The plasma surface treatment and ion implantation were utilized to improve the stability of charge storage in the SiO2 film electret. It was found that the SiO2 films treated by argon plasma with the arcing at 700 V for 15 min, or implanted by 150 keV (kilo electron volt) Ar+ with a dose of 2 x 10(11) cm(-2), after being negatively charged, showed a remnant negative potential as large as 90% of the primary value after being stored in a glass container with desiccant for 10 days. It was also found that after being negatively charged at room temperature and aged at 200-350 degrees C for several times, the SiO2 films implanted by 150 keV Ar+ had a relatively high remnant potential and it did not decay significantly even after being heated at the aging temperature of 200-350 degrees C in room atmosphere for 60 min. 2005 Elsevier B.V. All rights reserved.