Mohammad Nuzaihan Md Nor

Design and process development of silicon nanowire based DNA biosensor using electron beam lithography

Silicon nanowires (SiNWs) have their unique feature such as similar diameters to biomolecules, chemically tailorable physical properties, enable to apply in biomolecule detection and can be fabricated as a high performance field effect transistor (FET). This research describes the fabrication of silicon nanowire for DNA hybridization detection in biosensor application. The silicon nanowire with line-width of <100 nm is successfully fabricated by electron beam lithography and will follow by deposition of contact metals. Aurum is a suitable metal to make Ohmic contact with SiNWs and its exhibit electrical transport measurements of the devices. The presence of the hybridization DNA will induce electronic charge and changed the electronic properties of the transistor from which detectable electronic signals are generated.

The effect of softbaking temperature on SU-8 photoresist performance

One of the steps required during the fabrication of SU-8 mold for soft lithography is softbaking, which is conducted after the deposition of the photoresist. The purpose of softbaking is to stabilize the resist film and eliminate any remaining solvent through evaporation. This ensures that the resist surface is non-sticking, hence avoiding debris when transferring the patterns later. In this paper, we investigate the effects of softbaking temperature on the polymerization of SU-8 photoresist. The significance of this work is to optimize the fabrication process involved in producing SU-8 mold structures with thickness of 30 μm. This project involves a series of experiments covering softbaking temperatures ranging from 45° to 115° C. Experiments results show that softbaking temperature of 85°C results in completely stick and crack free structures. By this, a huge improvement obtained if compared to the result of processing at the standard soft bake temperature of 95°C. The soft bake temperature should not be taken lightly while optimizing SU-8 processing because it has a big influence on the material properties and the lithographic performance of the resist.

Fabrication of Silicon Nanowires by Electron Beam Lithography and Thermal Oxidation Size Reduction Method

A simple method for the fabrication of silicon nanowires using Electron Beam Lithography (EBL) combined with thermal oxidation size reduction method is presented. EBL is used to define the initial silicon nanowires of dimensions approximately 100 nm. Size-reduction method is employed for reaching true nanoscale of dimensions approximately 20 nm. Dry oxidation of silicon is well investigated process for self-limited size-reduction of silicon nanowires. In this paper, successful size reduction of silicon nanowires is presented and surface topography characterizations using Atomic Force Microscopy (AFM) are reported.

Hybrid elastomer-nanotube matrix for hydrophobic surface functionalization

Surface functionalization studies for re-creating a ‘Lotus Leaf’ effect (super-hydrophobic) have been carried out for the past few decades, looking for the material which can provide high transparency, low energy surface, and high surface roughness. However, the conventional fabrication processes of super-hydrophobic surface proposed by the previous researchers were reported to be complicated. Therefore, in this research, we had created an alternative ways to produce near-super-hydrophobic surfaces using simplest processing routes with a controlled modification. The fabrication of polydimethylsiloxane/multi-walled carbon nanotubes (MWCNTs) hybrid thin film matrix on glass to produce near-super-hydrophobic surfaces is presented in this paper. There are three important parameters studied in producing hydrophobic surfaces based on the hybrid thin films; concentration of polydimethylsiloxane, concentration of MWCNTs, and droplet sizes, respectively. The study is carried out using polydimethylsiloxane of varied cross linker ratio (10:1, 30:1, and 50:1) with MWCNTs concentration of 1, 10, and 15 mg for 0.5, 2.0, 5.0, and 10 μl droplet sizes. The resulting hybrid elastomer-nanotube matrix thin films show that hydrophobicity increased with increasing cross linker ratio and MWCNTs percentage in the polydimethylsiloxane solution. A near-super-hydrophobic surface can be created when using 15 mg of MWCNTs with 50:1 cross linker ratio polydimethylsiloxane thin films, measured on 10 μl droplet size. The hybrid thin films produced can be potentially tailored to the application of biosensors, MEMS, and even commercial devices.

Microfluidic structure fabrication using soft lithography and laser micromachine

Microfluidic structures are devices that are able to control fluids in the scale of micrometer and have been widely adapted in the application of lab-on-chip. There are many methods of producing microfluidic structures, with soft lithography and laser micromachine are the commonly reported techniques. This paper reports on the experiments conducted to investigate the formation of microfluidic structure by means of soft lithography method and laser micromachine technique. From soft lithography process, UV exposure time of 60 seconds and exposure energy of 160mJ/cm2 are considered as optimal exposure condition in producing the microfluidic structure. By using laser micromachine technique, the best laser energy intensity used to produce the structure is 14 mJ. We found that both techniques have its pros and cons, with laser micromachine technique involve less fabrication time and chemicals, while soft lithography method produced smoother microfluidic surface structure.

Fabrication and Characterization of Doped Polysilicon Nanowire for pH Sensor

This paper presents the characteristics of the doped polysilicon nanowire for pH sensors. The fabrication involved two chromium mask designs. Example the first mask is used for the polysilicon nanowire pattern and the other one is for pad patterning. It involved of photolithography, deposition, etching and wet oxidation process. Different length, number of polysilicon are fabricated and then subjected to voltage, current and pH measurement. APTES is being introduced to improve the sensitivity of the polysilicon nanowire. For the low pH, the conductivity is high, while for the high pH, the conductivity is low. The impact on investigating length is insignificant to the sensitivity of the doped polysilicon nanowire.

Fabrication of Poly-Si Nanowire Using Conventional Photolithography Technique

A simple method for the fabrication of polycrystalline silicon (poly-si) nanowires using conventional photolithography combined with thermal oxidation-size reduction method is presented. In our process, a polysilicon layer is deposited by low pressure chemical vapour deposition technique on SiO2 layer. Conventional photolithograpy is used to define the initial poly-si of dimensions 1 um. In order to miniaturize microwire to nanowire, size reduction method is employed using several time of dry thermal oxidation process. The characterization that is applied to measure the profile of poly-si nanowires using optical microscopy.

Negative Pattern Scheme (NPS) Design for Nanowire Formation Using Scanning Electron Microscope Based Electron Beam Lithography Technique

In this work, we report the used of Negative Pattern Scheme (NPS) by Electron Microscope Based Electron Beam Lithography (EBL) Technique in connection with scanning electron microscope (SEM) for creating extremely fine nanowires. These patterns have been designed using GDSII Editor and directly transferred on the sample coated with ma-N 2400 Series as the negative tone e-beam resist. The NPS designs having line width of approximately 100 nm are successfully fabricated at our lab. The profile of the nanowire can be precisely controlled by this technique. The optical characterization that is applied to check the nanowires structure using SEM and Atomic Force Microscopy (AFM).