藉由垂直磁異相性調控零場鐵磁共振頻率

Abstract

隨著無線通訊的發展，電子產品追求超高頻、高速、輕薄化以及低功耗等性能。電子裝置的操作頻率也因而不斷提高。應用在這些裝置中的集成電感在高頻的需求也因此逐漸增長。相較於非磁性集成電感，磁性集成電感可以提供較高的感值，但由於鐵芯材料的鐵損和鐵磁共振頻率的限制，在高頻應用中仍有許多挑戰。鐵磁共振頻率是決定電感工作頻率的一個重要參數，當頻率達到鐵磁共振頻率時，材料對交變磁場的能量吸收達到最大，同時電感的工作效能也因而大幅下降。因此，研發具有高鐵磁共振頻率的鐵芯材料是重要的。

在這篇論文中，我將在Pt/Co/Pt和W/CoFeB/MgO這兩種具有垂直磁異相性的膜層系統中，藉由設計膜層結構和鐵磁層厚度來調控垂直磁異相性強度，進而去調節材料的鐵磁共振頻率。我的研究分成兩部分，在第一部分，我會先在Pt/Co/Pt和W/CoFeB/MgO單層鐵磁層系統中，對鐵磁共振頻率和矯頑磁場作對鐵磁層厚度的分析，以找出最佳的厚度參數。在第二部分，我們將以最佳鐵磁層厚度參數做成Pt/Co/Pt和W/CoFeB/MgO多層鐵磁層系統，並對重複層數或結構做鐵磁共振頻率及矯頑磁場的調整。研究結果顯示，具有較強垂直磁異相性的樣品，可以使零場鐵磁共振頻率從零調至更高的頻段。總體來看，W/CoFeB/MgO多層鐵磁層系統相較Pt/Co/Pt多層鐵磁層系統有較大的鐵磁共振頻率以及較低的矯頑磁場，隨著重複層數增加仍可以維持在>10GHz的頻段，顯示了其作為高頻集成電感鐵芯材料的潛力。然而，相較於其他研究，W/CoFeB/MgO多層膜系統的矯頑磁場仍是大上許多，且為了能在實際應用中有明顯的感值增加，在更高層數的表現仍需要被研究。因此將其實際應用在高頻磁芯材料上還有許多的改善空間。

With the advancement of wireless communication, electronic products are striving for ultra-high frequency, high speed, lightweight, and low power consumption, leading to the operating frequency of electronic devices continuing to increase. In wireless communication applications, the integrated inductor is an indispensable component in the circuits. Consequently, there is a growing demand for integrated inductors designed for exceptional high-frequency performance. In contrast to non-magnetic integrated inductors, magnetic integrated inductors possess a relatively high inductance value. However, due to the core loss and the limit of the resonance frequency of the magnetic core materials, there are also some challenges in high-frequency applications. The ferromagnetic resonance frequency is a crucial parameter that determines the operating frequency of the inductor. When the frequency reaches the ferromagnetic resonance frequency, the magnetic material absorbs the energy from the alternating magnetic field, leading to a significant decrease in inductance. Hence, it is vital to develop a core material with a high ferromagnetic resonance frequency. In this paper, I will focus on four systems with perpendicular magnetic anisotropy, which are Pt/Co/Pt system, Pt/Co/Pt multilayer system, W/CoFeB/MgO system, and W/CoFeB/MgO multilayer system. The ferromagnetic resonance frequency and coercivity field will be investigated by modifying the PMA in these systems. The study is divided into two parts. In the first part, I will analyze the ferromagnetic resonance frequency and coercivity depending on the ferromagnetic layer thickness in Pt/Co/Pt and W/CoFeB/MgO systems to determine the optimal ferromagnetic layer thickness. In the second part, the Pt/Co/Pt multilayer system and the W/CoFeB/MgO multilayer system will be investigated with several repeats of the optimal ferromagnetic thickness. The results indicate the zero-field ferromagnetic resonance frequency (f_0) can be tilted away from 0 if a sample exhibits a sizable PMA strength. Overall, the samples in W/CoFeB/MgO multilayer system possess a higher f_0 (>14GHz) and lower coercivity field than those in the Pt/Co/Pt multilayer system. This high level of f_0 demonstrates their potential for high-frequency inductor core materials. However, the coercivity in W/CoFeB/MgO system is still considerable compared to other studies. To substantially enhance inductance in practical applications, further study on W/CoFeB/MgO multilayer systems with higher repetition of the ferromagnetic layer is needed. Therefore, it still needs lots of work to reach its full potential for the high-frequency magnetic core material.