於液態環境實現質量偵測之全差分 SOI-MEMS熱致動壓阻式環形振盪器

A Fully Differential SOI-MEMS Thermal Piezoresistive Ring Oscillator for Mass Sensing in Liquid Environment

柏麥嘉(Bhattacharya, Shashwat)

指導教授 ： 李昇憲

國立清華大學/工學院/奈米工程與微系統研究所/博士(2021年)

摘要

本文利用SOI晶片實現微機械振盪器，內容包含一個環形旋轉模態的共振器，該共振器採用全差動的設計，並使用熱致動壓阻感測的方式在水下環境中進行量測。此共振器的差動式設計使其達到了高達約64 dB 的饋通消除值，且此差動環形熱致動壓阻式共振器 (DR-TPR)的旋轉運動模態使其擁有能夠大幅度移除在液體環境中受到的粘性阻尼影響的特性。從量測結果得知，本研究所設計的共振器在去離子水中擁有高達537的品質因數值與8.5 dB的截止帶衰減量，另外本研究所設計的DR-TPR 品質因數在空氣和真空中分別擁有 3,893 和 5,741 的良好表現。在利用Zurich Instruments 的 HF2LI 鎖相放大器實現差動環形熱致動壓阻式振盪器 (DR-TPO)後，得到此振盪器在偏移頻率為1 kHz與10 kHz時的相位雜訊分別為 -77.6 dBc/Hz與-89.54 dBc/Hz。將此DR-TPO應用於質量感測能夠於液體環境中提供6.95 Hz 的艾倫偏差值，即能於液體環境中提供4.11 pg的質量解析度。而本文中亦展示了矽元件的鹽漬化，並使用羧化聚苯乙烯珠來改變共振器的頻率。透過此種技術，我們能夠用來識別在臨床和工業用途中具有廣泛應用的微小分子。DR-TPR表面上的羧化聚苯乙烯珠透過化學反應吸收小分子使得共振器產生相對應的負頻率漂移，並涵蓋了共振器表面上各種固定濃度的表徵。本研究展示了共振器在離子緩衝液體中的操作，這對其未來的應用性至關重要。DR-TPR 在磷酸鹽緩衝液 (PBS) 中的品質因數為 80。在本研究中，首次針對3-DOF的熱致動壓阻式 MEMS 耦合共振器的模態局部化的現象進行研究，並在大氣環境下達到令人滿意的品質因數值1,367。此外，與頻率漂移的單一對應共振器相比，利用耦合TPR元件的模態局部化改善了整體的靈敏度和共模抑制。且本研究發現，此種改善為所有模態局部化的耦合元件的通用特徵，因此本文能為更多未來在大氣條件下運行的不同的感測器設計開啟新的研究方向。

關鍵字

MEMS ； MEMS ； SOI MEMS 製程 ； 熱壓阻共振器 ； 振盪器 ； 相位雜訊 ； 全差動式 ； 粘性阻尼 ； 質量感測器 ； 聚苯乙烯珠 ； 耦合式共振器 ； 模態局部化

並列摘要

This work presents a silicon-on-insulator (SOI) MEMS oscillator that comprises a ring-shaped rotational mode resonator incorporating a fully differential design for operation in the aquatic environment using the thermal drive piezoresistive sense transduction. The differential scheme used in the resonator design achieves a high feedthrough cancellation value close to 64 dB. The differential ring-shaped thermal piezoresistive resonator (DR-TPR) operating in the rotational mode exhibits the characteristic of minimizing the effect of viscous damping in a liquid environment. It depicts a quality factor value as high as 537 with the stop-band rejection of 8.5 dB. The closed-loop measurement utilizes the HF2LI Lock-in Amplifier from Zurich Instruments for Differential Ring-shaped Thermal Piezoresistive Oscillator (DR-TPO) implementation. It shows a phase noise of -77.6 dBc/Hz at 1-kHz offset and -89.54 dBc/Hz at the offset of 10-kHz. The DR-TPO usage for mass sensing in a liquid environment can provide a high mass resolution of 4.11 pg corresponding to the Allan Deviation value of 6.95 Hz. The quality factors of the DR-TPR go to high values of 3,893 and 5,741 in air and vacuum, respectively. This work also shows salinization of the silicon device and uses carboxyl-polystyrene beads to vary the frequency of the resonator. It can work as enabling technology to recognize tiny molecules having broad implementations in clinical and industrial purposes. The resonator has a negative frequency shift corresponding to the chemical absorption of the carboxyl-polystyrene beads on the DR-TPR surface. It covers the characterization in various concentrations of immobilization on the resonator surface. The work presents the operation of the resonator in an ionic buffer liquid which is vital for its future applicability. The Q value is 80 in phosphate-buffered saline (PBS) using DR-TPR. In this work, for the first time, the phenomenon of mode-localization has been studied for a 3-DOF thermal piezoresistive MEMS coupled-resonator system accomplishing a satisfactory quality factor value of 1,367 in ambient condition. The utilization of mode-localization in coupled TPR adds the inherent improvement of sensitivity and common-mode rejection compared to the frequency shift counterparts to unlock gateways for the cognizance of different sensors operating in ambient conditions.

並列關鍵字

MEMS ； MEMS ； SOI MEMS process ； thermal piezoresistive resonator ； oscillator ； phase noise ； fully differential ； viscous damping ； mass sensor ； polystyrene beads ； coupled resonator ； mode localization

參考文獻

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