Stable DRIE-patterned SiO2/Si3N4 electrets

This paper presents a new manufacturing process aimed at making stable patterned electrets. Based on a preliminary DRIE step, these electrets have shown an excellent stability up to 4mC/m
²
; no charge decay has been observed in 450 days. The patterning pace has almost no effect on the electret stability down to 25μm and probably less. Stability tests have been performed at elevated temperatures (250°C during 2 hours), under X-rays and strong magnetic fields (Magnetic Resonance Imaging); again, no charge decay has been observed, validating their compatibility with medical implants and in particular with heartbeats vibration energy harvesters. A multi-point corona charger has also been manufactured to uniformly charge 200mm wafers at one time.