Eutectic bonding of Al-based high aspect ratio microscale structures

Abstract

Metal-based microelectromechanical systems (MEMS) have important advantages over Si-based MEMS. To form any functional metal-based microdevice from metallic high-aspect-ratio microscale structures (HARMS), proper assembly and packaging are required. In this paper, we report successful eutectic bonding of Al-based HARMS using Al-Ge intermediate layers. A series of Al-Ge composite thin films were vapor deposited. Their composition and micro-/nanoscale structure were characterized. The morphology of bonded Al structures was examined, including the morphology of separated surfaces.

Evaluation of eutectic bond strength and assembly of Al-based microfluidic structures

“…All AlGe depositions were carried out with a fixed Al cathode current of 1.0 A and a fixed Ge cathode current of 0.5 A, respectively. This deposition condition resulted in a Ge to Al composition ratio close to that corresponding to the AlGe eutectic composition of Al 70 Ge 30 (Mei et al 2007;Massalski 1986). One series of Al-Ge composite films were deposited on cuboid Al coupons, which were used to prepare tensile testing specimens for the evaluation of bond strength.…”

“…AlGe films were deposited by codeposition from two separate sputter sources, one for pure Al (99.99%) and the other for pure Ge (99.99%). Further details on Al-Ge sputter codeposition and structural characterization of Al-Ge nanocomposite thin films have been reported in our previous paper (Mei et al 2007). Substrates for Al-Ge thin film deposition included cuboid Al coupons (Al6061, 22 mm ·~22 mm ·~18 mm) with surfaces mechanically polished to less than 1 lm in roughness, polished Al foils (Al1100, 99%+)~800 lm in thickness, and replicated Al HARMS (Al1100, 99%+).…”

“…Several bonding methods, such as anodic bonding (Nese and Hanneborg 1993), direct bonding (Harendt et al 1991;Hunt et al 1991), and intermediate layer bonding (Hanneborg et al 1991), have been reported for Si-based microsystems. Recently, we have reported successful bonding of Al-based HARMS with Al-Ge eutectic intermediate layers (Mei et al 2007). Vapor phase deposited Al-Ge nanocomposite thin films were utilized to bond Al-based microchannels without excessive distortions of microscale features.…”

Bonding of Cu-based high aspect ratio microscale structures with Sn intermediate layers

“…From a HARMS mold insert, secondary HARMSs are replicated quickly and in parallel (Madou 2000). We have demonstrated successful HARMS replication by compression molding in Pb , Zn (Cao et al 2003), Al , Cu (Cao et al 2007), Ni , and NiTi .…”

“…Bonding of metal parts at elevated temperatures using chemically/structurally distinct intermediate layer(s) at the bonding interface can lower the bonding temperature, eliminate bulk melting of the parts to be joined, and increase the bond quality. Examples of bonding using eutectic intermediate layers include Si bonding with the Au-Si eutectic (Tiensuu et al 1994) and Al bonding with the Al-Ge eutectic (Mei et al 2007a(Mei et al , b, 2009b. We have previously explored bonding strategies for Cu-based HARMSs.…”