Detachable Flexible ISFET‐Based pH Sensor Array with a Flexible Connector

Abstract Flexible sensors that can detect different types of stimuli simultaneously from any surface are attractive in many fields, including the Internet of Things. An important function of a flexible sensor sheet is multiple sensing without sacrificing mechanical flexibility, conformability, and device cost on the macroscale. This study proposes a macroscale detachable pH sensor array consisting of a disposable pH sensitive membrane sheet and a reusable flexible transistor array via a flexible electrical connector. Mechanical flexibility and stable electrical connection are realized by a soft Ag electrode and sticky polydimethylsiloxane/polyethylenimine layer for the connector. After laminating the two sheets, a fundamental study reveals a sensitivity of about 66.5 mV per pH. Although a small potential change in the pH membrane is observed as the temperature changes, the pH value can be monitored using the detachable flexible transistor‐based pH sensor sheet with a sufficient resolution. As a proof‐of‐concept for solution diffusion monitoring using the pH change, a 5 × 5 array sensor sheet is successfully demonstrated. The sensor array can measure the pH distribution with a different pH diffuses into a solution bath within a few seconds.