Effect Of Light Illumination And Magnetic Field On Charge Storage Characteristics Of Ni-doped HfO₂ Thin Films

To enable higher transistor density,the channel length of a new generation of flash memory devices based on metal-oxide-semiconductor field-effect transistor?MOS-FETs?structures has shrink to less than 10 nm.Continuous scaling down g of gate oxide layer make the leakage current more pronounced.A nano-floating gate non-volatile memory?NFG-NVM?structure,in which separated metal nano-particles embedded in a high?dielectric layer serve as storage nodes has effectively solved this problem.In the 21st century,with the enlargement of human production and living area,the study on the dependence of memory device stability on the external environment is more and more important.In addition to ambient temperature and humidity,light illumination and strong magnetic field are two of general cases in wild environment.In the past decade,there were many research reports regarding on the enhancement of visible light illumination on charge storage characteristics of organic NFG-NVM devices,or discussing effects of visible light illumination on capacitance-voltage characteristics of MOS photo-detectors.In 2017,a new type of photovoltaic field effect transistor?FET?based on Si as the charge transport material and gel quantum dots as light absorbers was reported.This opened a new chapter on charge storage characteristics of inorganic NFG-NVM devices modulated-by light illumination.In this dissertation,a insulate HfO₂ film with high dielectric constant and high light transmittance is serves as the tunneling/control layer of the memory cell,and magnetic Ni nanoclusters with high work function as storage nodes.A MOS capacitor structure based on the Ni-doped HfO₂ thin film has been fabricated on an n-Si?100?substrate by magnetron sputtering.Microstructure investigation and chemical composition analyses show that a amorphous HfSi_x interface layer is formed between the amorphous HfO₂ film and the Si substrate and amorphous Ni clusters are embedded in the HfO₂ film matrix.Electrical performance measurements show that the Ni-doped HfO₂ film deposited under optimized preparation conditions exhibits a charge storage window width of².46V.Visible-light illumination stimulates and generates photo electron-holes pairs in Si substrate,and which subsequently separated into electron and holes derived by the applied electric field.These photocarrier tunnel through the HfO₂ layer and store into excess Ni storage nodes.This results in the increase of the charge storage capacity and the enlargement of the storage window width.Comparative experimental results have revealed that effects of visible light illumination on charge storage characteristics of the memory cell is depend on the light intensity,but not on the light wavelength.Under optimized light illumination conditions,the memory window width increases from3.45V to 6.12V,and the charge storage density adds nearly three times than before.Moreover,the charge storage/release endurance exceeds 10⁵ cycles under continuous light illumination,and the charge storage retention time>10⁵s.Those excellent charge storage properties shows potential applications in a new generation of optoelectronic memory devices.On the other hand,under the applied magnetic field,the memory window width decreases with the increase of the magnetic field,while the saturation capacitance increases with the magnetic field.This reveals preliminary modulation of the magnetic field on charge storage characteristics of the Ni-doped HfO₂ films.In summary,effects of visible light illumination and magnetic field on charge storage characteristics of Ni-doped HfO₂ films are positive and can be modulable,so that the Ni-doped HfO₂ films can be applied in a new generation of photovoltaic/electromagnetic non-volatile memory devices.