Spray-coated electret materials with enhanced stability in a harsh environment for an MEMS energy harvesting device

Anxin Luo,Yulong Zhang,Xiaoqing Zhang,Yixin Xu,Fei Wang,Yan Lu,Mi Zhang

doi:10.1038/s41378-021-00239-0

Abstract

The charge stability of electret materials can directly affect the performance of electret-based devices such as electrostatic energy harvesters. In this paper, a spray-coating method is developed to deposit an electret layer with enhanced charge stability. The long-term stability of a spray-coated electret is investigated for 500 days and shows more stable performance than a spin-coated layer. A second-order linear model that includes both the surface charge and space charge is proposed to analyze the charge decay process of electrets in harsh environments at a high temperature (120 °C) and high humidity (99% RH); this model provides better accuracy than the traditional deep-trap model. To further verify the stability of the spray-coated electret, an electrostatic energy harvester is designed and fabricated with MEMS (micro-electromechanical systems) technology. The electret material can work as both the bonding interface and electret layer during fabrication. A maximum output power of 11.72 μW is harvested from a vibrating source at an acceleration of 28.5 m/s2. When the energy harvester with the spray-coated electret is exposed to a harsh environment (100 °C and 98% RH), an adequate amount of power can still be harvested even after 34 h and 48 h, respectively.

Highlights

Electret materials have been used in various fields, such as pressure sensors, barometers and acoustic transducers in microphones[1,2,3,4,5], thanks to the quasipermanent electric charge feature in electrets
The harvested power from vibration is proportional to the square of the charge density in electret materials[10], which might decay once exposed to harsh environments at high humidity levels or high temperatures
Microscopic photographs of the bubbles and scanning electron microscope (SEM) images of the particles in the spray-coated electret layer are shown in Fig. 1b, c, respectively

Summary

Introduction

Electret materials have been used in various fields, such as pressure sensors, barometers and acoustic transducers in microphones[1,2,3,4,5], thanks to the quasipermanent electric charge feature in electrets. The harvested power from vibration is proportional to the square of the charge density in electret materials[10], which might decay once exposed to harsh environments at high humidity levels or high temperatures. It is necessary to promote the charge stability of electret materials for improving the performance of electrostatic energy harvesters.

Results

Conclusion