Process development for the formation of post-bonding biorecognition layers in microfluidic biosensors

Formation of the biorecognition layers within microfluidic sensor channels must be done after the completion of the channel structure since these layers cannot withstand the wafer bonding temperature. We propose a new post-bonding immobilization process to prepare the enzyme layers within microfluidic channels of electrochemical biosensors. An array of Pt vertical electrodes is electroplated using a SU-8 mold. The cured SU-8 is then removed by plasma etching to expose the Pt electrode and to define the fluidic channel cavity simultaneously. An array of enzyme posts is formed on the Pt surface by either electropolymerizing or photopolymerizing enzyme precursor solutions injected into the channel. Very little report is available about the reactive ion etching (RIE) of SU-8 that is the most critical step in this process. A systematic investigation on the RIE of SU-8 is conducted to obtain the maximum etch rate (1.2 mum/min.) based on different combinations of parameters of CF₄ and O₂ gas flow, RF power and time.