Abstract
Anodic bonding is broadly utilized to realize the structure support and electrical connection in the process of fabrication and packaging of MEMS devices, and the mechanical and electrical characteristics of the bonded interface of structure exhibit a significant impact on the stability and reliability of devices. For the anodic bonding structure, including the gold electrode of micro accelerometers, the elastic/plastic contact model of a gold–silicon rough surface is established based on Hertz contact theory to gain the contact area and force of Gauss surface bonding. The trans-scale finite element model of a silicon–gold glass structure is built in Workbench through the reconstruction of Gauss surface net by the reverse engineering technique. The translation load is added to mimic the process of contact to acquire the contact behaviors through the coupling of mechanical and electrical fields, and then the change law of contact resistance is obtained. Finally, the measurement shows a good agreement between the experimental results, theoretical analysis and simulation, which indicates there is almost no change of resistance when the surface gap is less than 20 nm and the resistance is less than 5Ω, while the resistance changes rapidly after the gap exceeds 20 nm.
Highlights
Anodic bonding is a silicon–glass electrostatically bonding technology proposed by Romerantz and Wallis, and it can steadily connect silicon wafer or metal pad to glass substrate under applied external heat and electrical energy without the need of adhesives [1,2]
The bonding quality of high-end MEMS devices, is necessary to be investigated carefully and comprehensively, including the observation of bonding surface [6], interfacial analysis [7,8] and surface morphology [9], among which the contact characteristics exhibit a significant impact on the impedance and stability of electrical signal between the silicon and metal pad
Jia focused on the mechanical field, thermal field and electrical field coupling contact behavior based on Gauss surface model [12]
Summary
Anodic bonding is a silicon–glass electrostatically bonding technology proposed by Romerantz and Wallis, and it can steadily connect silicon wafer or metal pad to glass substrate under applied external heat and electrical energy without the need of adhesives [1,2] This bonding process, is widely utilized in MEMS (micro-electrical-mechanical systems) device assembly and packaging due to its low bonding temperature, solid bonding interface and long-term stability [3]. The diversity and non-standardization of MEMS, made those results too specific to be applied to other devices or structures; the silicon-metal contact model involves a scale-span problem from the macro characterization to micro morphology, which was not considered in the current literature. A detailed modelling process and analysis is proposed in this paper to form a systematical study on the contact characteristics of a silicon–gold surface in the anodic bonding structure of micro accelerometers. The contact area extraction, modelling method of rough surface, contact resistance calculation and experimental verification are included to evaluate the bonding quality of micro accelerometers
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