35 research outputs found
Organic field-effect transistors as a test-bed for molecular electronics: A combined study with large-area molecular junctions
No full textThe contact resistance of a transistor using self-assembled monolayer (SAM)-modified source and drain electrodes depends on the SAM tunnel resistance, the height of the injection barrier and the morphology at the contact. To disentangle the different contributions, we have combined here the transmission line measurements in transistors with transport measurements of SAMs in large-area molecular junctions. The tunnel resistance of the SAM has been independently extracted in two-terminal large-area molecular junctions. We show that the tunneling resistance of the SAM can be added linearly to the contact resistance of the transistor with bare Au electrodes, to account for the increased contact resistance in the SAM-modified transistor. The observed agreement is discussed. The manifestation of the SAM in the contact resistance shows that transistors can potentially be used as an experimental test-bed for molecular electronics.
Large-Area All-Printed Temperature Sensing Surfaces Using Novel Composite Thermistor Materials
No full textSurfaces 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 Q4 A4-sized temperature sensing sheet consisting of over 400 sensors.</p
Manipulation of charge carrier injection into organic field-effect transistors by self-assembled monolayers of alkanethiols
No full textCharge carrier injection into two semiconducting polymers is investigated in field-effect transistors using gold source and drain electrodes that are modified by self-assembled monolayers of alkanethiols and perfluorinated alkanethiols. The presence of an interfacial dipole associated with the molecular monolayer at the metal/semiconductor interface changes the work function of the electrodes, and, hence, the injection of the charge carriers. The FET characteristics are analysed with the transfer line method and the hole injection into poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) and regio-regular poly(3-hexyl)thiophene (rr-P3HT) is investigated. The device parameters are corrected for the contact resistances of the electrodes and the mobilities of the polymers (MEH-PPV, µFET = 4 × 10-4 cm2 V-1 s-1 and rr-P3HT, µFET = (1–2) × 10-2 cm2 V-1 s-1) are determined. The contact resistance obtained for the SAM-modified electrodes is at least one order of magnitude larger than for untreated contacts.
Active-matrix IGZO array with printed thermistor for large-area thermal imaging
No full textThermal 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
Top-split-gate ambipolar organic thin-film transistors
No full textSplit-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
Real-time NO2 detection at ppb level with ZnO field-effect transistors
No full textWe present a functional real-time NO2 sensor based on a ZnO field-effect transistor. The dynamic response of the sensor is calculated using a phenomenological charge trapping model, using only experimentally determined parameters. This analytical model is implemented in the sensor protocol to create a hardware demonstrator sensor. We show that the partial NO2 pressure in ambient air can be monitored in real-time for concentrations as low as 40 ppb. The response is verified by simultaneously measuring the NO2 content with a calibrated reference sensor. A perfect agreement between the measured and reference data is obtained, which validates the methodology. The sensor is fabricated using standard IC technology, which can easily be miniaturized and used in handheld applications.
Toward Temperature Tracking With Unipolar Metal-Oxide Thin-Film SAR C-2C ADC on Plastic
No full text© 1966-2012 IEEE. The maturity of metal-oxide thin-film transistors (TFT) highlights opportunities to develop robust and low-cost electronics on flexible and stretchable substrates over large area in an industry-compatible technology. Internet-of-Everything applications with sensor nodes are driving the development of analog-to-digital converters (ADCs). In this paper, a self-biased and self-digital-controlled successive approximation ADC with integrated references and sensor read-in circuitry together with a printed negative temperature coefficient (NTC) sensor using unipolar dual-gate metal-oxide (InGaZnO) TFTs is demonstrated. The system is operated at a clock of up to 400 Hz and a total power dissipation of 245 mW (73 μW from analog) at a maximum power supply of 30 V is measured. The radio-frequency identification-ready ADC comprises of a total of 1394 indium-gallium-zinc oxide TFTs and 31 metal-insulator-metal capacitors. A figure of merit of 26 nJ/c.s. is achieved from the ADC driven from external microcontroller. The robustness of the various blocks of the chip is characterized and the yield is discussed.sponsorship: This work was supported by the European Research Council through the European Union's Horizon 2020 Research and Innovation Program (FLICs project) under Grant 716426. (European Research Council through the European Union's Horizon 2020 Research and Innovation Program (FLICs project)|716426)status: Publishe
