A. H. Azman

Deposition and characterization of ZnO thin film for FET with back gate biasing-based biosensors application

This paper presents the preparation and characterization of zinc oxide (ZnO) thin film prior deposition on the channel of field-effect transistor with back gate biasing (FET-BG) for biosensing application. Sol-Gel technique is a chosen method for the preparation of the ZnO seed solution, followed by the deposition process through spin coating technique on the silicon dioxide (SiO2). Prior to that, the SiO2 layer is grown on a silicon die. The ZnO seed solution is deposited at various numbers of coating layer (1, 3, and 5 coating layers), baked, and annealed prior to characterization of its surface morphological, structural, crystalline phase, and electrical characterization. The results obtained give a significant evidences for the future deposition process of the ZnO thin films as the FET-BG biosensor device on the silicon-on-insulator (SOI) wafer.

Characteristics of TiO2 thin film with back-gate biasing for FET-based biosensors application

Biosensors become a main attraction nowadays due to its importance towards human health. Its allow rapid and label-free detection that provides low cost clinical sampling. A FET device was fabricated from silicon-on-insulator (SOI) type of wafer with titanium dioxide (TiO2) thin film as a sensing medium. TiO2 was deposited by using sol-gel solution, spin coated on the device, patterned and anneal. The physical characterization by using AFM and XRD was conducted to confirm the thin film was a TiO2 and electrical characterization was to determine the electrical properties, stability and sensitivity of the devices. From the result AFM and XRD confirm the thin layer was a TiO2 layer with grain boundaries and several peaks of TiO2 anatase crystal structure. The current-voltage (I-V and Vbg-Id) show that the TiO2 thin film has a good electrical properties and sensitivity that very suitable in sensing application especially detecting biomolecules for disease detection.

The impact of minority carrier lifetime and carrier concentration on the efficiency of CIGS solar cell

This paper deals with minority carrier lifetime and carrier concentration of Cu(In, Ga)Se2 (CIGS)-based thin film solar cells with a ZnS(n)/CIGS(p) heterojunction structure. The structure is simulated in commercial numerical simulation and the impact of minority carrier lifetime in the CIGS absorber layer on the open circuit voltage, short circuit current density, fill factor and efficiency of the CIGS solar cell are investigated. The increase of minority carrier lifetime has also increased the CIGS solar cell performance. Similar effects are also observed at different carrier concentrations of CIGS layer. All these simulated results give a helpful indication for a practical fabrication process.

Optimization of time on CF4/O2 etchant for inductive couple plasma reactive ion etching of TiO2 thin film

In this work, we investigate the optimum etching of titanium dioxide (TiO2) using inductive couple plasma reactive ion etching (ICP-RIE) on our fabricated devices. By using a combination of CF4/O2 gases as plasma etchant with ratio of 3:1, three samples of TiO2 thin film were etched with different time duration of 10 s, 15 s and 20 s. The ion bombardment of CF4 gases with plasma enhancement by O2 gas able to break the oxide bond of TiO2 and allow anisotropic etch profile with maximum etch rate of 18.6 nm/s. The sample was characterized by using optical profilometer to determine the depth of etched area and scanning electron microscopy (SEM) for etch profile characterization.

Reactive Ion etching of TiO2 thin film: The impact of different gaseous

Titanium dioxide (TiO₂) is one of a metal oxide material group that shows a promising future in biosensors application. TiO₂ possess both physical and chemical resistant that can extend a device lifespan. However, etching of TiO₂ with very high selectivity is a challenging process in achieving good and desired profile particularly in nanometer scale. In this work, we present the anisotropic etch profile. Three types of ICP-RIE recipes are used i.e. CF₄/O₂, Ar/SF₆ and CF₄/Ar. Prior to that, the TiO₂ sol-gel is deposited on top of SiO₂ layer. All the results are optically and physically characterized by using 3D-surface profilometer and atomic force microscopy (AFM) and finally followed by electrical characterization.

Real-time detection by properties of tin dioxide for formaldehyde gas sensor

This paper presents real time detection of formaldehyde gas by using the properties of tin dioxide (SnO2) thin film on a formaldehyde gas sensor. SnO2 thin film is coated on aluminum IDE electrodes which is fabricated on a glass substrate by using sol-gel technique and annealed to get the crystallization of SnO2. The surface morphologies of the SnO2 thin film is examined and studied through atomic force microscopy (AFM). For the real-time detection, formaldehyde gas was inject inside the gas chamber. The hot plate with the temperature of 200°C inside the gas chamber is used to evaporate the formaldehyde gas, subsequently exposing it to the surface of SnO2 thin film. Electrical conductivity of the SnO2 thin film is increased and allowed current to flow through it. The potential difference at the gas sensor is measured using voltmeter. During real time detection, various amount of formaldehyde liquid which are 0.1 μl, 0.3 μl, and 0.5 μl are injected into the gas chamber, thus produced potential differences of 0.8 V, 2.2 V and 3.5 V, respectively.

Characterization of Difference Size of IDE Pattern for Formaldehyde Detection Sensor

This paper studies the effect of different gap sizes of IDE pattern on the surface morphology and electrical properties for the formaldehyde detection sensor. Two types of IDE chrome mask are designed to determine the ideal IDE pattern for formaldehyde gas detection by using conventional lithography. In the first method, IDE is transferred onto SiO2 layer. In order to ensure that the perfect pattern with minimum defect structure is obtained, the process parameters should be optimized and controlled. In the second method, the aluminium is deposited directly on SiO2/Si substrate by using IDE hard mask design plate. The fabricated IDE pattern is further validated through morphological and electrical characterization. The average gap size of IDE sensor is approximately 100 μm and 400 μm for IDE chrome and IDE hard mask respectively. The latter method is preferable since for formaldehyde gas sensing large size is needed and moreover the process is simple and requires low cost. Characterization of difference IDE pattern is demonstrated by various measurements.

Fabrication and characterization of polysilicon for DNA detection

We present the fabrication and electrical characterization of polysilicon and their properties with application in biomolecule sensors for DNA detection. Conventional photolithography technique was used to fabricate the DNA detection structure for two different wafer substrate i.e. N- and P-type. The fabrication processes involve of deposition, etching and oxidation to achieve the final structure. Surface modification, immobilization and hybridization were executed prior to electrical characterization by using cyclic voltammetry. It was observed that the modified surface with APTES achieved the highest current for both p- and n-type wafer with changes from 0.52 μA to 3.32 μA and from 0.57 μA to 2.52 μA respectively. Moreover, redox current of hybridization is observed approximately 22 % and 10 % larger than immobilized electrode for p- and n-type wafer.

Controlling growth rate of ultra-thin Silicon Dioxide layer by incorporating nitrogen gas during dry thermal oxidation

The continuing trend toward miniaturization of silicon devices is enforcing development of ultra-thin dielectrics. While the thermally grown SiO2 has been used as a gate dielectric ever since the decade of silicon device began, it appears that the electrical and physical properties of pure SiO2 are not good enough to provide acceptable for ultra-thin gate dielectric film. There are many available methods to control the ultra-thin film; In this paper we show a simple but promising method that incorporated nitrogen as a second gas in the dry oxidation process, on which the growth rate can be controlled. This method produce surface protective layers against impurity penetration, good interfacial characteristics and strengthens the oxide structure, which directly related to improvement the gate dielectric quality.

Design Architecture of field-effect transistor with back gate electrode for biosensor application

This paper presents the preparation method of photolithography chrome mask design used in fabrication process of field-effect transistor with back gate biasing based biosensor. Initially, the chrome masks are designed by studying the process flow of the biosensor fabrication, followed by drawing of the actual chrome mask using the AutoCAD software. The overall width and length of the device is optimized at 16 mm and 16 mm, respectively. Fabrication processes of the biosensor required five chrome masks, which included source and drain formation mask, the back gate area formation mask, electrode formation mask, front gate area formation mask, and passivation area formation mask. The complete chrome masks design will be sent for chrome mask fabrication and for future use in biosensor fabrication.