S. Johari

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.

Etch Performance of KRF Excimer Laser Micromachining Characterization on Silicon Material

Excimer laser micromachining enables us to overcome the conventional lithography-based microfabrication limitations and simplify the process of creating three dimensional (3D) microstructures.The objective of this study is to investigate the relation between the number of laser pulses, number of laser passes through the channel of ablation site and their etch performance. Parameters such as frequency, fluence and velocity were retained as constants. In this paper, we present a parametric characterization study on silicon using KrF excimer laser micromachining. From the result, the etch rate change were recorded as the two major laser parameters (Number of laser pulses and number of laser passes) were varied. Both parameters were showing declination profile however from comparing both graphs, it showed that etch rate dropped more steeply when varied number of laser passes rather than number of pulses.

Characterization of MEMS structure on silicon wafer using KrF excimer laser micromachining

This paper presents preliminary parametric studies of KrF laser micromachining ablation effects on Silicon. Four parameters are studied, namely laser energy, pulse rate, number of laser pulses, and Rectangular Variable Aperture (RVA) in X and Y direction. At present, the study is focused on the production of microchannels using laser micromachine, in which its dimension is examined and measured. We found that the number of laser pulse is non-linearly proportional with the ablated channel width, with the etching rate of approximately 1 to 5 um for 50 laser pulses. This is similar with the measured depth of the microchannel. The changes in the measured channel width are most significant when the laser energy is increased. Some debris and recast can also be observed around the edge of the microchannel particularly during the variation of the laser pulse frequency. When varying the RVA, it is observed that the surfaces of the ablated microchannels are not smooth with a lot of debris accumulated at the channel edge and a few discolorations. Finally, a microcantilever structure is fabricated with the aim of demonstrating the capability of the laser micromachine.

Microvalve-based microfluidic device for C. elegans manipulation

In this paper, we report on the integration of a force measurement application capable of continuously measuring the forces generated by C. elegans in motion with a series of controllable microvalves which have an additional ability to increase control over worm selection and manipulation. The three-layer device consists of a pneumatic layer at the top, and a fluidic layer at the bottom with a thin PDMS membrane which functions as a microvalve sandwiched in between. The pneumatic layer functions as valves, whose operation is controlled pneumatically. The fluidic layer contains of PDMS micropillars for resolving the worm force from the deflection of the cantilever-like pillars. The measured force is horizontal and equivalent to a point force acting at half of the pillar height. By carefully controlling the incorporated microvalves, the proposed device is able to select and direct worm movement and at the same time increase the number of force measurement results collected. The integration of the microvalve...

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.

PDMS micropillars for C. elegans force measurement

This paper reports on the fabrication of PDMS micropillars as force sensor for C. elegans locomotion measurement. Three different designs have been fabricated; starting from a channel like design with two parallel rows, to increasing the number of micropillar rows in Design 2, and finally a 9 × 9 mm square chamber with multiple arrays of PDMS pillars arranged in a lattice and honeycomb structure. Results of worm locomotion forces show that different parts of the worms body exert forces on five individual pillars that were in contact with the worm throughout its movement. The fabrication process of the PDMS device is also explained in detail, along with the device casting procedures. The final section discusses the challenges and limitations tackled in this research, in particular during the fabrication process.

Towards improving the etch performance of KrF excimer laser micromachining on silicon material

Excimer laser micromachining enables us to overcome the conventional lithography-based microfabrication limitations and simplify the process of creating three dimensional (3D) microstructures. The objective of these study are to investigate the relation between frequency (f), number of laser pulse (P), fluence (F) and their etch performance. This paper presents a parametric characterization study on silicon using KrF excimer laser micromachining. From the result, the etch rate change were recorded as the three major laser parameters (frequency, number of pulse and fluence) were varied. From the results, we found that the fluence has the highest influence on silicon etching rate due to factors of photothermal and photochemical, while frequency and the number of laser pulses do not change the energy.

Characterization of MEMS Materials Using Laser Micromachine

Laser micromachining technique was used in this work to produce two different microfluidic structure on three MEMS materials namely silicon, SU-8 photoresist and polydimethylsiloxane (PDMS). The operational parameters of the machine ablation effects on the materials, which are the laser energy, laser pulse rate and the laser size were also investigated. We found that this technique is capable to produce typical MEMS structure similar as being produced using conventional photolithography process.

Development of microstrip chebyshev low pass filters using laser micromachining

This paper describes the development of the 5th order Chebyshev microstrip low pass filter using both Advanced Design Software (ADS) simulation and laser micromachining fabrication technique. The significance of this work is the introduction of a new concept used to fabricate low-pass filter which is using laser micromachine. At present, laser micromachine is used to complement conventional photolithography process in the production of MEMS devices. The use of laser micromachining can lead to finer finishes, improved accuracy and less process overhead. The fabrication is implemented using silicon substrate, as opposed to the commonly used FR4 substrate. The simulation and measurement results of microstrip low pass filter fabricated using the micromachine have been compared and excellent agreement is observed. The rejection performance of the filter is improved when the gain is approximately 40dB. The return loss matching response is observed to be near to -20dB. The fabricated circuit cut-off frequency is closer to the simulated design frequency of 2.5GHz.