| Summary: | 博士 === 淡江大學 === 機械與機電工程學系博士班 === 95 === 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.
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