Polarization And Switching Dynamics Study Of Ferroelectric Hafnium Zirconium Oxide For FeRAM And FeFET Applications
As a scalable and CMOS compatible novel ferroelectric material, the ferroelectric HZO thin film has been the promising material for various applications and continues to attract the attention of researchers. Achieving strong ferroelectricity and fast switching speed in ultrathin FE HZO film are crucial challenges for its applications towards scaled devices.
The ferroelectric and anti-ferroelectric properties of HZO are investigated systematically down to 3 nm. The ferroelectric polarization, switching speed and the impact of ALD tungsten nitride electrodes are studied. Record high Pr on FE HZO and record high PS on AFE HZO are achieved with WN electrodes, especially in ultrathin sub-10 nm regime. The polarization switching speed of FE and AFE HZO, associated with C-V frequency dispersion, are also qualitatively studied. On the other side of the scaling limit, ferroelectric/dielectric stack superlattice structure is found to enhance the ferroelectricity in thick films which would have severely degraded.
Ultrafast direct measurement on the transient ferroelectric polarization switching is used to study the switching speed in FE HZO with a crossbar MFM structure. Sub-nanosecond characteristic switching time of 925 ps was achieved, supported by the nucleation limited switching model. The impact of electric field, film thickness and device area on the polarization switching speed is systematically studied. The ferroelectric switching speed is significantly improved compared to previous reports and more importantly is approaching GHz regime, suggesting FE HZO to be competitive in high-speed non-volatile memory technology. Record fast polarization switch speed of 360 ps is obtained in sub-μm crossbar array FE HZO MFM devices. It also unveils that domain wall propagation speed in HZO is the limiting factor for switch speed and more aggressively scaled devices will offer much faster switch speed.
The first experimental determination of nucleation time and domain wall (DW) velocity by studying switching dynamics of ferroelectric (FE) hafnium zirconium oxide (HZO) was performed. Experimental data and simulation results were used to quantitatively study the switching dynamics. The switching speed is degraded in high aspect ratio devices due to the longer DW propagation time or with dielectric interfacial layer due to the required additional tunneling and trapping time by the leakage current assist switch mechanism.
- Doctor of Philosophy
- Electrical and Computer Engineering
- West Lafayette