| At present,in order to meet the requirements of miniaturization of non-volatile memories,a wide variety of new nonvolatile storage memories have been widely studied,including resistive switching memories,charge trap memories,phase change memories,ferroelectric memories,etc.Among them,the resistive switching memories and charge trap memories are expected to be widely applied in large capacity nonvolatile memory devices.In recent years,the introduction of light into memory devices can greatly enrich the application scene of such light-controlled storage devices.On the one hand,the light-controlled resistive switching devices have attracted wide attention due to its unique mode of resistive switching.For example,controlled by a combination of electrical pulses and light,the light-controlled resistive switching devices are capable of detecting and storing photonic signals.Confidential data storage can be realized based on the light-controlled devices driven by a particular narrow width of wavelength.On the other hand,the storage characteristics of the charge storage devices can also be controlled by light.For instance,controlled by both light and electric,such devices are expected to be applied to optical touchpad,which provide the possibility for multifunctional applications of charge storage devices.In this thesis,we mainly focus on the light-controlled resistive switching device based on the structure of biological retina,which is prepared mimicking the retina structure.By means of changing the illumination and electrical conditions,the light-controlled switching characteristics are investigated.The applications in simulation of optoelectronic synaptic plasticity and light-controlled material implication logic operations are also studied.In addition,we also studied the effect of illumination on the storage performance of CuOx nanocrystalline charge trap memory devices.The main achievements are summarized as follows:1.According to the basic structure of retina,we choose p-Si as photoreceptor,HfO2 as synaptic layer and Pt as the membrane of ganglion cells.The optoelectronic devices mimicking the retina are prepared by atomic layer deposition,magnetron sputtering,maskless UV photolithography and focused ion beam etching.2.The light-controlled switching characteristics of such optoelectronic device are studied.The device can be switched on only under a combination of light and forward scanning voltage;and can be switched off under the negative scanning voltage,showing the light-controlled bipolar resistive switching behavior.The analysis of capacitance-voltage curve shows that the light-controlled resistive switching originates from the illumination modulated electron states in the depletion region of the Si surface,resulting in the redistribution of the voltage drop in the oxide layer and the semiconductor layer.The current-voltage curve of the device under illumination is in line with the Poole-Frenkel conduction mechanism.When the device is switched on,the oxygen vacancies in the oxide layer are redistributed,and the conduction mechanism is transformed into space-charge-limited-current conduction mechanism.Moreover,with the increasing of compliance current,the conduction mechanism of the device changes gradually from Poole-Frenkel conduction to space-charge-limited-current conduction,and finally changes to high field percolation conduction.The anti-fatigue and nonvolatile properties are investigated.Under the illumination of 450 nm,1 mW,the current ratio of around 104 is maintained over 200 consecutive switching cycles.Both the ON and OFF states stably retained their current values over 104 s,showing good retention performance.The rise and fall time of the device are 6 ms and 0.6 ms,respectively,which are better than those reported in the literatures.3.Light-controlled material implication logic operations are realized for the first time by using the p-Si/HfO2/Pt optoelectronic switches.Here,we use the p-Si/HfO2/Pt based optoelectronic switches to constitute a light-controlled IMP logic circuit.Formula calculating is also carried out to explore the characteristics of voltage distribution in IMP logic operation and the stability of light-controlled logic operation.The calculation shows that by choosing the proper series resistance(10 M?),we can reduce the influence of the threshold voltage instability on the light-controlled IMP operation,so as to improve the reliability of the light-controlled logic circuit.The experimental results show that by choosing the proper fixed resistance and operation voltage,the light-controlled IMP logic can only be executed correctly under the illumination of light,and the output logic state can be maintained for a long time.Based on the light-controlled IMP logic,light-controlled NAND,light-controlled OR and light-controlled NOR logic operations are also executed in the same devices,and the output logic state can also be maintained for a long time.4.The optoelectronic synaptic plasticity is studied by using the light-controlled resistive device.The results show that the change of the synaptic weight in the long-term potentiation part depends on the intensity of light,and the greater the intensity of light,the greater the change of the synaptic weight.Based on this optoelectronic plasticity,we study the dependence of photocurrent,responsivity,response time on modulation conditions such as compliance current,light intensity and wavelength.The following results are obtained:(1)different intermediate states can be obtained under various modulations of compliance current,light intensity and wavelength.The larger the compliance current,the stronger the intensity and the longer the wavelength,the higher the photocurrent state.(2)Stateful photoresponses in a single device can be regulated into different levels with different compliance current or optical power.The responsivity can be regulated across a wide range(over 104),depending on the regulation conditions.(3)The photoresponse time is also found to be stateful according to the regulation conditions.The response speed in both rise and decay period becomes faster as these optoelectronic devices are regulated into higher levels.The response period of the presented optoelectronic synaptic devices for artificial retinal devices is much faster than that of human retina and other artificial retina devices.This optoelectronic synaptic plasticity and stateful photoresponses can stimultaneously achieve sensing and neural processing,which have the exciting prospect in light-controlled cognitive and optical neuromorphic hardware.5.The charge storage devices based on CuOx nanocrystals are prepared by atomic layer deposition and magnetron sputtering,and the microstructure of CuOx nanocrystals is characterized by high resolution transmission electron microscopy.The results show that the copper film form a polycrystalline CuOx nanocrystalline after 700 ? thermal oxidation annealing,including two components of CuO and Cu2O.The effect of illumination on the performance of nanocrystal-based charge trap memory is tested.The test results show that the storage window of the charge can be significantly improved under illumination.When the scanning voltage is ±6 V,the storage window of the device increases from 2.8 V in the dark to 5.1 V under illumination,increasing 82%of the charge storage capacity.The programm/erase test of the device shows that the light has a significant influence on the program speed.Under illumination,the storage window begins to open when the pulse width reaches 10-3 s,and the flat band shift is 1.3 V,while the storage window starts to open until the pulse width is 1 s,and the flat band shift is 0.8 V in the dark.The anti fatigue test of the device shows that the charge storage capacity of the device has almost no attenuation in both dark and illumination conditions after program/erase 104 cycles,showing good anti fatigue performance.The data retention test shows that the illumination has a significant influence on the retention performance of the device after the device is programmed.The charge loss rate under illumination is slower than that in the dark,showing a better retention characteristic than that in the dark. |
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