Realizing improved performance of metal-insulator-semiconductor diodes with high-k MgO/SiOx stack

Abstract

With the development of metal-insulator-semiconductor (MIS) field-effect transistors, the thickness of silicon dioxide (SiO2) must be scaled down; however, it causes a large gate leakage current and a low on/off current ratio. Magnesium oxide (MgO) exhibits a dielectric constant as high as 11.2, which is about three times larger than that (3.9) of SiO2; thus the thickness of MgO can be three times greater than that of SiO2 and significantly reduces the gate leakage current. Nevertheless, a large lattice mismatch (22.5%) exists between MgO and Si materials. In the study, the MgO/SiOx stack dielectrics are employed to suppress the large lattice mismatch and improve the performance of MIS diodes. The MgO/SiOx stack largely reduces the oxygen vacancy of MgO from 75% to 52.3%; also the fixed oxide charge and interface trap charge density are drastically decreased from 1.3 × 1012 and 1.8 × 1013 to 8.2 × 1011 cm−2 and 7.8 × 1012 cm−2eV−1, respectively. Compared to the MIS diodes with a single MgO, the MgO/SiOx stack dielectrics suppress the gate leakage current by about two orders in MIS diodes; hence the rectification ratio is enhanced from 114 to 1032 at ±2V. Band-diagram shows that Fowler-Nordheim tunneling occurs at a high reverse-bias voltage, and the barrier height increases from 0.18 to 0.42 eV in the MIS diodes with single MgO and MgO/SiOx stack dielectrics, respectively. Nevertheless, the MIS diodes operate through a direct tunneling at low reverse-bias voltages.