monitor, shutter is opened, enough time is waited to reach to

the desired thickness and shutter is closed.

9. When the chromium deposition was completed, sample rota-

tion is stopped. The system is left for 2 h for cooling before

gold deposition.

10. Gold deposition starts at 100 A electrical current. The thick-

ness is monitored using crystal. Typically 50 nm thickness is

achieved using around 100 mg gold pellets.

11. After gold deposition, turn off the electrical current supply and

start the ventilation to disrupt the vacuum.

12. Take Cr/Au deposited COP samples from the device and stop

cooling water.

3.2.3

Cr/Au Etching to

Form Electrodes on Coated

COP Sample

1. Clean Cr/Au deposited COP sample with nitrogen and place

on the spin coater.

2. Immobilize the sample via vacuum and coat photoresist

(PR 1828) on the Cr/Au deposited COP sample at 500 rpm

for 2 s and 4000 rpm for 30 s.

3. Soft bake the photoresist coated COP sample for 1 min at

90
C.

4. Place the sample on the table of UV lamp and superimpose

electrode mask on it.

5. Expose to UV light at 365 nm wavelength and 20 mW/cm²

power density for 3 min.

6. Submerge the sample into the developer solution (MF319) and

shake in the direction of short edge to facilitate the opening of

the electrode fingers for 3 min.

7. When UV light exposed part of the photoresist disappear, clean

the sample via distilled water and dry with nitrogen.

8. Analyze the sample under microscope to check whether the

electrode fingers are opened or not.

9. Dip the COP sample into gold etchant (Potassium iodide and

iodine solution, Alfa Aesar, 44584) for 1 min to remove unpro-

tected gold regions. This should reveal clear interdigitated

electrodes (fingers).

10. After gold patterns are realized, remove photoresist via ace-

tone, IPA and distilled water, respectively. Finally, etch unpro-

tected chromium regions inside chromium etchant (Ceric

ammonium nitrate solution, Nichrome etchant, Alfa Aesar,

44585) for 20 s. Rinse it inside distilled water.

11. Dry the sample by nitrogen and analyze under microscope.

12. Cr/Au electrodes are formed on the COP sample.

Fabrication Protocol for Thermoplastic Microfluidic Devices: Nanoliter. . .

33