Micropunching Lithography for Generating Micro- and Submicron-patterns on Polymer Substrates

The overall goal of this work is to generate micro and sub-micron patterns on the top sidewall and bottom surfaces of a polymer substrate for various applications. This is accomplished by first coating intermediate and target polymer layers on a rigid surface. Next sharp and round edged mold structures are fabricated and used to emboss the substrate above the glass transition temperature of the intermediate polymer, which is below the melting temperature of the target polymer.

After the substrate cools, the mold is removed and micro and submicron patterns are revealed on the surfaces of the polymer substrates. The biomedical applications of micro punching lithography are first. The PPY microbiomes generated with cutting operation are used for glucose sensing.

Second, the HDP channels generated with drawing may be used as microfluidic channels inside labon chip devices for reducing the fluid flow friction. In this procedure, a silicone substrate, which is coated with intermediate polymer and a material to be printed, is heated above glass transition temperature of the intermediate polymer and below the melting or transition temperature of the targeted material. Next, the mold and the substrate are brought into physical contact under high pressure, followed by subsequent cooling.

Lastly, they're separated when their temperatures drop below the transition temperature of the intermediate polymer, thus completing the pattern transfer from the mold to the targeted layer. For this procedure, fabricated silicon molds of the required dimensions must be prepared using conventional UV lithography. Prepare the intermediate layer by selecting a non conducting PMMA sheet and place it on a rigid flat substrate.

A single conducting polymer can now be conventionally spin coated on top of the intermediate polymer. Additionally to spinco multiple conducting polymer materials cover the area around the first conducting polymer layer with adhesive tape. By taping and spin coating multiple layers can be coated at the desired locations on the substrate.

Next, emboss the substrate using a hot embossing machine for a few minutes and demold the substrate between 80 and 95 degrees Celsius at 1.5 millimeters per minute. In this procedure, the top layer is replaced by a combination of two and three polymers or metal layers respectively, to generate multi-layer microstructures. Fabrication of hetero junctions, diodes and capacitors are reviewed.

In order to generate a two layer PPY pdot hetero junction first spin coat, a 10 micrometer thick pdot layer onto the PMMA sheet. Next, bake the substrate at 80 degrees Celsius for one hour. Follow the baking with a spin coating one micrometer thick PPY film to obtain on the pdot layer and bake the substrate for five minutes.

To generate two layer aluminum pdot diodes spin coat a 10 micrometer thick pdot layer onto the PMMA sheet and bake the substrate for an hour. Then use thermal evaporation to coat a 200 nanometer thick aluminum film on the pdot layer. The substrate should be placed face down, and the chamber pressure should be set to five micro tour in the evaporator, a high voltage evaporates aluminum pellets.

Monitor the quartz thickness monitor until 200 nanometers is reached. Then cut the voltage to zero and vent the chamber before removing the sample. To generate three layer pdot, PMMA pdot capacitors.

Spinco, A 10 micrometer thick pdot layer on the PMMA sheet and make the substrate for an hour. Next spinco at 1000 RPM multiple times to obtain a 15 to 20 micrometers thick PMMA film on the pdot layer and bake the substrate for 30 minutes. After the PMMA layer is baked on spin coat a two to three micrometer thick pdot layer onto the PMMA film and bake the substrate for five minutes for all of the microstructures, emboss the substrate using the hot embossing machine for a few minutes after which demold the microstructures at 80 to 95 degrees Celsius at 1.5 millimeters per minute.

The drawing operation is similar to cutting, however, it uses a rigid mold with round edges and A-P-D-M-S mold. It also requires a smaller insertion force, a lower insertion speed, and a higher printing temperature. Begin making PDMS micro pillars by spin coating a micrometer thick layer of S 1813 on an SU eight mold.

The SU eight mold is generated using conventional UV lithography. Next spin coat PDMS onto the S 1813 coated SU eight mold at 1000 RPM and bake the sample at 85 degrees Celsius for three hours on a hot plate. After the PDMS layer is cured, wash the sample with acetone to dissolve the S 1813 and release the thin PDMS film from the SU eight mold.

Thus completing the micro pillar formed PDMS film now place the micro pillar formed PDMS film on a 1.5 millimeter thick HDPE sheet to print. Place an aluminum mold with rounded edges onto the PDMS film and HDPE sheet and bake it under pressure for an hour. The mold will then push the PDMS film down onto the soft HDPE sheet.

After the sample is cooled down to room temperature, remove the mold to finish making the channel on the HDPE sheet. During the process, part of this micro pillar formed PDMS film is transferred to the bottom and the two sidewalls of the channel. Using the MPL cutting operation single layer microstructures in PPY, PDOT and SPANI were made.

SEM was used to analyze a 300 micrometer wide straight line pattern and a 50 micrometer wide serpentine microwire pattern to test the sensitivity to humidity. A PPY MICROWIRE and a one square centimeter PPY film were both exposed to relative humidity levels, ranging from 45%to 85%Their sensitivity was measured as a change in resistance and compared. SEM was used to examine several multi-layer microstructures, including a 300 micrometer wide micro line shaped PPY pdot, hetero junction aluminum pdot diode, and a PDOT PMMA pdot capacitor using a keithley probe station.

With the pdot layer grounded and a bias potential of negative 20 volts to 20 volts applied to the PPY layer. The forward and reverse breakdown voltages of the PPY PDOT hetero junction were five volts and negative eight volts respectively. An aluminum pdot hetero junction was made by grounding the aluminum layer and applying a bias potential of negative five volts to five volts to the pdot layer measured at room temperature.

The forward and reverse breakdown voltages were three and negative 2.5 volts respectively. A pdot PMMA PDOT capacitor was made with the KEITHLEY probe station and the CV of the capacitor was measured at room temperature. The measured capacitance of the capacitor at low frequency bias was about 0.06 picofarad.

While the theoretically calculated quantity was 1.38, picofarad PDMS micro pillars were pressed into A-H-D-P-E sheets to form channel sidewalls. The average contact angle of the water droplet in HDPE channels was 145.5 degrees. The PDMS micro pillars are used to reduce the drag friction of HDPE channels.

A drop running over A-P-D-M-S film coated HDPE channel moves more slowly than a drop running across A-P-D-M-S micro pillar coded HDPE channel. This is due to the super hydrophobic nature of the channel as rendered by the PDM micro pillars. When doing these procedures, don't forget that working with photo resist, conducting polymers and volatile organic compounds can be hazardous, always take precautions, such as using personal protective equipments and working in a well ventilated area.