研究生: |
周正賢 Cheng-Hsien Chou |
---|---|
論文名稱: |
以C軸優選氮化鋁製作高頻聲波元件之研究 Fabrication of High Frequency Acoustic Devices by using Preferred C-axis Orientation Aluminum Nitride |
指導教授: |
黃金花
Jin-Hua Huang 林諭男 I-Nan Lin |
口試委員: | |
學位類別: |
博士 Doctor |
系所名稱: |
工學院 - 材料科學工程學系 Materials Science and Engineering |
論文出版年: | 2005 |
畢業學年度: | 94 |
語文別: | 中文 |
論文頁數: | 145 |
中文關鍵詞: | 表面聲波濾波器 、薄膜體聲波共振器 、氮化鋁 、濺鍍 、奈米微晶鑽石 |
外文關鍵詞: | SAW filter, FBAR, AlN, sputtering, UNCD |
相關次數: | 點閱:4 下載:0 |
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在手持式行動電話、全球衛星定位系統等需要輕量、小尺寸之高頻前端線路應用上,由於陶瓷製作之元件,在模組中體積太大,利用微加工製作聲波元件技術可將模組尺寸縮小。氮化鋁為聲速最快之壓電材料,在高頻線路的應用上,常可見到利用氮化鋁以製作元件,本論文先探討如何成長高品質c軸優選之氮化鋁材料,之後並與微加工製程整合,製作表面聲波與體聲波元件。
在表面聲波元件上,我們主要是利用高聲速之材料如奈米微晶鑽石,在其上利用緩衝層以成長高品質之c軸優選之氮化鋁,再利用黃光製程在氮化鋁上製作指叉狀電極,製作出403 MHz之氮化鋁/矽及850 MHz頻段之氮化鋁/奈米微晶鑽石表面聲波濾波器。
利用緩衝層TiN 150 nm/ Ti 100nm,可大幅提升其在氮化鋁在奈米微晶鑽石基板上之結晶性及c軸優選取向(FWHM=5.2°),而由二次離子縱深成分分析,其擴散現象也因為TiN阻擋層大幅降低,且在附著性測試上我們可得到其Critical Load為33.03 mN,附著性為測試試片最佳,此為在鑽石基板上成長較佳結晶性氮化鋁之方法,利用3um線寬製程之氮化鋁/奈米微晶鑽石基板可得到10200 m/s之表面聲速,頻率為850 MHz。
而薄膜體聲波共振器(FBAR)之結構中,氮化鋁成長在鉬/氮化矽上可以得到平坦之表面~2.811 nm,由TEM觀察在鉬金屬上氮化鋁較容易形成AlN(002)之晶面。目前利用體微加工技術製作鈦/氮化鋁/鈦/氮化矽之體聲波共振器其頻率為2.7GHz,損耗可達~ -5dB,而鉬/氮化鋁/鉬/氮化矽元件之機電耦合係數可達4.0~5.8%,Q值約220。而以BVD model,可將共振器之量測結果轉換為等效線路,利用線路值可預測元件之損耗之來源及效能,並可預測多階共振器串並聯後頻寬與插入損失之關係,得到濾波器之響應。並以此結果製作可得到中心頻率為1.68 GHz,頻寬為183 MHz之體聲波濾波器。
A high performance piezoelectric film, such as Aluminum nitride (AlN), combined with high acoustic wave velocity substrate, such as diamond, is a promising for applications as high frequency SAW devices. However, diamond films with smoother surface are urgently needed. We first grow diamond films using CH4/Ar plasma to result in a diamond film with very small grain size (< 10 nm), the ultra-nano-crystalline films (UNCD). Then we grow high quality AlN thin films on UNCD, using TiN 150 nm/Ti 100 nm buffer layer for enhancing the adhesion of the AlN on UNCD. The scratch test shows the critical load of the sample was 33 mN. By tuning the buffer layer and AlN deposition parameters, c-axis oriented AlN with a thickness of 1 µm were obtained by reactive RF-sputtering technique. The columnar structured AlN grains, with c-axis oriented almost perpendicular to the diamond surface were obtained. AFM image showed the average surface roughness (Ra) was less than 15 nm and the d33 value measured by PFM wax 4.9 pm/V. The AlN/TiN/Ti/UNCD thin films show good potential for Diamond SAW device applications. The measurement by using 3 □m linewidth IDT reveal the frequency was 850 MHz and the surface wave velocity was 10200 m/s.
For the film bulk acoustic wave device(FBAR), effect of buffer layer on the characteristics of the AlN thin films deposited on SiNx/Si substrate was systematically examined. Among the buffer layers examined, both Mo and Ti buffer layers can not only greatly enhance the (002) preferred orientation of the films, but also improve the smoothness of the AlN films, whereas the Al thin films contain large grains microstructure and resulting in rough surface and wide distribution of (002) preferred orientation of the films. AlN thin films with smooth surface with (r.m.s.< 5 nm) and narrow distribution of grains’ orientation, which is suitable for fabricating the devices. A thin film bulk acoustic wave resonator with resonance frequency around 2.7 GHz was fabricated from thus obtained AlN thin films and the insertion loss was about -5 dB. The electro-mechanical coupling coefficient was 4.0~5.8% of Mo/AlN/Mo was close to the theoretical value. Based on the resonator measurement, we can transform the characteristics into BVD equivalent circuit. The model not only provides the information of the loss term of the resonator but also can anticipate
the performance of the filter. Based on the simulation result, we can develop thin film bulk acoustic wave filter and improves its characteristics.
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