Reliability, besides the performance, is one of the important key factors of success of any technology. While a product should perform at best as desired, it must also be capable of working for intended period of life without any degradation or wear-out failure, caused by any operational parameter. For example it does no good to manufacture a super fast microprocessor if that fails within few seconds. For the product to meet the intended reliability we must understand the mechanisms that lead to unreliability or failure of the devices. The efforts to understand the fundamental physics of the mechanisms that lead to the failure of the devices has developed a branch of physics named as “reliability physics” of “physics of failure”. On the basis of the understanding of failure mechanism, new design rule can be followed and new material can be applied to improve the reliability of the product. Microelectronic technology also, which is one of the fastest growing technology, has been facing challenges posed by the reliability issues from time to time. There are number of physical failure mechanisms that can affect the reliability of a microelectronic device. Time dependent dielectric breakdown (TDDB), hot carrier damage and current induced damage of interconnects are only to name a few common mechanisms. Among these, the failure of interconnects due to current has been the oldest and persistence reliability issue since the beginning of development of the microelectronic technology. Understanding the physics of the processes that lead to failure of a current carrying film is the main interest of this thesis work. In this investigation, we have carried out a systematic study to understand stability of metal nanowires against damage caused by current stressing and its size dependency. We observe the wires of smaller diameter, having an electronic mean free path larger than or comparable to its diameter are more stable against current stressing. In wires of larger diameter (100 nm or more) the probability of the damage is more. This probably is due to presence of grain boundary type extended defects that allow low energy diffusion path. To our knowledge this is the first experimental investigation to study the stability of nanowires against high current and in-situ measurement of noise during current stressing on them. In the previous investigations by other groups observed that the nanowires without any passivation got damaged by stressing current density which was even lower than the one we used for stressing. To our knowledge this is the first observation of long lasting stability of nanowires, of dimension down to 15 nm, when they are encapsulated in dielectric, an environment that an interconnect has to see in the real integrated circuit devices. In the second chapter we will describe the sample preparation method, characterization of samples and the experimental setups we had used. The results of in-situ noise measurement are described in the third chapter. We will describe our in-situ scanning thermal microscopy study in the fourth chapter. Then in the fifth chapter, we will present our simulation investigations on current induced damage of film. Finally, we will put the concluding remarks on this thesis work and the results in the sixth chapter. We have studied similar damage processes in metal nanowires also. In an appendix we will present our approach and major results of this investigation.

In this thesis the InSb(111), InAs(111) and GaSb(001) surfaces have been studied by means of time- and angle-resolved photoemission spectroscopy based upon the femtosecond laser system. The pump-and-probe technique allows to analyse both electron states in the valence band and normally unpopulated electron states above the valence band, which can be occupied by transiently excited carriers at the optically pumped surface. The life time of excited carriers is analysed by controlling over the time delay between pump and probe pulses. Experimental studies of the InSb(111) surface and comparison with a previously studied InSb(110) surface show electron excitations in the bulk region with a minor surface contribution. Time-resolved experiments of carrier dynamics at the polar InAs(111)A and InAs(111)B surfaces show about the same life time of excited carriers, while no populated states above the valence band maximum have been found at the InAs(111)A due to the charge removal. Surface intergap electron states have been found at the GaSb(001) surface located at ~250 meV above the valence band maximum. Angle-resolved experiments showed a strong confinement of this state at the centre of the surface Brillouin zone. A new two dimensional angle-resolved multi-anode analyser for the femtosecond laser photoemission setup has been constructed. The analyser can resolve a cone opening angle of ~1º at a drift distance of ~0.5 m with an energy resolution of ~125 meV. A continuous series of binary system SrTiO3–PbZr0.52Ti0.48O3 has been grown by pulsed laser deposition (PLD) on sapphire substrate with crystalline quality control by x-ray diffraction (XRD). The maximum tunability has been tailored to room temperature, where STO�PZT (71/29) composition shows superior performance. A PbZr0.52Ti0.48O3 thin film pressure sensor has been fabricated by PLD and characterised by XRD and electrical measurements. The piezoelectric constant was found to be ~20 % higher compared to the bulk ceramics. A ferroelectric thin film electro-optical cell Na0.5K0.5NbO3/La0.5Sr0.5CoO3 (NKN/LSCO) on sapphire has been fabricated by PLD. Refractive indices and electro-optical coefficient of the cell were characterised by prism coupling refractometry. The tunability of the PLD fabricated 2 μm slot NKN thin film interdigital capacitor has been found ~23 % at 40 V bias voltage and frequency 1 MHz. / QC 20101015

Quasicrystals is a new kind of material that have several interesting aspects to it. The unusual atomic structure entails many anomalous and unique physical properties, for example, high hardness, and extremely low electrical and thermal conductivity. In thin films quasicrystals would enable new functional materials with a combination of attractive properties.In this work, AlCuFe and Nanoflex steel, materials that are known to form quasicrystals in bulk, have been deposited as thin films on Si and Al2O3 substrates using DC magnetron sputtering. These thin films were heat treated, and the formation and growth of different phases, among other approximant and quasicrystalline phases, were studied using mainly in-situ X-ray diffraction.During the project several problems with the formation of quasicrystals were encountered, and it is proposed how to overcome these problems, or even how to make use of them. Finally, the quasicrystalline phase was realized, although it was not completely pure. In the end some suggestions for future work is presented.

The demands for faster, smaller, and less expensive electronic equipments are basically the driving forces for improving the speed and increasing the packing density of microelectronic components. Down-scaling of the devices is the principal method to realize these requests. For future CMOS devices, new materials are required in the transistor structure to enable further scaling and improve the transistor performance. This thesis focuses on novel metal gate and high-κ dielectric materials for future CMOS technologies. Specifically, TiN and ZrN gate electrode materials were studied with respect to work function and thermal stability. High work function, suitable for pMOS transistors, was extracted from both C-V and I-V measurements for PVD and ALD TiN in TiN/SiO2/Si MOS capacitor structures. ZrNx/SiO2/Si MOS capacitors exhibited n-type work function when the low-resistivity ZrNx was deposited at low nitrogen gas flow. Further, variable work function by 0.6 eV was achieved by reactive sputter depositing TiNx or ZrNx at various nitrogen gas flow. Both metal-nitride systems demonstrate a shift in work function after RTP annealing, which is discussed in terms of Fermi level pinning due to extrinsic interface states. Still, the materials are promising in a gate last process as well as show potential as complementary gate electrodes. The dielectric constant of as-deposited (Ta2O5)1-x(TiO2)x thin films is around 22, whereas that of AlN is about 10. The latter is not dependent on the degree of crystallinity or on the measurement frequency up to 10 GHz. Both dielectrics exhibit characteristics appropriate for integrated capacitors. Finally, utilization of novel materials were demonstrated in strained SiGe surface-channel pMOSFETs with an ALD TiN/Al2O3 gate stack. The transistors were characterized with standard I-V, charge pumping, and low-frequency noise measurements. Correlation between the mobility and the oxide charge was found. Improved transistor performance was achieved by conducting low-temperature water vapor annealing, which reduced the negative charge in the Al2O3.

Delamination along thin film interfaces is a prevalent failure mechanism in microelectronic, photonic, MEMS, and other engineering applications. Current interfacial fracture test techniques specific to thin films are limited by either sophisticated mechanical fixturing, physical contact near the crack tip, non-representative test specimens, or complicated stress fields. Moreover, these techniques are generally not suitable for investigating fatigue crack propagation under cyclical loading. A fixtureless and noncontact experimental test technique is thus proposed and implemented to study interfacial fracture for thin film systems. The proposed test incorporates permanent magnets surface mounted onto micro-fabricated released thin film structures. An applied external magnetic field induces noncontact monotonic or fatigue loading to initiate delamination along the interface between the thin film and underlying substrate. Characterization of the film deflection, peel angle, and delamination propagation is accomplished through in situ optical techniques. Analytical and finite-element models are used to extract fracture parameters from the experimental data using thin-film peel mechanics. The developed interfacial fracture test has been demonstrated for Cu thin films on a SiO₂/Si substrate.

<p>When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell. A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon. In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity. The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped. A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.<br /> &nbsp / </p>

Pb(Zr₀.₅₂Ti₀.₄₈)O₃ (PZT) thin films are of interest for their large dielectric permittivity, ferroelectric, and piezoelectric properties. The material has been widely studied for use in high frequency transducers, multi-layered capacitors, and ferroelectric random access memory. Copper foils are an inexpensive, flexible substrate with a low resistivity which makes them ideal for many transducer and capacitor applications. PZT thin films on copper foils were produced by RF sputtering and crystallized under reducing conditions. Causes and prevention of a cuprous oxide interlayer are discussed. The film structure was characterized by XRD, SEM, and AFM. The permittivity was low, but remanent polarization increased to as high as ~40 μC/cm² as film thickness and crystallization temperature increased. Residual stresses were measured by x-ray diffraction using the sin²ψ method. The relative permittivity of the PZT/Cu films was measured as a function of applied AC electric field. By performing a Rayleigh analysis on this data one can determine the relative contributions of the intrinsic, reversible, and irreversible components to the permittivity. The residual stress could be correlated to the reversible part of the permittivity. The first order reversal curves (FORCs), which characterize the ferroelectric switching, give indications of the defect state of the film. Cantilever energy harvesters were fabricated. Large electrodes were able to be evaporated onto the films after oxidizing pinholes and cracks on a hot plate. Devices were tested on a shaker table at < 100 Hz. A dynamic model based on Euler-Bernoulli beam equations was used to predict power output of the fabricated devices. The observed output was comparable to model predictions. Resonant frequency calculations were in line with observed first and second resonances at ~17 Hz and ~35 Hz which were also close to those predicted by the dynamic model. / Graduation date: 2013

The development of functional flexible electronics is essential to enable applications such as conformal medical imagers, wearable health monitoring systems, and flexible light-weight displays. Intensive research on thin-film transistors (TFTs) is being conducted with the goal of producing high-performance devices for improved backplane electronics. However, there are many challenges regarding the performance of devices fabricated at low temperatures that are compatible with flexible plastic substrates. Prior work has reported on the change in TFT characteristics due to mechanical strain, with especially extensive data on the effect of strain on field-effect mobility. This thesis investigates the effect of gate-bias stress and elastic strain on the long-term stability of flexible low-temperature hydrogenated amorphous silicon (a-Si:H) TFTs, as the topic has yet to be explored systematically. An emphasis was placed on bias-stress measurements over time in order to obtain information on the physical mechanisms of instability. Drain current was measured over various intervals of time to track the degradation of devices due to metastability, and results were then compared across devices of various sizes under tensile, compressive, and zero strain. Transfer characteristics of the TFTs were also measured under the different conditions, to allow for extraction of parameters that would provide insight into the instability mechanisms. In addition to parameter extraction, the degradation and recovery of TFT output current was quantitatively compared for various bias-stress times across the different levels of strain. Finally, the instability mechanisms are modelled with a Markov system to further examine the effect of strain on long-term TFT operation. From the analysis of results, it was found that shallow charge trapping in the dielectric is the main mechanism of instability for short bias stress times, and did not seem to be greatly affected by strain. For longer bias stress times of over 10000 seconds, defect creation in the a-Si:H becomes a more significant contributor to instability. Both tension and compression increased defect creation compared to TFTs with zero applied strain. Compression appeared to cause the greatest increase in the rate of defect formation, likely by weakening Si-Si bonds in the a-Si:H. Tension appeared to cause a less significant increase, possibly due to a strengthening of some proportion of the Si-Si bonds caused by the slight elongation of bond length or because the applied tension relieves intrinsic compressive stress in a-Si:H film. A longer conduction path and greater dielectric area appears to increase the bias-stress and strain-related effects. Therefore reducing device size should increase the reliability of flexible TFTs.

Industrial production of hydrogen from the syngas, generated from steam reformation of natural gas or coal gasification, sets conditions for hydrogen separation membranes in terms of operating conditions. An alternative source for hydrogen is a syngas generated by gasification of municipal solid wastes which are likely to set more stringent conditions for the separation membranes. There is therefore, a growing demand for separation membranes with improved permeability and particularly of low cost. Among various alternatives, metallic membranes are particularly attractive due to their high selectivity and permeability for hydrogen, exemplified by palladium (Pd). However, due to high cost of Pd there is still a demand to develop alternative metallic membranes that are of low cost and have improved durability. Efforts have therefore concentrated on either alloying Pd so as to reduce its cost or on alternative membrane compositions of particularly b.c.c. structure. The current study deals with hydrogen separation membranes and aims to develop infrastructure for rapid identification of membrane compositions with improved permeability. The study is made up of three parts / i) development of sputter deposition system that would allow deposition of multiple compositions in a single experiment, ii) development of substrate material that would support the thin film membranes and would allow permeability measurement and iii) development of a set-up to measure the permeability of the thin film membranes. In the present thesis, a sputter deposition system incorporating three targets was successfully constructed. The system as tested with palladium-niobium-titanium (Pd-Nb-Ti) ternary system after necessary adjustment would yield thin films of homogenous thickness (&le / 7%) over a sample area of &asymp / 150 mm diameter. A total of 21 substrates each in 19 mm diameter arranged in triangular form in the substrate holder could successfully be deposited where composition distributions covered a greater portion of Pd-Nb-Ti ternary phase diagram. The structure of the deposited thin films can successfully be controlled by substrate temperature as well as by the pressure of plasma gas (argon). With the help of these parameters, structural diversity can also be produced beside the compositional variation. As for substrates, two materials were investigated. These were titanium dioxide (TiO2) modified porous stainless steel (PSS) and anodic porous alumina (AAO). TiO2 modified PSS due to its associated surface roughness leads to the deposition of films with defected structure which as a result is not gas tight. AAO produced via anodization of aluminum foil had a regular (40-60 nm) pore structure that provides a suitable surface for thin film depositions which could be defect free. However, AAO is very delicate and fragile which makes it difficult to adapt it as a support material for permeability measurement/hydrogen separation purposes. Finally, a set-up was developed for measurement of hydrogen permeability which is capable of measurement over a wide pressure and temperature conditions, i.e. hydrogen pressures up to 10 bar and temperature as high as 450 &deg / C. It is recommended that so as to identify compositions with improved permeability, Nb or a similar metal which has extremely high permeability could be used as a support material. This would tolerate the evaluation of the films which are not totally defect free.

In this thesis study, fabrication and doping of silicon thin films prepared by electron beam evaporation equipped with effusion cells for solar cell applications have been investigated. Thin film amorphous Si (a-Si) layers have been fabricated by the electron beam evaporator and simultaneously doped with boron (B) and phosphorous (P) using effusion cells. Samples were prepared on glass substrates for the future solar cell operations. Following the deposition of a-Si thin film, crystallization of the films has been carried out. Solid Phase Crystallization (SPC) and Metal Induced Crystallization (MIC) have been employed to obtain thin film crystalline Si. Crystallization was performed in a conventional tube furnaces and Rapid Thermal annealing systems (RTA) as a function of process parameters such as annealing temperature and duration. Produced films have been characterized using chemical and structural characterization techniques such as Raman Spectroscopy, X-Ray Diffractometer and Secondary Ion Mass Spectrometer (SIMS). The electrical properties of the films have been studied using Hall Effect and I-V measurements as a function of doping. We have demonstrated successful crystallization of a-Si by SPC at temperatures above 600 &deg / C. The crystallization occurred at lower temperatures in the case of MIC. For doping, P was evaporated from the effusion cell at a temperature between 600 &deg / C and 800 &deg / C. For B, the evaporation temperature was 1700 &deg / C and 1900 &deg / C. The thickness and the band gap of the Si films were determined by ellipsometry method and the results were compared for different evaporation temperatures. The effect of doping was monitored by the I-V and Hall Effect measurements. We have seen that the doping was accomplished in most of the cases. For the samples annealed at relatively high temperatures, the measured doping type was inconsistent with the expected results. This was attributed to the contamination from the glass substrate. To understand the origin of this contamination, we analyzed the chemical structure of the film and glass by X-ray Fluorescence (XRF) and seen that the glass is the main source of contamination. In order to prevent this contamination we have suggested covering the glass substrate with Si3N4 (Silicon Nitride) which act as a good diffusion barrier for impurities.