Archives for January 2015

Fabrication of Interdigitated Electrodes (IDE’s) by Conventional Photolithography Technique for pH Measurement Using Micro-Gap Structure

January 12, 2015 By Editor

Abstract – Micro interdigitated electrodes (IDE’s) have successfully been fabricated and characterized amperometrically for the electrochemical detection of the pH concentration and bio-molecules. In the present work, aluminium (Al) is used act as the metal contact (electrodes) deposited on the silicon substrate using a thermal evaporator (PVD) vacuum coater. The simple conventional photolithography was applied to fabricate the micro-gap capacitive transducer. IDE’s mask is designed using the aid of AutoCAD software for the detection of bio-substance which is an extremely small scale in size before being transferred to commercial chrome mask. The fabricated micro-gap sensor will then further evaluated through surface topology and electrical characteristic. The surface topology was implemented using AFM, LPM, SEM and HPM. The electrical measurements were carried out using a Dielectric analyzer (DA) with 2400 source meter (KEITHLEY) to examine the electrical characteristics such as capacitance and conductance. Purchased pH buffer solutions which varied from pH4 to pH 10 is dropped on the surface of microelectrode and the effect on it is investigated for the application in pH measurement. This study has proven that an increase in the concentration of acidic to alkaline pH leads to proportional to the capacitance.

Corresponding Author: Uda Hashim
Corresponding Author’s Email: uda@unimap.edu.my

Full text: PDF

Fluorescence-Signaling Aptasensor for ATP and PDGF Detection on Functionalized Diamond Surface

January 2, 2015 By Editor

Abstract – An aminated diamond-based aptasensor is presented for adenosine triphosphate (ATP) and platelet-derived growth factor (PDGF) detection. In this work, a signal-off detection method was employed to provide a sensitive, selective and reusable platform for the simple detection of PDGF and ATP. The detection limit of 0.2 nMand 0.2 μMof PDGF and ATP were achieved, respectively. It was also demonstrated in this study that the aptasensor is selective for PDGF and ATP over other biomolecules. In addition, the reusability of the aptasensor was confirmed by performing multiple cycles, which shows that diamond is a promising candidate as a material for biosensor applications. Moreover, this detection system does not require a target label and it is unaffected by non-specific binding.

Corresponding Author: Ruslinda Abdul Rahim
Corresponding Author’s Email: ruslinda@unimap.edu.my

Full text: PDF

Effect of different solvents on the structural and optical properties of zinc oxide thin films for optoelectronic applications

January 2, 2015 By Editor

Abstract – Zinc oxide (ZnO) seed solutions were prepared using 4 different solvents, namely, methanol (MeOH), ethanol (EtOH), isopropyl alcohol (IPA) and 2-methoxyethanol (2-ME). The prepared seed solutions were used to synthesize ZnO thin films using a low-cost sol–gel spin-coating method. The effect of different solvents on the structural and optical properties of ZnO thin films was investigated by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and an ultraviolet–visible–near infrared spectrophotometer (UV–vis–NIR). The images obtained in the FESEM and AFM showed that the thin film prepared using 2-ME has the smallest grain size. Moreover, the X-ray diffraction (XRD) results showed that the synthesized ZnO films are polycrystalline with preferred orientation along the (002) plane, whereas the IPA- derived films have a preferred orientation on (101) plane. The ZnO thin film synthesized with 2-ME has the highest transmittance (>90%), lowest surface roughness of 3.131 nm and highest band gap energy of 3.28 eV. The experimental data are in agreement with the calculated results by specific models of refractive index.

Keywords – Zinc oxide, Solvents, Optical, Structural, Sol–gel

Corresponding Author: Foo Kai Loong
Corresponding Author’s Email: klfoo@unimap.edu.my

Full text: PDF

On the MOSFET Threshold Voltage Extraction by Transconductance and Transconductance-to-Current Ratio Change Methods: Part II-Effect of Drain Voltage

January 2, 2015 By Editor

Abstract – In this paper, we study the effect of the drain voltage on the threshold voltage extraction in long-channel MOSFETs by the transconductance change and transconductance-to-current ratio change methods, using analytical modeling and experimental data obtained on advanced UTB SOI MOSFETs. It is shown that, although these two methods have the same physical background, they feature radically different behaviors with respect to the drain voltage effect. In particular, the transconductance change method yields a threshold voltage value, which regularly increases with drain voltage, and interpretation, as well as analytical expression for this dependence, is provided. In contrast, for the transconductance-to-current ratio change method, the increase of the extracted threshold voltage value with drain voltage is smaller and rapidly saturates; hence, the threshold voltage extraction is more stable and reliable. Modeling derivations are found to be in excellent agreement withmeasurements on long-channel UTB SOI MOSFETs as well as 2-D simulations.

Keywords – MOSFET threshold voltage extraction, transconductance change method, transconductance-to-current ratio, unified charge control model (UCCM).

Corresponding Author: Mohd Khairuddin Md Arshad
Corresponding Author’s Email: mohd.khairuddin@unimap.edu.my

Full text: PDF