Harding University Course Catalog 1988-1989

Catalog of Harding University 1988-1989https://scholarworks.harding.edu/catalogs/1050/thumbnail.jp

Modeling capillary forces for large displacements

Originally applied to the accurate, passive positioning of submillimetric devices, recent works proved capillary self-alignment as effective also for larger components and relatively large initial offsets. In this paper, we describe an analytic quasi-static model of 1D capillary restoring forces that generalizes existing geometrical models and extends the validity to large displacements from equilibrium. The piece-wise nature of the model accounts for contact line unpinning singularities ensuing from large perturbations of the liquid meniscus and dewetting of the bounding surfaces. The superior accuracy of the generalized model across the extended displacement range, and particularly beyond the elastic regime as compared to purely elastic models, is supported by finite element simulations and recent experimental evidence. Limits of the model are discussed in relation to the aspect ratio of the meniscus, contact angle hysteresis, tilting and self-alignment dynamics

Charge transport in solution processable polycrystalline dual-gate organic field effect transistors

\u3cp\u3eDual gate organic thin film transistors based on solution processable fluorinated 5,11 bis(triethylsilylethynyl) anthradithiophene semiconductor were fabricated. Top (Teflon, ε\u3csub\u3er\u3c/sub\u3e =2.1) and bottom (SiO\u3csub\u3e2\u3c/sub\u3e, ε\u3csub\u3er\u3c/sub\u3e =3.9) gate dielectrics with different dielectric constants were chosen. Top gate mobilities >1 cm\u3csup\u3e2\u3c/sup\u3e /Vs and bottom gate mobilities >0.1 cm\u3csup\u3e2\u3c/sup\u3e/V s were achieved. Temperature dependent mobility measurements show thermally activated charge transport and a comparative analysis is performed in the framework of two models representing polaron hopping as well as hopping in Gaussian density of states (DOS), respectively.\u3c/p\u3

Active-matrix IGZO array with printed thermistor for large-area thermal imaging

\u3cp\u3eThermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution.\u3c/p\u3

Top-split-gate ambipolar organic thin-film transistors

\u3cp\u3eSplit-gate ambipolar organic transistor technology is gaining interests as a practical solution for the implementation of complementary transistors. It is known that conventional ambipolar transistors suffer from poor DC gain, noise margin, and high power consumption, as they do not have a well-defined off-state region. A split-gate device structure enables ambipolar transistors operating in a controlled unipolar mode (both p-type and n-type), resulting in superior inverter characteristics. A key challenge in previously reported split-gate ambipolar organic thin-film transistors is the strong current-voltage instabilities due to charge trapping at the dielectric interface. Here, the first split-gate ambipolar organic transistors with top-gate/bottom-contact structure are demonstrated. Compared to the previous split-gate devices, the top-split-gate ambipolar organic transistor exhibits superior electrical properties. The proposed device shows hysteresis-free I-V characteristics as well as higher bias stress stability. Furthermore, the complementary inverter circuit using the proposed transistors is also demonstrated, which results in a higher output swing and DC gain compared to the baseline ambipolar inverter.\u3c/p\u3

Origin of multiple memory states in organic ferroelectric field-effect transistors

In this work, we investigate the ferroelectric polarization state in metal-ferroelectric-semiconductor-metal structures and in ferroelectric field-effect transistors (FeFET). Poly(vinylidene fluoride-trifluoroethylene) and pentacene was used as the ferroelectric and semiconductor, respectively. This material combination in a bottom gate-top contact transistor architecture exhibits three reprogrammable memory states by applying appropriate gate voltages. Scanning Kelvin probe microscopy in conjunction with standard electrical characterization techniques reveals the state of the ferroelectric polarization in the three memory states as well as the device operation of the FeFET. © 2012 American Institute of Physics.status: publishe

Shift dynamics of capillary self-alignment

\u3cp\u3eThis paper describes the dynamics of capillary self-alignment of components with initial shift offsets from matching receptor sites. The analysis of the full uniaxial self-alignment dynamics of foil-based mesoscopic dies from pre-alignment to final settling evidenced three distinct, sequential regimes impacting the process performance. The dependence of accuracy, alignment time and repeatability of capillary self-alignment on control parameters such as size, weight, surface energy and initial offset of assembling dies was investigated. Finally, we studied the influence of the dynamic coupling between the degenerate oscillation modes of the system on the alignment performance by means of pre-defined biaxial offsets.\u3c/p\u3

Origin of multiple memory states in organic ferroelectric field-effect transistors

In this work, we investigate the ferroelectric polarization state in metal-ferroelectric-semiconductor-metal structures and in ferroelectric field-effect transistors (FeFET). Poly(vinylidene fluoride-trifluoroethylene) and pentacene was used as the ferroelectric and semiconductor, respectively. This material combination in a bottom gate—top contact transistor architecture exhibits three reprogrammable memory states by applying appropriate gate voltages. Scanning Kelvin probe microscopy in conjunction with standard electrical characterization techniques reveals the state of the ferroelectric polarization in the three memory states as well as the device operation of the FeFET

Large-area all-printed temperature sensing surfaces using novel composite thermistor materials

\u3cp\u3eSurfaces which can accurately distinguish spatial and temporal changes in temperature are critical for not only flow sensors, microbolometers, process control, but also future applications like electronic skins and soft robotics. Realizing such surfaces requires the deposition of thousands of thermal sensors over large areas, a task ideally suited for printing technologies. Negative temperature coefficient (NTC) ceramics represent the industry standard in temperature sensing due to their high thermal coefficient and excellent stability. A drawback is their complex and high temperature fabrication process and high stiffness, prohibiting their monolithic integration in large area or flexible applications. As a remedy, a printable NTC composite that combines a rapid and scalable all-printed fabrication process with performances that are on par with conventional NTC ceramics is demonstrated. The composite consists of micrometer-sized manganese spinel oxide particles dispersed in a benzocyclobutene matrix. The sensor has a B coefficient of 3500 K, with a 4.0% change in resistance at 25 °C, comparable to bulk ceramics. The selected polymer binder yields a composite exhibiting less than a 1 °C change in resistance to changes in humidity. The sensor's scalability is validated by demonstration of a A4-sized temperature sensing sheet consisting of over 400 sensors.\u3c/p\u3