Investigation Of Optoelectronic Synapse Devices Made From Transition Metal Oxides

This dissertation focuses on the optimization of the functional layers and the bionic performance of the optoelectronic synaptic devices.In the material family of transition metal oxides（TMOs）,the strongly correlated electronic system leads to the independence of electron orbits,charges,electron spins and crystal lattices,and therefore the TMOs materials usually exhibit rich and unique physical properties when modified or modulated by doping,alloying,oxygen content adjusting and interfacial engineering,receiving special attention and application in the field of electronics and optoelectronics.In this dissertation,several TMOs were modified and/or engineered and then used as the basic functional layers to construct optoelectronic synaptic devices with excellent performance.The photoelectric response abilities and the neural morphemic behaviors of the device have been investigated deeply and systematacially.It is shown that the optoelectronic synaptic devices demonstrate many better characteristics such as wide band and fast response,as well as durable response abilities when stimulated by a pulse laser from visible to near-infrared region,realizing the simulation of many typical synaptic plasticities and bionic behaviors.The testing devices also perfectly present image sharpening in the process of image recognition,and show strong stabilities under varied environmental conditions based on their excellent performance.It is therefore found that the newly developed optoelectronic synaptic devices based on TMOs are of great significance in the field of bionic vision systems and artificial intelligence.The main contents and results are summarized as follows:（1）The modified SrTiO₃:Cu（STO:Cu）film was deposited by magnetron sputtering in order to broaden the light absorption range of the intrinsic STO film.By means of UV-Vis-NIR method,the influence of the film thickness and the amount of Cu doping on the light absorption of the STO films has been investigated,and an enhanced light absorption from visible to near infrared has also been successfully realized.Then,a mono-functional-layer optoelectronic synaptic device with two-terminals structure was constructed based on the STO:Cu film with a better photoelectric sensibility from visible to near infrared wavelength.Finally,multiple neuromorphic behaviors like EPSC,PPF and learning experience and other biomimetic functions have been successfully realized based on the optoelectronic synaptic device.On the STO:Cu-based mono-functional-layer optoelectronic synaptic device.（2）To further improve the photoelectric response characteristics such as sensitivity,speed,gain and non-volatility,a memristive bilayered optoelectronic synapse device structured as ITO/STO:Cu/CAO/ITO with a heterojunction was constructed by introducing a second functional layer was produced,and the performance of the synaptic device was successfully improved by using the built-in electric field.Many typical synaptic plasticities with the preprocessing function in image recognition have also been realized,indicating a potential application in the bionic vision system.（3）By combining water bath method with magnetron sputtering technique,a nanostructured core-shell composite mixture of CAO@ZnO was successfully fabricated,and hence the optoelectronic synaptic device structured as ITO/CAO@ZnO/ITO was produced with an enhanced photocurrent response in the visible light range.It is found that the device could produce an ultra-high photocurrent gain,and generate an excitatory postsynaptic current at as high asμA level even at a low optical power.Besides,the optoelectronic synaptic devices with core-shell nanostructures can simulate a variety of synaptic plasticities at the microscopic level,such as EPSC,PPF,STP,SNDP,and"advanced behavior"similar to human intrinsic learning and memory functions.It is indicated that the present study might be named as a new benchmark for the application of optoelectronic synaptic devices in the field of artificial intelligence.（4）Based on the principle of localized plasma enhancement effect,Ti O₂:Au modified film was obtained by means of Au-doping,which successfully expanded the optical absorption of pure Ti O₂ thin film from ultraviolet to near infrared light.Then,a plasma-enhanced optoelectronic synaptic device was constructed through combining n-type Ti O₂:Au film with p-type Ni O film.Based on the successfully simulation of the basic neural morphologic behavior,the influence of the external environment on the operation stability of the testing device was also studied,showing that the stability of the device in both high and low temperature as well as in humid environment was slightly affected at early time,but it can recover to the original state in a shorter time.This research would lay a foundation for the practical engineering application of optoelectronic synaptic devices in the field of bionic vision system and artificial intelligence.