Development of MEMS device for biological analysis

In this dissertation, the objective is to integrate an electrostatic microelectromechanical systems (MEMS) comb drive actuator with a novel microfluidic device for a micro analysis system of biological samples. Although electrostatic actuators have been integrated into microsystems owing to integrated circuit (IC) compatible processing and materials, they have yet gained little attention in microfluidic systems because of many potential obstacles such as electrolysis, electrode polarization, heating problems in the fluidic medium. In order to effectively avoid these detrimental factors, a novel microfabrication method is employed to geometrically isolate electrostatic actuators from the functional microfluidic components using a hydrophobic stop-valve architecture implemented by selective flip chip bonding techniques. The 2 x 2 packaged device has two components. The bottom part consists of the comb drive actuator and electrode pads away from the fluidic components to prevent electrical contact. The top part is composed of a biocompatible SU-8 seal ring and capping silicon layer for containing the fluidic medium. The packaged devices are characterized using electrical capacitance measurements, microfluidic finite simulations, scanning electron microscopy, and contact angle measurements. These techniques verify the electrostatic actuation and successful stop valve performance of the devices. As microfluidic devices are increasingly used to perform biological experiments with living cells, this work suggests the possibility of adapting an integrated electrostatic microelectromechanical fluidic device to biomedical applications. Specifically the focus here is on in vitro cellular response to environmental mechanical stimulations. As part of an integrated hybrid device, the MEMS comb drive actuators are capable of applying controlled force and displacement to immobilized single cells or a small group of cells. Using a novel hydrophobic stop-valve architecture and selective surface functionalized method, it is demonstrated that MEMS device is very suitable for biochemical and mechanical analysis of biological samples. More importantly, the electrical and microfluidic packaging by flip chip bonding technique has been demonstrated successfully as a key-point to the development of integrated microfluidic systems for biological analysis.