M. N. M. Nuzaihan

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.

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.

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.

Fabrication of poly-silicon microwire using conventional photolithography technique: Positive resist mask vs aluminium hard mask

We have demonstrated a simple and low-cost method to fabricate poly-silicon microwire by conventional photolithography technique. There are two different steps process flow were involved in the conventional photolithography technique which are employed the positive resist as a mask and aluminium (Al) as hard mask. Low pressure chemical vapour deposition (LPCVD) was used to deposit 50 nm poly-silicon layer on the Si-SiO2-Si3N4 layer. Wire mask must be first designed using AutoCAD before patterning onto chrome mask. Initially the 300 nm thick layer of positive resist is coated on the sample. Subsequently, the coated sample were exposed to UV light for 10 seconds and followed by development process. The critical part in this development process is to control the development time and resist profile. There are three types of resist profile problems such as underdevelopment, incomplete development and overdevelopment resist profile. These resist profiles problems can negatively affect in the subsequent etch process. Next process is an etching process. For positive resist as a mask process flow, the developed sample was loaded into SAMCO Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) 10iP to anisotropic etching of poly-silicon for 7 seconds. Meanwhile, for Al as a hard mask, the developed sample was dipped into Aluminium (Al) etchant for 3 minutes then followed by resist stripping and anisotropic etching of poly-silicon as similar to the resist mask process flow. Finally, the dimensions and etch profiles of <; 1um poly-silicon microwire were morphologically characterized using optical microscopy.

Fabrication and characterization of undoped polysilicon nanowire for pH sensor

Polysilicon has great benefit in application of pH sensor due to the unique properties and easiness to use top-down approach. In this paper, we present fabrication and characterization of undoped polysilicon nanowire (NW) for pH sensor application. The fabrication processes steps involve were photolithography, etching, deposition and oxidation. 3-aminopropyltriethoxysilane or APTES were used to enhance the sensitivity of polysilicon layer as well as able to provide surface modification by undergoing protonation and deprotonation process. Surface analysis using SEM were used for surface morphology analysis. Different types of pH solution provide different resistivity and conductivity towards polysilicon surface. In addition, voltage, current, conductance against pH level are characterized and compared. Alkaline solution has the higher current as compared to acidic. This was due to the polysilicon layer contains more holes which are easily being attracted by - SiO to the surface and hence, forming a strong channel from source to drain. Results obtain reveal a linearity of pH measurement with a corresponding sensitivity of 4.65 nS/pH.

Probing the Ph measurement of self-alligned polysilicon nanogap capacitor

With their bright potential in effective sensing, nanogap capacitor show promise as a device to measure wider aspect of dielectric properties. In this paper, we demonstrate the effectiveness of nanogap capacitor in detecting the changes of pH measurement via Dielectric analyzer (C-V and C-F characterization) as its stables under each reading and repeatability. The purpose of this paper is to report on the fabrication and electrical characterization of nanogap device. We introduce the conventional lithographic combined with the size expansion technique for the transition from micro (3.13µm) to nanosized (42nm) gap. The evolution of gaps nanogap pattern expansions were verified by using SEM by controlling the dry oxidation time of device. Then, Ti/Au layer were deposited onto the final device for probing purpose. Different level of pH (3, 5, and 10) has been tested and conformed by repeating each test. About 10 µm of pH liquid were dropped using pipette in the middle of gap probing (2-wire measurements) is done on the Au pad fabricated on the nanogap device. 10 µm of pH liquid were dropped using pipette onto the target and the reading will be taken. Probing is done via dielectric analyzer on the couple of gold pad apart of the capacitive nanogap biosensor to investigate the effect of excitation frequency and voltage on capacitance sampling.