Charging, long-term stability, and TSD measurements of SiO2 electrets

SiO₂ layers with thicknesses of 150 nm, 1 μm, and 2.5 μm were either thermally grown or made by chemical vapor deposition on silicon wafers. Negative and positive charging of the free SiO₂ surface was performed by means of liquid-contact, corona, and electron-beam methods. Partially penetrating electrons were used to charge the volume of 2.5-μm-thick SiO₂ layers. The good charge stability of negatively charged SiO₂ is demonstrated in isothermal measurements at room temperature and at 350°C as well as in TSD experiments. In the isothermal measurements, positively charged samples showed a somewhat faster decay than negatively charged ones. The decay curves of negatively charged samples at elevated temperature can be interpreted with a simple theory based on carrier drift and compensation by conductivity. In the measured TSD spectra, the difference between differently charged samples is that the main peak of a positively charged sample appears at a much lower temperature than the peak of a negatively charged one. Samples positively charged with the corona or liquid contact method also show lower peak performance temperatures than samples positively charged with the electron-beam method