射頻(RF) MEMS開關(guān)的模擬、制備和力學(xué)分析

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目 錄
摘要----------------------------------------------------------------------------------I
Abstract--------------------------------------------------------------------------III
第一章 緒論----------------------------------------------------------------------1

1.1 RF MEMS開關(guān)的研究概況---------------------------------------------------------1
1.2本文主要工作--------------------------------------------------------------------------8
第二章 電容型RF MEMS開關(guān)的設(shè)計與制備---------------------------10

2.1電容型RF MEMS開關(guān)的工作原理---------------------------------------------10
2.2設(shè)計考慮------------------------------------------------------------------------------12
2.3 RF MEMS開關(guān)的制備-------------------------------------------------------------17
2.4本章小結(jié)------------------------------------------------------------------------------19
第三章 RF MEMS開關(guān)的失效分析---------------------------------------20

3.1 RF MEMS開關(guān)的實驗測試-------------------------------------------------------20
3.2斷裂失效------------------------------------------------------------------------------23
3.3粘著失效------------------------------------------------------------------------------27
3.4殘余應(yīng)力和應(yīng)力梯度引起的失效------------------------------------------------30
3.5本章小結(jié)------------------------------------------------------------------------------33
第四章 RF MEMS開關(guān)的力電模型----------------------------------------34

4.1現(xiàn)有的微開關(guān)理論模型------------------------------------------------------------34
4.2新的RF MEMS開關(guān)力電模型---------------------------------------------------37
4.3基于無量綱數(shù)的分析---------------------------------------------------------------41
4.4本章小結(jié)------------------------------------------------------------------------------45
i 目錄
第五章 RF MEMS開關(guān)力電模型的數(shù)值模擬----------------------------46

5.1問題描述------------------------------------------------------------------------------46
5.2數(shù)值算法的實現(xiàn)---------------------------------------------------------------------48
5.3數(shù)值結(jié)果分析------------------------------------------------------------------------52
5.4數(shù)值結(jié)果的擬合---------------------------------------------------------------------58
5.5數(shù)值模擬和實驗結(jié)果的比較------------------------------------------------------62
5.6本章小結(jié)------------------------------------------------------------------------------64
第六章 分形粗糙表面的粘著塑性變形------------------------------------65

6.1粘著接觸問題介紹------------------------------------------------------------------65
6.2單粗糙峰塑性變形理論------------------------------------------------------------68
6.3塑性變形粗糙表面的粘著接觸模型---------------------------------------------69
6.4討論------------------------------------------------------------------------------------73
6.5本章小結(jié)------------------------------------------------------------------------------78
第七章 總結(jié)與展望------------------------------------------------------------79

7.1本文總結(jié)------------------------------------------------------------------------------79
7.2工作展望------------------------------------------------------------------------------80
附錄 A RF MEMS開關(guān)閾值電壓一階近似解----------------------------82
附錄 B粗糙峰高度分布和粘著數(shù)的不同表達(dá)式-------------------------84
參考文獻(xiàn)--------------------------------------------------------------------------86
攻讀碩士期間完成的論文和受到的獎勵-----------------------------------93
致謝--------------------------------------------------------------------------------94
ii 摘要
摘 要
由于相對于傳統(tǒng)的固體開關(guān)，射頻微電子機(jī)械系統(tǒng)(Radio Frequency Microelectromechanical Systems, RF MEMS)開關(guān)具有很多優(yōu)點(diǎn)，已引起了廣泛的關(guān)注和研究興趣。本文分為以下五部分。
第一部分，本文研究的電容型RF MEMS開關(guān)由復(fù)合膜橋和濺射了傳輸線的玻璃襯底組成。基于微波、材料和機(jī)械設(shè)計因素的考慮，這里選擇具有高介電常數(shù)的Ta2O5作為開關(guān)中的介電層，以提高器件的關(guān)/開電容比率。為了更好的研究開關(guān)的性能，多種不同結(jié)構(gòu)的開關(guān)被設(shè)計，其中既有直梁結(jié)構(gòu)，也有彎曲梁結(jié)構(gòu)。通過硅玻璃陽極鍵合和ICP刻蝕技術(shù)制備出RF MEMS開關(guān)器件。
第二部分，在RF MEMS開關(guān)的驅(qū)動電壓測試和SEM形貌觀察時，觀察到許多典型的失效現(xiàn)象，經(jīng)過分析將之歸納為三個主要的失效模式：斷裂、粘著、殘余應(yīng)力和應(yīng)力梯度引起的變形失效。并且對失效模式的失效機(jī)制和降低失效的防范措施進(jìn)行了分析和討論。
第三部分，綜合考慮殘余應(yīng)力、梁軸向伸長、及邊緣場效應(yīng)，建立了關(guān)于RF MEMS開關(guān)的新的力電模型。通過對模型控制方程的無量綱化，得到四個無量綱數(shù)，其中一個表示單位長度梁上的彎曲力和靜電力之比，其余三個分別對應(yīng)于軸向伸長、殘余應(yīng)力和邊緣場效應(yīng)的影響。
第四部分，本文利用一種半解析的數(shù)值方法，對前面建立的新模型實現(xiàn)了有效的數(shù)值計算。隨后，通過數(shù)值分析對結(jié)構(gòu)行為中涉及的基本材料參數(shù)、幾何參數(shù)和無量綱數(shù)的影響和重要程度分別進(jìn)行了分析討論。其中在三個影響因素中，殘余應(yīng)力和梁的軸向伸長相對于邊緣場效應(yīng)要顯著的多。并且通過理論、數(shù)值和實驗結(jié)果的比較說明此模型和數(shù)值模擬有利于提高理論預(yù)測的精確性。
第五部分，對于納微系統(tǒng)中一個重要的科學(xué)問題——表面間的接觸問題，本文采用一種更為廣泛的表面粗糙高度的描述方式——分形分布，對于固體表面間的粘著塑性接觸變形行為進(jìn)行了研究。得到了實際接觸面積、全部載荷和需要的分離力的一般表達(dá)式。此分析不再局限于高斯或者指數(shù)的分布形式。但是作為特例，對于其中的粗糙因子取1/2和1時，結(jié)論將分別退化為已有的高斯分布和指
I 摘要
數(shù)分布的情形。

關(guān)鍵詞:
微電子機(jī)械系統(tǒng)(MEMS),射頻(RF) MEMS 開關(guān),鍵合,閾值電壓,吸合,殘余應(yīng)力,邊緣場,粘著,分形圖形,分離力

II Abstract
Abstract
This thesis includes five parts as follows.
In the first part, Capacitance RF MEMS (Radio Frequency Microelectromechanical Systems) switches are designed and fabricated. The device consists of a composite membrane, suspended over a center conductor, and one gsubstrate sputtered with transmission line. Ta lass 2O5 with high dielectric constant is selected as dielectric layer for high off/on ratio of capacitance. In quest of better performance, various structures are designed, which include straight beam and meander beam. Then the switches are fabricated by silicon-glass bonding and ICP etching technology.
In the second section, during the actuating-voltage testing and SEM observation of RF MEMS switches, many typical failure phenomena are obtained, from which three main failure modes, i.e., fracture, adhesion (stiction) and residual stress and stress gradient induced deformation, are concluded. The associated failure mechanisms are analyzed, and the related approaches to mitigate those failure modes are discussed.
Thirdly, a new electromechanical model of RF MEMS switches is developed, in which the residual stress inherent in microstructure, the axial stretching of movable beam, and the fringing field effect are taken into account. Four dimensionless numbers are derived by making dimensionless of the governing equation of the developed model. One of those dimensionless numbers denotes the ratio of the bending force to the electrostatic force per unit length of beam. The others represent the relative importance of the axial stretching of beam, the residual stress, and the fringing field, respectively.
The fourth part fulfills a valid numerical calculation on the behavior of RF MEMS switches based on the new model mentioned above, using a semi-analytical method. The qualitative relationship and importance between the material and
III Abstract
geometrical parameters on the threshold voltage are achieved, and the corresponding analysis with the dimensionless numbers is conducted too. The residual stress and the axial stretching prove significant in comparison with the fringing effect. The comparison among experiment, theory, and numerical results approves that the developed model and the relevant numerical computation can improve the accuracy of theory.
In the final part of the thesis, since adhesive contact is one of main problems on micro/nano scales, it is required to make more in-depth understanding. A theoretical model is developed to describe the adhesive plastic deformation with fractal distribution of microasperity heights. General expressions of real contact area, total load and the required separation force are obtained. Thus this analysis goes beyond the Gaussian and exponential distributions. As special cases, for 21=α and 1=α, the obtained results can be reduced to those of Gaussian and exponential distributions, respectively.
Key Words: Microelectromechanical Systems (MEMS), Radio Frequency (RF) MEMS switches, Bonding, Threshold voltage, Pull-in, Residual stress, Fringing field, Adhesion (stiction), Fractal geometry, Separation force

部分參考文獻(xiàn)

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