REACTIVE GAS JET DEPOSITION OF SILICON NITRIDE THIN FILMS FOR PASSIVATION OF NEURAL MICROPROBES

THE OBJECTIVE OF THIS PROJECT IS TO TEST THIN-FILM SILICON NITRIDE, DEPOSITED BY "REACTIVE" GAS JET DEPOSITION (GJD), AS A WATER-IMPERMEABLE, PASSIVATING LAYER FOR IMPLANTABLE NEURAL MICROELECTRODES AND CONNECTING CABLES. TO BE SERVICEABLE IN NEUROLOGICALLY HANDICAPPED SUBJECTS, SUCH MICROPROBES REQUIRE LONG-TERM PROTECTION FROM REACTIVE EXTRACELLULAR FLUIDS; SILICON NITRIDE FILMS ARE EXCELLENT BARRIERS TO WATER AND ALKALINE IONS. GJD USES SUPERSONIC GAS JETS TO CONVECT SPECIES TO UNHEATED SUBSTRATES WHERE DEPOSITION CAN OCCUR AT NEAR ROOM TEMPERATURE. THIS IS USEFUL FOR ENCAPSULATING MICROPROBE ASSEMBLIES WHERE MATERIALS OF LOW THERMAL STABILITY, E.G., POLYMERS, ARE PRESENT. SILICON NITRIDE FILMS MADE BY LOW-TEMPERATURE REACTIVE GJD ARE FOUND TO BE HARD, ADHERENT,PINHOLE FREE, AND OF HIGH BREAKDOWN STRENGTH. SILICON NITRIDE FILMS WILL BE DEPOSITED ON TEST STRUCTURES THAT SIMULATE THE TOPOGRAPHICAL AND CHEMICAL FEATURES OF MICROPROBES AND THEN WILL BE TESTED FOR CHEMICAL, ELECTRICAL, AND MECHANICAL STABILITY IN IONIC SOLUTION. POSITIVE RESULTS IN PHASE I WILL BE A PRELUDE TO THE COATING AND TESTING OF ACTUAL MICROPROBE ASSEMBLIES IN PHASEII. REACTIVE GJD IS EASILY ADAPTED AS A COMMERCIAL ENCAPSULATION PROCESS.