Flexible microfluidic devices made of poly(dimethylsiloxane) (PDMS) were manufactured by soft lithography, and tested in detection of ionic species using optical absorption spectroscopy and electrical measurements. PDMS was chosen due to its flexibility and ease of surface modification by exposure to plasma and UV treatment, its transparency in UV-Vis regions of the light spectrum, and biocompatibility. The dual-detection mechanism allows the user more freedom in choosing the detection tool, and a functional device was successfully tested. Optical lithography was employed for manufacturing templates, which were subsequently used for imprinting liquid PDMS by thermal curing. Gold electrodes having various widths and distances among them were patterned with optical lithography on the top part which sealed the microchannels, and the devices were employed for detection of ionic species in aqueous salt solutions as well as micro-electrolysis cells. Due to the transparency of PDMS in UV-Vis the microfluidics were also used as photoreactors, and the in-situ formed charged species were monitored by applying a voltage between electrodes. Upon addition of a colorimetric pH sensor, acid was detected with absorption spectroscopy.
Organic flexible electronics is an emerging technology with huge potential growth in the future which is likely to open
up a complete new series of potential applications such as flexible OLED-based displays, urban commercial signage, and
flexible electronic paper. The transistor is the fundamental building block of all these applications. A key challenge in
patterning transistors on flexible plastic substrates stems from the in-plane nonlinear deformations as a consequence of
foil expansion/shrinkage, moisture uptake, baking etc. during various processing steps.
Optical maskless lithography is one of the potential candidates for compensating for these foil distortions by in-situ
adjustment prior to exposure of the new layer image with respect to the already patterned layers. Maskless lithography
also brings the added value of reducing the cost-of-ownership related to traditional mask-based tools by eliminating the
need for expensive masks. For the purpose of this paper, single-layer maskless exposures at 355 nm were performed on
gold-coated poly(ethylenenaphthalate) (PEN) flexible substrates temporarily attached to rigid carriers to ensure
dimensional stability during processing. Two positive photoresists were employed for this study and the results on plastic
foils were benchmarked against maskless as well as mask-based (ASML PAS 5500/100D stepper) exposures on silicon
A computer-controlled laser beam recorder with a wavelength of 405 nm has been employed for patterning the deposited resist with feature sizes varying from a few hundreds of nanometers to tens of micrometers. Four inch silicon templates for hot embossing source/ drain electrodes and metallic circuit for a disposable biosensor were obtained. SEM and optical microscopy reveal accurate transfer of developed photoresist structures into the underlying silicon wafer after plasma dry etching. Etch depths between 100 - 600 nm were obtained on the templates, and were further transferred into the imprinted plastic substrate and the metallic layer.