AN INTEGRATED CHEMICAL SENSOR WITH MULTIPLE ION AND GAS SENSORS

An integrated chemical sensor with multiple ion and gas sensors, composed of four ISFETs (pH, Na+, K+ and Cl-) and two gas sensors (P(O2) and P(CO2) on a 4 mm x 4 mm chip, is realized using semiconductor processing. The ISFETs are based on an Si3N4-gate ISFET, and use polymeric membrane except for the pH ISFET. The P(O2) sensor is a miniaturized Clark-type sensor, consisting of a Pt cathode and Ag/AgCl anode patterned by the lift-off process. The P(CO2) sensor is a miniaturized Severinghaus-type sensor using a pH ISFET. All of the ISFETs show sensitivities over 50 mV/decade, and a linear range between 1 x 10(-4) and 5 x 10(-1) mol/l. The sensitivities of the P(O2) and P(CO2) sensors are 0.35 nA/mmHg and 42 mV/decade, respectively, and their response times are 30 s and 1 min, respectively. The integrated chemical sensor with multiple ion and gas sensors could be used for clinical analysis.