Flexible Dual-Modal Sensors Based on Single-Crystalline Silicon Membranes for Continuous Monitoring of Photoplethysmography and Skin Temperature

Abstract

Flexible dual-modal sensors that can monitor two signals play important roles in biomedical applications, along with the recent progresses of epidermal or bioimplantable electronic devices with diagnostic or therapeutic functionalities. However, techniques for flexible dual-modal sensors mainly rely on integrating multiple sensing units on a platform, thus inducing extra costs and complexities associated with the fabrication and data processing. In this paper, a flexible dual-modal sensor is presented, which contains only one sensing unit, i.e., single-crystalline silicon-based diode, for the real-time, independent, and continuous monitoring of light and temperature. Operation modes for photodetection and temperature sensing of the flexible dual-modal sensor are switchable by controlling the biased condition. In addition, both experimental results and theoretical calculations indicate that the crosstalk between light and temperature can be conveniently decoupled by short-circuit current and forward current of silicon-based diodes. Finally, the flexible dual-modal sensor is implemented as a platform to realize the continuous monitoring of photoplethysmography (PPG) and skin temperature of fingertips. These presented results offer paths to the construction of multifunctional, flexible bioelectronic devices or integrated platforms for biomedical uses.

Keywords: Silicon membranes; decoupling mechanism; epidermal electronics; flexible dual‐modal sensors; health monitoring.