Novel Devices Based On Relaxor Ferroelectric PMN-PT Single Crystals

Owing to the ultrahigh piezoelectric coefficient and electromechanical coupling factors,Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃?PMN-PT?complex perovskite single crystals have been widely used in the piezoelectric devices such as medical ultrasonic transducers and underwater acoustic transducers.However,as an outstanding representative of relaxor ferroelectrics,the excellent pyroelectric and ferroelectric properties of PMN-PT single crystals have not yet been fully exploited in practical application.It is of great significance to extend their application in areas other than piezoelectric devices.In this dissertation,we explored the applications of these materials in information technology by developing several novel prototype devices based on PMN-PT single crystals.An optothermal field effect transistor?FET?was constructed on the rhombohedral PMN-26PT single crystal.The two dimensional?2D?MoS₂ monolayer was chosen as the channel semiconductor materials.The working mechanism of this FET was studied by investigating the relationship between the drain current of MoS₂ channel and the infrared illumination.It was found that the FET can be gated with infrared illumination and the modulation process is reversible.The infrared response is attributed to the polarization change of PMN-26PT gate insulator induced by the pyroelectric effect.Hence,the drain current of the FET can be remotely controlled by infrared photons without appling a gate voltage.Such a fusion of pyroelectric effect and the interface engineering of 2D materials provides an effective strategy for the‘photon revolution'of FET.A pyroelectric coefficient as high as 7.5×10^-4 C/m²·K was obtained in PMN-28PT single crystal after poling along the[111]direction.The extinction of all angles between0 to 90^o was observed by the ploarizing light microscopy,indicating the‘1R'single domain structure.Then,an ultra-broadband photodetector was monolithically integrated on such a[111]-oriented PMN-28PT single crystal by implementation of siliver nanowires?Ag NWs?as the transparent top electrode.A systematic study of the photoresponse was carried out.The photodetector generated pyroelectric current signals under the illnmination with wavelength ranging from UV to terahetz?THz?.Enhanced current signals was found at short wavelengths,which was possibly caused by the excitation of surface plasmons in Ag NWs.In addition,the photodetector with optimized device architecture also showed a dramatic improvement in operation frequency up to 3kHz,which was an order of magnitude higher than that of traditional pyroelectric photodetector.A poly?vinylidene fluoride??PVDF?porous film and a polystyrene?PS?nanospheres array were deposited on PET substrates respectively to fabricated a low cost arch-shaped triboelectric nanogenerator?TENG?.The TENG could generate an output voltage as high as 220V,which was suffieient to initiate the polarization switching in ferroelectric materials.The feasibility of this new poling process was theoretically and experimentally verifited.Meanwhile,a bottom gated ferroelectric FET was fabricated on a PMN-35PT single crystal,with pentacene as the channel material.The ON/OFF current ratio of this ferroelectric FET was higher than 10³.Inspired by abovementioned results,we further demonstrated an integrated module of self-powered ferroelectric transistor memory through the combination of a TENG and a ferroelectric FET.The stored information could be easily written in the memory system with mechanical energy,which sloved the power consumption problem of information writing in ferroelectric nonvolatile memories.