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Durable nitrate sensor by surface modification
(2016-11-25)
Chaisriratanakul, W.
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Bunjongpru, W.
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Jeamsaksiri, W.
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Srisuwan, A.
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Porntheeraphat, S.
This work presents the development of nitrate sensor based on Ion Sensitive Field Effect Transistor (ISFET) technology to achieve longer device's lifetime. This lifetime depended on the adhesion of PVC ion-selective membrane on the Si<inf>3</inf>N<inf>4</inf> sensing membrane of ISFET. The adhesion level directly affected the leaching of plasticizer. Such improvement utilized surface modification techniques by immersing the sensing membrane in the solution of 5% 3-mercaptopropyl-trimethoxysilane (MPTMS)/methanol. The modified surface was detected through the change of hydrophobicity and thickness of MPTMS using the contact angle measurement and ellipsometry techniques. The appropriate time for immersion was 18 h. The modified surface achieved the optimal hydrophobicity with contact angle of 100.32°. The presence of MPTMS film was confirmed by detecting the thiol-group using Fourier Transform Infrared (FTIR) spectrophotometry and Auger Electron Spectroscopy (AES). The PVC ion-selective membrane was then immobilized on the surface to create nitrate sensors with the following characteristics. The Nitrate-Nitrogen detection limit = 2.44 ppm with linear range from 5 to 60 ppm at sensitivity of 56 mV/dec. (R2 = 1). The response time was 90 s. Finally, this nitrate sensor could extend the total utilization lifetime from 8 to 17 weeks.
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Optical band engineering of metal-oxynitride based on tantalum oxide thin film fabricated via reactive gas-timing RF magnetron sputtering
(2016-11-25)
Khemasiri, N.
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Jessadaluk, S.
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Chananonnawathorn, C.
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Vuttivong, S.
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Lertvanithphol, T.
In this paper, we demonstrate a novel technique, as called reactive gas-timing (RGT) RF magnetron sputtering, to control and design an optical band engineering of TaON thin films without an external heating substrate temperature and post annealing treatment process. The influence of the oxygen intervals ranged from 5 to 60 s on deposition rate, chemical composition and optical properties of TaON thin films were investigated. The chemical composition was characterized by auger electron spectroscopy (AES). The optical properties were determined by UV–Vis spectrophotometer and spectroscopic ellipsometry. The nitrogen atomic concentration of the TaON thin films deposited by RGT decreased when the oxygen gas-timing intervals increased. In addition, the RGT sputtered TaON films could be demonstrated band gaps engineering from 1.90 to 2.15 eV.
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Non-enzymatic urea sensor using molecularly imprinted polymers surface modified based-on ion-sensitive field effect transistor (ISFET)
(2016-11-25)
Rayanasukha, Y.
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Pratontep, S.
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Porntheeraphat, S.
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Bunjongpru, W.
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Nukeaw, J.
A novel molecularly imprinted electrochemical sensor based on ISFET device has been developed for urea detection sensor. The molecularly imprinted polymers (MIPs) were prepared by photopolymerization on the surface of ISFET device using PMMA and urea as the functional polymer and molecular template, respectively. The fabricated sensors were characterized by potentiometry and UV-Vis spectroscopy. The preparation conditions were optimized for performance of the sensors, i.e. drop-cast volume and incubation time. The MIP modified ISFET sensors has linear range response from 1.0 × 10− 4 to 1.0 × 10− 1 M with the limit of detection of 1.0 × 10− 4 M (S/N = 3). The MIP modified ISFET sensors also exhibit excellent reproducibility, repeatability and stability, as well as high selectivity to urea.
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Silicon nitride thin films deposited by reactive gas-timing magnetron sputtering for protective coating applications
(2015-01-01)
Khemasiri, N.
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Paleeya, N.
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Sae-tang Phromyothin, D.
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Horprathum, M.
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Porntheeraphat, S.
Silicon nitride is a promising alternative to carbon based materials for protective coatings, owing to its compatibility with existing silicon-based microfabrication. The complexity of the fabrication processes and contaminations hamper fine-tuning to obtain desirable coating properties. We have explored the reactive gas-timing rf plasma sputtering technique for silicon nitride thin film deposition as an alternative method to fine-tune the film properties. The gas-timing technique controls the on-off sequence of the sputtering gas (Ar) and the reactive gas (N<inf>2</inf>) during deposition. We focus this investigation to the effect of the Ar:N<inf>2</inf> gas timing ratio (10:0, 10:1, 10:3, 10:5, 10:7 and 10:10) on the composition, the morphology, the corrosion resistance, and the hardness properties of the films, in comparison to the films deposited by conventional reactive sputtering with Ar-N<inf>2</inf> gas mixture. These deposited silicon nitride films were characterized by Auger electron spectroscopy, Raman spectroscopy, and atomic force microscopy. The chemical resistance was measured by the electrochemical corrosion test in sulfuric acid, while the hardness properties were obtained by nanoindentation. The results reveal that although the nitrogen content in the films increases only slightly when the N<inf>2</inf> timing is prolonged, the corrosive current of the films decreases abruptly. A thin passivating oxidized layer is found to play a major role in the corrosion resistance. In contrast, the hardness properties exhibit a uniform variation with the N<inf>2</inf> timing. The gas-timing sequence may induce morphological changes the underlying silicon nitride films. The highest hardness obtained by the gas-timing technique almost doubles that produced by the conventional mixed gas sputtering. Thus the reactive gas-timing technique suggests a new route to selectively control the properties of silicon nitride films with minor modification to existing microfabrication processes.
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Tantalum oxide bio-photonics thin film grown by gas-timing innovation technique
(2013-09-18)
Khemasiri, N.
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Porntheeraphat, S.
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Horprathum, M.
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Chananonnawathorn, C.
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Bunjongpru, W.
Tantalum oxide (TaxOy) as high refractive index material has been grown on p-type silicon and quartz substrates by R.F. magnetron sputtering with our innovative technique called "reactive-gas timing". The reactive gas timing technique is an on-off time period sequence between argon (Ar) and oxygen (O2) plasma during sputtering process. The technique of gas-timing plays the effect on the properties of TaxOy thin film. The bombarded Ar-plasma was varied at 2, 5 and 8 sec, while the period of reactive O2-plasma was kept at 5 sec in this experiment. The physical and optical properties were investigated by using X-ray diffraction (XRD), Atomic Force Microscope (AMF), UV-Visible spectrometer and Spectroscopic Ellipsometer, respectively. The XRD spectra and AFM photographs show all films are amorphous phase with smooth feature. Meanwhile the transmittance of sputtered thin film decreases with 10% and the absorption edge shifts to lower energy with the increasing of the argon period from 2 sec to 8 sec. The refractive index as showed by ellipsometry slightly increases from 2.08 to 2.17 at wavelength 550 nm with the increasing of argon period from 2 sec to 8 sec. The increasing of the refractive index might dues to tantalum (Ta) rich which consists in thin films. The Ar-plasma period in the deposited film plays an important role on the properties of the TaxOy thin films especially as optical refractive index material. © 2013 SPIE.
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Very low drift and high sensitivity of nanocrystal-TiO 2 sensing membrane on pH-ISFET fabricated by CMOS compatible process
(2013-02-15)
Bunjongpru, W.
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Sungthong, A.
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Porntheeraphat, S.
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Rayanasukha, Y.
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Pankiew, A.
High sensitivity and very low drift rate pH sensors are successfully prepared by using nanocrystal-TiO <inf>2</inf> as sensing membrane of ion sensitive field effect transistor (ISFET) device fabricated via CMOS process. This paper describes the physical properties and sensing characteristics of the TiO <inf>2</inf> membrane prepared by annealing Ti and TiN thin films that deposited on SiO <inf>2</inf> /p-Si substrates through reactive DC magnetron sputtering system. The X-ray diffraction, scanning electron microscopy and Auger electron spectroscopy were used to investigate the structural and morphological features of deposited films after they had been subjected to annealing at various temperatures. The experimental results are interpreted in terms of the effects of amorphous-to-crystalline phase transition and subsequent oxidation of the annealed films. The electrolyte-insulator-semiconductor (EIS) device incorporating TiON membrane that had been obtained by annealing of TiN thin film at 850 °C exhibited a higher sensitivity (57 mV/pH), a higher linearity (1), a lower hysteresis voltage (1 mV in the pH cycle of 7 → 4 → 7 → 10 → 7), and a smaller drift rate (0.246 mV/h) than did those devices prepared at the other annealing temperatures. Furthermore, this pH-sensing device fabrication process is fully compatible with CMOS fabrication process technology. © 2012 Elsevier B.V. All rights reserved.
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XAFS analysis of indium oxynitride thin films grown on silicon substrates
(2013-01-01)
Amnuyswat, K.
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Saributr, C.
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Thanomngam, P.
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Sungthong, A.
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Porntheeraphat, S.
Local structure of indium oxynitride thin films grown on silicon substrates was investigated by X-ray absorption fine structure technique incorporated with first principle calculations. The thin films were grown by using reactive gas timing radio frequency (RF) magnetron sputtering technique with nitrogen (N<inf>2</inf>) and oxygen (O<inf>2</inf>) as reactive gasses. The reactive gasses were interchangeably fed into sputtering system at five different time intervals. The gas feeding time intervals of N<inf>2</inf>:O<inf>2</inf> are 30:0, 30:5, 30:10, 30:20 and 10:30s, respectively. The analysis results can be divided into three main categories. Firstly, the films grown with 30:0 and 30:5s gas feeding time intervals are wurtzite structure indium nitride with 25 and 43% oxygen contaminations, respectively. Secondary, the film grown with 10:30s gas feeding time intervals is bixbyite structure indium oxide. Finally, the films are alloying between indium nitride and indium oxide for other growth condition. The fitted radial distribution spectra, the structural parameters and the combination ratios of the alloys are discussed. © 2012 John Wiley & Sons, Ltd.
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Enhanced electrochromic performance of sol-gel derived WO 3 thin films assisted by electrospun PVA nanofibers
(2012-10-29)
Paipitak, K.
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Rattanarak, J.
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Pakdeeyingyong, D.
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Techitdheera, W.
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Porntheeraphat, S.
The paper describes the results obtained on the enhanced electrochromic performance of Tungsten oxide (WO <inf>3</inf>) thin films assisted by electrospun PVA nanofibers. WO <inf>3</inf> was fabricated by spin coating technique with tungsten powder as starting precursor. The effect of electrospun-PVA nanofibers layer on structural, chemical composition, surface morphology and electrochromic properties of the films were characterized by X-ray diffractometer (XRD), X-ray photo-emission spectroscopy (XPS), scanning electron microscope (SEM) and UV-VIS spectrophotometer. The XRD analysis suggested that the crystalline of WO <inf>3</inf> can be identified as a monoclinic WO <inf>3</inf> structure. XPS investigations also confirmed the existence of characteristic peaks of W. The significant enhancement of electrochromic properties of the films is achieved by additive electrospun-PVA nanofiber layer. © (2012) Trans Tech Publications, Switzerland.
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UV-enhanced photodetector with nanocrystalline-TiO 2 thin film via CMOS compatible process
(2011-12-01)
Bunjongpru, W.
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Panprom, P.
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Porntheeraphat, S.
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Meananeatra, R.
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Jeamsaksiri, W.
This research presents nanocrystal titaniumdioxide (nanocrystal-TiO <inf>2</inf>) film deposition technique with CMOS compatible process [1] to extend the optical response bandwidth of silicon based photodetecting devices toward ultraviolet range [2]. The thin films were initially deposited as Titanium Nitride (TiN) using DC magnetron reactive sputtering system. It was then annealed under nitrogen atmosphere at 800°C. After analyzing crystal structures and surface morphology with X-ray diffraction and FE-SEM systems, it was found that the deposited thin films showed the crystal phase of TiO <inf>2</inf> oriented along (200) plane of Rutile crystal structure with 50 nm grain size and increasing with film thickness. Using electroreflectance (ER) spectroscopy measurement [3], the bandgap of nanocrystal-TiO <inf>2</inf> was revealed to be 3.16 eV. PN-heterojunction photodiodes were fabricated with Nanocrystal-TiO <inf>2</inf>/SiO <inf>2</inf>/p-Si structures. Interdigitated aluminum structures were used as electrodes. By varying the thickness of nanocrystal-TiO <inf>2</inf> film, i.e. 30, 60, and 90 nm, the devices could response further into the UV range. The absorption edge wavelength investigated by photoresponse measurement was at 275 nm and shifting to the shorter wavelength as a function of the nanocrystal-TiO <inf>2</inf> grain size due to quantum confinement phenomenon [4]. The nanocrystal-TiO <inf>2</inf>/SiO <inf>2</inf>/p-Si photodetector had dark current = 5.31nA (2V), photocurrent = 0.9 uA, rise time = 58 us, fall time = 47 us at 30 nm thickness of TiO <inf>2</inf>. © 2011 IEEE.
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Characterization of Sol-gel derived Ti-doped tungsten oxide electrochromic thin films
(2011-01-01)
Paipitak, K.
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Kahattha, C.
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Techitdheera, W.
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Porntheeraphat, S.
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Pecharapa, W.
Ti-doped WO<inf>3</inf> electrochromic thin films were deposited onto F-doped tin oxide (FTO) substrates using spin coating technique. The as-deposited films prepared with various concentration of titanium were annealed in air at 500°C. The effect of Ti-doping concentration on structural, surface morphology and optical properties of the films were characterized by X-ray diffractometer, scanning electron microscope and UV-VIS spectrophotometer. The results show that the crystalline of WO<inf>3</inf> can be identified at 2θ values of 24.14° corresponding to 200 orientation. In addition, It was found that the electrochromic performance of WO<inf>3</inf> can be enhanced by small doping concentration of titanium due to structural modification of the films. © 2011 Published by Elsevier Ltd.
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