雷射干涉重力波天文台為了量測重力波訊號，架設了大型麥克森干涉儀，並在2015年首次量測到重力波訊號。為了增加量測重力波的數量以及準確性，降低外在雜訊的干擾提升偵測器的靈敏度就極為重要，本實驗研究製作的光機械共振器即為有效提升偵測器靈敏度的方法之一。
西澳大學團隊為了提升偵測器靈敏度設計了光機械共振器，而Cat-flap為此共振器的元件之一。其結構是利用低機械損耗的氮化矽薄膜懸吊矽基板，並在矽基板的雙面上鍍製Ta2O5和SiO2堆疊之高反射鏡結構。Cat-flap能使訊號在光機械共振器內產生optical dilution的作用，藉由optical dilution理論得知，若提升Cat-flap元件的Q factor以及降低Cat-flap結構的共振頻率，可使整體訊號的靈敏度獲得提升，故本實驗會以研究如何成功製作高Q factor以及低共振頻率的Cat-flap為主要實驗目標。
本論文可分為兩大部分，前部分會進行Cat-flap製作設計及品質說明，而後半部會介紹Cat-flap製作中產生的問題以及結構特性探討。
首先經由模擬結果發現薄膜懸吊矽基板的位置會影響Cat-flap 的Q factor，當薄膜懸掛在矽基板中間時Q factor會比薄膜懸掛在側邊高，故本實驗針對製作中間懸吊Cat-flap的共振頻率、結構製作、反射率模擬以及製作問題進行分析及探討。
共振頻率模擬我們以各別改變懸吊薄膜厚度以及長度進行，考慮製作可行性，以懸吊薄膜長度30μm以及厚度100nm時為較佳結構，基頻約為17.5Hz。
本文嘗試三種方式製作中間懸吊鍍膜區，其中考慮了鍍膜表面粗糙度以及結構調整的彈性後，得知bosch乾蝕刻製作為最佳的方式。為了使Cat-flap在共振器作用，懸吊矽基板上的高反射鏡品質就非常重要。在本論文第三章將進行薄膜結構反射率的模擬，高反射鏡堆疊薄膜是以17 pair的Ta2O5/SiO2堆疊。其中因蝕刻製程的關係，決定設計在反射薄膜的上下鍍製保護層，總結構共36層。經實驗結果發現鍍膜實際厚度與設計厚度差0.1%~0.36%，藉由macleod光學模擬考慮鍍膜誤差後反射率約達99.999719%(2.81ppm)品質。
本論文第二部分會說明三個製作改善以及三個製作特性。製作改善有以下方式：1.藉由鍍膜夾具設計有效改善材料應力造成coating mask彎曲的問題降低高反射鏡鍍膜邊緣階梯效應的區域2.在進行高反射鏡鍍膜前鍍製一層氮化矽保護層避免KOH蝕刻基板3.降低KOH蝕刻時間改善懸掛薄膜邊緣破裂問題。
在特性方面會介紹以下三種特性：1.在矽基板要被KOH蝕刻完畢時，因為應力釋放的關係懸吊的矽基板會向蝕刻方向擺動2. Cat-flap脫離液面時，懸吊的矽基板會往蝕刻開口較大的方向有劇烈擺動3. cat-flap懸吊矽基板的重心會落在懸吊薄膜的延長線上。
本實驗已完成中間懸吊cat-flap製作，後續將由西澳大學將元件放入光機械共振器中進行量測及測試。

In order to measure gravitational waves signals the Laser Interferometer Gravitational-Wave Observatory (LIGO) set up a large Michelson interferometer. In 2015, LIGO had finally measured the gravitational waves signals for the first time in history. For increasing the quantity and accuracy of gravitational waves, reducing external noise has become extremely important. In this experiment, the optical-mechanical resonator is one of the methods to improve the sensitivity of the detector.
The University of Western Australia team designed an optical-mechanical resonator to improve the sensitivity of the detector, and cat-flap is one of the components of this resonator. By using low mechanical loss silicon nitride films to suspend the silicon substrate, and coating high reflective mirror on both sides of the silicon substrate. Cat-flap can let the signal have optical dilution in the optical-mechanical resonator. According to the optical dilution theory, if the Q factor of the cat-flap is increased and the resonant frequency is lower, the overall signal can be more sensitivity. Therefore, this experiment will focus on how to produce Cat-flap successfully with high Q factor and with low resonance frequency as the main experimental target.
Through the simulation, it found that the position of the film suspension substrate affects the Q factor of cat-flap. When the film suspended in the middle of the substrate, the Q factor will be higher than the film hanging on the side. Therefore, this experiment aimed at making the center suspension cat-flap with its resonance frequency, structure fabrication, reflection simulated, and fabrication issues analyzed and explored.
The resonance frequency simulation is carried out by varying the thickness and length of the suspension film. Considering the feasibility of fabrication, the preferred structure is a suspension film length of 30 μm and a thickness of 100 nm, and the fundamental frequency is about 17.5 Hz.
The center suspension coating area is fabricated in three ways, taking into account the roughness of the coating surface and the flexibility of the structural adjustment, and the bosch dry etching process is the best way.
In order to make Cat-flap act in the resonant cavity, the quality of the high reflective mirror is very important. The high reflective mirror is made by 17 pairs of Ta2O5/SiO2 stack. In the third chapter of this thesis, the reflection of the coating structure will be simulated. Because of the etching process, we design the protective layer on the upper and lower sides of a reflective mirror. The experimental show that the actual thickness of the coating has an error with 0.1%~0.36%, and the reflection is about 99.999719% (2.81ppm) with considering the coating error by Macleod optical simulation.
In the second part of this thesis, we will introduce three improvements and three production features. In terms of improvement: 1. the coating clamp design effectively reduces the high reflective mirror coating edge step effect. 2. To deposits a layer of silicon nitride to avoid KOH etching silicon substrate before doing the high reflective mirror coating. 3. By reducing the KOH etching time to improve the edge cracking of the suspended film.
In terms of characteristics: 1. when the silicon substrate etched by KOH the pendulum during the stress release will oscillate in the etching direction. 2. To bring Cat-flap out of the water surface, the pendulum will oscillate sharply in the direction of the larger etching opening. 3. The center of gravity of the cat-flap suspension substrate falls on the extension line of the suspension film.
In this experiment, the center suspension cat-flap has completed, and it will place into the optical-mechanical resonator for measurement and testing.

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