The fundamentals of room temperature bonding methods-surface activated bonding (SAB) and sequentially plasma-activated bonding (SPAB)-are reviewed with applications for packaging of microelectromechanical systems (MEMS) and microfluidic devices. The room temperature bonding strength of the silicon/silicon interface in the SAB and SPAB is as high as that of the hydrophilic bonding method, which requires annealing as high as 1000°C to achieve covalent bonding. After heating, voids are not observed and bonding strengths are not changed in the SAB. In the SPAB, interfacial voids are increased and decreased the bonding strength. Water rearrangement such as absorption and desorption across the bonded interface is found below 225°C. While voids are not significant up to 400°C, a considerable amount of thermal voids above 600°C is found due to viscous flow of oxides. Before heating, interfacial amorphous layers are observed both in the SAB (8.3 nm) and SPAB (4.8 nm), but after heating these disappear and enlarge in the SAB and SPAB, respectively. This enlarged amorphous layer is SiO2, which is due to the oxidation of silicon/silicon interface after sequential heating. The bonding strength, sealing, and chemical performances of the interfaces meet the requirements for MEMS and microfluidics applications.
In this paper, we report a novel LiNbO3 ridge waveguide fabrication technique based on the combination of Annealed
Proton-Exchanging (APE) and precise diamond blade dicing. The process is ultra compact and compatible with
periodically polled LiNbO3 (PPLN). By selecting optimized fabrication conditions, ridge waveguide with low
propagation loss and single transmission mode can be formed at 1064nm and 1500nm wavelength, respectively. Such
APE ridge waveguides have potential applications in optical communication, biomedical detection, and especially in
nonlinear wavelength conversion.
The sequentially plasma activated bonding (SPAB) of silicon/silicon interface has been characterized after annealing up
to 900°C for packaging of micro- electro mechanical systems (MEMS) and microfluidic devices at low temperature. The
bonding strength of the interface in the SPAB was as high as that of the conventional hydrophilic bonding method,
which requires annealing as high as 1000°C to achieve covalent bonding. The interfacial voids evolution with annealing
temperatures has been correlated with the bonding strength. Although the rearrangement of water such as absorption and
desorption across the bonded interface was found below 225°C, the voids were not significant up to 400°C. Annealing
above 600°C resulted in a considerable amount of thermal voids due to viscous flow of oxides. The thermal voids were
grown preferentially at the plasma induced defect sites. The contact angle and roughness of the sequentially plasma
(reactive ion etching plasma followed by microwave radicals) treated surfaces have been observed to explain the void
formation and reduction of the bonding strength of the interface. The plasma induced defect sites such as nanopores and
craters have been indentified using an atomic force microscope. The electron energy loss spectroscopy showed oxygen
deficiency in the nanometer thick interfacial amorphous silicon oxide.
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