Investigation of Au/Si Eutectic Wafer Bonding for MEMS Accelerometers

Abstract

Au/Si eutectic bonding is considered to BE a promising technology for creating 3D structures and hermetic packaging in micro-electro-mechanical system (MEMS) devices. However, it suffers from the problems of a non-uniform bonding interface and complex processes for the interconnection of metal wires. This paper presents a novel Au/Si eutectic wafer bonding structure and an implementation method for MEMS accelerometer packaging. The related processing parameters influencing the Au/Si eutectic bonding quality were widely investigated. It was found that a high temperature of 400 °C with a low heating/cooling rate of 5 °C/min is crucial for successful Au/Si eutectic bonding. High contact force is beneficial for bonding uniformity, but the bonding strength and bonding yield decrease when the contact force increases from 3000 to 5000 N due to the metal squeezing out of the interface. The application of TiW as an adhesion layer on a glass substrate, compared with a commonly used Cr or Ti layer, significantly improves the bonding quality. The bonding strength is higher than 50 MPa, and the bonding yield is above 90% for the presented Au/Si eutectic bonding. Furthermore, the wafer-level vacuum packaging of the MEMS accelerometer was achieved based on Au/Si eutectic bonding and anodic bonding with one process. Testing results show a nonlinearity of 0.91% and a sensitivity of 1.06 V/g for the MEMS accelerometer. This Au/Si eutectic bonding process can be applied to the development of reliable, low-temperature, low-cost fabrication and hermetic packaging for MEMS devices.

Gauge to simultaneously determine the electrical conductivity, the Hall constant, and the Seebeck coefficient up to 800 °C

“…13 only show measurements of constantan, since silicon cannot be contacted via Au-Pt thermocouples. Au and Si form an eutectic at 363 • C (Li et al, 2017) that led to the dissolution of the thermocouples. In general, the choice of the thermocouple materials must be verified before measurement.…”

Cryogenic ion trap system for high-fidelity near-field microwave-driven quantum logic

“…The Ti creates an adhesion layer and the Au provides a chemically passive surface finish. At the elevated temperatures used to bond the surface trap to the cryogenically-cooled pillbox (see section V), the Ti would start to diffuse into the Au layer [48]; the Pt layer acts as a diffusion barrier between the Ti and Au surfaces [49], ensuring a pure Au finish. To create the surface trap electrodes, a 6 µm photo-resist was applied to the top side, and then selectively exposed to UV light through a mask.…”

Development and Characterization of Low Temperature Wafer-Level Vacuum Packaging Using Cu-Sn Bonding and Nanomultilayer Getter

“…Until now, most studies on the simultaneous application of Cu-Sn bonding and a getter material with actual microsensors have involved processing at temperatures of 300 °C or higher [ 16 , 17 , 18 , 19 , 20 , 21 ]. This is because the high activation temperature of the getter material deposited on the cover wafer degrades the effectiveness of the low-temperature Cu-Sn bonding material deposited on both sides of the device and on the cover wafer.…”