Solid state electrochemical sensors

Abstract

A solid state electrochemical sensor includes a conductive base layer which supports a chemically sensitive membrane, a guard ring layer located below the base layer and insulated therefrom by a dielectric insulator ring layer. The two ring layers define a central hole through which access to the underside of the base layer is provided. The side wall of the hole is coated with a dielectric oxide layer and a metal conductor is laid on the oxide layer and is ohmically bonded to the base layer. A second dielectric oxide layer covers the metal conductor and a metallic inner guard layer covers the second dielectric oxide layer and is in ohmic contact with the guard ring layer. A CMOS buffer amplifier (voltage follower amplifier) is formed on the lower surface of the guard ring layer. The input to the buffer amplifier is coupled to the conductor in ohmic contact with the base layer and the output of the buffer amplifier is coupled to the guard ring. The guard ring and the metallic inner guard layer form an active shield (guard) around the conductor which transmits the potential of the membrane to the amplifier. The amplifier powers the guard to the same potential as the membrane which insures that the membrane potential is read properly without corruption due to capacitive loading by parasitics, shorting caused by leakage currents, or capacitively coupled noise.