Simulation and fabrication of an interposer for electrical testing of fine-pitch wafer-level packages

Master'sMASTER OF ENGINEERIN

Toward Sustainable Transparent and Flexible Electronics with Amorphous Zinc Tin Oxide

The present thesis addresses a sustainable approach to mechanically flexible and transparent electronic devices based on the amorphous oxide semiconductor zinc tin oxide (ZTO) as abundant and low-cost alternative to already industrially established materials such as amorphous indium gallium zinc oxide. ZTO thin films are deposited by radio frequency long-throw magnetron sputtering at room temperature to generally enable the implementation of common photolithography processes and further facilitate patterning of digital circuit elements on thermally unstable organic substrates. Starting with the most basic device building blocks of integrated circuitry, various types of field-effect transistors are fabricated by implementation of amorphous ZTO as active channel material. Metal-semiconductor field-effect transistors and pn heterodiode based junctions field-effect transistors as well as conventional metal-insulatorsemiconductor field-effect transistors are then compared regarding their electrical performance and long-term stability over a couple of months. A decisive step toward the successful interconnection of fundamental digital circuit elements, such as previously demonstrated simple inverters, is to ensure sufficient output level compatibility between the signals of associated logic components. Accordingly, the Schottky diode field-effect transistor logic approach is adapted for amorphous ZTO based devices in order to facilitate cascading of multiple inverters consisting of unipolar devices. Field-effect transistor properties as well as the circuit design have been continuously improved to enhance the overall performance in terms of functionality and low-voltage operation. Corresponding logic inverters are finally integrated in ring oscillator circuits to gain insights into the dynamic properties of digital circuit building blocks based on amorphous ZTO. Ultimately, ZTO has been fabricated on mechanically flexible polyimide substrates to determine the elastic and electrical properties of amorphous ZTO thin films in dependence on external tensile and compressive stress induced by mechanical bending. Further, associated flexible metal-semiconductor field-effect transistor are investigated regarding their performance stability under tensile strain.Die vorliegende Arbeit umfasst die Herstellung und Charakterisierung aktiver elektrischer Bauelemente und integrierter Schaltkreise auf Basis des amorphen Oxidhalbleiters Zink-Zinnoxid (ZTO). Als vielversprechende nachhaltige und kostengünstigere Alternative zu dem bereits industriell etablierten Halbleiter Indium-Gallium-Zinkoxid wird insbesondere die Eignung von ZTO in optisch transparenter sowie mechanisch flexibler Elektronik untersucht. Um entsprechend Kompatibilität mit thermisch instabilen organischen Substraten sowie herkömmlichen Fotolithografieverfahren zu gewährleisten, beschränkt sich die Züchtung von ZTO-Dünnfilmen mittels Hochfrequenz-Magnetron-Distanzkathodenzerstäubung ausschließlich auf Herstellungsprozesse bei Raumtemperatur. Zunächst wird auf die Umsetzung verschiedener Feldeffekttransistor-Typen auf Basis amorphen ZTOs eingegangen, welche elektrisch charakterisiert und schließlich vor dem Hintergrund der Anwendung in integrierten Schaltkreisen vergleichend gegenübergestellt werden. Neben konventionellen Metall-Isolator-Halbleiterstrukturen wird vor allem näher auf Metall-Halbleiter-Feldeffekttransistoren sowie Sperrschicht-Feldeffekttransistoren auf der Grundlage von pn-Heteroübergängen eingegangen, da diese hauptsächlich in Bereichen hoher geforderter Schaltfrequenzen zum Einsatz kommen. Da integrierte Schaltkreise auf Basis unipolarer Feldeffekttransistoren eines Ladungsträgertyps inkonsistente Signaleingangs- sowie -ausgangspegel aufweisen, wird die Schottky- Dioden-Transistorlogik adaptiert, um entsprechend die Verknüpfung mehrerer Logikgatter auf Basis amorphen ZTOs zu gewährleisten. Durch geeignete Signalrückkopplung werden komplexere Schaltungen wie Ringoszillatoren realisiert, welche anhand von Laufzeitanalysen Aufschluss über die Schaltgeschwindigkeit ZTO basierter Feldeffekttransistoren geben. Abschließend werden amorphe ZTO-Dünnfilme auf flexiblen Polyimid-Substraten hergestellt und bezüglich der elastischen sowie elektrischen Eigenschaften in Abhängigkeit von exzessivem mechanischen Stress untersucht. Darüber hinaus werden flexible Metall-Halbleiter-Feldeffekttransistoren hinsichtlich ihrer Funktionalität und Stabilität gegenüber durch Biegeprozesse induzierte Verspannungen elektrisch charakterisiert

A time-based approach for multi-GHz embedded mixed-signal characterization and measurement /

The increasingly more sophisticated systems that are nowadays implemented on a single chip are placing stringent requirements on the test industry. New test strategies, equipment, and methodologies need to be developed to sustain the constant increase in demand for consumer and communication electronics. Techniques for built-in-self-test (BIST) and design-for-test (DFT) strategies have been proven to offer more feasible and economical testing solutions.Previous works have been conducted to perform on-chip testing, characterization, and measurement of signals and components. The current thesis advances those techniques on many levels. In terms of performance, an increase of more than an order of magnitude in speed is achieved. 70-GHz (effective sampling) on-chip oscilloscope is reported, compared to 4-GHz and 10-GHz ones in previous state-of-the-art implementations. Power dissipation is another area where the proposed work offer a superior solution compared to previous alternatives. All the proposed circuits do not exceed a few milliWatts of power dissipation, while performing multi-GHz high-speed signal capture at a medium resolution. Finally, and possibly most importantly, all the proposed circuits for test rely on a different form of signal processing; the time-based approach. It is believed that this approach paves the path to a lot of new techniques and circuit design skills that can be investigated more deeply. As an integral part of the time-based processing approach for GHz signal capture, this thesis verifies the advantages of using time amplification. The use of such amplification in the time domain is materialized with experimental results from three specific integrated circuits achieving different tasks in GHz high-speed in-situ signal measurement and characterization. Advantages of using such time-based approach techniques, when combined with the use of a front-end time amplifier, include noise immunity, the use of synthesizable digital cells, and circuit building blocks that track the technology scaling in terms of area and speed

DNA-based conducting polymer nanowires for biosensor applications

PhD ThesisNovel DNA-based conductive polymer nanowires formed from thienyl-pyrrole derivatives have been synthesized and characterised by high-resolution ES-MS, ¹H and ¹³C NMR spectroscopy. Bulk DNA-templating of these materials is demonstrated by FTIR, while relative control over nanowire dimensions and deposition is shown by AFM. The electronic properties of these materials were investigated by Scanned Conductance Microscopy (SCM) and two-point I-V measurements. The resistance of the DNA/polymer nanowires, determined from variable temperature I-V measurements, was found to be in the range of 10¹²-10¹⁴Ω. Nanowire conductivity values were calculated to be in the range of 1.9x10-⁷-3.75x10-⁴S cm-¹ at 303K. FTIR data demonstrates the availability of the alkyne group in bulk DNAtemplated materials for subsequent nanowire functionalisation using ‘click’ chemistry. Efforts to couple 3-azido propanol and ssDNA probe DNA is also presented.EPSRC