Research On Preparation Of Negative Capacitance Field Effect Transistors Based On Hf_0.5Zr_0.5O₂ Thin Film

With the shrinking size of silicon-based field effect transistors,power consumption has become a major factor hindering the development of metal oxide semiconductor field effect transistors（MOSFET）.The key to solving the problem of power consumption is to break through the limits of Boltzmann thermodynamics and achieve subthreshold swing（SS）below 60 m V/dec.Negative capacitance field effect transistor（NCFET）adds ferroelectric materials into the gate structure,and uses the polarization reversal characteristics of ferroelectric materials to realize negative capacitance,which can break through the Boltzmann thermodynamic limit and achieve extremely low SS value.It is considered as one of the most promising low-power candidate devices in the sub 10 nm stage of integrated circuits.Hafnium oxide based ferroelectric materials still have good ferroelectric properties in sub 10nm,and are compatible with MOS technology,which is very suitable for high performance and low power devices.However,the research on hafnium oxide based thin film materials is still in the early stage.In this paper,we mainly focus on the ferroelectric properties of zirconium doped hafnium oxide ferroelectric thin films(Hf_0.5Zr_0.5O₂,HZO),and study the electrical properties of negative capacitance field effect transistors fabricated on the basis of HZO thin films.The specific work is as follows:The ferroelectric properties of HZO thin films were prepared and studied.The HZO thin films were prepared by magnetron sputtering,and were rapidly annealed.The crystal orientation and ferroelectric properties of HZO films at different annealing temperatures（450-650℃）were analyzed.It was found that the ferroelectric properties firstly increase and then decrease with maximum near 550℃.The thickness of HZO thin film was studied in the range of sub 10 nm.It was found that the ferroelectric properties increased with the increase of the thickness of the film.The ferroelectric properties of Al₂O₃/HZO stack structure are studied by changing the thickness of Al₂O₃ thin film of the capacitance matching layer.It is found that the ferroelectric properties gradually weaken with the increase of the thickness of Al₂O₃.When the thickness of Al₂O₃ is 2 nm,the ferroelectric properties of Al₂O₃/HZO stack structure are the strongest.Two-dimensional MoS₂ negative capacitance field effect transistor based on HZO was prepared and studied.By analyzing the design criteria of NCFET,the principle of obtaining extremely low subthreshold swing and the capacitor matching rule are discussed.The NCFET was prepared and its structure and properties were characterized.By changing the annealing temperature and thickness of the HZO film and the thickness of the capacitance matching layer Al₂O₃,the influence on the electrical properties of two-dimensional MoS₂ NCFET was studied.According to the capacitance matching results,completing the process preparation of NCFET,the 6 nm HZO film annealed at 550℃was prepared,and the 2 nm Al₂O₃ was used as the gate dielectric layer.Two-dimensional MoS₂ channel was prepared by mechanical stripping and dry transfer.The subthreshold swing of the device breaks through the Boltzmann thermodynamic limit,dropped to 27.9 m V/dec.Moreover,the hysteresis of the device is very small,and the off-state current is low(I_on/I_off reaches 1.58×10⁷).In addition,it is also observed the drain induced barrier rising effect and negative differential resistance effect.