鈮酸鋰薄膜壓電共振器之製作與特性分析

Fabrication and Characterization of Lithium-Niobate Thin Film MEMS Piezoelectric Resonators

陳偉祥(TAN WEI SIANG)

指導教授 ： 李昇憲

國立清華大學/工學院/奈米工程與微系統研究所/碩士(2015年)

摘要

本文是利用單晶X-切面鈮酸鋰薄膜(Single Crystal X-cut Lithium Niobate, 簡稱X-cut LiNbO3)製作高機電耦合係數(Electromechanical Coupling Coefficient，簡稱kt^2)的水平剪切模態之平板聲波共振器。元件設計初期是利用有限單元分析法(FEM)進行模擬，模擬出SH波模態的頻率與共振時的運動狀態，並且計算出kt^2再與過去文獻之理論計算結果進行比較，以驗證FEM模擬的正確性。根據Kuznetsova et al.的理論計算結果，於X-切面的SH0波模態擁有最高之機電耦合係數27.4%，因此成為本次研究的重點。製程方面，本團隊向國外購買單晶X-切面鈮酸鋰薄膜晶片，並採用表面微加工製程(Surface Micromachining)技術來製作共振器元件。本團隊依據現有學術界有限的製程資源設計了兩種不同的製程流程，並且測試製程的可行性。此製程大致分成三個階段，第一階段為黃光微影，主要負責定義電極與蝕刻槽；第二部分為LiNbO3的蝕刻製程；第三部分為利用氫氟酸(Hydrogen fluoride, 簡稱HF)蝕刻LiNbO3下方的二氧化矽，以讓薄膜釋放，使結構懸浮。此研究製作出來的壓電共振器量測結果之Q值為60，機電轉換係數為15.8%，運動阻抗為28.5 kΩ。

關鍵字

單晶X-切面鈮酸鋰薄膜 ； 共振器 ； 高耦合係數 ； 水平剪切模態平板聲波共振器

並列摘要

This work implements single crystal X-cut thin film Lithium Niobate (LN) in order to achieve a high electromechanical coupling coefficient kt^2.of the shear horizontal acoustic plate wave (SH-APM) resonators. The design of the device is carried out by the Finite Element Method (FEM) that can simulate the frequency of the SH0 mode resonators and their mode shape, and we use their frequency response to calculate the coupling coefficient that would be compared with the theoretical analysis and numerical result of prior arts; then we can confirm the validation of our simulation approach. In literature, the resonator possesses a high coupling coefficient at SH0 mode using the X-cut Lithium Niobate, which becomes our target in this work. In the fabrication process, we obtain off-the-shelf single crystal X-cut Lithium Niobate dies and we are using surface micromachining technology to fabricate the resonators. We design two fabrication process flows using the limited academic process resources and test the feasibility of the fabrication process. This process is roughly divided into three parts; the first part is photolithography, primarily responsible for defining the electrodes and etching holes; the present process for fabrication uses two masks. The second part is Lithium Niobate etching process. The third part is to etch the silicon dioxide; thus we use the wet HF to release the thin film structure. This study successfully demonstrated measurement results of the piezoelectric resonator with quality factor of 60, the electromechanical coupling coefficient of 15.8%, and motional impedance of 28.5 kΩ, respectively.

並列關鍵字

Single Crystal X-cut Thin Film Lithium Niobate ； Resonators ； High Coupling Coefficient ； Shear Horizontal Acoustic Plate Wave (SH-APM) Resonator

參考文獻

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