Wafer-Scale Room-Temperature Bonding of Smooth Au/Ti-Based Getter Layer for Vacuum Packaging

This study demonstrates room-temperature bonding using a getter layer for the vacuum packaging of microsystems. A thick Ti layer covered with an Au layer is utilized as a getter layer because it can absorb gas molecules in the package. Additionally, smooth Au surfaces can form direct bonds for hermetic sealing at room temperature. Direct bonding using a getter layer can simplify the vacuum packaging process; however, typical getter layers are rough in bonding formation. This study demonstrates two fabrication techniques for smooth getter layers. In the first approach, the Au/Ti layer is bonded to an Au layer on a smooth SiO₂ template, and the Au/SiO₂ interface is mechanically exfoliated. Although the root-mean-square roughness was reduced from 2.00 to 0.98 nm, the surface was still extremely rough for direct bonding. In the second approach, an Au/Ti/Au multilayer on a smooth SiO₂ template is bonded with a packaging substrate, and the Au/SiO₂ interface is exfoliated. The transferred Au/Ti/Au getter layer has a smooth surface with the root-mean-square roughness of 0.54 nm and could form wafer-scale direct bonding at room temperature. We believe that the second approach would allow a simple packaging process using direct bonding of the getter layer.

Recent Advances in Thermoplastic Microfluidic Bonding

Microfluidics is a multidisciplinary technology with applications in various fields, such as biomedical, energy, chemicals and environment. Thermoplastic is one of the most prominent materials for polymer microfluidics. Properties such as good mechanical rigidity, organic solvent resistivity, acid/base resistivity, and low water absorbance make thermoplastics suitable for various microfluidic applications. However, bonding of thermoplastics has always been challenging because of a wide range of bonding methods and requirements. This review paper summarizes the current bonding processes being practiced for the fabrication of thermoplastic microfluidic devices, and provides a comparison between the different bonding strategies to assist researchers in finding appropriate bonding methods for microfluidic device assembly.

Geometrical Effects on Ultrasonic Al Bump Direct Bonding for Microsystem Integration: Simulation and Experiments

This study employed finite element analysis to simulate ultrasonic metal bump direct bonding. The stress distribution on bonding interfaces in metal bump arrays made of Al, Cu, and Ni/Pd/Au was simulated by adjusting geometrical parameters of the bumps, including the shape, size, and height; the bonding was performed with ultrasonic vibration with a frequency of 35 kHz under a force of 200 N, temperature of 200 °C, and duration of 5 s. The simulation results revealed that the maximum stress of square bumps was greater than that of round bumps. The maximum stress of little square bumps was at least 15% greater than those of little round bumps and big round bumps. An experimental demonstration was performed in which bumps were created on Si chips through Al sputtering and lithography processes. Subtractive lithography etching was the only effective process for the bonding of bumps, and Ar plasma treatment magnified the joint strength. The actual joint shear strength was positively proportional to the simulated maximum stress. Specifically, the shear strength reached 44.6 MPa in the case of ultrasonic bonding for the little Al square bumps.

A novel ultrasonic precise bonding with non-constant amplitude control for thermalplastic polymer MEMS

Ultrasonic bonding has been emerging paving the way in micro assembly, with the high demand in fusion quality control. Under this background a novel ultrasonic precise bonding method based on non-constant amplitude control is proposed. A two-step bonding process, including frictional heating and viscoelastic heating, divided by the vibration propagation is designed. In step I, initial melting of the contacting surfaces is achieved at the amplitude bigger than the critical value. In step II, the whole interfacial fusion is realized at smaller amplitude to weaken the ultrasonic cavitation effect. The primary parameters in this method, including the amplitudes for the two steps and the conversion point, are studied. Results indicate that whole fusion bonding can be achieved with the flaws restrained. The proportion of cavity reduces to less than 2% when the amplitude for step II is set at a smaller value.

Microchannel Deformation of Polymer Chip in In-Mold Bonding

Microchannel deformation is a problem which often occurs in the thermal bonding of polymer microfluidic chip, and which is significantly determined by bonding parameters. In this paper, numerical analysis of the microchannel deformation in the process of in-mold bonding polymer chip was conducted, using Young's modulus and shear relaxation modulus of polymethylmethacrylate (PMMA) obtained in creep tests. Adhesion between the top and two lateral walls of microchannel was observed in the results, which can be attributed mainly to the viscoelastic deformation of PMMA. It was also revealed that the maximum percent deformation of microchannel is in height, and that bonding temperature had greater effect on the deformation of microchannel than bonding pressure and bonding time. The deformation of microchannel in simulation were consistent with those of experiment under the optimized parameters of 105 °C, 2 MPa and 240 s.

Disposable microfluidic substrates: transitioning from the research laboratory into the clinic

As more microfluidic applications emerge for clinical diagnostics, the choice of substrate and production method must be considered for eventual regulatory approval. In this review, we survey recent developments in disposable microfluidic substrates and their fabrication methods. We note regulatory approval for disposable microfluidic substrates will be more forthcoming if the substrates are developed with the United States Pharmacopeia's biocompatibility compliance guidelines in mind. We also review the recent trend in microfluidic devices constructed from a hybrid of substrates that takes advantage of each material's attributes.