微機電微波濾波器之製作與改良

  Analysis and Fabrication of Micromachined Microwave Filter

 

摘要

 

本論文的研究主旨在將以microshield方式設計的15 GHz指叉型 interdigital)帶通濾波器以微機電的方式完成加工製造及量測,並且使用電腦模擬分析微波濾波器設計與薄膜製程整合的尺寸大小對濾波器設計規格的影響,經過電腦模擬後,可以對邊緣寬度、共振微帶長度、微帶與邊緣間的距離及housing對頻率的影響作一清楚的闡述,可提供設計者對於模擬設計microshield指叉型(interdigital)微波濾波器的經驗法則,以及調整的方向,按照此方式,可以快速的調整微波濾波器的設計誤差。

在製程上,經過不斷的改進,在設計與製作上經過詳細的評估與研究,各項製程已逐漸確定,實驗內容將討論濺鍍、微影蝕刻、封裝製程中,各種製程參數的選定以及對元件的影響,包含薄膜品質、附著性等。在薄膜技術方面,本論文利用射頻磁控濺鍍法(RF sputtering),沉積中間層鈦(Ti1000 Å及金(Au)薄膜 3 μm,經過實驗,TiAu金屬薄膜在100℃,Ar 80 sccm,工作壓力0.05 torr,經回火熱處理後有較佳的結晶與附著性。而在蝕刻技術方面,自背面蝕刻Si晶片後,再利用雙面對準機完成正面對準,將Si晶片以剝離(lift off)技術完成電路的佈局(layout)。

此外,經由頻率的量測,驗證 25 ℃到100 ℃的溫度對於以microshield line的架構所完成的濾波器,中心頻率並無飄移,其原因乃是共振微帶線乃鍍於於由SiO2/Si3N4 所組成的薄膜上,此薄膜的熱膨脹係數甚小,且此薄膜,四周固定於基材上,故幾乎不因溫度變化而變形,連帶地使共振微帶的尺寸,不因溫度變化而改變。

本研究藉由微機電的加工方式,建立起整個完整的製造流程,並且完成以微機電製程技術達到高頻率的微波狹帶濾波器設計。

 

 

ABSTRACT

 

This research is aimed to manufacture 15 GHz narrow-band bandpass microshield interdigital filters with MEM technology. By using computer aided simulation the relationship between the geometry of the thin film membrane and the electromagetic characteristics of the filter has been established. The relationships among the edge of microshield filter, length of microstrip, space between strip and edge, and housing height are found, some methods to decrease the diffucuities in manufacturing processes are suggested.

The manufacturing process of the filter is resulted from the technologies of semiconductor processes including RF sputtering, photolithography, etching and package technologies. The filter structure on silicon wafers consists of four layers SiO2/Si3N4/Ti/Au. The experimental results of sputtering showed that under the conditions of substrate temperature of 100, R.F. sputtering power of 100W, pressure of 0.05 torr, and Ar flow rate of 80 sccm, the quality of the Ti/Au films in terms of  crystallization and adherence strength to the substrate is good enough. After anisotropic silicon backside etching, the circuit layout on the membrane of SiO2/Si3N4 can be finished by using lift off technology .

The performance of the filter is measured on HP 85122A network analyzer. The filter is also put on a hot plate , so that the temperature of the filter can be changed from 25 to 100 during transmission measurement. The results show that the center frequency of the filter did not drift at a noticeable level. The reason is that the dimension of the membrane of SiO2/Si3N4 would not been affected by the temperature variation,so the size of microstrip on the top of the membrane only change very little.