Study On Organic Thin Film Memristors Based On Biomaterials

Up to now,although the traditional Complementary Metal-Oxide-Semiconductor Transistor(CMOS)technology and Von Neumann architecture computer system have made great progresses and developments,but now more and more complicated information and data explosion problem make the traditional technology face great challenges.The brain-like nervous system thus has gradually entered scientists’ fields of vision.It is well known that the brain,the highest par’t of the human central nervous system,dominates all activities in the body and regulates the balance between the body and the surrounding environment.As the most basic structure and functional unit of nervous system,neuron plays an important role in a whole complex and precise brain activity.It is worth noting that synapse,as an important structure in information transmission between neurons,have attracted extensive attention from neuroscientists,biologists and even physicists.With advances in neuroscience,scientists have gained insight into how the nervous system processes and stores information by exploring synaptic plasticity and memory in model systems from worms to humans.In recent years,researchers have developed more neuron-like synaptic electronic devices to emulate the learning and memory function of the biological synapses,promoting the rapid development of the brain-like nervous systems.Memristor,as a two terminal device whose resistance can be modulated by the current through the device,has been used to construct a variety of different artificial synapses,so as to realize the plasticity simulation of synapses.With the developments of memristors,metal oxides,two-dimensional materials,and organic materials have been used to construct artificial synapses based on different memristor structures,so as to meet the in-depth application of the study of the human brain nervous system.Although many achievements have been made in the study of memristors,the research on organic memristors with new peculiarities(such as good biosafety,biodegradability and biocompatibility.)is necessary in diverse applications of memristors.In this thesis,we will focus on the employment of organic materials(such as poly(2-vinyl naphthalene),etc.)and biological materials(e.g.,ovalbumin,methyl cellulose,and egg white,etc.)as a charge storage layer or dielectric layer,supplemented by simple spin coating method and mature thermal evaporation technique,to fabricate new organic memristors based on biological materials,and use it to emulate synaptic plasticity(such as the short-term or long-term plasticity,potentiation and depression,etc.).The specific contents are as follows:Chapter 1:Firstly,it offers a brief overview of the basic structure and functions of neurons and synapses,and focuses on the basic concepts and important roles of synaptic plasticity.Secondly,the research background,theoretical model,electrical characteristics,and biological applications of memristor are described in detail.Thirdly,the research progress of memristor in synaptic emulation is described.Finally,the research significance and content of this thesis are given.Chapter 2:Firstly,the components,working principles and operation methods of instruments and equipment involved in this thesis are introduced in detail.Secondly,the main information of reagent consumables involved in the experiment is briefly introduced.Thirdly,the fabrication process of different types of organic memristors is described in detail.Finally,the characterization and data processing methods of different types of memristor devices are briefly summarized.Chapter 3:The device structure and electrical characterization of polymer electret based organic memristor and its application in synaptic emulation are systematically described.Specifically,the polymer-based organic memristor was successfully fabricated by thermal evaporation and spin-coating technique.It is found that the structure of the device can transform from three-terminal charge storage transistor to two-terminal memristor structure by floating the gate electrode and adopting asymmetric source/drain electrodes,so as to realize the memristive characteristics of a two-terminal organic memristor.In addition,the mechanism model shows that the resistance state of the organic memristor is modulated by the number of holes which trapped in polymer electret.It is important that the organic memristor constructed by this method can be used to emulate the basic behaviors of synapses,including synaptic potentiation and depression(long-term plasticity and short-term plasticity).This study lay a solid experimental foundation for the subsequent study of organic memristors based on biological materials.Chapter 4:The device structure and electrical characterization of organic thin film memristor based on ovalbumin are described,and emulation of synaptic behavior is studied.Specifically,the organic thin film memristor based on the ovalbumin was fabricated by a simple solution spin-coating method.Due to the high viscosity of ovalbumin and rough layer surface,it’s a challenge to grow pentacene materials with large grains,thus poly3-hexylthiophene was selected as the semiconductor layer in this device.It is found that the organic memristor has stable memristive characteristics.In addition,the constructed organic memristor can also emulate some basic synaptic behaviors,including synaptic potentiation and depression,pair-pulses facilitation,etc.Chapter 5:The device structure and electrical characterization of organic memristor based on methylcellulose,as well as the working mechanism,are described.To be specific,the organic memristor based on methylcellulose dielectric layer was prepared by a simple spin-coating method.Methylcellulose is utilized as the dielectric layer where the high content of hydroxyl contributes to high proton mobility.On this basis,it is found that the organic memristor shows memristive characteristics which have great potential to emulate synaptic behaviors.This study further laid a solid experimental foundation for further research in this thesis.Chapter 6:The device structure and electrical characterization of bi-direction hysteresis organic memristor based on egg white are systematically described.To be specific,the bi-directional hysteresis organic memristor based on egg white was prepared by a simple solution spin-coating method.It is found that the egg white layer plays a key role in the current bi-directional hysteresis phenomenon.In short,the protein in egg white can induce charge trapping effect,and this effect dominated in high voltage,slow frequency scanning condition,while the ions in egg white can induce ion distribution effect,this effect dominated at low voltage,high frequency scanning,thus the hysteresis direction can be modulated by scanning condition.Further studies have shown that the organic memristors can achieve synaptic plasticity emulation,such as short-term plasticity and long-term plasticity.The study provides significant information for the further development of new implantable biomaterial-based organic memristors.In summary,this thesis focuses on organic thin film memristor research by using a solution-processed method to construct the devices based on biological materials with good biocompatibility and biosafety,which may have great potential in artificial intelligence applications.