PiezoNEMS: Semiconductor nanowires and heterostructures for sensing and energy harvesting

In this paper we present new concepts of piezoresistive and piezoelectric devices based on nanowires and heterostructured nanowires, that could be integrated in future IC devices for sensing and/or mechanical energy harvesting. In a first part we introduce a new method to investigate the piezoresistive properties of nanodevices such as 50nm Fully Depleted SOI field effect transistors and nanowires, based on an ultrathin membrane. This new technique is used to apply large strain in the devices (up to a few hundreds of GPa), and can also be used for dynamic studies. While in transistors and nanowires the change in mobility or resistance is limited to a few %, the applied stress can drastically change the electrical properties of tunnel junction nanowires or heterostructured nanowires. In such devices, the current change could be in the order of a few decades, leading to ultra-sensitive strain or pressure sensors. In a second part, we study the electromechanical properties of different kinds of individual piezoelectric nanowires, such as ZnO and GaN, and GaN/AlN/GaN heterostructured nanowires. We present an original technique to study the electromechanical properties of such piezoelectric nanowires, based on an AFM set-up. In particular we show a large enhancement of the piezoelectric properties of nanowires and even more drastically when considering hetero-structured nanowires.