Silicon thin films for mobile energy electronics

Consumer needs for mobile devices include the requirement for longer battery life, so that recharging can be performed less frequently or eliminated completely. To this end a key component of any mobile system is a high power and high energy density battery. An alternative to better batteries is for mobile devices to harvest some of their own energy. Solar energy is an accessible, free and environmentally friendly source of energy, making it ideal for powering mobile devices. In this work we present a low deposition temperature (150°C), thin-film solar power harvesting system. Low deposition temperature of thin film silicon and associated alloys allows for fabrication on plastic in order to realize lightweight and robust integrated systems. The system consists of a thin film transistor (TFT) circuit and thin film photovoltaic (PV) array. The circuit functions as a simple DC-DC regulator and maximum power point tracking unit (MPPT). Amorphous silicon (a-Si:H) is used as the primary thin-film material for the fabrication of the devices. One of the challenges when fabricating devices at low temperatures is the high defect density in a-Si:H due to hydrogen clustering. In here the He in addition to the SiH4 and H2 is used to minimise hydrogen clustering. Using the optimised films, TFT and PV devices are fabricated, and analysed. Low deposition temperatures influence TFT properties. Contact resistance and dynamic instability of TFTs are considered. New extraction methods and their effect on device mobility are presented. A power conditioning TFT circuit is proposed. A model is developed to analyse the circuit’s output stability as a function of stressing and light intensity. System efficiency and its dependence on circuit efficiency and solar cell utilisation are discussed. The PV array and the TFT circuit are fabricated using lithography techniques, with a maximum process temperature of 150°C. The circuit can provide a degree of output power stability over a wide range of light intensities and stressing times, making it suitable for use with SC. In this work peak system efficiency of 18% is achieved. Despite the circuit’s low efficiency, it has the advantage of fabrication on plastic substrates and better integrability within mobile devices

Punctate inner choroidopathy: A review

Punctate Inner Choroidopathy (PIC), an idiopathic inflammatory multifocal chorioretinopathy that predominantly affects young myopic women, appears to be relatively rare, but there is limited data to support accurate estimates of prevalence, and it is likely that the condition is under-diagnosed. The etiological relationship between PIC and other conditions within the 'white dot syndromes' group remains uncertain. We, like others, would suggest that PIC and multifocal choroiditis with panuveitis (MCP) represent a single disease process that is modified by host factors (including host immunoregulation) to cause the range of clinical phenotypes seen. The impact of PIC on the patient is highly variable, with outcome ranging from complete spontaneous recovery to bilateral severe sight-loss. Detection and monitoring has been greatly facilitated by modern scanning techniques, especially OCT and autofluorescence imaging, and may be enhanced by co-registration of sequential images to detect change over time. Depending on the course of disease and nature of complications, appropriate treatment may range from observation to systemic immunosuppression and anti-angiogenic therapies. PIC is a challenging condition where treatment has to be tailored to the patient's individual circumstances, the extent of disease, and the risk of progression

Flexible electronics: The next ubiquitous platform

Thin-film electronics in its myriad forms has underpinned much of the technological innovation in the fields of displays, sensors, and energy conversion over the past four decades. This technology also forms the basis of flexible electronics. Here we review the current status of flexible electronics and attempt to predict the future promise of these pervading technologies in healthcare, environmental monitoring, displays and human-machine interactivity, energy conversion, management and storage, and communication and wireless networks

Long-term culture of pluripotent stem-cell-derived human neurons on diamond – a substrate for neurodegeneration research and therapy

Brain Computer Interfaces (BCI) currently represent a field of intense research aimed both at understanding neural circuit physiology and at providing functional therapy for traumatic or degenerative neurological conditions. Due to its chemical inertness, biocompatibility and stability, diamond is currently being actively investigated as a potential substrate material for culturing cells and for use as the electrically active component of a neural sensor. Here we provide a protocol for the differentiation of mature, electrically active neurons on microcrystalline synthetic thin-film diamond substrates starting from undifferentiated pluripotent stem cells. Furthermore, we investigate the optimal characteristics of the diamond microstructure for long-term neuronal sustainability. We also analyze the effect of boron as a dopant for such a culture. We found that the diamond crystalline structure has a significant influence on the neuronal culture unlike the boron doping. Specifically, small diamond microcrystals promote higher neurite density formation. We find that boron incorporated into the diamond does not influence the neurite density and has no deleterious effect on cell survival

Flat-panel compatible photovoltaic energy harvesting system

In this work, an amorphous silicon (a-Si:H) thin-film transistor (TFT) circuit designed for charging of intermediary energy storage devices using photovoltaic (PV) solar cell arrays is demonstrated and analyzed. The proposed circuit combines the functionality of a linear DC-DC voltage regulator and a maximum power point tracking unit (MPPT). The circuit reduces the dependence of the charging voltage on light intensity and offers relatively stable operation when electrically stressed. The effects of light intensity and the PV array size on the system and circuit efficiencies as well as on PV utilization are investigated. A peak system efficiency of 18% is demonstrated. Although this is significantly lower than state-of-the-art switch mode DC-DC voltage regulator and MPPTs, the combined use of thin-film technology and low fabrication temperatures (below 150 $^{\circ}{\hbox{C}}$) allow its integration within a wide range of mobile devices, making it an attractive solution for energy harvesting systems. © 2006 IEEE

Thin film power harvesting system for displays

Long battery life is a critical requirement for mobile devices. Energy harvesting from ambient sources or recycling is a possible means of extending the battery life. Flat panel displays are ideal for this due to their relatively high power consumption, large external surface area and the use of transparent substrates such as glass and eventually plastic. This paper presents design considerations for successful integration of a thin-film power harvesting system for displays. An energy harvesting system, using amorphous silicon (a-Si:H) photo-voltaic (PV) array, a-Si:H thin film transistor (TFT) charging circuit and thin film supercapacitor, is demonstrated as one possible example of a thin film power harvesting system. The ultimate goal is to seamlessly integrate the power harvesting system with the display panels on rigid or flexible substrates. © 2012 JSAP

Effect of threshold voltage instability on field effect mobility in thin film transistors deduced from constant current measurements

The field effect (FE) mobility of thin film transistors is normally extracted using static measurement methods, which inherently rely on the assumption that the device remains stable during the measurement duration. However, these devices, particularly those based on emerging materials, can show large instability during the measurement, typically exhibiting hysteresis in the static characteristics. This letter looks at the effect of threshold voltage shift in FE mobility extracted using the conventional method, and introduces an alternative and more accurate technique of measuring device characteristics. The technique decouples the effect of transient phenomena, thus permitting extraction of the true device FE mobility, which turns out to be either over or underestimated depending on the magnitude and direction of threshold voltage shift. © 2009 American Institute of Physics

Large Area Electronics

Progress made in thin film technology in the last century has underpinned some of the major developments in large area electronics, which encompass devices ranging from displays and imaging arrays to solar cells. The thin-film transistor backplane has become the key component in active matrix flat-panel displays based on liquid crystal technology and organic light emitting diodes, and large area (human size) bio-medical imaging. The technology also forms the basis of thin film solar cells which occupy a significant portion of the energy market. This chapter provides an overview of some of the most important breakthroughs in the field of large area electronics

Large Area Electronics

Progress made in thin film technology in the last century has underpinned some of the major developments in large area electronics, which encompass devices ranging from displays and imaging arrays to solar cells. The thin-film transistor backplane has become the key component in active matrix flat-panel displays based on liquid crystal technology and organic light emitting diodes, and large area (human size) bio-medical imaging. The technology also forms the basis of thin film solar cells which occupy a significant portion of the energy market. This chapter provides an overview of some of the most important breakthroughs in the field of large area electronics

Pulsed-radio frequency plasma enhanced chemical vapour deposition of low temperature silicon nitride for thin film transistors

The growth of low temperature silicon nitride using radio frequency (RF) plasma enhanced chemical vapour deposition (PECVD) is associated with high porosity and surface roughness due to the short surface diffusion length of adsorbed radicals during the deposition. In this work we present pulsed-RF PECVD as a means of achieving a film with smoother surface and reduced density of voids. The growth process and the longer surface diffusion length are discussed as the main reason behind improvement of film density while maintaining the substrate temperatures. The deposited films exhibit improved electrical performance with 72% reduction in breakdown probability compared with conventional continuous-wave RF PECVD films. A low interfacial defect density with a field effect mobility of 1.1 cm2/V.s and subthreshold slope of 0.3 V/dec, was achieved when used as a gate dielectric in thin film transistors. © 2012 Elsevier B.V. All rights reserved