Suspended channels and channel actuators for microfluidic application

We have developed a novel process for building microfluidic systems that stresses Access, Integration, Isolation, and Motion. It is the foundation for building systems that include electronics, optics, thermal control, and other microelectromechanical structures for containment, control and sensing of fluids.;The Suspended Channel Process (SCP), as it is called, allows fabrication of channels suspended above the substrate as well as channels embedded in the substrate. Suspending the channels above the substrate---in essence, removing the substrate from around the channels---gives an unparalleled degree of access to the fluids within the channels. This includes improved access electrically, optically, and physically, opening the way for integration of techniques utilizing electric fields and optics. It also increases the ability to thermally isolate and locally probe regions.;The process builds upon SCREAM, a technology underlying a wide variety of analytic and high performance microelectromechanical systems (MEMS). This allows us to integrate and apply a broad range of devices and capabilities already developed and characterized. Integration of a well-studied torsional system and integration of a method for making electrical isolation segments are two examples that are discussed.;The process itself is straightforward, can take as few as two masks, and allows a high degree of control over the dimensions of the channels. By design, the core of single crystal silicon (SCS) beams can be removed leaving a hollow interior that can carry fluids. Thus, portions of actuators or entire actuators can contain and carry fluids. The result is total integration of channels with actuators and other high aspect ratio structures. The ability to move and vibrate channels is one consequence. With it, lateral and torsional actuators incorporating moving channels have been built, as well as systems combining channels with heaters, diodes, resistors, and capacitors.;To illustrate the process, we have designed and built a viscosity-sensitive torsional oscillator. Experiments have been performed relating the damping of the system to the fluid's viscosity. Two theories for modeling this fluid-structure interaction are discussed.