Charge storage characteristics of MIS structures employing dual-insulator composites of HfO2–SiO2 and SrTiO3–SiO2

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Abstract
Two MIS versions have been fabricated employing rf‐sputtered dual insulator structures comprised of 1000 Å HfO2‐20 Å SiO2 and 1000 Å SrTiO3‐20 Å SiO2. The high‐dielectric‐constant insulators in combination with a 20‐Å layer of silicon dioxide permit the transfer of charge by tunneling into traps at the dual‐insulator interface to occur at considerably lower voltages than comparable structures employing silicon nitride or aluminum oxide. It was found that trap density and, hence, the degree of flat‐band voltage shift could be altered by sputtering 50‐Å layers of selected materials at the insulator‐SiO2 interface. The devices employing hafnium dioxide show promise in an application as a nonvolatile electrically alterable memory element. Although the strontium titanate devices exhibit a low threshold voltage for onset of charge transfer, the charge retention characteristics are poor.

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