Organic transistor based circuits as drivers for planar microfluidic devices

The work presented in this dissertation is focused on integrating organic transistor based circuits with planar microfluidic devices for discrete droplet handling. Discrete droplet based microfluidic systems are being increasingly investigated for lab-on-a-chip type applications. An essential component of a lab-on-a-chip system is the drive circuitry that runs the system. Conventionally, a variety of schemes have been implemented for acting as drivers for microfluidic devices. Organic transistor based circuits offer a viable and cost-effective option for serving as drivers for planar microfluidic devices. The magnitudes of voltages and the time scales involved in implementing these discrete droplet based systems are in good agreement with the values of voltages that can be reliably generated using organic transistor based circuits. Thus, the union of two cost-effective technologies with the ability to perform a wide variety of functions in a lab-on-a-chip type system would be highly desirable. A simple, planar microfluidic device with an open structure is implemented on a glass substrate. The device is optimized for reliable and repeatable performance using Cytop as the insulating dielectric. Cytop provides a highly hydrophobic surface for reversible wetting to take place on the application of electrical voltage. Various organic transistor based circuits are fabricated using Pentacene as the p-type semiconducting material and N,N'-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN₂) as the n-type material. A top contact inverter, which is the most basic complementary metal oxide semiconductor circuit is fabricated and used as the driver for the planar microfluidic device. The output voltages generated by the inverter are used to actuate discrete water droplets over adjacent electrodes and also to perform merging of droplets, which is another basic functional operation that is performed on lab-on-a-chip type assemblies. Reliable and repeatable performance of the microfluidic device as well as the CMOS circuit is achieved. This work presents the first implementation of a discrete droplet based device driven by electrical voltages generated by an organic transistor based circuit. The physical mechanisms that are responsible for the motion of droplets have been investigated and contributions from electrowetting forces and dielectrophoretic forces have been resolved.