Harding University Course Catalog 1988-1989

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

Roadmap on printable electronic materials for next-generation sensors

The dissemination of sensors is key to realizing a sustainable, ‘intelligent’ world, where everyday objects and environments are equipped with sensing capabilities to advance the sustainability and quality of our lives—e.g., via smart homes, smart cities, smart healthcare, smart logistics, Industry 4.0, and precision agriculture. The realization of the full potential of these applications critically depends on the availability of easy-to-make, low-cost sensor technologies. Sensors based on printable electronic materials offer the ideal platform: they can be fabricated through simple methods (e.g., printing and coating) and are compatible with high-throughput roll-to-roll processing. Moreover, printable electronic materials often allow the fabrication of sensors on flexible/stretchable/biodegradable substrates, thereby enabling the deployment of sensors in unconventional settings. Fulfilling the promise of printable electronic materials for sensing will require materials and device innovations to enhance their ability to transduce external stimuli—light, ionizing radiation, pressure, strain, force, temperature, gas, vapours, humidity, and other chemical and biological analytes. This Roadmap brings together the viewpoints of experts in various printable sensing materials—and devices thereof—to provide insights into the status and outlook of the field. Alongside recent materials and device innovations, the roadmap discusses the key outstanding challenges pertaining to each printable sensing technology. Finally, the Roadmap points to promising directions to overcome these challenges and thus enable ubiquitous sensing for a sustainable, ‘intelligent’ world

Ferroelectric switching of poly(vinylidene difluoride-trifluoroethylene) in metal-ferroelectric-semiconductor non-volatile memories with an amorphous oxide semiconductor

Ferroelectric polarization switching of poly(vinylidene difluoride-trifluoroethylene) is investigated in different thin-film device structures, ranging from simple capacitors to dual-gate thin-film transistors (TFT). Indium gallium zinc oxide, a high mobility amorphous oxide material, is used as semiconductor. We find that the ferroelectric can be polarized in both directions in the metal-ferroelectric-semiconductor (MFS) structure and in the dual-gate TFT under certain biasing conditions, but not in the single-gate thin-film transistors. These results disprove the common belief that MFS structures serve as a good model system for ferroelectric polarization switching in thin-film transistors. cop. 2015 AIP Publishing LLC

Radiation-induced conductivity in poly(phenylene vinylene) derivatives

\u3cp\u3eUsing the pulse-radiolysis time-resolved microwave conductivity technique the mobility and decay kinetics of radiation-induced charge carriers is studied in a series of poly(2,5-dialkoxy-phenylene vinylene) derivatives. The lower limit to the sum of the mobilities of the positive and negative charge carriers. Σμ(min), depends strongly on the alkoxy functionalization and ranges from 1.2·10\u3csup\u3e-7\u3c/sup\u3e to 1.4·10\u3csup\u3e-6\u3c/sup\u3e m\u3csup\u3e2\u3c/sup\u3eN/V·s at room temperature. Σμ(min) increases with the degree of order in the material. The after-pulse conductivity decay kinetics are disperse and are controlled by a combination of charge recombination and trapping.\u3c/p\u3

Space charge limitation on the response time of organic photodiodes

\u3cp\u3eThe dynamic response of an organic bulk heterojunction photodiode to small changes in applied bias or light intensity is investigated as function of the intensity of a constant background illumination by means of photoimpedance and transient photocurrent measurements. For bias voltages close to the open circuit voltage we find that the response timescale with the square root of the light intensity. The results can be quantitatively explained in terms of a space charge limitation on the photocurrent as predicted by Goodman and Rose (J. Appl. Phys. 42, 2823 (1971)). The relaxation time of the diode at open circuit corresponds to the lifetime of the slowest charge carrier in the diode. This relaxation time is determined by the dielectric constant and the smallest of the two carrier mobilities in the bulk heterojunction. This illustrates the importance of balanced carrier mobilities for obtaining diodes with fast response time at low bias for e.g. imaging arrays.\u3c/p\u3

Dual-gate organic thin-film transistors

\u3cp\u3eA dual-gate organic thin-film transistor is realized using solution-processed organic semiconductor and insulator layers. Electrodes are made from gold. Compared to conventional single-gate transistors, this device type has a higher on current and steeper subthreshold slope. We show that the improved performance is the result of a nonconstant threshold voltage rather than formation of a second accumulation channel. Formation of a second accumulation channel does occur but the field-effect mobility associated with this channel is a factor 104 lower than the primary channel due to the relatively rough insulator-semiconductor interface.\u3c/p\u3

Polaron pair formation, migration, and decay on photoexcited poly(phenylenevinylene) chains

\u3cp\u3ePoly(2-(3,7-dimethyloctoxy)-5-methoxy-1,4-phenylenevinylene), (dMOM-PPV), undergoes a thermochromic transition on heating in benzene at approximately 35°C from a red gel to a yellow solution. The latter is metastable on cooling to room temperature and eventually reverts to the gel form after several hours. The absorption and emission spectrum of the gel can be resolved into two components, one which is identical with that for the solution and which is therefore associated with single-strand segments, and a second of similar spectral shape but lower energy which is ascribed to aggregated segments. Photoexcitation of dMOM-PPV in both the gel and solution results in a transient change in the microwave conductivity as monitored using the time-resolved microwave conductivity (TRMC) technique. The change in microwave conductivity for the gel is approximately an order of magnitude larger than for the solution. No TRMC transient is found on flash photolysis of a benzene solution of a dMOM-PPV derivative with 13% nonconjugated units in the polymer backbone. The effects are attributed to formation of mobile charge carriers (polaron pairs) on a single polymer chain in the case of the solution, whereas in the gel interchain charge transfer results in the predominant formation of charge carriers located on separated chains. The product of the quantum efficiency for polaron pair formation, φ\u3csub\u3ep\u3c/sub\u3e, and the sum of the mobilities, Σ\u3csub\u3eμ\u3c/sub\u3e, is φ\u3csub\u3ep\u3c/sub\u3eΣ\u3csub\u3eμ\u3c/sub\u3e = (2.0 ± 0.3) × 10\u3csup\u3e-8\u3c/sup\u3e m\u3csup\u3e2\u3c/sup\u3e/Vs and (2.0 ± 0.5) × 10\u3csup\u3e-9\u3c/sup\u3e m\u3csup\u3e2\u3c/sup\u3e/Vs for the gel and solution respectively. The decay in microwave conductivity is nonexponential and extends to hundreds of nanoseconds.\u3c/p\u3

High-performance all-polymer integrated circuits

\u3cp\u3eIn this letter, we demonstrate the integration of all-polymer field-effect transistors in fully functional integrated circuits with operating frequencies of several kHz. One of the key items is an approach to incorporate low-Ohmic vertical interconnects compatible with an all-polymer approach. Inverters, NAND gates, and ring oscillators with transistor channel lengths down to 1 μm have been constructed. Inverters show voltage amplification at moderate biases and pentacene seven-stage ring oscillators show switching frequencies of a few kHz. The potential to realize large integrated circuits is demonstrated by a 15 bit code generator circuit using several hundreds of devices. The proposed concept was evaluated for three solution-processable organic semiconductors.\u3c/p\u3