Properties of SiO2 electret films charged by ion implantation for MEMS-based energy harvesting systems

This paper presents the results of charging SiO2 thin film electret by ion implantation. A maximum charge density of 16 mC m(-2) has been shown using 500 nm thermal oxide. Charge is reproducible and stable in time. Two types of ions were used for ion implantation: phosphorus (P+) and boron (B+). Directly after implantation, it was found that charging with B+ resulted in more stable surface potential compared to charging with P+, but after 50 days the difference is negligible. The extrapolated long-term stability of SiO2 electrets charged by ion implantation is around 1 year. SiO2 is a promising electret for energy harvesting, which can be charged in a reproducible and stable way by ion implantation. The results are compared to corona charging of SiO2. The developed process can be used to realize vibration-based capacitive energy harvester systems using CMOS-compatible processes.