Improvement of the reliability of potassium-ion electrets thorough an additional oxidation process

Abstract

Potassium-ion electrets, which mainly consist of amorphous silica and permanently store negative charge, are vital elements of small autonomous vibration-powered generators. However, negative charge decay is sometimes observed to cause issues for applications. In this study, we propose an improved guideline for the fabrication of potassium-ion electrets by first-principles calculations based on density functional theory, which shows that yield reduction can be suppressed by additional oxidation. Moreover, we experimentally confirm that the additional oxidation step effectively extends the lifetime of potassium-ion electrets.

MEMS Electrostatic Energy Harvester Developed by Simultaneous Process for Anodic Bonding and Electret Charging

“…When polarizing the electret film in this work, on the other hand, potassium ions are displaced to the cathode side using the physics similar to that of anodic bonding as documented in detail elsewhere. (37)(38)(39) These two processes are substantially the same from an ion-migration viewpoint. We only need to figure out a total process so as not to mitigate the built-in potential of anodic bonding during the subsequent electret formation.…”

“…In step (C), to form the silicon oxide film including potassium ions, the surface of the silicon substrate is thermally oxidized for 8 h at a furnace temperature of 1000 ℃ using a water bubbler containing an aqueous solution of potassium hydroxide (KOH); the detailed process has been reported elsewhere. (37)(38)(39) In step (D), the SiN patterns on both sides of the silicon substrate are removed by RIE, partially exposing the silicon surface for later use. In step (E), a 500-µm-thick Tempax glass is prepared by sand blast to form a 160-µm-deep recess.…”