應用於電壓控制振盪器之三層多晶矽可變電容設計

Abstract

本論文主要在以三層多晶矽表面微加工製程之架構下，以微機電技術設計一靜電式可變電容，以期能取代應用於通訊系統中之傳統可變電抗器，藉由微機電技術提高被動元件的品質因子，因而提昇電路的效能。本論文首先介紹三層多晶矽表面微加工製程，及光罩設計時須注意的一些設計規範，其次敘述微機電靜電式可變電容的運作原理及元件設計考量，並且應用微機電模擬軟體IntelliSuite來輔助設計及分析元件特性。接著介紹振盪器的理論，並將此微機電靜電式可變電容用於取代以柯比茲振盪器為架構所設計的電壓控制振盪器電路，完成電壓控制振盪器之設計。最後針對實驗結果與理論分析之間的差異提出解釋，並討論可能造成可變電容品質因子降低之原因，以及如何改善並提高元件之性能，以期能對未來相關之研究有所幫助。

The thesis demonstrates a micromachined electro-mechanically tunable capacitor based on three-layer polysilicon surface micromachining process. The performance of voltage-controlled oscillator was improved by replacing the convention varactor with high quality tunable capacitor implemented by micromachining technology. We firstly introduce the three-layer polysilicon surface micromachining process and the specification of mask design. Secondly, we utilize finite element analysis software, IntelliSuite, to assist the design and characterize the device. With the simulation results, we are able to complete the oscillation theory using Colpitts oscillator to accomplish the voltage-controlled oscillator with MEMS tunable capacitor. Finally we discuss the difference between experiment result and theory. Here, the possible reason for the tunable capacitor to posses low quality factor is presented. Furthermore, the methods to improve the performance of tunable capacitor were presented at the final conclusion.