As the size of transistors continues to scale down, the use of conventional SiO2 as a gate dielectric material is approaching physical and electrical limits. The principal limitation is high leakage current due to quantum mechanical tunneling of carriers through the thin gate oxide. To reduce gate leakage current, high dielectric constant (high κ) gate materials, such as HfO2, ZrO2 and Al2O3 and their silicates, have drawn a great deal of attention in recent years. Due to their high dielectric constants, high k gates can be made much thicker than SiO2 while achieving the same gate capacitance. The result is lower leakage current—sometimes, several orders of magnitude lower.
This article by Keithley Application Engineers examines reasons and methods to qualify high k materials.