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Developing a Vital Signal Detection Electrode for Fabric Substrate Using a High-Performance Conductive Carbon-Based Ink
(2025-01-01)
Chansaengsri, K.
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Tunhoo, B.
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Onlaor, K.
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Thiwawong, T.
Merging electrophysiology signal monitoring technology with wearable devices offers interesting future health care options. This study presented carbon-based screen-printing inks produced by mixing a graphite composite with a polymer emulsion to bind with flexible fabric substrates and tested with 10,000 bending cycles. The prepared carbon-based ink performed well for electrical conduction and vital signal response. Adding calcium carbonate resulted in a microstructure of graphite that decreased the electrical sheet resistance and resistance to 11.61 Ω/ and 0.127 Ω. The signal-to-noise ratio of the electrocardiogram (ECG) was 31.02 dB with built-in front-end powering noise filtration. Noninvasive blood pressure (NIBP) was achieved by bio-impedance measurement and showed outstanding systolic and diastolic pressure values with a correlation coefficient of 0.799, and exhibited a similar interval time to define the same precise heart rate. The ECG data from the prepared electrode were applied to the machine learning models. The Random Forest (RF) model exhibited the optimized prediction value, with an F1 score of 99.9%. Equipment made from carbon screen-printing inks showed potential for health care monitoring with no excessive pressure, dry processing, and repeatability as a flexible wearable bio-electronic device.
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Preparation of pH Sensor Based on Extended-Gate Field-Effect Transistor with Spinel ZnCo2O4 Thin Films by Electrostatic Spray Deposition
(2023-12-01)
Keawkusonwiwat, S.
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Tunhoo, B.
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Onlaor, K.
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Thiwawong, T.
Electrostatic spray deposition was applied to prepare pH sensing with spinel ZnCO<inf>2</inf>O<inf>4</inf> thin films based on the measurement of extended-gate field-effect transistors (EGFET). The influence of annealing temperatures on the characteristics of the prepared films was analyzed. The structural and morphological properties of the annealed ZnCo<inf>2</inf>O<inf>4</inf> films were assessed by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and contact angle measurement. The effect of the ZnCo<inf>2</inf>O<inf>4</inf> annealing temperature on the characteristics of pH sensing for the prepared ZnCo<inf>2</inf>O<inf>4</inf> films in EGFET measurement were examined with pH buffer solutions in a pH range of 2–12 at room temperature. The sensing films annealed at 550°C demonstrated a high voltage and current sensitivity at 67.6 mV/pH and 1.033 (µA)½/pH, with linearity values of 0.9968 and 0.9991, respectively. Moreover, the annealed 550°C ZnCo<inf>2</inf>O<inf>4</inf> film exhibited low hysteresis at 4.99 mV and high retention stability. The results revealed that the pH sensing of the ZnCo<inf>2</inf>O<inf>4</inf> EGFET device showed a super-Nernstian sensitivity, which indicated the influence of the surface properties of the annealed film. Therefore, the ZnCo<inf>2</inf>O<inf>4</inf> film should be considered a potential option for the pH sensing layer in EGFET applications.
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Structural, Optical, and Electrical Properties of Sputtered ZnO Thin Films and Their Application in Transparent Memory Devices
(2022-12-01)
Tunhoo, B.
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Kaewkusonwiwat, S.
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Thiwawong, T.
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Onlaor, K.
We report on the fabrication of ZnO thin films using a lab-made DC sputtering process. The ZnO films were prepared at several applied sputter voltages at fixed deposition times. The properties of the deposited films were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and UV–visible spectroscopy. The ZnO thin films exhibited a polycrystalline phase in the dominant (100) plane, with film thicknesses in the order of approximately 50–80 nm. In addition, a transparent memory device based on the ZnO film was successfully fabricated with a device structure of ITO/ZnO/EVA/ITO. The fabricated device exhibited high optical transparency of approximately 70% in the visible light region. The fabricated memory device demonstrated memory properties with a maximum ON/OFF current ratio of 4.66 × 103 and showed good retention properties.
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Transparent and flexible humidity sensor based on graphene oxide thin films prepared by electrostatic spray deposition technique
(2020-08-01)
Songkeaw, P.
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Onlaor, K.
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Thiwawong, T.
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Tunhoo, B.
In this work, transparent and flexible humidity sensors based on graphene oxide film were prepared using the electrostatic spray deposition technique. Graphene oxide (GO) powder was synthesized using the modified Hummer’s method, which was used as a precursor for thin-film deposition. The properties of GO films were characterized by X-ray diffraction, field-emission scanning electron microscope, Raman spectroscopy, Fourier transform infrared spectroscopy, and UV–Vis spectrophotometer. The effect of substrate temperature on the sensor properties was observed. The impedance of the device exhibited a lower value when increasing the relative humidity level. In addition, the device showed high sensitivity of more than 1117.3, fast response with 5 s, more than 60% optical transparency, and flexible property more than 2000 cycles. In addition, the equivalent circuit models of the devices were evaluated from complex impedance measurements used to explain the sensing mechanisms of the device.
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Electrical Bistable Properties of P-25 TiO2 Nanoparticles Composited with PVP for Memory Devices
(2019-10-01)
Ukakimaparn, P.
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Chantarawong, D.
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Songkeaw, P.
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Onlaor, K.
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Thiwawong, T.
In this work, P-25 titanium dioxide nanoparticles (TiO<inf>2</inf> NPs) were composited with poly-vinylpyrrolidone (PVP) at various concentrations of TiO<inf>2</inf> NPs. The bistable memory devices were fabricated by spin coating from a prepared PVP:TiO<inf>2</inf> NPs solution on indium tin oxide (ITO) electrodes with the device structure of ITO/PVP:TiO<inf>2</inf> NPs/Al. The maximum ON/OFF current ratio of the bistable memory devices was approximately 105 at a reading voltage of +1 V. The mechanism of the memory device can be expressed by theoretical fitting between the experimental results and conduction models. Moreover, a retention time test for continuous read operations of the device is presented.
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Transparent write-once-read-many-times memory devices based on an ITO/EVA:rGO/ITO structure
(2018-10-01)
Songkeaw, P.
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Tunhoo, B.
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Thiwawong, T.
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Onlaor, K.
Fully transparent electronic devices play an important role in electronic applications. Well-known examples are the wearable devices and transparent displays; their applications are transparent memory devices of interest. The transparent write-once-read-many-times (WORM) memory devices based on synthesized graphene oxide (GO) blended in poly (ethylene-co-vinyl acetate) (EVA) had been fabricated by a thermal roll lamination technique in which the synthesized GO inside the EVA matrix was reduced into reduced graphene oxide (rGO) during the lamination process. The memory devices exhibited an optical transmittance of more than 60% in the visible light region. The conduction mechanisms of the memory devices were identified using theoretical models based on the current–voltage (I–V) curves. The fitted I–V results were described by the conductive filaments in which electrons were transported through the rGO direct contacts. In addition, the maximum ON/OFF current ratio of the transparent WORM memory device was approximately 5 × 105, and the retention time tests showed two current states with good data retention properties under different temperatures.
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Paper-based flexible piezoelectric nanogenerator using fibrous polymer/piezoelectric nanoparticle composite material
(2018-06-14)
Chansaengsri, K.
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Onlaor, K.
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Tunhoo, B.
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Thiwawong, T.
Piezoelectric nanogenerators (PENGs) based on micro-fibre of polyvinylidene fluoride (micro-fibre polyvinylidene fluoride (PVDF)). Flexible nanogenerator was developed by addition nanoparticle composition. This PENG fabricated using micro-fibre PVDF/BaTiO3, which was deposited on paper interdigitate substrate by wire electrode free surface electrospinning method. The device from micro-fibre PVDF performed open-circuit voltage and short-circuit current of 13 mV and 380 nA recently. The device from composite material addition value of open-circuit voltage and short-circuit current of 528 mV and 661 nA recently.
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AFM force distance curve measurement for surface investigation of polymers compound blend with metal nanoparticles
(2017-01-01)
Koetniyom, W.
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Suhatcho, T.
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Treetong, A.
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Thiwawong, T.
The atomic force microscopy (AFM) has been used to perform surface force measurements in contact mode to investigate surface properties of model systems in the nanoscale. Two different polymers compound are observed include Polydimethylsiloxane (PDMS) and Polyvinylidene fluoride (PVDF). Both polymers compound are blended with metal nanoparticles consist of gold and silver by compare with the pristine polymer. The results from adhesion force and surface roughness tests are inversed. The adhesion force is increased with the NPs concentration whereas the surface roughness is decreased. Hydrophobic and hydrophilic properties of the polymer have been studied by employing contact angle. However, variation of contact angle of polymer nanocomposites is confirmed the hydrophobicity of PDMS while PVDF is certainly different around 70-77° of Ag NPs and 70-81° of Au NPs.
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Modification of structural and vibrational properties of ZnO nanoparticles prepared by simple chemical precipitation method
(2016-01-01)
Chaithanatkun, N.
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Onlaor, K.
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Thiwawong, T.
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Tunhoo, B.
In this work, zinc oxide (ZnO) nanoparticles were synthesized by simple chemical precipitation method in the present of zinc nitrate as zinc precursor and sodium hydroxide as hydroxide precursor. The vitamin C was used as modifier media to modify the structural properties of ZnO nanoparticles. The microstructures of ZnO nanoparticles were characterized by field emission scanning electron microscope (FE-SEM) and transmission electron microscope (TEM). Selected area electron diffraction (SAED) patterns showed that polycrystalline hexagonal phase of ZnO. The defects and impurity contents in nanoparticles were investigated by Fourier transform infrared (FT-IR) spectroscopy. The results show few carboxylate and hydroxyl impurities for larger particles when addition modifier increases. Surface areas of nanoparticles were measured by Brunauer Emmett Teller (BET) method. In addition, the results exhibited the dramatically change in structural properties of ZnO nanoparticles due to the effect of vitamin C.
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Electrical switching and conduction mechanisms of nonvolatile write-once-read-many-times memory devices with ZnO nanoparticles embedded in polyvinylpyrrolidone
(2014-01-01)
Onlaor, K.
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Thiwawong, T.
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Tunhoo, B.
We reported on the influence of zinc oxide nanoparticles (ZnO NPs) on the electrical bistable behavior of nonvolatile write-once-read-many-times (WORM) memory devices based on an indium-tin oxide/polyvinylpyrrolidone (PVP):ZnO NPs/aluminum (ITO/PVP:ZnO/Al) structure. The maximum ON/OFF current ratio of the nonvolatile WORM memory devices was approximately 3 × 103 and the devices remained in the ON state even after the applied voltage was turned off. In addition, reliability studies for response time and once write/continuous read operations of the optimal ZnO NPs concentration are presented. The response times of both rise-time and fall-time were about 3 and 6 μs respectively. The conduction mechanisms of all voltage regions of the device were analyzed by theoretical models and electron trapping in the ZnO NPs of the electron tunneling among a PVP matrix was discussed. © 2014 Elsevier B.V. All rights reserved.

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