| dc.description.abstract | In this study, we enhanced the performance of back-end-of-line process compatible FeCaps and FeFETs by integrating a TiN/Mo/2.5nm-TiN metal gate with angstrom-laminated HZO ferroelectric thin films. Material differences between the ferroelectric film and each component were analyzed through first-principles calculations and various physical characterization techniques including XRD, XPS, and TEM. A comparative electrical analysis was conducted on the FeCaps and FeFETs, focusing on switching speed, power consumption, endurance, data retention, and multi-level cell (MLC) operation capabilities.
The experimental results discussion is divided into two parts: FeCaps and FeFETs. The FeCap achieved an endurance of 1011 cycles, maintaining a 2Pr value of 34 μC/cm² under an electric field of 3.4 MV/cm. This is attributed to the higher energy barrier for oxygen vacancy migration in angstrom-stacked HZO and a 6.86% reduction in non-lattice oxygen ratio compared to solid-solution HZO. The metal Mo, with its low thermal expansion coefficient, enhances the orthorhombic phase proportion of HZO and forms high work function electrodes in oxidation with TiN, further reducing leakage current and improving endurance by five orders of magnitude. Through the NLS model analysis, although the ultra-thin TiN oxidation slightly reduced the polarization value, the increased grain size of HZO reduced the activation field, resulting in a 28-fold increase in switching speed under low electric fields. Arrhenius equation fitting shows that the capacitor can maintain data for ten years at 109.6°C. By adjusting the writing voltage to achieve partial polarization switching, the higher Schottky barrier helps reduce charge injection, hence maintaining stable endurance after 109 cycles for each polarization state, also demonstrating the feasibility of TLC operation. The metal gate part of the FeFET also adopts the TiN/Mo/2.5nm-TiN structure, where the deposition of the Mo layer causes oxygen migration from the SiO2 interface layer forming MoOx, thereby reducing the thickness of the low dielectric constant interface layer. The embedded ultra-thin TiN prevents the diffusion of reactive metal into HZO. This device, optimized for effective writing voltage, concentrates the external electric field on the ferroelectric layer, mitigating the charge trapping effects caused by interface defects, and maintains a memory window of 1.25V even after 1011 write/erase cycles. Through threshold voltage switching formula fitting, the device′s ultimate switching speed is estimated to be about 20 ns. It also exhibits a highly reliable data retention capability of ten years at 108.9°C and has the potential for high-density storage as QLC. Under low writing voltage, eight threshold voltages distributed still show no disturbance by reading after 108 cycles. The advantages of these FeCaps and FeFETs are expected to be applied in emerging non-volatile, high-density storage ferroelectric memory. | en_US |