Device Physics And Applications Of Neuromorphic And Biomimetic Devices Based On Two-dimensional Materials And Van Der Waals Heterostructures

The development of Information Technology relies on the process of semiconductor technology,very large-scale integrated circuit and computer architecture.However,with the advent of big data era and boom of artificial neural network,semiconductor technology and computer technology suffer a great shock.Neuromorphic computing,which aims to mimic the information process of neural system,gives birth to large amounts of biomimetic devices based on new materials and structures.Various applications of biomimetic devices require more tunabilities in materials properties.Two-dimensional(2D)materials,with atomic thickness and flatness,have shown outstanding properties in electronics and optoelectronics and became the research focus in field of advanced materials.By stacking different 2D materials vertically,the van der Waals heterostructure could accommodate abundant electronic and optoelectronic performance.Further,the properties of 2D materials and van der Waals heterostructure are easily regulated by environment changing since their large surface-to-volume ratio.Hence,abundant means of properties tuning makes 2D materials and their heterostructures an ideal platform for different kinds of biomimetic devices.Specifically,inspired by receptors on membrane of neural cells,we implemented graphene transistor in heavy ions detection.The graphene transistor was endowed with ability of specific and high-sensitivity Pb2+detection by surface modification of aptamer(8-17 DNAzymer),which could combine with Pb2+ specifically for its structure.Then,we also successful measured the Pb2+ concentration in human blood,suggesting that our devices could work in the solution with various ions.Then,we made a research in the unique gate-tunable photoresponse of WSe2/h-BN/Al2O3 heterostructure devices.The factors which influenced this phenomenon,like light intensity and wavelength,gate voltage as well as materials thickness,were carefully studied.Furthermore,we indicated that the behaviors of bipolar cells could be mimicked with performances of WSe2/h-BN/Al2O3 devices.At last,we configured 2D array with WSe2/h-BN/Al2O3 devices and mimicked the behaviors of receptive fields(RFs),the core of image preprocessing in retina.Apart from that,a reconfigurable RF was demonstrated experimentally and implemented in image stylization,edge enhancement,contrast correction,noise reduction and "Event-driven" moving detection.By imitating the biological visual system,we realized an artificial visual system via combing our artificial RF with artificial neural network(ANN)accelerator composed of memristive devices,to recognize 15000 images of handwritten numerals.This manuscript focuses on the demonstration of manipulating graphene transistor in biomimetic detection,and the application of van der Waals heterostructures based on transition metal dichalcogenides(TMDCs)in retina bipolar cells mimicking and image processing.Outstanding performances of these devices suggest a high application prospect of 2D materials and van der Waals heterostructures in biomimetic detection and neuromorphic computing.Specifically,in the first chapter,we start with the development of computer architecture and the problems,pointing out that these issues could be alleviated by learning from biological neural system.A detailed introduction about how neural system process the information in high efficiency is also included in first chapter.In the second chapter,we talk about device fabrication,including method of mechanical exfoliation,sputter,electron-beam evaporator and 2D materials transfer technique.The details in photolithography and electron-beam lithography are also presented.At last,we focus on the key points in different steps of device fabrication.The main content of third chapter is build-up of measuring instruments and programming of control software.The forth chapter focus on graphene bionic sensor for detecting Pb2+.We take 8-17DNAmyer as aptamer,which could combine with Pb2+selectively for its structure.We use 8-17DNAmyer to functionalize the graphene and realize the specific detection of Pb2+in human blood.The fifth chapter study the gate-tunable photocurrent in WSe2/h-BN/Al2O3 heterostructure.The change of source-drain current under irradiation could be positive and negative,which might be from the electron transfer between WSe2 and h-BN,as well as the electron tunneling from back gate through Al2O3.The device performance is further improved by reducing the thickness of heterostructure.In the six chapter,we build up the 2D photodetecting array based on WSe2/h-BN/Al2O3 devices,which could mimic the behavior of bipolar cells and receptive field in biological retina.This endows our array with the ability of "near data processing".We also realize reconfigurable receptive for different functionalities of image processing.By combing our array with memristor array,15000 handwritten numerals are recognized successfully with accuracy of more than 80%.The seventh chapter is conclusion and outlook.We suggest that neuromorphic computing would develop in three aspects:first,more process with physics.More device physics should be combined with work mechanism of neural system;second,more device connection.Functionalities in information processing depend on circuit design,which relies on the modified connections between neuromorphic devices;third,more simple but useful functionalities.We could learn from insects because they evolve so many useful functionalities in confining neural system,which is inspiration for how to design a simple but powerful neuromorphic circuit.