MICROCHANNEL DESIGN ISSUES Susan Beatty Anne Samuel Kunal Thaker

PRELIMINARY OUTLINE Assumptions Control Level of Design General Functions/ Constraints Problems Device Fabrication Materials

ASSUMPTIONS/ CONTROL LEVEL Assume externally pumped fluid flow –No need to design on-chip pumping Neglect the bio-chemistry at the test sites –Only consider how the fluid is to be transported Must incorporate multi-level microfluidic channels Control Level –Passive Microfluidics (Simple channels) –Active Microfluidics (Channels + Active control devices to manipulate fluid flow through numerous possible paths)

GENERAL FUNCTIONS/CONSTRAINTS A problem and/or functions of a design must be established prior to the consideration of a possible final design –Two possible problems have been defined which incorporate the required assumptions Controllably route each of three input lines to any one of eight different test sites (located on two levels of microchanneling) –Requires multi-level micro fluidics –Requires controllable microfluidics (must be able to control which Input line is fed to which of the eight test sites)

GENERAL FUNCTIONS/CONSTRAINTS Route each of three Inputs(R,B,Y) to output each to two outputs original color will mix with one other color to create secondary colors

POTENTIAL PROBLEMS Junction –On/ off valve –1 or 2 devices Actuation –Electric –Pressure –Pressure and Electric Geometry of the junction

Major Device Fabrication Alternatives Surface Micromachining –Standard deposition and etching techniques to remove only a small fraction of the wafer volume –Potential for use of sacrificial layers in sequential SU8 deposition Bulk Micromachining –Removing bulk section of a wafer –Typically followed by wafer bonding for micro fluidics applications Mold –Use of a mold, on which multiple polymer layers can be cured and sequentially layered

Predominate Bio-Micro Fluidics Materials PDMS-Polydimethylsiloxane PMMA-Polymethylmethacrylate SU8 Pyrex Glass Silicon

Mask Design for Molds Spin SU8(negative resist) on Si wafers Expose using mask (channel mask and interconnect mask) Develop both molds

Mask Design for Molds Spin SU8(negative resist) on Si wafers Expose using mask (channel mask and interconnect mask) Develop both molds Bottom layer Middle layer top layer I/O

Mask Design From molds spin on PDMS less than the vertical dimension From channel mold make two layers From interconnect mold make one layer Stack three layers in channel, interconnect, channel (90 o rotation from first channel layer) order

Mask Dimensions For initial preliminary fabrication larger dimensions are better Approximate channel and interconnect width 150  m Channel length 45mm Reservoirs 300  m diameter (total length channel and reservoir 45.6mm Distance between channels 300  m Mold feature height 300  m