Enhanced tunneling in stacked gate dielectrics with ultra-thin HfO2 (ZrO2) layers sandwiched between thicker SiO2 layers

There has been a search for alternative dielectrics with significantly increased dielectric constants, K, which increases in physical thickness proportional to K, and therefore would significantly reduce direct tunneling. However, increases in k to values of 15–25 in transition metal and rare earth oxides are generally accompanied by decreases in the conduction band offset energy with respect to Si, EB, and the effective electron tunneling mass, meff, which mitigate gains from increased thickness. A novel technique, based on stacked dielectrics, is used to obtain the tunneling mass-conduction band offset energy product. When combined with optical measurements of tunneling barriers, this yields direct estimates of the tunneling mass.