UV Ozone bonding of PDMS to glass, Si, and pnc-Si
Hi all,
After experimenting with UV ozone bonding of PDMS to glass, Si, and pnc-Si for the past few weeks with Mike, we have reached the following conclusions:
1. The bonding of PDMS to glass is always stronger than the bonding of PDMS to Si and pnc-Si, given that all receive same treatment of UV ozone bonding.
2. The longer the exposure of PDMS to UV ozone treatment, the more hydrophilic the surface of PDMS. This finding is consistent with Binh’s contact angle measurements (Binh is from the Lisa DeLouise Lab), in which 30 min of UV ozone exposure did not produce significant contact angle change (~ 100 degrees, still hydrophobic), but 1 hr of exposure did (70 degrees). We hypothesize that the higher the hydrophilicity of the PDMS surface, the more substantial the degree of surface modification (namely, the displacement of CH3 with OH on the surface of PDMS), the better the bonding to Si-based substrate.
Currently we have high yields of well-bonded substrate using the following protocol:
1. Treat PDMS with both the primary and the secondary UV ozone unit for 1 hr.
2. Flip the PDMS onto the Si-based substrate to be bonded.
3. Leave the PDMS/Si-based substrate overnight.
PS 1: The primary unit shines UV light on the PDMS to remove organic contaminants, and the secondary unit provides the ozone gas.
PS 2: Even though 1 hr of exposure to UV ozone significantly improve the bonding, the PDMS and Si and pnc-Si still did not bond within 30 min. So just to be safe we always leave the PDMS/Si-based substrate overnight.
Henry