| 摘要: | 本研究通過結合TiN/Mo/2.5nm-TiN的金屬閘極與埃米層狀HZO鐵電薄膜，優化了後段製程相容的鐵電電容和鐵電電晶體性能。通過第一原理計算和XRD、XPS、TEM等物性分析鐵電薄膜與各元件的材料差異，並針對FeCaps與FeFETs的切換速度、功耗、耐久性、數據保留性以及多層儲存單元（Multi-Level Cell, MLC）操作進行電性比較分析。
實驗結果討論分為FeCap和FeFET兩部分。FeCap在耐用度上達到1011次循環，並在3.4 MV/cm電場保持34 μC/cm²的2Pr值。這得益於埃米堆疊HZO的氧空缺移動能障較高和相較固溶體HZO降低了6.86%的非結晶氧比例。金屬Mo因其低熱膨脹係數提升HZO的正交相比例，並且與TiN共同氧化形成高功函數電極，進一步降低漏電流，提升了五個量級的耐久度。透過NLS模型分析，儘管超薄TiN氧化稍微降低了極化值，但HZO晶粒尺寸增大，降低活化電場，使其在低電場操作下的切換速度提高28倍。Arrhenius方程擬合結果顯示，該電容在109.6°C下仍能保持十年的數據。通過調整寫入電壓實現部分極化切換，較高的蕭特基能障幫助減少電荷注入，因此各個極化狀態在109次循環下仍展現出穩定的耐久性，也展現了TLC操作的可行性。FeFET的金屬閘極部分同樣採用TiN/Mo/2.5nm-TiN，此結構由於Mo層的沉積導致氧氣從SiO2界面層遷移並形成MoOx，從而減少了低介電係數界面層的厚度，而嵌入超薄TiN能夠防止反應性金屬滲入HZO。由於此元件優化寫入有效電壓，使得外加電場集中於鐵電層，改善了介面缺陷造成的電荷捕捉效應，即便經過1011次的寫入/擦除循環，其記憶視窗仍保持在1.25V。通過閾值電壓切換公式擬合，推算出元件極限切換速度約為20ns。並展現出高可靠的108.9 oC十年資料保留性能，同時還具有QLC的高密度存儲潛力。在低寫入電壓下，八個閾值電壓分布在電場循環至108次後仍然不受讀取干擾。以上FeCap和FeFET的優勢有望應用於新興非揮發性的高密度存儲鐵電記憶體中。
;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. |
