Syed Nadeem Akhtar

Ionic Polymer Metal Composites

Ionic polymer metal composites (IPMCs) are electro-active polymers with excellent electromechanical coupling properties. They are efficient candidates in many advanced technological applications such as actuators, artificial muscles, biomimetic sensors, etc. The manufacturing of electrodes for IPMCs is very critical in their electromechanical coupling. Force optimization, selection of cations and particle size distribution within the IPMC structure, etc. are the various factors, which determines their efficiency. In this chapter, we briefly discuss the structure, components and working mechanisms of IPMCs. The synthesis and characterizations of IPMCs are discussed in detail with the help of examples. A brief outlook on the modeling and potential applications of IPMCs is also included.

Excimer Laser Micromachining Using Binary Mask Projection for Large Area Patterning With Single Micrometer Features

Excimer laser micromachining using binary mask projection has been investigated for rapid patterning of single micrometer features over large areas of various substrates. Simple limit for depth of focus that determines the depth to width aspect ratios is given and verified for different materials. Binary mask projection technique is found to conformally reproduce the mask features from the millimetre to the micrometer scale under proper focusing conditions. Large arrays of 1 lm and 15 lm holes on Kapton are made with high resolution and uniform periodicity. Material removal rate (MRR) for the laser machining of these holes are examined and the machining efficiency for these are found to have different dependence on the fluence. A saturation of hole-depth with increasing number of pulses is obtained. [DOI: 10.1115/1.4024880]

Microfeature edge quality enhancement in excimer laser micromachining of metal films by coating with a sacrificial polymer layer

A novel technique for enhanced excimer laser micromachining of metallic thin films by first coating the metal film with a thin polymer film is presented. The sacrificial polymer film acts as a protective and a clamping layer, preventing the metal film from undergoing cracking and damage during the laser ablation. The machined patterns are characterized regarding their quality in terms of edge roughness, lateral overcut and boundary integrity in proximity machining. Significant improvement in these aspects is observed when the machining is carried out on metal films coated with thin polymer films. Details of the effects of the fluence and spot overlap on the micromachined patterns are investigated. The technique allows sharp machining of micropatterns on thin metal films, over length scales ranging from hundreds of micrometers down to a single micrometer, thereby proving to be the only technique that can be used to laser micromachine thin films at the length scale of a single micrometer. This technique is expected to be useful for large scale patterning of metallic films, particularly for plasmonic applications and infrared/terahertz metamaterials.

Simulations and experiments on excimer laser micromachining of metal and polymer

Abstract. Excimer laser at 248 nm has been used to micromachine holes and channels on stainless steel and polymethyl methacrylate using mask projection methods. The machining is numerically simulated considering the laser beam as a heat source only, thermal diffusion, and melt vaporization. The depth and width of the machined features at different pulse energies and number of pulses are measured by optical profilometry. Both the depth and the aspect ratio (depth-to-width) are found to increase with increasing number of pulses and pulse energies. The depth predicted by the simulations based on the thermal ablation model is closer to the experimental observations for steel as compared with that for the polymer. This allows for the quantification of the contribution of thermal ablation processes in the excimer laser machining of metals and polymers. High-energy pulses are found to have higher ablation efficiency in case of metal and lower ablation efficiency in case of polymer.

Microfeature Edge Quality Optimization in Excimer Laser Ablation of Metallic Film

Excimer laser ablation of thin films finds an advanced application in the manufacture of integrated circuits and it is desirable in the process that the size of the ablated region is close to the design and clean ablation takes place at the edges. In practice, the boundaries of the ablated region are irregular, the features are oversized and spattering is observed inside the ablated region. This work studies the edge roughness, channel width and boundary integrity as indicators of quality of ablation. Experiments are conducted with varying fluence, shot overlap and pitch (inter-channel distance) to generate different features. The edge roughness and channel width are found to have little dependence on spot overlap but are greatly influenced by the fluence. The overcut (channel width) is more at higher fluence but repetitive pulses do not affect the overcut. The range of parameters of ablation are identified from these experiments that lead to optimum edge roughness, channel width and boundary integrity.© 2013 ASME

Fabrication of Micro Lens Array by Excimer Laser Micromachining

Micro Lens arrays are widely used in optical devices such as photo-sensors, digital projectors, photovoltaic cells, 3D imaging etc. These have traditionally been fabricated by photolithography, moulding and embossing, reactive ion etching and electroforming. These processes are wet processes and require expensive setup and running cost. A novel method is presented in this work that allows fabrication of micro lens array using excimer laser micromachining. The fabrication has been done using mask projection with work piece scanning. A KrF excimer laser has been used to micro machine lenses on a poly (methyl methacrylate) substrate. The surface profile of the lens array is measured and then related to the laser-material coupling and the energy of the laser pulses. Using this method, it is possible to fabricate micro lenses down to a diameter of 5 µm over a considerably large area.

Optimization of laser machining process for the preparation of photomasks, and its application to microsystems fabrication

Abstract. Conventional photolithography normally utilizes a photomask for patterning light onto a chemical resist film. Therefore, the accuracy of microfabrication is highly dependent on the accuracy of the photomasks. Fabrication of hard masks involves the use of expensive laser pattern generators and other sophisticated machines using very high-precision stages and the necessary control instrumentation; therefore, an inexpensive strategy is highly necessary for laboratory-level fabrication. As this technology is primarily based on raster scanning of a laser beam, the mask making as such becomes a low-throughput process. A strategy of high-throughput manufacturing of hard masks with laser micromachining using a one-step exposure process of a chromated glass slide through a micromachined aluminum shadow mask is proposed. The features that are finally embedded in the mask are highly demagnified and well focused. Optimization of the laser machining process is carried out by considering all processing parameters. The features are characterized using an optical microscope, a scanning electron microscope, and a self-developed image analysis code. Geometrical methods are used to estimate the average edge roughness and feature size. We have also validated the usage of these masks by performing microfabrication on films made of photoresist.

Experimental Investigation of Formability Enhancement Using Hydraulic Counter Pressure Assisted Warm Deep Drawing

Deep drawing processes are widely utilized in mechanical industries for producing several typologies of products ranging from computer industry to automotive components, from house products to furniture products. The goal of this study is to verify experimentally the warm deep drawing process assisted with hydraulic counter pressure as a suitable alternative to conventional deep drawing as a means for producing defect-free sheet metal parts. Using specific process parameters like blank holding pressure, blank diameter and temperature, wrinkle-free parts with deeper draws could be produced. An enhancement in LDR from 2.06 in conventional deep drawing to 2.16 in warm deep drawing with a lower blank holding pressure is achieved. The lower blank holding pressure leads to lesser thickness variation in the product this reducing the occurrence of fracture at the punch radius. The hydraulic counter pressure helps in reduction of wrinkles and enhancement of formability. The improvement in the LDR was observed around 200°C for warm deep drawing. This process reduces the forming restrictions of many materials, can produce complicated shapes and reduces the costs of material and die.