Research On HfAlO-Based Ferroelectric Capacitors And Ferroelectric Field-Effect Transistors

Traditional ferroelectric field-effect transistors(FeFETs)use lead zirconate titanate(PZT),strontium bismuth titanate(SBT)and other ferroelectric materials as the ferroelectric layer in gate stack.These traditional ferroelectric materials limit the development of FeFETs,due to the poor scalability,uncompatibility with the CMOS process and interface issues.Since the discovery of ferroelectricity in hafnium-oxide based films with good scalability and CMOS process compatibility,FeFETs have achieved breakthrough progress.Most traditional FeFETs are fabricated with two structures(MFIS and MFMIS).The MFIS structure faces interface problems between ferroelectric layer and oxide layer,resulting in the issues such as threshold voltage shift,leakage current and depolarization field.While the MFMIS structure has problems such as poor reliability of floating gate metal,temperature mismatch between ferroelectric process and transistor process.In this work,based on ferroelectric hafnium-aluminum oxide(HfAlO),we demonstrated a FeFET in series with a HfAlO ferroelectric capacitor to form the MFMIS structure,which effectively overcame the interface problem of the traditional structure and further developed the FeFET.The work can be divided into the following three parts.Firstly,the HfAlO ferroelectric capacitors were prepared with the ALD method,and the rapid thermal annealing process was used to obtain the ferroelectric characteristics.The ferroelectric analyzer RT66B and the semiconductor parameter analyzer B1500A were used to measure the ferroelectric characteristics of the ferroelectric capacitors,including hysteresis loop,polarization current response and instantaneous current characteristics.The measurement results show that the ferroelectric capacitors prepared in this work have good ferroelectric characteristics with a small leakage current.Secondly,the traditional field-effect transistors were fabricated,and their output and transfer characteristics were measured to obtain relevant parameters.Based on the data obtained from the measurement,relevant models were built in the Sentaurus TCAD tool for further simulation.The simulations data was compared with the experimental data for calibration,which was used for the further simulation of the FeFET with the MFMIS structure.Finally,the FeFET in series with a HfAlO ferroelectric capacitor was successfully demonstrated for memory application.On this basis,the impact of the ferroelectric capacitor with different thicknesses and areas was further investigated.It was revealed that the memory window of the FeFET had a significant correlation with the ferroelectric capacitor.By decreasing the thickness and area of the ferroelectric capacitor,the memory window of the FeFET was improved,which could be verified through the TCAD simulation tool and capacitance matching model.In this thesis,we successfully demonstrated the HfAlO-based ferroelectric capacitors and FeFETs for memory application.With the series-connected ferroelectric capacitor,in addition to optimizing the characteristics of ferroelectric memory,we can effectively avoid the interface-caused undesirable effects in traditional ferroelectric memory during film stacking.These results provide a solution for the development of the FeFETs and show high potential for future ferroelectric memory application.