Effect Of Nanoscale Change On Ferroelectric Performance Of Novel Zirconium Doped Hafnium Oxide

With the rapid development of big data,5G mobile communications,cloud computing,the Internet of Things,artificial intelligence and other new generation of information technology,storage capacity,reliability and security of data have become important factors affecting the development of information digitization.As the carrier of data,memory material plays an important role in information dissemination.Ferroelectric properties were observed in Si doped HfO2 thin films by German researchers in 2011,leading integrated circuit researchers to refocus on ferroelectric transistors.As one of the new generation of non-volatile memory devices,ferroelectric transistor has attracted extensive attention for its fast operation speed,low power consumption and non-volatile properties.Compared with traditional perovskite ferroelectric materials,doped HfO2 thin films are compatible with existing CMOS processes,with low crystallization temperature,good retention properties and excellent ferroelectric properties at the nanoscale.With the continuous development of Moore’s law,the device feature size is constantly shrinking,and it is helpful for researchers to design and optimize the device performance by studying the change of the ferroelectric properties of the doped hafnium oxide film with polycrystalline structure at the advanced nanoscale.Based on the above situation,this thesis took Zr-doped HfO2 ferroelectric film（HfZrOx）as the research object,we prepared three kinds of HfZrOx capacitors at different nanoscale,explored the influence of nanoscale change on the basic ferroelectric characteristics and reliability of HfZrOx capacitors.Furthermore,based on IFM switching dynamics model,we studied the influence of nanoscale change on the polarization switching characteristics of HfZrOx capacitors,which provided a reference for film thickness process design to improve the performance of HfZrOx-based non-volatile ferroelectric memory.The main research contents and conclusions of this thesis are as follows:1.Ferroelectric properties of HfZrO_x capacitors at different nanoscaleThree kinds of HfZrO_x capacitors at 6 nm,10 nm and 20 nm were prepared by atomic layer deposition（ALD）process.The P-V characteristics of HfZrO_x capacitors at different nanoscale were investigated.Its results show that the remanent polarization value P_r at saturated state increases first and then decreases with the increase of film thickness.PUND test results show that the saturated polarization switching current is related to the film thickness.The results of C-V characteristic test show that the dielectric constant of HfZrO_xcapacitor decreases with the electric field cycles,and HfZrO_x capacitors show different frequency characteristics at different nanoscale,and the dielectric constant of HfZrO_xcapacitor remains high at high frequency.HfZrO_x capacitors were prepared under different annealing conditions.The results show that increasing annealing temperature and annealing time can improve the remanent polarization value of HfZrO_x capacitors.Increasing annealing temperature and annealing time can increase the dielectric constant of HfZrO_xcapacitor at 6 nm,but decrease the dielectric constant of HfZrO_x capacitor at 10 nm and 20nm.2.Reliability of HfZrO_x capacitors at different nanoscaleThe P-V characteristic curve and current voltage curve of HfZrO_x capacitor are tested in the initial state and after 10³ electric field cycles.The results show that the remanent polarization value and polarization current of HfZrO_x capacitor increase with the increase of electric field cycles.Using PUND test,it is found that the pure polarization switcing current of HfZrO_xcapacitors also increases with the electric field cycles,showing a wake-up effect.The number of operation pulse cycles before the breakdown of HfZrO_x capacitors was measured.It is found that under the same electric field,the polarization value of HfZrO_x capacitor at 6nm is the smallest,but the endurance is the best.The influence of the amplitude and frequency of the operation pulse on the endurance of HfZrO_xcapacitor was further investigated.The results show that decreasing the amplitude of the operation pulse and increasing the frequency of the operation pulse can improve the endurance of HfZrOx capacitor.The leakage current test results show that decreasing the amplitude of the operation pulse and increasing the frequency of the operation pulse can effectively reduce the defect generation of HfZrO_x film,and slow down the fatigue process caused by the electric field cycles.3.The influence of nanoscale change on polarization switching properties of HfZrO_xcapacitorsThe frequency response of P-V characteristics of HfZrO_x capacitors at different nanometer scales shows that the higher frequency is,the larger coercive field is.The 20 nm coercive electric field（E_c）of HfZrO_x capacitors is the smallest,indicating that the film thickness can affect the polarization reversal characteristics.The results of polarization switching characteristics of HfZrO_x capacitors at different nanoscale show that the polarization switching charge is related to the amplitude and width of the writing pulse.The larger the writing pulse amplitude is,the shorter the time needed for HfZrO_x capacitors to reach the saturated polarization switching state is;and the larger the writing pulse width is,the smaller the electric field intensity needed for HfZrO_x capacitors to reach the saturated polarization switching state is.IFM model is utilized to extract the the characteristics model parameters of different nanoscale HfZrO_x in the process of polarization switching:activation energy E_a,switching time loss₀ and the uniformity of electric field distribution inside the filmσ.The results show that 20 nm HfZrO_x capacitor polarization switching requires the least amount of energy,shortest polarization switching time and the field distribution inside the film is uniform.The combined action of these factors results in faster polarization switching of 20nm HfZrO_x capacitor.Compared with 6 nm and 10 nm HfZrO_x capacitors,it takes the shortest time to reach saturated polarization and requires the smallest applied electric field.These results indicate that increasing the thickness of HfZrO_x film can optimize the switching speed of HfZrO_x film,which provides a reference for non-volatile memory applications.