氮化鋁薄膜型體聲波元件之設計與製作

Design and fabrication of aluminum nitride thin film bulk acoustic wave devices

邱冠勳(Kuan-Hsun Chiu)

指導教授 ： 黃瑞星

國立清華大學/電機資訊學院/電子工程研究所/博士(2007年)

摘要

薄膜體聲波元件製作的高頻帶通濾波器、雙工器及感測器已經證實具有可積體化的能力。本論文將針對薄膜體聲波元件的設計分析、模擬與製作做一完整的敘述。

本論文中的體聲波元件是以具C軸指向性的氮化鋁薄膜當作壓電材料層。此氮化鋁薄膜是以反應式濺鍍技術沈積在白金基底上。本論文研究幾個關鍵濺鍍製程參數對沈積的氮化鋁薄膜C軸指向性造成的影響，以尋求最佳化的濺鍍沈積參數沈積出具有高C軸指向性的氮化鋁薄膜，其C軸半高寬值為2.7°。

本論文利用微積電製程與乾蝕刻技術成功研發出製作薄膜型體聲波共振器的製程。此製程具備良率高及成本低的優點，且與半導體製程相容性高。利用此製程製作的薄膜型體聲波共振器具有高共振頻率（例如串振頻率為1974百萬赫茲）、高機電偶合係數（約6.1％）及高品質因子（大於974）的特性。此共振器將用來製作高頻帶通濾波器、雙工器、壓力感測器及溫度感測器。

在元件設計方面，本研究使用Mason模型及Butterworth Van-Dyke（BVD）等效電路來分析、模擬及設計體聲波共振器元件，也利用高頻量測對每個元件進行特性的量測來驗證設計的準確性。

本研究所研製的高頻帶通濾波器。此濾撥器的通帶頻寬為60百萬赫茲，範圍介於1850至1910百萬赫茲；其通帶損耗小於2分貝其非通道阻抗大於25分貝。量測結果顯示濾波器的頻率響應特性和模擬結果非常吻合。

本研究也研製一個雙工器。此雙工器的傳送通帶範圍在1850至1910百萬赫茲且其接收端通帶範圍在1930至1990百萬赫茲；其傳送通帶損耗與接收通道損耗分別小於5.5分貝及6分貝；其傳送非通道阻抗與接收非通道阻抗分別大於35分貝及30分貝。

本研究也利用體聲波元件製作一個具有偵測壓力及溫度雙功能的感測器。其量測結果顯示此感測器在量測範圍內具有高靈敏度及高線性度。此感測器的熱敏感度為25.02 ppm/℃（溫度範圍介於攝氏10度至80度之間）；經過熱循環測試，此感測器沒有熱遲滯現象。此感測器的壓力敏感度為336.2 ppm/bar（相對大氣壓力範圍介於0至2.07巴之間）；經過壓力循環測試，此感測器也沒有壓力遲滯現象。

關鍵字

濾波器 ； 體聲波共振器 ； 雙工器 ； 氮化鋁 ； 溫度感測器 ； 壓力感測器

並列摘要

Film bulk acoustic wave devices show considerable promise as an integrated solution for RF bandpass filter, duplexer and sensor. This thesis is devoted to the analysis, design, and fabrication of film bulk acoustic wave devices, which are targeted for RF front-end in communication devices and sensors.

The film bulk acoustic wave device uses c-axis oriented aluminum nitride (AlN) thin film as its piezoelectric layer. Comprehensive studies on the relationships between the key deposition process parameters and the properties of sputter deposited c-axis oriented AlN thin films are presented. These AlN films were deposited on Pt electrode by reactive magnetron sputtering under various deposition conditions. A polycrystalline AlN film with highly c axis-preferred orientation was achieved. The XRD rocking curve shows a narrow peak measured was 2.7°.

This thesis also covers the description of the studies on developed a dry backside silicon etching process to fabricate a number of devices including a membrane type film bulk acoustic wave resonator (FBAR), a ladder type bandpass filter, a FBAR duplexer and FBAR based sensors. The membrane type thin film FBAR was fabricated by high aspect ratio silicon etching process. The quality factor of this FBAR is estimated to be 974 and the electromechanical coupling constant is 0.063. The resonance and anti-resonance frequencies are 1.888 GHz and 1.940 GHz, respectively. This FBAR is a high Q device and is suitable for making a ladder type filter.

A ladder type bandpass FBAR filter was fabricated based on our membrane type FBAR. This thesis also developed a 1.9 GHz RF transmitter (Tx) filter. This FBAR based filter has potential of simple process to achieve high yield and hence low cost. The measured in-band insertion loss, return loss and the broadband rejection of the Tx filter were 2 dB, 9 dB and 25 dB, respectively. The filter has band pass of 60 MHz bandwidth from 1850 to 1910 MHz. A duplexer was also fabricated based on our FBAR technology. The duplexer has transmitted and received band pass of 60 MHz bandwidth from 1850 to 1910 MHz and 1930 to 1990 MHz, respectively.

A FBAR-based sensor for the simultaneous measurement of temperature and pressure with high sensitivity was fabricated and characterized. Temperature or pressure sensing is determined by the change in the series resonant frequency of the FBAR device when exposed to a measurement environment. For temperature sensing, measurement results show a sensitivity of 25.02 ppm/℃, a nonlinearity less than ±0.005 % over the measurement range of 10 to 80 ℃, and a hysteresis within ±0.005 % in one temperature cycle. In pressure sensing, measured results show a sensitivity of 336.2 ppm/bar, a nonlinearity less than ±0.004 % over the measurement pressure range of 0 to 2.07 bar, and a hysteresis within ±0.007 % in one pressure cycle.

參考文獻

1. Ballato, Proceedings of IEEE Ultrasonics Symposium, San Antonio, TX, November 3-6, 1996, IEEE, 1996, p. 575.

5. V. M. Ristic, Principles of Acoustic Devices, Krieger Pub Co, Toronto Ontario, 1983.

7. F. S. Hickernell, 12th International Conference on Microwaves and Radar, Krakow, Poland, May 20-22, 1998, IEEE, 1998, p. 159.

9. W. P. Mason, Physical acoustics: Vol. 1, Academic Press, NY, 1964.

19. X. Cao, J. Luo, T. Chen and, K. Chen, 1998 5th International Conference on Solid-State and Integrated Circuit Technology, Beijing, October 21-23, 1998, IEEE, 1998, p. 696