Multilayer MicrofluidicsProblem DefinitionProblem ScopeInitial Material ChoicesSlide 5Slide 6Project DevelopmentDevice Design: Stage 1 (Initial Microchannel Design Concept)Device Design: Stage 1 (Initial Microchannel Design Concept)Device Design: Stage 2 (Modified Microchannel Design)Slide 11Slide 12Slide 13Slide 14Stage 2 - 1st TrialStage 2 - 2nd TrialPhase 2 - 2nd Trial Successes & ProblemsPhase 2 – Experimental ProcedurePhase 2 – Channel LayoutProcessing ProblemsProcessing Problems ContinuedDevice Design: Stage 3 (Pressure Actuated Valve Test Design)Slide 23Device Design: Stage 3 (Pressure Actuated Valve Design)Device Design: Stage 3 (Pressure Actuated Valve Test Design)Slide 26Slide 27Slide 28Slide 29Alternative DesignsAlternative DesignsAlternative Designs (Piezoelectric)Future WorkSummaryMultilayer MicrofluidicsENMA490Fall 2003Brought to you by: S. Beatty, C. Brooks, S. Dean, M. Hanna, D. Janiak, C. Kung, J. Ni, B. Sadowski, A. Samuel, K. ThakerProblem DefinitionMotivation–BioMEMS research is growing rapidly, but restricted to single layer microfluidics–Development of a multilayer microfluidic design would increase flexibility Goal–Design, construct, and test a controllable microfluidic device with at least two fluid levels–Identify appropriate materials, processes, and device geometriesProblem ScopeRequirements–To make a two-level microfluidic device–To incorporate active control elementsConstraints–Assume external fluid control–Neglect biochemical reactions in channels–Keep design feasible for manufacturingInitial Material ChoicesDesired Characteristics•Ease of patterning and use in microfabrication•Chemically inert•Low Cost / Obtainable•Optically transparent•Specific Elastic modulus (flexible, rigid)Initial Material ChoicesSubstrate Material•Silicon•Relatively inexpensive•Commonly used in microelectronics•Well known properties and processing techniques•Pyrex•Transparent to visible light•Allows visual monitoring of micro channels•More expensive than siliconInitial Material ChoicesMicrochannel Material•Poly(dimethylsiloxane) or PDMS•Inexpensive•Poor surface adhesion – releasable from mold•Highly flexible •modulus of 2.5 MPa•SU-8•Is a photoresist•High aspect ratios obtainable•Good surface adhesion to silicon and pyrex•Very rigid – complementary to PDMS •modulus of 4000 MPaProject DevelopmentDefined ProblemDivided into research groups (BioMEMS, Materials, Devices, and Circuits)Developed Stage 1(Initial Microchannel Design Concept)Developed and tested Stage 2(Modified Microchannel Design)Modified design to integrate vertical vias for multilevel fluid flowDeveloped and tested Stage 3 (Final Design: Pressure Actuated Valve Design)Developed fluid control device to manipulate fluid flowSummarized manufacturing and experimental results of final designDevice Design: Stage 1(Initial Microchannel Design Concept)•Objective–To create an initial design for a multilayer micro fluidic device•Initial design elements–90o orientation of fluid layers–Vertical interconnects at channel intersections–Each layer has same design- reduces number of molds–Versatility of fluid pathsBottom layerMiddle layerTop layerI/OI/ODevice Design: Stage 1 (Initial Microchannel Design Concept)•Materials –Stackable PDMS layers–Silicon substrate–SU-8 molds•Processes–Create a channel mold and an interconnect mold using SU-8 –Create PDMS layers from SU-8 mold: two layers from channel mold, one interconnect layer–Stack layers on substrate starting with a channel layer, interconnect layer and second channel layer at 90o orientationDevice Design: Stage 2(Modified Microchannel Design)Objective–To test the viability of a two-level passive micro-fluidic deviceModifications from Stage 1–Moved reservoir positions to fit existing packaging–Created discrete flow paths to test flow on individual layers and between layers–Increased all dimensions to facilitate fabrication and testingDevice Logic–Five distinct fluid paths–11 I/O–Two distinct channel levels–One interconnect level–One Top Cover levelDevice Design: Stage 2(Modified Microchannel Design)Device Geometry–Chosen for process compatibility–Rectangular micro-channels–Square Interconnects–Circular reservoirsMaterials–SU-8 used as a mold for the PDMS layers–All PDMS layers stacked on a Silicon substrateCritical DimensionValuePDMS Layer Height100m Micro-channel Width500m Interconnect Width1000m Interconnect Depth1000m Reservoir Diameter0.4 cmDevice Design: Stage 2(Modified Microchannel Design)Process Sequence and Mask Design1. Begin with four polished Si wafers2. Spin SU-8 (negative photoresist) on the Si wafers and pre-bake at 95°C3. Align each of the four wafers with one of the four masks shown below and expose the SU-8 to ultraviolet light, then post-bake at 95°C 4. Develop the SU8 so that the unexposed areas are removed–Results in four distinct SU8 molds Micro-Channel Layer 1 Interconnect Layer Micro-Channel Layer 2 Top Cover LayerDevice Design: Stage 2(Modified Microchannel Design)5. Spin PDMS on the SU8 molds less than the vertical dimension of the SU-8 protrusions–Mix PDMS (Sylgard 184, Dow-Corning) 10:1 with curing agent–Spin on PDMS–Dip the Si wafer in a sodium dodecyl sulfate(SDS) adhesion barrier and allow it to dry naturally–Bake in box furnace for 2 hours at 70°C6. Delaminate and stack all four PDMS layers in the following order: Micro-channel Layer 1, Interconnect Layer, Micro-channel layer 2, Top Cover Layer Micro-Channel Layer 1 Interconnect Layer Micro-Channel Layer 2 Top Cover LayerDevice Design: Stage 2(Modified Microchannel Design)Final Expected Result:Stage 2 - 1st TrialProblems•Thickness of PDMS layers•Interconnects •Delamination•Air bubblesStage 2 - 2nd TrialFabrication•Successfully made and aligned four layers•Layers had very few defects•All interconnects joined two different layers•Entire wafer looked very good- no rough edges, no air bubbles between layers, no cratersPhase 2 - 2nd TrialSuccesses & Problems•Liquid to flow in all channels–all the way through 2 out of 5 channels•Tracked fluid flow using bright food coloring•Tested the effects of vertical interconnects•No capillary action–had to use pressure from syringe•problems•Pressure caused delamination•Effects of vertical interconnectsPhase 2 – Experimental