Single-crystalline group III-nitride (III-N) thin films have excellent piezoelectric properties, making them very promising for various industrial fields and biomedical areas. 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. III-N thin-film based flexible piezoelectric sensors (FPS) have been developed for the applications in personal-healthcare monitoring system and extreme environments. These sensors are ideal for overcoming the limitations of existing piezoelectric devices as they are flexible, biocompatible, efficient, and robust.

In a recent study, high electromechanical conversion efficiency and mechanical flexibility are demonstrated 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 FPS is used as a pressure detector for biomedical approach. The sensors are attached to several spots of human body, such as forearm, face and forehead to obtain signal from each part.

First, we utilize the arrayed-FPSs as muscle motion sensor on forearm for rehabilitation study simulating brain stroke. In addition, the FPSs generate distinguished voltages from specific motions. Then, designed software is applied to conduct simple game from the combination of signals. Second, abnormality of eyeball motions is related to brain disorders from the literatures. The arrayed-FPSs are attached on the human face (temple area) and the response signals are collected for eye blinking and eyeball movements. Third, the study also describes a surface-functionalized FPS that can 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 shows excellent sensitivity and selectivity.

In summary, this study provides a comprehensive set of results from materials, device manufacturing techniques, electromechanical researches, and simulations to illustrate the novel aspects associated with the FPSs using single-crystalline III-N thin films in several biomedical fields.