Soft Lithography Practicum MAE 165 Spring 2010 Professor Madou Tuesday Group: Jeff Draper Amanda Evans David Szeto

Contents Background and introduction Background and introduction Process of soft lithography Process of soft lithography Advantages and disadvantages Advantages and disadvantages Future developments in soft lithography Future developments in soft lithography

What is Soft Lithography? Lithography = Greek for “to write in stone” Lithography = Greek for “to write in stone” Called “soft” because it is typically used on elastomeric materials such as PDMS (polydimethylsiloxane) Called “soft” because it is typically used on elastomeric materials such as PDMS (polydimethylsiloxane) The technique underwent rapid expansion from The technique underwent rapid expansion from Uses photolithography to make a mold for PDMS, which gets permanently bonded onto glass to make a microfluidic device. Uses photolithography to make a mold for PDMS, which gets permanently bonded onto glass to make a microfluidic device.

Lithography Process Step 1: Create PDMS Mixture PDMS stands for Polydimethylsioloxane PDMS stands for Polydimethylsioloxane Tape around the edges of the mask Tape around the edges of the mask Follow a 10:1 weight ratio of Silicon Elastomer Base to Silicon Elastomer Curing Agent Follow a 10:1 weight ratio of Silicon Elastomer Base to Silicon Elastomer Curing Agent –roughly 30g of base and 3g of curing agent A pipette is used to achieve desired weight of Silicon Elastomer Curing Agent A pipette is used to achieve desired weight of Silicon Elastomer Curing Agent Mix the PDMS gel vigorously to ensure equality throughout. Mix the PDMS gel vigorously to ensure equality throughout. –It should turn from a clear to a white color

Lithography Process Step 2: Pour onto Mold and De-Gas Pour mixture onto the photoresist mold Pour mixture onto the photoresist mold The mask was premade The mask was premade –Made by photolithography. The PDMS gel contained air bubbles which must be removed through a vacuum or/and through just letting it sit. The PDMS gel contained air bubbles which must be removed through a vacuum or/and through just letting it sit. –de-gas PDMS to protect integrity

Lithography Process Step 3: Cure the PDMS Cure the PDMS by heating it on a hot plate at 100C for roughly 10 min. Cure the PDMS by heating it on a hot plate at 100C for roughly 10 min. –Curing at a lower temperature, such as 60C, for much longer durations is ideal To help ensure equal heating, cover molds with tin foil to create a convection oven-like affect. To help ensure equal heating, cover molds with tin foil to create a convection oven-like affect. Once cured, pull it off of hot plate and let the PDMS cool Once cured, pull it off of hot plate and let the PDMS cool

Lithography Process Step 4: Cut and Mount PDMS After PDMS solidified and cooled, take a sharp knife and cut out PDMS parts. After PDMS solidified and cooled, take a sharp knife and cut out PDMS parts. –The desired part will be a negative of the mold. Mount the part to a glass slide, punch holes into desired location for fluid injection. Mount the part to a glass slide, punch holes into desired location for fluid injection. The process is then complete The process is then complete

Advantages/Disadvantages/Applications Advantages Advantages –Low cost –Fast production –Easily accessible –Does well with small details Disadvantages Disadvantages –PDMS is a soft structure –PDMS has a high thermal expansion Applications Applications –MEMS Devices –Sensors –Micoreactors –Microfluidics