Study On Electrical And Photoelectric Properties Of Field-effect Transistors Based On Novel Hafnium Oxide-based Ferroelectric Films

In recent years,high-tech fields such as the Internet of Things,cloud computing,optical communications,and artificial intelligence have put forward higher performance requirements for logic devices,memory chips,and optoelectronic devices.Hafnium oxide-based ferroelectric thin film is a brand-new ferroelectric material that is fully compatible with the silicon process platform.It has robust ferroelectricity and good scalability,which helps to realize high-performance logic,storage,and optoelectronic devices.At present,the microscopic mechanism of ferroelectric origin,and the kinetic process of polarization reversal,etc.of hafnium oxide-based ferroelectric thin films are still unclear,and device design based on this film is still in its infancy.Therefore,this thesis mainly focuses on the key scientific issues of the material properties,and high-performance optoelectronic devices applications of novel hafnium oxide-based ferroelectric thin films.This thesis mainly studies the ferroelectric properties of zirconium-doped hafnium oxide ferroelectric film and its physical mechanism,and explores the ultralow-subthreshold-slope and hysteresis-free negative capacitance field-effect transistor based on this ferroelectric film and its high-sensitivity photodetection mechanism.The main contents and conclusions are as follows:1.Atomic layer deposition method is used to prepare high-quality hafnium oxide-based ferroelectric thin films.Microscopic crystal structures and phase components of the films are characterized.Atomic layer deposition method is used to prepare uniform zirconium-doped hafnium oxide ferroelectric films with a thickness of 10 nm.The ratio of zirconium to hafnium element is 1:1 measured by X-ray photoelectron spectroscopy.Annealed samples with and without Ti N upper electrode are characterized by X-ray diffraction analysis,relative permittivity test,and high-resolution transmission electron microscopy.Results show that the annealed samples with Ti N upper electrode have more non-centrosymmetric orthogonal phases and larger resident polarization.Furthermore,the impacts of the growth conditions on the crystalline phase composition of hafnium oxide-based ferroelectric thin films and the evolution law between the crystalline phases are summarized combined with the crystallographic symmetry relationship.2.Electrical characteristics of hafnium oxide-based ferroelectric thin film capacitors are studied,and physical mechanism of ferroelectric polarization reversal is analyzed.The piezoelectric loop,hysteresis loop,ferroelectric domain switching characteristics,and fatigue characteristics of the capacitor structure of hafnium oxide-based ferroelectric films are characterized through a piezoelectric force microscope and a ferroelectric tester.On this basis,the pyroelectric coefficient of hafnium oxide-based ferroelectric films is tested to verify the spontaneous polarization properties of the film.In addition,through current-voltage curves at different temperatures and different frequencies,the kinetic process of ferroelectric polarization reversal of the film is explored,which provides a powerful experimental basis for understanding the origin of ferroelectric polarization of the film.3.Based on high-performance hafnium oxide-based ferroelectric thin films,a hysteresis-free ferroelectric negative capacitance field-effect transistor with ultra-low subthreshold slope is showed.Metal-ferroelectric-semiconductor and metal-ferroelectric-insulator-semiconductor field-effect transistors are designed and prepared.Research results show that introducing the Al₂O₃ insulating layer can effectively improve the quality of the interface between hafnium oxide-based ferroelectric thin film and two-dimensional material semiconductor,effectively reduce the electrical hysteresis of the transistor,and can satisfy the condition of capacitance matching relationship to achieve a lower subthreshold slope.According to the transfer characteristic curve of the metal-ferroelectric-insulator-semiconductor field-effect transistor,it is calculated that the minimum subthreshold swing at room temperature is17.64 m V/dec,the average is 45 m V/dec,and the electrical hysteresis is almost completely eliminated.4.Relying on the synergy of several mechanisms such as photogating effect,ferroelectric negative capacitance effect,and voltage amplification effect,the highly sensitive photodetection function of negative capacitance field-effect transistor is realized.Experimental results show that if the operating voltage of the transistor is set to the threshold voltage point in the dark state,the dark current of the device can be well suppressed;when illuminated,the threshold voltage point of the device shifts to the left,and taking advantage of photogating effect and ferroelectric negative capacitance effect can effectively improve photocurrent and photodetectivity of the device.The above phenomenon is due to the fact that the voltage amplification effect of ferroelectric negative capacitance effect depletes the channel electrons,effectively suppressing the dark current of the device.When illuminated,multi-layer Mo S₂ absorbs photon energy and excites electron-hole pairs.A large number of holes are captured by the defect states,thereby prolonging the carrier life,and improving the photoconductivity gain.At the same time,changes in ferroelectric capacitance will cause the surface potential of the semiconductor channel to decrease,allowing more electrons to cross the channel barrier,thereby achieving high photoresponsivity and photodetectivity.The highly sensitive photodetection mechanism of ferroelectric negative capacitance field-effect transistors can be widely used in low-dimensional semiconductor optoelectronic devices,providing new ideas and methods for realizing high-performance photodetector devices.