Preparation and Characteristic Evaluation of Silica-agglomerate Electret with Ultra-thin PTFE Layer for Ultrasonic Sensor

Abstract

Influence of formation of silica agglomerates on a ultra-thin fluororesin electret on the characteristics of the charge-retention and the aero-ultrasonic sensor was investigated. The ultra-thin PTFE layer (thickness was 2.8 µm) was obtained by spin-coating and silica agglomerates were formed by spraying droplets of colloidal silica. The formation of PTFE/silica agglomerate composite layer on PTFE layer resulted the larger and more flat agglomerates than the formation of single layer of silica agglomerates on the PTFE layer. The measurement of the charge retention of the obtained electrets after 24 h at RT and at 250℃ revealed that the formation of PTFE/silica-agglomerate composite layer on the ultra-thin PTFE layer enhanced the charge retention. Furthermore, the electret condenser sensor (ECS) fabricated using the silica-agglomerate electret on the ultra-thin PTFE layer exhibited the excellent sensitivity and high resonance frequency compared with conventional ECS with PFA layer (thickness was 12.5 µm).