Abstract The uniformity of conductive materials is an important property in thin film electronic applications such as solar cells and light emitting diodes (LED). Such uniformity variations are often very small, invisible or below the surface of the film and thus are difficult to detect even when using high-resolution characterization devices. Thus, surface measurement instruments such as profilometer, atomic force microscope, or scanning electron microscope can all encounter remarkable challenges. The uniformity of films can also be analyzed by conductivity measurements. However, they do not provide the precise spatial uniformity information of a large area sample. To be able to investigate systematically the defects of conductive thin films an appropriate sample preparation method was constructed. In addition, a synchronized heating and IR-imaging based system (called synchronized thermography = ST) was developed to overcome the limitations of existing characterization methods. ST performance was tested and analyzed by measuring the single and multi-layer structures. In this work, Indium Tin Oxide (ITO) and poly(3,4-ethylenedioxy-thiopene):poly(styrene-sulfonate) (PEDOT: PSS) were used as examples of conductive thin films. Obtained results show that ST is capable of localizing even small defects from thin film structures based on a single IR-image. In order to make automatic identification of the defect locations and the sizes of the defects, a data processing algorithm was implemented. The performed experiments have proven ST capable of determining the conductivity of the films and the critical bending curvature of ITO. Based on thin film multi-layer PEDOT:PSS measurements, the results suggest use of the ST-method is also suitable for thickness measurements. ST with automatic data processing is a simple method to localize small defects in large-area thin film structures. This approach opens up new possibilities in measuring industrial scale manufacturing processes. / Tiivistelmä Johtavien materiaalien tasalaatuisuus on tärkeä ominaisuus ohutkalvoelektroniikan sovelluksissa kuten aurinkokennoissa ja valoa emittoivissa diodeissa (LED). Tasalaatuisuuserot ovat usein erittäin pieniä, näkymättömiä tai ne sijaitsevat pinnan alla, joten niiden havaitseminen on vaikeaa jopa korkean resoluution karakterisointivälineillä. Niinpä pintaa mittaavat laitteet kuten profilometri, atomivoimamikroskooppi ja skannaava elektronimikroskooppi kohtaavat merkittäviä haasteita. Pinnan tasalaatuisuutta voidaan analysoida myös johtavuusmittauksilla. Ne eivät kuitenkaan anna täsmällistä spatiaalista informaatiota suurista näytteistä. Johtavien ohutkalvojen rikkoutumien systemaattista tutkimista varten kehitettiin oma näytteiden käsittelymenetelmä. Lisäksi kehitettiin synkronoituun lämmitykseen ja infrapunakuvantamiseen perustuva mittaussysteemi (menetelmän nimi: synkronoitu termografia = ST), jolla pyritään ratkaisemaan nykyisten menetelmien rajoitukset. ST-menetelmää testattiin ja analysoitiin mittaamalla yksi- ja monikerroksisten kalvojen rakenteita. Indiumtinaoksidia (ITO) ja poly(3,4-etyleenidioksi-tiofeeni):poly(styreeni-sulfonaatti):a (PEDOT: PSS) käytettiin esimerkkeinä johtavista kalvoista. Tulokset osoittavat, että ST kykenee paikallistamaan pienetkin virheet ohutkalvorakenteista jopa yhden infrapunakuvan perusteella. Automaattisen tiedonkäsittelyn algoritmi implementoitiin identifioimaan virheiden paikkariippuvuuksia ja kokoja. Tehdyt kokeet osoittavat, että ST-menetelmä soveltuu kalvojen johtavuuden ja ITO:n kriittisen taivutussäteen määrittämiseen. Monikerroksisiin PEDOT:PSS rakennemittauksiin perustuen ST-menetelmä näyttäisi soveltuvan myös ohutkalvojen paksuuksien määrittämiseen. ST-menetelmä yhdistettynä automaattiseen mittaustiedon prosessointiin on yksinkertainen menetelmä paikallistamaan pieniä virheitä suuripinta-alaisilla näytteillä. Tämä lähestymistapa avaa uusia mittausmahdollisuuksia teollisuuden tuotantoprosesseihin.

Scientists have recently discovered simultaneous photoconductivity and photochromism (i.e., optical switching upon light exposure) of oxygen-containing rare-earth metal hydrides (REMHO). A deep understanding of these extraordinary optical and electrical properties can open the door to advanced technological uses such as smart windows. This thesis work is to establish a correlation between the photochromism of these materials with their photoconductive response and comprehend the underlying physics behind them. The samples were grown by reactive magnetron sputtering. The dynamics of the photochromic effect were observed by recording the time-resolved relative transmittance of the films during photodarkening and bleaching using a UV-vis spectrometer. The samples were characterized electrically by employing the two-point probe resistance measurement. The depth profiles of the concentration of chemical elements were extracted from Ion Beam Analysis. A systematic study was performed to see how the photoconductive and photochromic responses of the REMHO thin films depend on the wavelength and intensity of the illuminating light as well as the chemical composition of the films. Both effects showed i) higher response for shorter wavelength, ii) a cut-off near a similar wavelength, iii) saturation near UV region, and iv) similar relaxation time but with different kinetics. Multiple measurements performed on the same sample showed that the previous measurement affects the next measurement indicating a memory effect. Finally, the photoconductive response showed an increase with increasing oxygen concentration.

No description available.

Die vorliegende Dissertation behandelt Charakterisierung, Modellbildung sowie Anwendung einer magnetfeldgestützten Hohlkathoden-Bogenentladung. Hohlkathoden sind seit den 1960er Jahren Gegenstand grundlagen- sowie anwendungsorientierter Forschung und werden seit 20 Jahren am Fraunhofer-Institut für Elektronenstrahl- und Plasmatechnik für die Anwendung auf dem Gebiet der Vakuumbeschichtung weiterentwickelt. Ziel dieser Arbeit ist es, die technologischen Fortschritte physikalisch zu verstehen und gezielte Weiterentwicklungen für spezifische Einsatzgebiete zu ermöglichen. In der untersuchten Hohlkathodenbauform ist das aus Tantal bestehende, vom Arbeitsgas Argon durchströmte Kathodenröhrchen koaxial von einer Ringanode sowie von einer Magnetfeldspule umgeben. Die Entladung wird durch Hochspannungspulse gezündet, worauf sich ein diffuser Bogen im Röhrchen (internes Plasma) ausbildet. Das Röhrchen wird von Plasmaionen auf hohe Temperaturen geheizt, die eine thermionische Emission von Elektronen ermöglichen, welche das Plasma speisen. Das technologisch nutzbare externe Plasma wird im Vakuumrezipienten durch Wechselwirkung der Gasteilchen mit Strahlelektronen aus der Kathode erzeugt. Bei starker Reduktion des Arbeitsgasflusses wird die Entladung durch das Magnetfeld der Spule stabilisiert. Der experimentelle Befund, dass dadurch Plasmadichte und -reichweite sowie ggf. die Ladungsträgerenergien im Rezipienten aufgrund des intensiveren Elektronenstrahls wesentlich gesteigert werden können, wird durch ortsaufgelöste Langmuir-Sondenmessung, optische Emissionsspektroskopie und energieaufgelöste Massenspektrometrie ausführlich belegt und nach der Lösung von Strom- und Wärmebilanzgleichungen durch die Verhältnisse im Kathodenröhrchen begründet. Neben Argon werden auch typische Reaktivgase der Vakuumbeschichtung im Hohlkathodenplasma betrachtet: zum einen Stickstoff und Sauerstoff, die in reaktiven PVD-Prozessen (physikalische Dampfphasenabscheidung) zur Beschichtung mit Oxid- bzw. Nitridschichten zum Einsatz kommen und durch Ionisation, Dissoziation und Anregung im Hohlkathodenplasma verbesserte Schichteigenschaften ermöglichen; zum anderen Azetylen, das bei PECVD (plasmagestützte chemische Dampfphasenabscheidung) von amorphen wasserstoffhaltigen Kohlenstoffschichten z. B. für tribologische oder biokompatible Beschichtungen genutzt wird. Azetylen wird durch Streuprozesse mit Elektronen und Ionen im Plasma aufgespalten, wodurch schichtbildende Spezies erzeugt werden, die am Substrat kondensieren. Durch die Wahl der Plasmaparameter sowie durch abgestimmte Substratbiasspannung und Substratkühlung lassen sich die Beschichtungsrate einstellen sowie polymer-, graphit- oder diamantartige Eigenschaften erzielen. Neben der Plasmadiagnostik mittels energieaufgelöster Massenspektrometrie werden die erzeugten Kohlenstoffschichten vorgestellt und hinsichtlich Härte, Zusammensetzung und Morphologie analysiert. / In the present thesis, characterization, modeling and application of a magnetically enhanced hollow cathode arc discharge are presented. Since the 1960s, hollow cathodes are being studied in basic and applied research. At Fraunhofer Institute for Electron Beam and Plasma Technology, further development concerning the application in vacuum coating technology has been carried out for about twenty years. The present work targets on physically understanding the technological progress in order to enable specific further development and application. In the investigated hollow cathode device, a ring-shaped anode and a magnetic field coil are arranged coaxially around the tantalum cathode tube, which is flown through by argon as the working gas. The discharge is ignited by high voltage pulses establishing a diffuse arc within the cathode tube (internal plasma). The cathode is being heated by the plasma ions to high temperatures, which leads to thermionic emission of electrons sustaining the plasma. The external plasma in the vacuum chamber, which can be used for technological applications, is generated by collisions of gas atoms with beam electrons originating from the cathode. In the case of strongly reduced working gas flow, the discharge is stabilized by the magnetic field of the coil; the related experimental findings such as significantly increased plasma density and range as well as higher charge carrier energies in the external plasma are extensively proved by spatially resolved Langmuir probe measurements, optical emission spectroscopy, and energy-resolved ion mass spectrometry. Furthermore, the results are correlated to the conditions within the cathode tube by solving the current and heat balance equations. Besides argon, typical reactive gases used in vacuum coating are examined in the hollow cathode plasma, too. First, nitrogen and oxygen, which are applied in PVD (physical vapor deposition) processes for the deposition of oxide and nitride layers, are ionized, dissociated, and excited by plasma processes. In the case of practical application, this plasma activation leads to improved film properties. Second, acetylene is used as a precursor for PECVD (plasma-enhanced chemical vapor deposition) of amorphous hydrogenated carbon films, e.g. for tribological or biocompatible applications. Acetylene is cracked by electron and ion scattering in the plasma providing film-forming species to be deposited on the substrate. The deposition rate as well as the polymeric, graphitic, or diamond-like properties can be controlled by plasma parameters, a defined substrate bias, and substrate cooling. The hollow cathode-generated acetylene plasma has been characterized by energy-resolved ion mass spectrometry, and the carbon films obtained are analyzed regarding hardness, film composition, and morphology.

No description available.

Man’s desire to replicate/mimic the nature’s creation provided an impetus and inspiration to the rapid advancements and progress made in the sensors and actuators technology. A normal human being has five basic sensory organs, which helps and guides him in performing the routine tasks. This underlines the importance of basic sensory organs in a human life. In a similar fashion, sensors and actuators are of paramount importance for most of the science and engineering applications. The aim of the present thesis work is to explore the application of piezoelectric ZnO thin films deposited on a flexible substrate for the development of sensors and actuators. Detailed study was performed on the suitability of three different flexible substrates namely Phynox, Kapton and Mylar. However, Phynox alloy substrate was found to be a suitable substrate material for the above mentioned applications. Sputtering technique was chosen for the deposition of ZnO thin films on to Phynox substrate. The necessary process parameters were optimized to achieve good quality piezoelectric thin films. In the present work, sensors have been developed by utilizing the direct piezoelectric effect of ZnO thin films deposited on Phynox alloy substrate. These includes a flow sensor for gas flow rate measurement, impact sensor for non-destructive material discrimination study and a Thin Film Sensor Array (TFSA) for monitoring the impact events. On the other hand, using the converse piezoelectric effect of ZnO thin films, actuators have also been developed. These include a thin film micro actuator and a Thin Film Micro Vibrator (TFMV) for vibration testing of micro devices. The thesis is divided into following seven chapters. Chapter 1: This chapter gives a general introduction about sensors and actuators, piezoelectric thin films, flexible substrates, thin film deposition processes and characterization techniques. A brief literature survey of different applications of piezoelectric thin films deposited on various flexible substrates in device development is presented. Chapter 2: A novel flexible metal alloy (Phynox) and its properties along with its applications are discussed in this chapter. ZnO thin films were deposited on Phynox substrate by Rf reactive magnetron sputtering technique. The sputtering process parameters such as: Ar:O2 gas ratio, substrate temperature and RF power were optimized for the deposition of good quality piezoelectric ZnO thin films. The deposited ZnO thin films were characterized using XRD, SEM, AFM and d31 coefficient measurement techniques. Chapter 3: It reports on the comparative study of properties of piezoelectric ZnO thin films deposited on three different types of flexible substrates. The substrate materials employed were a metal alloy (Phynox), polyimide (Kapton), and polyester (Mylar). Piezoelectric ZnO thin films deposited on these flexible substrates were characterized by XRD, SEM, AFM and d31 coefficient measurement techniques. A vibration sensing test was also performed for the confirmation of good piezoelectric property. Compared to the polymer flexible substrates, the metal alloy flexible substrate (Phynox) was found to be more suitable for integrating ZnO thin film for sensing applications. Chapter 4: The development of a novel gas flow sensor for the flow rate measurement in the range of L min-1 is presented in this chapter. The sensing element is a Phynox alloy cantilever integrated with piezoelectric ZnO thin film. A detailed theoretical analysis of the experimental set–up showing the relationship between output voltage generated and force at a particular flow rate has been discussed. The flow sensor is calibrated using an in-house developed testing set-up. Chapter 5: This chapter is divided into two sections. Section 5.1 reports on the development of a novel packaged piezoelectric thin film impact sensor and its application in non-destructive material discrimination studies. Different materials (Iron, Glass, Wood and Plastic) were successfully discriminated by using the developed impact sensor. The output response of impact sensor showed good linearity and repeatability. The impact sensor is sensitive, reliable and cost-effective. Section 5.2 reports on the development of a Thin Film Senor Array (TFSA) for monitoring the location and magnitude of the impact force. The fabricated TFSA consists of evenly distributed ZnO thin film sensor array. Chapter 6: It consists of two sections. Section 6.1 reports on the fabrication of micro actuator using piezoelectric ZnO thin film integrated with flexible Phynox substrate. A suitable concave Perspex mounting was designed for the actuator element. The actuator element was excited at different frequencies for the supply voltages of 2V, 5V and 8V. The developed micro actuator has the potential to be used as a micro pump for pumping nano liters to micro liters of fluids. Section 6.2 reports the design and development of a portable ready to use Thin Film Micro Vibrator (TFMV). The TFMV is capable of providing the vibration amplitude in the range of nanometer to micrometer. A thin silicon diaphragm was used as a test specimen for its vibration testing studies using the developed TFMV. The TFMV is light-weight and have internal battery, hence no external power supply is required for its functioning. Chapter 7: The first section summarizes the salient features of the work presented in this thesis. In the second section the scope for carrying out the further work is given.

Improved fabrication of poly(vinylindenefluoride)-hexafluoropropylene (PVDF-HFP) thin films is of particular interest due to the high electric coercivity found in the beta-phase structure of the thin film. We show that it is possible to obtain high-quality, beta-phase dominant PVDF-HFP thin films using a direct approach to Langmuir-Blodgett deposition without the use of annealing or additives. To improve sample quality, an automated Langmuir-Blodgett thin film deposition system was developed; a custom dipping trough was fabricated, a sample dipping mechanism was designed and constructed, and the system was automated using custom LabVIEW software. Samples were fabricated in the form of ferroelectric capacitors on substrates of glass and silicon, and implement a unique step design with a bottom electrode of copper with an aluminum wetting layer and a top electrode of gold with an aluminum wetting layer. Samples were then characterized using a custom ferroelectric measurement program implemented in LabVIEW with a Keithley picoammeter/voltage supply to confirm electric coercivity properties. Further characterization using scanning electron microscopy and atomic force microscopy confirmed the improvement in thin film fabrication over previous methods.

Indiana University-Purdue University Indianapolis (IUPUI) / Improved fabrication of poly(vinylindenefluoride)-hexafluoropropylene (PVDF-HFP) thin films is of particular interest due to the high electric coercivity found in the beta-phase structure of the thin film. We show that it is possible to obtain high-quality, beta-phase dominant PVDF-HFP thin films using a direct approach to Langmuir-Blodgett deposition without the use of annealing or additives. To improve sample quality, an automated Langmuir-Blodgett thin film deposition system was developed; a custom dipping trough was fabricated, a sample dipping mechanism was designed and constructed, and the system was automated using custom LabVIEW software. Samples were fabricated in the form of ferroelectric capacitors on substrates of glass and silicon, and implement a unique step design with a bottom electrode of copper with an aluminum wetting layer and a top electrode of gold with an aluminum wetting layer. Samples were then characterized using a custom ferroelectric measurement program implemented in LabVIEW with a Keithley picoammeter/voltage supply to confirm electric coercivity properties. Further characterization using scanning electron microscopy and atomic force microscopy confirmed the improvement in thin film fabrication over previous methods.