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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.
;
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. (R<sup>2</sup> = 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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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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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.
;
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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The effect of ion implantation on ISFET-sensing membrane
(2010-02-05)
Piyananjaratsri, R.
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Bunjongpru, W.
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Chaowicharat, E.
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Trithaveesak, O.
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Saeteaw, K.
This research studied the effect of ion implantation on electrical properties of ISFETs. In the experiments the sensing membrane area were implanted with 3 types of ions (Boron(B), Phosphorus(P), and Arsenic(As)). After the implantation without annealing, the IV-characteristics of Source/Drain (P-N junction) of ISFET were performed and compared with the behaviour before implantation. In addition, the response to acid-alkaline (sensitivity) of ISFET were also studied. From the results the leakage current of source-drain, P-N junction like, decreases significantly after the implantation. However, this process damaged the devices so that the response to acid-alkaline are lost. © (2010) Trans Tech Publications.
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Effect of exposure energy, focus range, and surface reflection on the photolithography process of contact hole patterning
(2008-10-07)
Sonboonton, R.
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Chaowicharat, E.
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Meesapawong, P.
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Ladthidej, J.
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Titiroongruang, W.
The patterning the contact holes by photolithography process, in this case polysilicon contacts, is the process to produce electrical connection between metal layer and polysilicon gates or metal layer and source/drain. The photolithography process can control size and shape of the contact hole patterns on photoresist before permanently patterned by etching process and then metallization. The contact holes were specified to have the size of 0.8 micron after the photolithography process. In order to achieve this, the process parameters to be considered are exposure energy, focus length of the lens system, and the effect of light reflecting from the film topography underneath. Since in the previous processing step, the attempt to reduce the film topography was done by planarization using BPSG. By adjusting the exposure energy and focus, the optimal condition, to produce 0.8 micron contact holes, was found to be energy of 305 mJ/cm and focus of-1.0 μm. © 2008 IEEE.

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