Abstract
A novel three-dimensional (3D) hermetic packaging technique suitable for capacitive microelectromechanical systems (MEMS) sensors is studied. The composite substrate with through silicon via (TSV) is used as the encapsulation cap fabricated by a glass-in-silicon (GIS) reflow process. In particular, the low-resistivity silicon pillars embedded in the glass cap are designed to serve as the electrical feedthrough and the fixed capacitance plate at the same time to simplify the fabrication process and improve the reliability. The fabrication process and the properties of the encapsulation cap were studied systematically. The resistance of the silicon vertical feedthrough was measured to be as low as 263.5 mΩ, indicating a good electrical interconnection property. Furthermore, the surface root-mean-square (RMS) roughnesses of glass and silicon were measured to be 1.12 nm and 0.814 nm, respectively, which were small enough for the final wafer bonding process. Anodic bonding between the encapsulation cap and the silicon wafer with sensing structures was conducted in a vacuum to complete the hermetic encapsulation. The proposed packaging scheme was successfully applied to a capacitive gyroscope. The quality factor of the packaged gyroscope achieved above 220,000, which was at least one order of magnitude larger than that of the unpackaged. The validity of the proposed packaging scheme could be verified. Furthermore, the packaging failure was less than 1%, which demonstrated the feasibility and reliability of the technique for high-performance MEMS vacuum packaging.
Highlights
Encapsulation is crucial for microelectromechanical systems (MEMS) sensors, since it can shield the sensitive and fragile structures from the influence of the external environment to obtain a highSensors 2019, 19, 93; doi:10.3390/s19010093 www.mdpi.com/journal/sensorsSensors 2018, 18, x FOR PEER REVIEWSensors 2019, 19, 93 performance
The vertical interconnection structures fabricated by a Pyrex glass reflow process, medium transmit an electrical signal, has the advantages of good isolation, negligible where thetolow-resistivity silicon pillars surrounded by the insulated glass act as the medium parasitics, to transmit and low crosstalk
Good electrical interconnection was realized by using the silicon vertical feedthrough
Summary
Encapsulation is crucial for microelectromechanical systems (MEMS) sensors, since it can shield the sensitive and fragile structures from the influence of the external environment to obtain a highSensors 2019, 19, 93; doi:10.3390/s19010093 www.mdpi.com/journal/sensorsSensors 2018, 18, x FOR PEER REVIEWSensors 2019, 19, 93 performance. Encapsulation is crucial for microelectromechanical systems (MEMS) sensors, since it can shield the sensitive and fragile structures from the influence of the external environment to obtain a high. Sensors 2018, 18, x FOR PEER REVIEW. On account of the feature of customization, that the packaging requirements for various. MEMS sensorsOn areaccount different, cost accounts for of the total fabrication [1]. Of the packaging feature of customization, thatover the 50%. Choosing a suitablethe packaging solution is significant in order tothe obtain performance. MEMS sensors are different, packaging cost accounts for over. 50% of totalbetter fabrication cost [1] MEMS sensorsOn areaccount different, cost accounts for of the total fabrication [1]. performance.
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