Multilayer MicrofluidicsProblem DefinitionProblem ScopeInitial Material ChoicesSlide 5Project DevelopmentDevice Design: Stage 1 (Initial Microchannel Design Concept)Device Design: Stage 1 (Initial Microchannel Design Concept)Device Design: Stage 2 (Modified Microchannel Design)Slide 10Slide 11Slide 12Processing ProblemsStage 2 (Experimental Results: Trial 1)Stage 2 (Experimental Results: Trial 2)Stage 2 (Test Results: Trial 2)Stage 2 (Test Procedure)Stage 2 (Channel Layout)Device Design: Stage 3 (Pressure Actuated Valve Test Design)Slide 20Device Design: Stage 3 (Pressure Actuated Valve Test Design)Device Design: Stage 3 (Pressure Actuated Valve Design)Slide 23Slide 24Stage 3 (Fabrication Results)Alternative Valve DesignsAlternative Valve DesignsFuture WorkSummaryWe learned to work as a team!Multilayer 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 ScopeDesign Requirements–Two-level microfluidic network–Active control elementsMaterial Requirements–Ease of patterning and use in microfabrication–Chemically inert–Low Cost / Obtainable–Optically transparent–Specific Elastic modulus (flexible, rigid)Constraints–Assume external fluid control–Neglect biochemical reactions in channels–Keep design feasible for manufacturingInitial 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 moldsProcesses–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)Device 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 levelReservoir (I/O)InterconnectDevice 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 Dimension ValuePDMS Layer Height100m Micro-channel Width500m Interconnect Width1000m Interconnect Depth1000m Reservoir Diameter 0.4 cmDevice Design: Stage 2(Modified Microchannel Design)Process Sequence 1. 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 four masks 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 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°CDevice Design: Stage 2(Modified Microchannel Design)6. Delaminate and stack all four PDMS layers in the following order: Micro-channel Layer 1, Interconnect Layer, Micro-channel layer 2, Top Cover LayerProcessing Problems•Substantial amount of cracking in SU-8 layer•Layer assembly problems–Razor blade/ tweezers method–Layer thickness–Wrinkles–Air pockets•Feature alignment–Extremely difficult–InaccurateCracks in reservoir region of SU-8 moldStage 2 (Experimental Results: Trial 1)Problems•Thickness of PDMS layers•Interconnects •Delamination•Air bubblesStage 2 (Experimental Results: Trial 2)Improvements•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 cratersStage 2 (Test Results: Trial 2)Problems•No capillary action–had to use pressure from syringe•Pressure caused delamination•Functionality of vertical interconnectsSuccesses•Liquid flow in all channels–Completely through 2 out of 5 channels•Tracked fluid flow using bright food coloring•Tested the effects of vertical interconnectsStage 2 (Test Procedure)Stage 2 (Channel