Smartphone Display Based Photolithography to Fabricate Microdevices

We demonstrate a smartphone-based low cost photolithography technique that can be easily adapted, especially in university laboratories. In the initial experiments, we used only the display from a smartphone as the source of light and successfully transferred micrometer sized patterns in an optical mask on to a silicon wafer coated with photoresist microposit S1805. The fabricated patterns were identical to the features in the optical mask and had minimum critical dimension variation of 800 nm. However, the exposure time required to polymerize the photoresist film with adequate dosage of light was long (up to 40 minutes). In the next stage, we optimized the setup by making use of irradiation from UV LED arrays attached to the opposite long edges of the smartphone and reduced the required exposure time by 50%. Finally, we extended the lithography experiments to showcase potential of the proposed smartphone-based lithography as a lowcost tool to perform maskless lithography. For the later, an interdigital transducer (IDT) design was displayed and successfully transferred as a pattern on to a photoresist coated wafer sample. Further metallic electrodes of the IDT was fabricated on the sample through lift-off process, where the transferred pattern was utilized as sacrificial layer in the process. Finally, the fabricated IDT was verified as a sensor to detect conductivity of liquid samples, and thus, demonstrating the usability of the technique in designing laboratory exercises.