Charge Retention in a Patterned ${\rm SiO}_{2}/{\rm Si}_{3}{\rm N}_{4}$ Electret

The electret consisting of a Si₃N₄ pattern on a SiO₂ layer is studied. A charge pattern on 1.3 μm-wide Si₃N₄ electret lines is successfully formed with a voltage of 80 V between charged pattern and substantially discharged SiO₂. The method for making a charge pattern is optimized for reaching the highest voltage on narrow lines. A yearlong sample aging on open air shows that there is no dependence of charge retention on line width within the 1 cm^-1.3 μm range. Considering the decay of surface potential during 1 year, the estimated charge lifetime in the patterned electret exceeds 75 years.