Fig. 2: Fabricating process for the as-proposed electrochemical free chlorine sensor.

a A clean silicon wafer. b oxidation process. c Preparation of BDD film by FHCVD. d Preparation of aluminum mask by a lift-off process. e Preparation of BDD electrode by O-RIE process. f Removing Al mask. g Preparation of Pt electrode by sputtering process. h Wet etching of silicon. i Preparation of Ag/AgCl electrode. j Bonding silicon wafer and glass wafer