Fabrication and characterization of micro dissolved oxygen sensor activated on demand using electrolysis

Abstract

This paper presents a novel dissolved oxygen (DO) sensor that can be activated on demand by explosion of a thin SiO2 film from electrolysis. The proposed sensor is composed of (1) three electrodes (working, counter, and reference electrodes) for the measurement of the concentration of oxygen in water, (2) a solid electrolyte covering the three electrodes, (3) a polydimethylsiloxane (PDMS) cavity, and (4) a sensor cap, which is a thin SiO2 film with patterned electrodes (cathode and anode) for electrolysis. The working and counter electrodes are patterned using Cr/Au (100Å/1000Å). The reference electrodes are patterned using Ti/Ag (100Å/1000Å), followed by chlorination to form Ag/AgCl. Using cyclic voltammetry (CV) and chronoamperometry measurements, the fabricated DO sensor was activated by explosion of the thin SiO2 film of the sensor cap. Before the voltage was applied to the electrodes (cathode and anode) at the sensor cap for the electrolysis, the proposed DO sensor showed a current of 600nA at a voltage of −900mV by CV measurement between the working and counter electrodes. After the voltage was applied to the electrodes at the sensor cap for the electrolysis, the proposed DO sensor showed a current of 1.8μA at a voltage of −900mV by CV measurement. For chronoamperometry, the proposed DO sensor was subjected to electrochemical measurements with a fixed voltage of −900mV vs. Ag/AgCl for 2000s. Applying the voltage for electrolysis, the current of the proposed DO sensor between the working and counter electrodes was increased by explosion of the SiO2 film, which is the sensor cap.