INTEGRATED MOS CHEMICAL SENSORS UTILIZING INORGANIC INSERTION COMPOUNDS

SOLID STATE CHEMICAL SENSORS BASED ON CHEMICALLY ACTIVE THINFILMS INCORPORATED AS GATE METALS IN FIELD EFFECT TRANSISTORS WOULD BE USEFUL AS GAS ANALYZERS FOR ROBOTIC PLANETARY EXPLORERS AND CABIN/STATION ATMOSPHERES. THESE DEVICES CAN BE SUBJECT TO MICROMINEATURIZATION, AND INTEGRATED INTO CIRCUITS CONTAINING, ON A SINGLE CHIP, ALL CALIBRATION, ANALYSIS AND READOUT FUNCTIONS. THE PROBLEM WITH PRESENT SENSORS OF CONFIGURATION CATALYTIC METAL/SIO2/SI IS THEIR LACK OF SPECIFICITY AND LONG TERM INSTABILITY. WE PROPOSE TO INVESTIGATE NEW STRUCTURES WHERE AN INSERTION COMPOUND IS INTERPOSED BETWEEN THE METAL AND THE SIO2. THE INSERTION COMPOUND IS CHOSEN TO BE SELECTIVE OF MOLECULE OR ATOM SIZE OR STRUCTURE. THE INSERTION LAYERS OF INTEREST ALSO UNDERGO A CHANGE IN ELECTRICAL CONDUCTIVITY ON INSERTION OF THE SPECIES TO BE SENSED OR ITS BIPRODUCT INTO ITS CRYSTALLINE LATTICE. THESE REACTIONS ARE HIGHLY REVERSIBLE. THE RESULT IS A CHANGE IN THE CAPACITANCE OF THE METAL-INSULATOR-SEMICONDUCTOR STRUCTURE, WHICH IS ULTIMATELY REALIZED AS A CHANGE IN SOURCE-DRAIN CURRENT IN A FIELD EFFECT TRANSISTOR. IN PHASE I, IT IS PROPOSED TO SURVEY A VARIETY OF CATALYTIC METAL/INSERTION COMPOUND BILAYERS IN SIMPLE MIS DIODE STRUCTURES FOR CHEMICAL SENSITIVITY WITH IMPROVED SELECTIVITY, REVERSIBILITY AND STABILITY COMPARED TO PRESENT TECHNOLOGY. PHASE II WILL BE EMPLOYED TO STUDY THE FABRICATION OF DIODE ARRAYS AND THE USE OF PATTERN RECOGNITION LOGIC TO INTERPRET ARRAY RESPONSE FOR ANALYSIS OF GASEOUS MIXTURES.