Highly Sensitive Charge-Couple Device-based Flexible pH Sensor for Wearable Health Care Application

Abstract

This study reports a highly sensitivity wearable flexible pH sensor using a charge-couple device (CCD) structure. Multi-cycle charge transfer and accumulation depending on pH value realize higher sensitivity than that of the Nernst theory (i.e. 59 mV/pH at room temperature (R.T.)). One difficulty to form the CCD structure on a flexible film is the semiconductor junction due to thermal budget issue for doping injection into semiconductor films. To address this, Schottky junction controlled by an external gate bias is proposed. By optimizing the structure and fabrication process, flexible CCD-based pH sensor is successfully demonstrated. In addition to the study of its fundamental characteristics, real-time sweat pH monitoring is carried out as the first proof-of-concept by attaching the device on an arm. The results show that this flexible pH sensor would be helpful to detect a biological information from sweat.