The term piezotronics refers to electronic devices, whose central function, like the electrical conductivity, can be changed by altering electrostatic potential barriers by mechanical stress through the piezoelectric effect. The coupling between piezoelectric and semiconducting properties opens the pathway to the development of electronic devices with additional functionality. In the past, the changes in potential barrier which were achieved, are only in the order of meV or a few percentage of the total height of the potential barrier.
Instead of metal-semiconductor Schottky-barriers, this presentation describes the approach of inserting the chemistry of a polycrystalline varistor ceramic into a bicrystal interface with well-defined polarization conditions. The methodology is based on bonding two well-aligned single crystals of ZnO with an intermediate thin polycrystalline sacrificial layer of doped ZnO. Subsequent high temperature treatment grows the single crystals into the sacrificial layer and consumes the polycrystalline materials either partially or fully. For full growth, we will show how stress can tune the potential barrier in head-to-head and tail-to-tail orientation of the polarization vector to enhance/lower the conductivity across individual ZnO bicrystal interfaces. Surpassing the stress sensitivity of previous piezotronic systems. Furthermore, we demonstrate that single crystal – polycrystal – single crystal structures with optimized orientation of the polarization vector in the single crystalline material can further increase the stress sensitivity. Structures with different thicknesses of remaining polycrystalline material are obtained by the application of different high temperature treatments. Microstructural analysis sheds light on the grain growth within the polycrystal and the epitaxial growth of the single crystalline material into the polycrystal. The prepared structures close the gap between varistor piezotronics based on bulk ceramics with random orientation of the polarization vector and bicrystal piezotronics with perfect orientation of the polarization vector, demonstrating the capability of microstructural engineering for varistor-based piezotronic devices.