Device Design: Stage 2

(Modified Microchannel Design)

Device Objective – To test the viability of a two-level passive micro-fluidic device Modifications 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 testing Device Logic – Five distinct fluid paths – 11 I/O – Two distinct channel levels – One interconnect level – One top cover level Interconnect Reservoir (I/O)

Device Design: Stage 2

(Modified Microchannel Design)

Device Geometry

– Chosen for process – compatibility Rectangular micro – – channels Square interconnects Circular reservoirs

Critical Dimension

PDMS Layer Height Micro-channel Width Interconnect Width Interconnect Depth Reservoir Diameter

Value

100 m m 500 m m 1000 m m 1000 m m 0.4 cm

Materials

– – SU-8 used as a mold for the PDMS layers All PDMS layers stacked on a Silicon substrate

Device Design: Stage 2

(Modified Microchannel Design)

Process Sequence 1.

Begin with four polished Si wafers 2.

3.

Spin SU-8 (negative photoresist) on the Si wafers and pre-bake at 95°C 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°C

Device 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 Layer

Device Design: Stage 3

(Pressure Actuated Valve Design)

Fluid Flow Modeling – Assumed fluid flow rate based on fluid velocity • Based on literature search: 1500 cm/minute = 2.5 E5 μm/sec • Fluid flow rate: 1.25 E 10 μm 3 /sec = 0.0125 cm following properties for the fluid flow path: • Fluidic resistance and pressure gradient: 3 /sec – Used the fluid flow rate calculated to determine the R = ΔP/Q [(N*s)/m 5 ] • Reynolds number: R e = ( r vD h )/μ • Velocity: v = Q/A • Cycle time t = Length/v

Device Design: Stage 3

(Pressure Actuated Valve Design)

Fluid Flow Modeling Results – R (circular cross section) = 8μL/(πr 4 ) • μ = fluid viscosity= 0.01 g/sec*cm • L = Length of channel • r = Radius of channel – R (rectangular cross section) ~ 12μL/(wh 3 ) • w = Width of the channel • h = Height of the Channel – Total Fluidic Resistance = R R + R M + R I + R V

R

R

Path Region Reservoir Micro-channel Interconnect Valve Total Path

+ R

M

+ R

I

Fluidic Resistance (g/sec*cm 4 )

33 9264000 24 3000000 12264057

+ R

V

Pressure Gradient (Torr)

0.00031

86.9

0.00023

28.13

115.03054

R

Total

Reynolds Number

4.0

41.7

12.5

48.1

Velocity (cm/sec) Time (sec)

0.1

20.7

25 1.3

125 0.15

0.016

0.00008

20.86608