Active Microfluidic Components with Semiconductor Technology Compatible Materials and Methods

Lab-on-chip and micro total analysis systems have attracted great interest from both research communities and the commercial sectors over the past 30 years after the first introduction of microfluidics as an individual subject in the 1980s. A typical integrated active lab-on-chip device consists of fluidic parts represented by micropumps and microvalves to precisely drive and control the routing, timing, and mixing of fluids, and of non-fluidic parts represented by electrical and optical components for device control and extra functionalities. Firstly developed on silicon-based microelectromechanical systems, the complexity and energy efficiency for active microfluidic devices have been constantly improved over the years. However, the silicon-based technology route is less preferred when a large vibrating amplitude is needed for meaningful microfluidic operations, apart from its high cost per unit area. Developed for decades, Polydimethylsiloxane (PDMS)-like materials and the corresponding soft-lithography method have enabled fast prototyping and have allowed boosting the actuating amplitude by orders of magnitude compared to silicon-based devices. Nevertheless, the integration of PDMS-like polymers in industrial semiconductor environments is undesirable for mid and large-scale production.

In this thesis, we evaluate potential solutions to enhance the industrialization of microfluidics. Particularly, we focus on the development of two indispensable active microfluidic components, integrated active micropump and active microvalve, with semiconductor technology compatible materials and fabrication methods. Two different semiconductor-grade polymers, polyimide and polyisoprene-based elastomer, are utilized to build up membrane-based active microfluidic components. Based on three actuation methods, piezoelectric, pneumatic and electrostatic actuators are fabricated on glass substrates using standard cleanroom facilities and fabrication environment.

Specifically, a piezoelectrically driven active micropump is developed with polyimide as the vibrating membrane. We explore the integration method of applying a thin layer of polyimide to a microfluidic layer with the help of different laser sources, as well as the design rules of efficient micropump geometries, especially the fixed geometry nozzle/diffuser elements used as the fluid rectifier to regulate flow direction.

To cope with the need of pinching a 30 μm deep microfluidic channel for the active microfluidic application, different elastomer candidates featured with low Young’s modulus in the range of MPa are screened, with a particular focus on the chemical compatibility to several acids and solvents to enable the lithography based metal patterning. Apart from developing the route to integrate the thin layer elastomeric film to a microfluidic channel layer, we investigate the direct metallization possibility of the elastomer using conventional physical vapor deposition and lithography-based patterning methods by looking into the theoretical and experimental optimization of metal/polymer bi-layer stack. A hybrid electrostatic-pneumatic active microvalve configuration is proposed and developed.

By carefully choosing the proper driving mechanisms, either integrated electromechanical couplings such as piezoelectric or electrostatic driving methods, or external driving forces such as a pneumatic source, we successfully demonstrate proof-of-concept devices for three types of active microfluidic transducers that are fabricated in a standard cleanroom environment. The supreme compatibility of the proposed materials and processing methods to semiconductor and flat panel display environment paves the way for future industrialization of lab-on-chip systems towards a higher degree of integration and the possibility for mass production.