Investigation On The Physical Mechanism And Modeling Techniques Of Terahertz Field Effect Transistor

Field-effect transistors based on complementary metal-oxide-semiconductor（CMOS）processes have attracted extensive attention for applications in the millimeter-wave and terahertz frequency bands due to the increasing cutoff frequencies.At the same time,due to the high working frequency,the parasitic effect and distribution effect of the transistor become more complex,which affects the input and output characteristics of the transistor.The commonly used transistor models are not enough to accurately characterize the working characteristics of transistors in the terahertz frequency band,which is not enough to support the design requirements of terahertz integrated circuits.Based on the above problems,this thesis studies related technologies such as high-frequency effect modeling and parameter extraction for terahertz silicon-based field effect transistors.The main work is as follows:Firstly,aiming at the non quasi-static effects that are most likely to appear and affect the device performance in terahertz band,based on the device physics,an accurate non-quasi-static analytical model is studied by calculating and solving the continuity equation and transport equation.Subsequently,the model is optimized according to the actual working conditions of the device,and the channel length modulation effect and parasitic capacitance are added to the model.The validity of the model is verified by the device simulation tool Sentaurus TCAD based on solving basic physical partial differential equations.On this basis,in view of the gate distribution effect that is easy to occur in devices with large gate width in the terahertz frequency band,the transmission line of transistors is analyzed along the gate width,and the small transistor without gate distribution effect is used to scale and model the large transistor with gate distribution effect to characterize the gate distribution characteristics of devices.Then a transistor model which can accurately describe both gate distribution effect and non quasi-static effect is obtained.For a transistor with a cutoff frequency of 100GHz,the model is in good agreement with TCAD simulation in 100MHz-1THz.In order to fit the practical application,based on the previous physical analysis,a small-signal equivalent circuit model including high-frequency distribution effect and high-frequency parasitic effect is proposed,and an accurate parameter extraction method is given.The accuracy of the model at different biases is verified by TCAD simulation.For a transistor with a cut-off frequency of 100GHz,the model can work efficiently up to400GHz.Then,for transistors with large gate width,the applicability of the original model is extended by considering the gate distribution effect.The effective frequency of the model is greatly improved compared with the original model.Finally,based on the 0.25μm CMOS process,the device in the millimeter-wave frequency band is tested on-chip,the available equivalent circuit model of the millimeter-wave transistor is established,and the accurate parameter extraction method is given.The results show that the proposed model can work effectively up to 40GHz for the transistors with the highest cut-off frequency（peak f_t）of 40GHz.In conclusion,the high frequency modeling of field effect transistors in this thesis has practical guiding significance for establishing the compact model of terahertz transistors and has practical significance for the design optimization of terahertz integrated circuits.