Development of an electrostatic peristaltic gas micropump and nanochannel fabrication technique

Microfluidics refers to devices and methods for controlling and manipulating fluid flows with length scales less than a millimeter. By miniaturizing the size, microfluidic systems lead to many benefits including decreased cost in manufacturing, use, and disposal; reduced consumption of expensive samples and reagent; decreased time of analysis; reduced production of potentially harmful by-products; increased separation efficiency; and increased portability as in the case of a portable system. By taking advantage of microfluidic systems, many applications that utilize the micro-scale have been proposed such as micro total analysis systems (μTAS), implantable drug delivery system for high precision flow control, microchips integrated into computers to circulate coolant, as well as micro pumping for portable gas chromatography (GC) system. In a microfluidic system, the micropump is an essential component as an actuation sources to provide the driving force to mobilize fluids (liquid and gas) in a system. In this dissertation, development of an electrostatic valve-less peristaltic micropump for gas pumping is discussed. The micropump consists of a Si chamber and a flexible polymer diaphragm. Electrodes are patterned on a chamber floor and on a diaphragm. A 4-sequence signal made by a custom-made logic circuit makes a peristaltic motion of the diaphragm and pumps gas in one direction. A single chamber and a 4-electrode design reduce the dead volume of the micropump and eliminate a need of complicated structure such as valves. The maximum flow rate is about 40 µl/min at 95 V and 14 Hz operation. To improve the performance of the micropump, the chamber design and the electrode pattern are modified. First, a stepwise chamber fabricated by a 3D fabrication technique is utilized to reduce the dead volume and improve the backward flow control. The dead volume of the stepwise chamber is about 10-fold smaller and the flow rate increases about 30 % at low frequency regime (< 6 Hz) than a vertical chamber. And a multi-electrode design is utilized to increase the characteristic frequency and the flow rate. As the number of electrodes increases and the width of the electrodes get narrower, the chamber is divided into smaller cells and the characteristic frequency increase. By operating the device at higher frequency regime, the maximum flow rate increase up to 248 µl/min with 16 electrodes at 160 V and 1400 Hz operation. Finally, a double-sided chamber is utilized to increase the stroke volume with the same area of the chamber. The double-sided chamber has two fixed electrodes; one on the top chamber and the other on the bottom chamber. Although this design increases the stroke volume 4 times bigger than a single-sided chamber theoretically, the actual test results show about 9 times bigger flow rate. The power consumption per unit flow rate of a double-sided chamber is 67 µW/sccm, which is about 10-fold smaller than a single-sided chamber (870 µW/sccm.) The latter part of this dissertation is about fabrication of nanofluidics components including nanopores and nanochannels. A nanopore with an embedded electrode is fabricated on a 20 µm thick SU-8 layer by using a focused ion beam. The diameter of the nanopore is about 500 nm. 100 mM phosphate buffer is used as an electrolyte and transported by electroosmotic effect. Using a non-dimensionalized model, the flow rate of the electrokinetic flow is estimated as 0.47 mm/s at 5 V DC. In addition, a nanochannel fabrication method using detachment lithography is developed and discussed. Since a patterned adhesive is used as a spacer and a channel wall, this method can be applied to various material including Si, glass, and polymer. The low curing temperature (~140°C) enables integration of metal electrodes and surface treatment such as SAM layer inside the nanochannels before bonding. A microchannel/nanochannel device is fabricated using this technique and a simple filling test is performed