Piezotronic sensors
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roduction The piezotronic effect can change the electrical response of a system toward various influencing physical factors.1,2 This allows for the development of highly sensitive sensors for applications, especially in micro- and nanoelectromechanical systems (MEMS/NEMS) for robotics, photoelectric sensors, and environmental and health monitoring.3–5 Piezotronics is defined as a mechanically induced change in the potential barrier height, hence the most obvious application is stress or strain sensing. A fast (within the realm of a few microseconds) and high electrical signal resulting from the mechanical excitation is also important for piezotronic sensors. This results in short response times and high sensitivity, respectively. Piezotronics is discussed here for a wide range of applications, including adaptive tactile sensing for electronic skins.3,6,7 Piezotronic stress measurements can also be used to indirectly quantify other physical quantities such as magnetic fields.8 Due to the deformation of a magnetostrictive material, the resulting stress can be sensitively determined when coupled with a piezotronic system. For chemical and optical sensor applications, it is not necessarily the piezotronic effect itself that is the mechanism behind the working principle, rather, a large enhancement in sensing properties can be achieved when the piezotronic or piezo-phototronic effect is used.4,5,9,10
In the case of p–n junctions and Schottky contact-based light sensors, modulation of the barrier height allows for control of charge-carrier separation, transport, and recombination (piezo-phototronic effect). This leads to tunability of the photoelectric response and hence increases the sensitivity of optical sensors. Similarly, the sensitivity of Schottky contact-based chemical sensors can be optimized by piezotronics.4,11
Stress and strain sensors Compared to commercially available technologies for stress and strain sensors, piezotronics exhibits huge advantages with respect to response time and sensitivity of stress and strain. The response time of a piezotronic nanodevice can be
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