薄膜式微型壓力感測器暨熱挫曲式驅動器之設計與研製

Design and Fabrication of the Diaphragm-Type Micro Pressure Sensors and Thermal Buckled Actuators

王信雄(Hsin-Hsiung Wang)

指導教授 ： 楊龍杰

淡江大學/工學院/機械與機電工程學系博士班/博士(2007年)

https://doi.org/10.6846/TKU.2007.00939

摘要

薄膜結構在微機電技術所製作的微小元件中，係相當重要之關鍵結構，因此本研究將討論微觀尺度下薄膜的力學特性，包括了結構變形的力學分析以及薄膜受力時熱變形狀態，希望了解薄膜之特性表現，並以薄膜結構作為關鍵零件發展感測器與驅動器，並整理出各種元件之理論輸出公式，方便於設計元件之初，即可先行了解元件性能，加快元件設計與製造之速度。
感測器的部分將以微型壓力感測器作為探討的主要對象，本文提出三項壓力計的創新製程，首先改良傳統的全平面薄膜，設計加強島塊於中央位置，增加薄膜強度，製作新型高壓力負載壓力感測器，且利用ANSYS模擬受力時之電壓理論輸出。並且提出以低溫製程之聚二甲基矽氧烷(polydimethylsiloxane, PDMS)微模造技術整合微壓力感測陣列，製作微流道壓力現地量測系統之概念。
第二項創新是以高分子材料PDMS，取代一般工業應用中壓力計下方的玻璃晶片，作為封裝材料；借重PDMS的低溫製程特性與價格低廉優勢，大幅降低壓力計之封裝成本。並比較傳統Pyrex #7740玻璃之陽極接合封裝製程與新型PDMS封裝製程所製作之壓力計輸出性能，比較後發現二者之性能表現於伯仲之間，文中並探討PDMS之洩漏機制。
第三項創新則是利用目前相當成熟之互補式金屬氧化物半導體(CMOS)製程代工的方式，搭配正面蝕刻的加工技法，製作五十微米見方之壓力感測器，其中，壓力薄膜材料為氧化矽，壓電阻則是由多晶矽所組成，並利用金屬犧牲層掏空的方式懸浮壓力薄膜。由於受限於CMOS代工製程中的限制以及遵守代工廠之設計法則，薄膜結構將與以往所呈現之形狀大相逕庭，傳統理論分析的難度將大大提昇，因此將以有限元素模擬分析軟體ANSYS，分析此種特殊薄膜之受力特性，尋找壓電阻最佳位置並先行預測其輸出特性。
驅動器部分則是利用微米尺度薄膜熱傳速度快的特性，配合特殊之結構設計，製作熱挫曲式膜片振動幫浦，以ANSYS模擬受熱時薄膜之熱固耦合作動現象，預測其效能。實際製作之驅動元件可在僅提供3伏特的驅動電壓下，以不超過攝氏40度的工作溫度進行驅動，利用雷射干涉儀量測作動時之狀況發現其最大變型量為0.35微米，截止頻率為1000赫茲。
除了矽基壓力感測器外，本文亦提出利用壓電薄膜聚偏二氟乙烯(PVDF)製作一可撓式力感測器之概念，設計一特殊電極用以測量穩態之壓力負荷，由於PVDF薄膜之可撓性，希冀未來能應用於非平面或不規則表面之力量量測。

關鍵字

薄膜結構 ； 壓阻式壓力感測器 ； 聚二甲基矽氧烷 ； 封裝 ； 金屬氧化物半導體微機電製程 ； 熱挫曲式制動器 ； 聚偏二氟乙烯

並列摘要

Diaphragm-type structure is the most important configuration applied in the MEMS device. In this thesis, the mechanical and thermal-mechanical performances of the diaphragm structures are discussed. Some analytic and numerical solutions of the deformation equation of diaphragms are summarized in this research to predict the performance, stress and strain distribution, of diaphragm structures and to speed up the design and fabrication of micro devices
In the sensor fabrication, this thesis proposes three innovations of pressure sensors. The first one is the configuration modification of the diaphragm structure to fabricate a piezo-resistive pressure sensor which is applied in a high-pressure measurement. A strengthened diaphragm with adding a square fixed mesa is demonstrated to be elegant over the conventional design of piezoresistive high-pressure sensors. This argument is justified by the numerical simulation of the FEM software ANSYS through analyzing the stress of the silicon membrane as well as deriving the ideal output voltage of the high-pressure sensor. This calculated result of sensor performance is compared with the testing data of sensor prototype. This work also describes a fabrication concept of combining the mature silicon bulk-micromachining and new-developed low-temperature surface micromachining technologies to make the microfluidic system chip with both the sensing elements and the flowing channels. By using such an on-site measurement system we can implement the microfluidic experiment in the microchannel much easily and cost-effectively.
The second innovation is to use a polymer material, PDMS, as a packaging material to seal the pressure chamber underneath the diaphragm. PDMS is a well-known material in MEMS technology recently. It is not only cheap but also has a merit of easily processing. We completed piezoresistive pressure sensors, made by the same batch, with different packaging materials of Pyrex glass and PDMS sheet in the paper, respectively. Spin-coating is accessed to control the thickness of PDMS sheet by assigning the silicon and Teflon disks as the supporting substrates for PDMS sheets. The sensors packaged by the PDMS room temperature bonding herein verified the similar performance as the ones packaged by the conventional anodic bonding through pressure testing.
The third innovation is to fabricate a piezoresistive pressure sensor with a diaphragm size of 50μm × 50μm by utilizing CMOS MEMS technology. The material of the sensor diaphragm is silicon dioxide, and the piezoresistors are made by polysilicon. For releasing the diaphragms of the micro pressure sensors, this work proposes to use front-side etching technique with etching holes of 5 μm×5μm only. Finally, we use gelatin and parylene to seal the etching holes.
Besides, a design and fabrication of a novel micro actuator device is also described in this research. This work presents a novel diaphragm type thermo-buckled microactuator with only a driving voltage of 3V and under a working temperature about 40℃. It’s a sandwich structure composed of a platinum (Pt) resistor between two parylene films with different thickness. The platinum resistor is assigned as a heating source. Therefore, the parylene diaphragm with different thickness of top and bottom layers is heated by the embedded Pt resistor. The different temperature rise along the thickness direction of the parylene diaphragm not only generates an out-of-plane thermo-buckling deformation, but also induces an asymmetric deflection inclined to upward or downward direction. The maximum displacement of the diaphragm is verified as 0.35 μm experimentally and with the cut-off frequency of 1000 Hz by an AC voltage of 3V in peak-to-peak magnitude.
This study also proposes a concept of fabricating a flexiable pressure sensor array made by a piezoelectric material PVDF foil. This sensor array is supposed to apply to measuring the pressure by a high-frequency AC carrier excitation.

並列關鍵字

diaphragm ； piezoresistive pressure sensor ； PDMS ； package ； CMOS MEMS ； thermal buckled actuator ； PVDF

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