射頻微機電式電感器的最佳化設計

Abstract

為了滿足高性能可攜式無線傳輸系統的需要，眾多的微機電式被動元件:例如:高性能射頻電感器、可調式電容器、傳輸線和射頻開關器;已經被廣泛的發展並且應用於前端射頻積體電路中。然而此類的高性能微機電式被動元件卻容易受外界的影響，例如:壓力的干擾、熱機械力的干擾、重力加速度的干擾等等…。在此篇論文中，傳統的微機電式懸浮電感器的電性可靠度已被研究。根據整合機械模擬軟體(ANSYS)與高頻結構模擬軟體(HFSS)所做的機械結構與電磁特性分析，我們提出了一種能夠完全與CMOS射頻積體電路後段製程相容的最佳化微機電式螺旋電感器。利用引入三明治式的介電層薄膜，我們能夠加強元件的機械強度並且提供更好的訊號穩定度。根據模擬的結果，當承受外界近似一個加速度的干擾時，近似4nH的新式微機電式十字介電層薄膜電感器於8GHz的頻率時，能夠比傳統的懸浮式電感器減少7.79%的感值變化。同時此種設計能夠有效的減少由於工作溫度改變所造成的感值變化。相較於傳統的塊材薄膜支撐式懸浮電感器，這個新式的設計能夠在8GHz的頻率時，減少11.7%由於55°C溫度變化所造成的感值變化。從量測的結果得知最佳化的電感器能夠與傳統的微機電式懸浮電感器一樣，具有等同於傳統式整合於晶片上的電感器四倍的品質常數。因此我們相信我們所提出的新式微機電式電感器不僅能夠有高品質常數的優異表現，此外更能提供寬頻射頻積體電路更高的穩定度。

In order to satisfy the increasing demand of high performance portable wireless system, several micromachined passive components, such as high performance RF inductor, tunable capacitor, transmission line, and switches, have been widely developed and utilized for the RF (radio-frequency) front-end circuits. However, the micromachined passive components tend to be affected by the external disturbance, such as air pressure disturbance, mechanical thermal force disturbance and gravity disturbance. In this thesis, the electrical reliability of the conventional micromachined suspended inductor has been fully investigated. Based on the co-simulation of the ANSYS and the HFSS (High Frequency Structure Simulator) simulators used for the mechanical and electromagnetic analyses, respectively, an optimum micromachined spiral inductor is proposed and fabricated with fully CMOS compatible post-processes for RFIC applications. Via the incorporation of a sandwich dielectric membrane (0.7□m SiO2/ 0.7□m Si3N4/ 0.7□m TEOS) to enhance device structure rigidity, the inductor can have better signal stability. As compared by the simulation results, the new design of a ~4nH micromachined inductor with a cross shaped dielectric membrane can have less 7.79% inductance variation than the conventional one while both devices operate at 8GHz but with 10 m/sec2 acceleration. Meanwhile, the design can also effectively eliminate the inductance variation caused by the working temperature change (□T=55°C). In comparison with the conventional suspended inductor with a blanket membrane support and the one with the optimum design, less than 11.7% inductance variation up to 8GHz can be obtained due to the temperature change. Since the measurement results show that the optimum inductor can have similar electrical performance to the as-fabricated suspended inductor, which has 4 times Q (quality factor) improvement than the inductor without the underneath substrate removal, it’s our belief that the new micromachined inductors can have not only high Q performance but also better signal stability suitable for wide range RFIC applications.