ON-CHIP FERROELECTRIC ENERGY STORAGE CAPACITORS FOR SILICON SOLAR CELLS

WHEN A SOLAR CELL ARRAY IS DESIGNED TO POWER AN ELECTRIC MOTOR CAR OR IS USED FOR A SPACE MISSION, A FAVORABLE POWER-TO-WEIGHT RATIO IS IMPORTANT FOR ITS ENERGY STORAGE UNIT. COMPARED WITH BATTERIES, THE MOST FREQUENTLY USED ENERGY STORAGE TECHNOLOGY, A THIN FILM FERROELECTRIC (FE) CAPACITOR BANK, CAN BE OF LOWER COST AND YIELD A HIGHER POWER-TO-WEIGHT RATIO. IN SINGLE CRYSTAL FORM, FE MATERIALS HAVE SUPERIOR DIELECTRIC PROPERTIES, SUCH AS A LARGE DIELECTRIC CONSTANT AND A HIGH BREAKDOWN VOLTAGE. THICK FILMS OF FE MATERIALS HAVE ALREADY BEEN USED IN METAL-INSULATOR-METAL (MIM) CAPACITORS AND ARE WELL CHARACTERIZED. THE TECHNICAL CHALLENGE IN THIS PROJECT WILL BE TO GROW HIGH QUALITY FERROELECTRIC THIN FILMS WITH LARGE DIELECTRIC CONSTANT AND LOW LEAKAGE CURRENT ON SILICON (SI) SUBSTRATE. IN PHASE I, A MULTILAYER MIM CAPACITOR ENERGY STORAGE UNIT FOR SI SOLAR CELLS WILL BE DEVELOPED. THIS UNIT CAN BE DEPOSITED AT THE BACK OF A SOLAR CELL WAFER TO PROVIDE ON-CHIP ENERGY STORAGE. THIS STACKED CAPACITOR UNIT OFFERS EASE OF FABRICATION AND AVOIDS THE VARIOUS LEAKAGE MECHANISMS FOUND IN TRENCH STRUCTURES. ITS STRUCTURE IS COMPACT AND SHOULD BE SUITABLE FOR WAFER SCALE PRODUCTION (COMPATIBLE WITH THAT FOR SI SOLAR CELLS).