1,721,023 research outputs found
An enzyme-based lactate sensor incorporating a three-dimensional complementary inverter for high sensitivity
No full textEnzyme-based biochemical sensors based on organic field-effect transistor (OFET) have gained attention for their potential applications as low-cost, disposable, wearable sensors. They take advantage of inducing drain current change in OFET from enzymatic reaction, however, the induced current signal is not stable and signal-to-noise ratio is not large enough to be easily detected. In this study, we propose a new strategy of an extended-gate type inverter incorporating three-dimensional complementary organic field-effect transistors (3D-COFETs) for lactate detection with higher sensitivity. In the device structure of 3D-COFETs, a bottom-gate p-type OFET is vertically integrated on a top-gate n-type OFET with the gate shared in-between, and complementary inverter is implemented with this transistor-on-transistor structure. For lactate detection, enzyme-functionalized gold electrode is used as an extended-gate of complementary inverter, and it composes biofuel cell with Ag/AgCl reference electrode in aqueous media. We have observed that the enzymatic redox chain reaction of lactate occurring in the biofuel cell causes potential difference between the two electrodes which results in switching voltage shift in the complementary inverter. The proposed 3D-COFETs structure itself has advantages in sensing applications within complementary integrated circuit systems thanking to its higher transistor density. The output signal from the detection of lactate levels using the proposed 3D-COFETs inverter is expressed in voltages which is more stable than current signals and sensitivity is higher compared with that of single OFET-based biochemical sensors because the voltage shift induced from enzymatic reaction is amplified by the gain of the inverter. It is expected that the proposed biochemical sensor incorporating 3D-COFETs is a promising candidate for highly sensitive biosensors in practical applications.1
Electrical Reliability Enhancement in Organic Thin-film Transistors and Circuits Using a Hydroxyl-containing Polymer Blend as Gate Dielectric
No full textA polymer gate dielectric is one of the key elements of solution-processed organic thin-film transistors (TFTs) for low-cost and large-area electronic applications. In the past few decades, a hydroxyl-containing polymer blend of poly(4-vinylphenol) (PVP) and poly(melamine-co-formaldehyde) (PMF) has been widely used as gate dielectric due to its low leakage current, high dielectric constant, and good chemical compatibility in organic TFTs.1) However, the polymer blend has been compatible only with suitably engineered expensive plastic substrates due to its high annealing temperature (typically higher than 175 ºC) to remove hydroxyl groups that cause the substantial hysteresis phenomenon in the current-voltage characteristics.2,3) In this work, we investigated the influence of various PVP:PMF blend conditions such as weight ratio (0.2:1 to 5:1) and annealing temperature (100 to 200 ºC) on the device performances in 6,13-bis(triisopropylsilylethynyl) organic TFTs (Figs. 1 and 2). We found that the organic TFT using the PVP:PMF blend with the weight ratio of 0.5:1 and annealing temperature of 100 ºC showed negligible hysteresis, high on/off drain current ratio, and low gate-leakage current. Fourier transform infrared spectroscopy measurements provided the evidence that the optimized condition of PVP:PMF blend is strongly related to the minimization of non-hydrogen-bonded hydroxyl groups. Finally, we successfully demonstrated transistors and diode-connected inverters on a 3-μm-thick flexible parylene film. This work shows that the reduction of non-hydrogen-bonded hydroxyl groups in polymer dielectrics can effectively lower the process temperature and enhance the device electrical reliability on inexpensive plastic substrates.1
Optimization of cross-linked poly(4-vinylphenol) gate dielectric for low-temperature vertically stacked organic thin-film transistors and logic circuits on a flexible substrate
No full textA polymer gate dielectric is one of the key elements of high-performance solution-processed organic thin-film transistors (OTFTs) for low-cost, large-area, flexible electronic applications. For the past decade a poly(4-vinylphenol) (PVP) dielectric cross-linked with poly(melamine-co-formaldehyde) (PMF) has been widely used due to its low leakage current, high capacitance, and high chemical compatibility in OTFTs. However, the cross-linked PVP (cPVP) dielectric has been compatible only with suitably engineered expensive plastic substrates due to its high curing temperature (typically >150 °C). In this study, we sought to find the optimum PVP:PMF weight ratio to fabricate low-temperature, solution-processed OTFTs on polyethylene naphthalate. We investigated the influence of different cPVP conditions such as PVP:PMF weight ratio (0.2:1 to 5:1) and annealing temperature (100 to 200 °C) on the performances of 6,13-bis(triisopropylsilylethynyl):polystyrene blend OTFTs. We found that the OTFT using the PVP:PMF with the weight ratio of 1:2 showed negligible gate-bias stress, low gate leakage current, and strong chemical resistance in common solvents, even though the dielectric film was annealed at 100 °C. Fourier transform infrared spectroscopy measurements provided the evidence that device performances were influenced by the weight ratio and annealing temperature of the cPVP dielectric due to the presence of free and hydrogen-bonded hydroxyl groups. Finally, we demonstrated vertically integrated OTFTs with the optimized cPVP dielectric to form three-dimensional universal logic NAND gate. This work shows that cPVP is a suitable dielectric material to fabricate flexible electronic devices and circuits on inexpensive plastic substrates with high transistor density and high yield.1
An enzyme-based wearable lactate sensor incorporating complementary organic field effect transistors for high sensitivity
No full textEnzyme-based biochemical sensors based on organic field-effect transistor (OFET) have gained attention for their potential applications as low-cost, wearable sensors. They take advantage of inducing drain current change in OFET from enzymatic reaction, however, the current signal is not stable and signal-to-noise ratio is not large enough to be easily detected. In this study, we propose a new strategy of an extended-gate type inverter that incorporates complementary OFETs for lactate detection with high sensitivity.
In the device structure of transducer circuit, a bottom-gate p-type OFET is vertically integrated on a top-gate n-type OFET, and complementary inverter is implemented to convert the current signal to a voltage output for simple design of readout circuit with high sensitivity.1) For lactate detection, enzyme-functionalized gold electrode is used as an extended gate of complementary inverter, and it composes biofuel cell with Ag/AgCl reference electrode in aqueous media.2) We have observed that the enzymatic redox chain reaction of lactate occurring in the biofuel cell causes potential difference between the two electrodes which results in switching voltage shift in the complementary inverter.
The output signal from the detection of lactate levels using the proposed device is expressed in voltages which is more stable than current signals and sensitivity is higher compared with that of single OFET-based sensors because the voltage shift induced from enzymatic reaction is amplified by the gain of the inverter. Enzyme-functionalized lactate sensor is also optimized to be the most sensitive at the concentration range of ~5 mM to 100 mM, which makes the sensor most suitable for sensing of lactate levels of human sweat (20 mM to 60 mM).3) The sensor is fabricated on a flexible substrate for conformal contact with human skin.
It is expected that the proposed sensor shows the possibility of a low cost, wearable sensor2
Low-Temperature, Solution-Processed, 3-D Complementary Organic FETs on Flexible Substrate
No full textVertical stacking of thin-film transistors is an effective way to reduce the footprint of a device, thus increases transistor density in complex flexible electronic applications without reducing the feature size and resolution of the patterning tools. In this paper, we report a 3-D complementary organic FET fabricated on a plastic substrate by stacking a bottom-gate top-contact p-type transistor on a top-gate bottom-contact n-type transistor with a gate shared between the two. We used high-performance polymer semiconductors, poly [(E)-2, 7-bis (2 decyltetradecyl) 4 methyl 9 (5 (2 (5 methylthiophen 2 yl) vinyl) thiophen 2 yl) benzo [lmn] [3, 8] phenanthroline-1, 3, 6, 8 (2H, 7H)-tetraone] for n-type devices and poly [2, 5-bis (7-decylnonadecyl) pyrrolo [3, 4-c] pyrrole-1, 4 (2H, 5H)-dione-(E) 1,2 bis (5 (thiophen 2 yl) selenophen 2 yl) ethene] for p-type devices to fabricate the vertically stacked organic transistors along with a Cytop and cross-linked poly (4-vinylphenol) bilayer and Poly (Methyl Methacrylate) gate dielectric. A 3-D flexible complementary organic inverter exhibits a maximum static voltage gain of ?18 V/V and high noise immunity of up to 60% of VDD/2. The 3-D transistors show hysteresis-free I-V characteristics despite of low-temperature processes. Moreover, we discuss the influence of cross-linker concentration and the processing temperature of the PVP dielectric film on the degree of hysteresis in I-V characteristics. ? 2017 IEEE.111sciescopu
An enzyme-based wearable lactate sensor with subthreshold operation of a dual-gate organic transistor for high sensitivity
No full textEnzyme-based biochemical sensors based on organic thin film transistors (TFTs) have gained much attention for their potential applications as low-cost and bio-compatible wearable sensors. In such applications, the enzymatic redox reaction integrated into individual TFT induces an amplified concentration-dependent drain current. For the realization of wearable devices, however, low power consumption is essentially required and not to mention high sensitivity. In this work, we exploit subthreshold operation of an extended-gate type dual-gate TFT for lactate detection with low power and high sensitivity. In the dual-gate TFT configuration, the top gate is separated and extended from the device to serve as an extended sensing gate (ESG) on which lactate oxidase enzyme is functionalized. The enzyme-functionalized ESG composes biofuel cell with Ag/AgCl reference electrode in aqueous media. We have observed that the enzymatic redox chain reaction of lactate occurring in the biofuel cell causes potential difference between the ESG and the reference electrode, which results in threshold voltage shift in the dual-gate TFT. Moving forwards, through strategic subthreshold operation of dual-gate TFT where its subthreshold slope (SS) is higher than single-gate transistor, it enabled not only lower power consumption but also higher sensitivity in comparison to operation in single-gate transistor. The device is fabricated on a flexible substrate for a skin-like wearable sensor, illustrating its potential as a wearable biochemical sensor.1
Reverse-Offset-Printed, Phase-Separated, Organic Nonvolatile Memory Thin-Film Transistor
No full textReverse-offset-printed organic nonvolatile memory thin-film transistors (TFTs) are fabricated on a large-area substrate for the first time. Finely patterned electrodes (a line width of 15 um and a channel length of 10 um) were reverse-offset-printed through three steps of ink coating, patterning and transfer using Ag-nanoparticle ink. The memory devices were configured in a bottom-gate bottom-contact TFT structure with a high-k gate blocking insulator poly(vinylidene fluoride-co-trifluoroethylene). A blend ink of a small-molecule p-type organic semiconductor dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene and a tunneling polymer polystyrene were fabricated using air-pulse nozzle printing. The tunneling layer was formed during an active layer printing process with blend ink by phase separation of small-molecule and polymer. The printed memory TFTs with the phase-separated tunneling layer exhibited significantly improved VTH shifts (≈3 times), programmed/erased current ratio (>103 A/A), switching speed (10 y). We believe our finding is applicable to wearable electronics, smart Internet-of-Things devices and neuromorphic computing devices.2
All-Solution Processed Organic Nonvolatile Memory Thin-Film Transistor Fabricated with Reverse Offset Printing
No full textAll-solution processed printed organic nonvolatile memory thin film transistors (TFTs) are demonstrated on a large-area substrate. Finely patterned electrodes were fabricated by reverse offset printing with a line width of 15 um and a channel length of 10 um. The memory devices were configured in a bottom-gate bottom-contact TFT structure with a high-k gate blocking insulator poly(vinylidene fluoride-co-trifluoroethylene) (Fig. 1a). A blend ink of a small-molecule p-type organic semiconductor dithieno[2,3-d;2′,3′-d′]benzo[1,2-b;4,5-b′]dithiophene and a tunneling polymer polystyrene were fabricated using air-pulse nozzle printing. The tunneling layer was formed during an active layer printing process with blend ink by phase separation of small-molecule and polymer. The memory devices were manufactured in the same steps as TFT. The printed memory TFTs with the phase-separated tunneling layer exhibited significantly improved on/off ratio (>103 A/A), switching speed (10 years) (Fig. 1b). We believe our finding is applicable to wearable electronics, smart Internet-of-Things devices and neuromorphic computing devices.1
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