Soyoun Jung

Temperature sensor using thermal transport properties in the subthreshold regime of an organic thin film transistor

In this letter, a temperature sensor based on an organic thin film transistor is proposed and discussed in terms of its linearity and reliability of the variation in the subthreshold drain current with temperature. The saturation mobility exhibits thermally activated hopping and temperature-deactivated behavior in different temperature ranges, but the saturation current shows very little change compared to the subthreshold current that is linearly varied with temperature from 273to453K. In addition, sensor reliability can be ensured by placing a time delay between consecutive measurements to release the charges trapped in the dielectric/semiconductor interface, the so-called bias-stress effect.

Protein Biosensors Based on Polymer Nanowires, Carbon Nanotubes and Zinc Oxide Nanorods

The development of biosensors using electrochemical methods is a promising application in the field of biotechnology. High sensitivity sensors for the bio-detection of proteins have been developed using several kinds of nanomaterials. The performance of the sensors depends on the type of nanostructures with which the biomaterials interact. One dimensional (1-D) structures such as nanowires, nanotubes and nanorods are proven to have high potential for bio-applications. In this paper we review these three different kinds of nanostructures that have attracted much attention at recent times with their great performance as biosensors. Materials such as polymers, carbon and zinc oxide have been widely used for the fabrication of nanostructures because of their enhanced performance in terms of sensitivity, biocompatibility, and ease of preparation. Thus we consider polymer nanowires, carbon nanotubes and zinc oxide nanorods for discussion in this paper. We consider three stages in the development of biosensors: (a) fabrication of biomaterials into nanostructures, (b) alignment of the nanostructures and (c) immobilization of proteins. Two different methods by which the biosensors can be developed at each stage for all the three nanostructures are examined. Finally, we conclude by mentioning some of the major challenges faced by many researchers who seek to fabricate biosensors for real time applications.

Point-of-care temperature and respiration monitoring sensors for smart fabric applications

Advances in smart sensors, miniaturization, and related technologies leading to the emergence of smart fabrics are prerequisites to the construction of a point-of-care (POC) system for continuous health monitoring and illness prevention. Low manufacturing cost, light weight, portability and flexibility are among the requirements for smart sensors when embedded into smart fabrics. Organic semiconductor technology has recently been envisioned to meet these requirements, and to encourage the development of organic semiconductor based sensors because of its low process temperature and potential for very low cost manufacturing. In this paper, we present flexible sensors based on an organic semiconductor capable of measuring physiological parameters such as strain and temperature, adopting pentacene thin film transistors (TFTs) and Wheatstone bridge structures. It is expected that these sensors, integrated into textile structures, will enable real time POC monitoring of a patients respiration rate, skin temperature, body heat flow and body temperature at an early stage.

In vitro evaluation of flexible pH and potassium ion-sensitive organic field effect transistor sensors

Acute myocardial ischemia is a state of trauma of the heart muscle caused by occlusion of oxygenated blood supply. It is accompanied by an increase in potassium and hydrogen ion concentrations in the heart muscles. A flexible substrate based ion-sensitive field effect transistor (ISFET) has been designed to measure the concentration of potassium and hydrogen ions with high specificity. Double exponential smoothing technique was used to calculate background noise and explain the dependence of drain current on reference voltage and ion concentration in saturation mode of the ISFET.

Field-Controllable Flexible Strain Sensors Using Pentacene Semiconductors

In this letter, we present the first flexible strain sensor based on pentacene semiconductors, employing a transistor-like Wheatstone bridge configuration, where the ON/OFF state of the sensor is controlled by the bottom gate bias. The sensor was characterized with bending at 0deg, 45deg, and 90deg with respect to the bridge bias direction for different strains of 1deg/infin, 1.25deg/infin, 1.67deg/infin, and 2.5deg/infin. The sensitivity values at the ON state for the 0deg, 45deg, and 90deg bending exhibit 1.6, 7.2, and 4.1 nA/deg/infin, respectively, revealing the highest sensitivity for the diagonal (45deg) direction. It is expected that this field-controllable strain sensor leads to a reduced circuit complexity and a reduced cost when embedded into a large-area sensor array system by eliminating the need for additional switching devices.

Pentacene-Based Low-Voltage Strain Sensors With PVP/

Field-controllable pentacene-semiconductor-based strain sensors were fabricated with hybrid gate dielectrics using polyvinyl phenol (PVP) and high-k inorganic tantalum pentoxide (Ta2O5) onto polyethylene naphthalate films. The Ta2O5 gate-dielectric layer combined with a thin PVP layer to form very smooth and hydrophobic surfaces turns out to improve the molecular structures of pentacene films significantly. The PVP-Ta2O5 hybrid-gate-dielectric films exhibit a high dielectric constant of 19.27 and a leakage-current density of as low as 100 nA/cm2 . The sensors employing a thin-film-transistor-like Wheatstone bridge configuration able to operate at reduced voltage (~ 4 V) show good device characteristics with a field-effect mobility of 1.89 cm2/V · s and a threshold voltage of -0.5 V. The strain sensor characterized with bending at 45° with respect to the bridge bias direction with different bending radii of 50-, 40-, 30-, 20-, and 8-mm displays output signals improved in linearity in a low range of operating voltages.

\hbox{Ta}_{2}\hbox{O}_{5}

This paper proposes an optical method which allows determination of the organic compound concentration in water by measurement of the UV (ultraviolet) absorption at a wavelength of 250 nm~300 nm. The UV absorbance was analyzed by means of a multiple linear regression model for estimation of the total organic carbon contents in water, which showed a close correlation with the UV absorbance, demonstrating a high adjusted coefficient of determination, 0.997. The comparison of the TOC (total organic carbon) concentrations for real samples (tab water, sea, and river) calculated from the UV absorbance spectra, and those measured by a conventional TOC analyzer indicates that the higher the TOC value the better the agreement. This UV absorbance method can be easily configured for real-time monitoring water pollution, and built into a compact system applicable to industry areas.

Hybrid Gate Dielectrics

Variations in concentrations of ions in biological systems can be important events in the onset of a physiological disorder. In an episode of myocardial ischemia, acidosis and elevation of potassium ion concentration has been observed in the extra-cellular matrix of the myocardium. As a spectrum of markers, they can help detect onset of ischemia as well as infarctions. In this study, Flexible Organic Ion-Sensitive Field-Effect Transistors (ISFETs) have been characterized to detect Ischemia-like variations in pH and potassium ion concentration. Detection capabilities, of the sensors, have been shown as pure chemical concentration to current signal transduction of the ISFET. Independent of peripheral amplifier-converter circuits, they are standalone sensors. The sensors have been evaluated for their sensitivity and signal resolution. Calibration expression, following a thermo-electric model for device operation, represents an explicit relations between transistor drain current and ion concentrations. Signal conditioning, by normalization, has been attempted to make the calibration expression explicit in ion-concentration. Finally a reliable detection strategy, in differential mode, is proposed for a reference electrode free device.

Detection of Organic Compounds in Water by an Optical Absorbance Method.

In this study, we present the first flexible strain sensors based on pentacene-carbon nanotubes (CNTs) composite thin Alms employing a Wheatstone bridge configuration. The sensors were characterized with bending at 0, 45, and 90 degrees with respect to the bridge bias direction, applying strains of 1, 1.25, 1.67, and 2.5 0/00, respectively. It was noted that the output signal of the sensors is substantially enhanced with the addition of CNTs, resulting from the improvement in conductivity of the sensing active layer. This strain sensor using the CNTs-organic semiconductor matrix composite thin films as the active layer fabricated on flexible substrates is expected to possess better reliability as compared with conventional metallic foils and inorganic semiconductor strain sensors because of their low Youngs modulus (~5 GPa).

Drain Current Centric Modality: Instrumentation and Evaluation of ISFET for Monitoring Myocardial Ischemia Like Variations in pH and Potassium Ion Concentration

Design and fabrication of Organic Thin Film Transistor (OTFT) based miniaturized piezoelectric sensor is presented in this investigation. The device is fabricated on flexible polyethylene naphthalate (PEN) film, using the small-molecule hydrocarbon pentacene as the semiconductor layer and solution-processed polyvinylphenol as the gate dielectric. Field effect mobility of the OTFT is greater than 0.01 cm2/Vs, Ion/Ioff current ratio greater than 105. The piezoelectric polymer, Polyvinylidene Fluoride (PVDF) is used as the sensor layer that is attached over the extended gate metal electrode of the OTFT. OTFT, which is in close proximity with sensor, serves as the amplifier to amplify the signal generated by piezoelectric sensor.