研究目的
To study a novel 3D hermetic packaging technique for capacitive MEMS sensors using through silicon via (TSV) to simplify fabrication, improve reliability, and enhance performance.
研究成果
The 3D hermetic packaging technique using TSV and GIS reflow is feasible and reliable for capacitive MEMS sensors, simplifying fabrication by using silicon pillars as both electrical feedthrough and fixed capacitance plates. It significantly improves performance, with quality factors increased by an order of magnitude and packaging failure below 1%, demonstrating high vacuum encapsulation suitable for applications like gyroscopes.
研究不足
The technique is specific to capacitive MEMS sensors and may not be directly applicable to other types. The vacuum level achieved is below 1 Pa, but higher vacuums might be required for some applications. The process relies on specific materials (e.g., Pyrex glass) and may have thermal stress considerations. Scalability to larger wafers or different geometries is not fully explored.
1：Experimental Design and Method Selection:
The study employs a glass-in-silicon (GIS) reflow process for fabricating the encapsulation cap with TSVs, combined with anodic bonding for hermetic sealing. Theoretical models for damping and quality factor in MEMS gyroscopes are used.
2：Sample Selection and Data Sources:
A 4-inch low-resistivity silicon wafer (0.0009 ?·cm) and Pyrex glass wafer are used. Samples include fabricated encapsulation caps and capacitive gyroscopes.
3：0009 ?·cm) and Pyrex glass wafer are used. Samples include fabricated encapsulation caps and capacitive gyroscopes.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Equipment includes deep reactive ion etch (DRIE) system, furnace for reflow, chemical mechanical polishing (CMP) machine, inductively coupled plasma (ICP) etcher, atomic force microscope (AFM), probe station with B1500A semiconductor device analyzer, scanning electron microscope (SEM), Laser Doppler Dynamic Signal Analyzer, and MATLAB software for data analysis. Materials include photoresist, silicon wafers, Pyrex glass, and metal electrodes.
4：Experimental Procedures and Operational Workflow:
Steps involve photolithography and DRIE to create silicon molds, anodic bonding of silicon and glass in vacuum, glass reflow at 1050°C, lapping and CMP to form feedthroughs, ICP etching for cavities, anodic bonding for encapsulation, and characterization of electrical properties, surface roughness, and gyroscope performance.
5：Data Analysis Methods:
Resistance measured using four-probe method with B1500A, surface roughness measured with AFM, quality factor calculated from time-domain and frequency-domain responses using MATLAB for FFT, and statistical analysis of packaging failure rates.
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