Low Temperature “click” Wafer Bonding of Off-stoichiometry Thiol-ene (oste) Polymers to Silicon

INTRODUCTION Common bonding techniques for lab-on-chip (LOC) microfluidic devices require surface bio-functionalization to be performed in-situ after the chip has been packaged due to the bio-incompatible features of the bonding technique, including high temperature requirements (e.g. thermal bonding of thermoplastics), use of organic solvents (e.g. PMMA bonding) or plasma activation (e.g. PDMS bonding). This severely limits widespread use of LOC’s since functionalization after packaging is a slow and expensive chip-level processes compared to standard batch surface functionalization such as array spotting [1]. One suggested method that enables surface modification before bonding is the use of patternable liquid UV-curable glue as an intermediate layer [2]. While being a biocompatible and low-temperature process, a liquid glue layer risks blocking the channels upon solidification. Another proposed method involves a thiol-ene polymer formulation (NOA 81) in which one substrate contains a thin layer of uncured polymer material that is subsequently UV-polymerized [3]. These surfaces however, have a short shelf life and the bond to silicon substrates is based on adhesive forces, not covalent bonds, which make them vulnerable to solvents. We recently introduced a family of OSTE (Off-Stoichiometry Thiol-Ene) polymers, compatible with the soft-lithography process and developed specifically for lab-on-chip applications to replace PDMS [4,5]. In contrast to PDMS, these novel OSTE-polymers feature tunable mechanical properties, excellent chemical barrier properties and a large number of chemically reactive anchors (thiol or allyl) at the surface after polymerization.