The Cross-scale Model Of FeFET And Its Microscopic Regulation Mechanism Of Macroscopic Electrical Properties

Ferroelectric field effect transistors(FeFETs)has been recognized as one of the most promising new memories due to its high read/write speed,low power consumption and high radiation resistance.To achieve true commercialization,there were still some failure problems that need to be solved,including maintaining performance loss,fatigue,and imprint failure.The dislocations,oxygen vacancies,depolarization field and other microstructures were the fundamental factors which affect the transistor's current.In-depth study of the influence mechanism and influence law of microstructure on leakage current was important to reveal the failure mechanism of the FeFET and subjectively use these microscopic factors to prevent its failure.The specific research contents are as follows:(1)A universal cross-scale model of MFS(metal-ferroelectric-semiconductor)structured ferroelectric field effect transistors was established and verified.I combined the phase field theory with the current equation in the semiconductor device to derive the weak form of the relevant partial differential equation,and solved the equation using the finite element method.The model successfully linked the domain structure with the current in the transistor channel,and the obtained transistor transfer characteristic curve agreed with the experimental results,which proved the correctness of the model.The simulation results showed that the downward c-domains on the lower surface of the ferroelectric layer determined the channel conductivity in an enhanced n-type FeFET.(2)Considering the additional stress-strain field caused by dislocations,a FeFET cross-scale model of the MFS structure containing dislocations was established.I used this model to study the influence of the position of dislocations,the density of dislocations,and the intensity of dislocations on the electrical performance of transistors.Interfacial dislocations induced imprint behavior in ferroelectric films.Internal dislocations had less influence on ferroelectric thin films than interfacial dislocations,since they reduced only the coercive field.However,the effects of dislocations on transistor electrical properties were not simply determined by the average film polarization.The downward c-domains on the lower surface of the ferroelectric layer determined the channel conductivity in an enhanced n-type FeFET.When the dislocations were located at the interface between the ferroelectric thin film and the Si substrate,dislocations pinned downward c-domains at the lower surface of the ferroelectric layer,increasing the voltage required toggle the channel.When the dislocations were located inside the ferroelectric thin film,the region below the dislocations was almost a single a-domain.In this case,the small number of c-domains at the lower surface of the ferroelectric film causes the FeFET memory window to nearly disappear and thus causes memory failure.So,the effect of internal dislocations on the electrical performance was more pronounced than interface dislocations.Internal dislocations should be avoided as much as possible in the experiment.(3)A cross-scale model of the FeFET with a MFIS(Metal-FerroelectricInsulation-Semiconductor)structure was established to study the effects of depolarization fields on the electrical performance of transistors.The depolarization field significantly reduced the residual polarization value of the hysteresis loop and the storage window.From the perspective of the domain,the depolarization field suppressed the the domain switching and the greater the intensity of the depolarization field,the more obvious the inhibition.The result was that the transfer curve in the transistor was shifted to the right,causing the transistor to read the information in error.