Single-crystalline group III-nitride (III-N) thin films are very promising by their excellent piezoelectric properties for various industrial fields and biomedical areas due to their advantages. Piezoelectric pressure sensors (PPSs) using III-N thin films have the merits of remarkable biocompatibility, mechanical, chemical and thermal stability, and simple fabrication without extra electric poling. In order to fabricate the flexible PPSs (F-PPSs), well-known layer-transfer method was applied to III-N thin films.

We recently demonstrated high electromechanical conversion efficiency and mechanical flexibility from single-crystalline Group-III-nitride (III-N) semiconductor thin films which already possess excellent properties of thermal and chemical stability, no harm to human body and environments, and radiation hardness. The properties make the film ideal choice of piezoelectric devices that are flexible, biocompatible, efficient, and robust to overcome the limitations of the existing piezoelectric devices. In this study, III-N thin-film based flexible piezoelectric sensors (FPS) was developed for the applications in personal-healthcare monitoring system and extreme environments.

First, this study describes the FPS as a pressure sensor in harsh conditions. The sensor is attached on a diaphragm at high temperatures, which is connected to high pressure. The output voltages are measured and analyzed with temperature using intrinsic carrier concentration and Young’s modulus effects.

Second, the arrayed-FPSs are attached on human face (temple area) and the response signals are collected for eye blinking and eyeball movements. Abnormality of them is related to brain disorders.

Third, the surface-functionalized FPS is described to measure the concentration of the human stress hormone. Cortisol from the sweat of the stressful human body is monitored by the change of resonant frequency. The sensor show excellent sensitivity and selectivity.

Overall, this study includes a complete set of results from materials, device manufacturing techniques, electromechanical researches, simulations and theoretical calculations to illustrate associated novel aspects in F-PPSs using single-crystalline III-N thin films.