaced after their lifetime which seem to be a less attractive option in applications where systems are placed out of reach for humans as WSN nodes or in some of biomedical systems which are kept inside human body. The need for a self-supporting system i.e. a system that produces energy by itself and supports all the modules by powering them by itself is increased. A harvesting system that harvests energy from the ambience and converting that energy into electrical form and supplying the power to loads or storing in a battery is the solution for all the problems mentioned above. Solar, thermal, vibration and RF are the sources in the ambience from which energy can be harvested and supplied to load or charged into a battery. Availability of a single energy source(thermal,vibration,solar,RF) at all instances cannot be guaranteed creating a situation of insufficient supply of power to loads or unable to charge the load capacitor to the required voltage. Usage of multiple sources for harvesting energy is a prominent solution to the above mentioned problem. Designing a microscale energy harvesting from multiple sources is the main motto behind the current work.TEG and piezo are compatible to be used alternatively in the system because of their close resemblance in their energy densities. Therefore TEG and piezo have been used as two input sources for the system. The other modules in the system include design of a buck boost power converter that switches between buck and boost modes depending on the source connected to the system and the input voltage available at the input. The other module being a digital controller that generates clocks for power switches, signals that decide if TEG or PV need to be connected to the system.Intra source selection block for TEG array where multiple TEG sources switch between series or parallel depending on the voltage available across each TEG source so as to increase the net power from the TEG. The load is a capacitor that needs to be charged to 1.8V where the system stops working once the capacitor gets charged to the desired voltage. Idea of sharing a single inductor between two different sources without using two power converters for individual sources is implemented. Using the dead time of inductor current of TEG for PV source is the main thought behind the development of the current system. System is designed considering all the specifications, constraints, functionalit