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.
We report the low-temperature bonding of a lithium niobate (LiNbO3) chip with gold (Au) thin film to a silicon (Si)
substrate with patterned Au film for hybrid-integrated optical devices. The bonding was achieved by introducing the
surface activation by plasma irradiation into the flip-chip bonding process. After the Au thin film (thickness: 500 nm)
on the LiNbO3 chip (6 mm by 6 mm) and the patterned Au film (thickness: 2 μm) on the Si substrate (12 mm by 12 mm)
were cleaned by using argon (Ar) radio-frequency (RF) plasma, Au-Au bonding was carried out in ambient air with
applied static pressure (~50 kgf). The LiNbO3 chips were successfully bonded to the Si substrates at relatively low
temperature (< 100 °C). However, when the bonding temperature was increased to be greater than 150 °C, the LiNbO3
chips cracked during bonding. The tensile strength (calculated by dividing the total cross-sectional area of the initial,
undeformed micropatterns) of the interface was estimated to be about 70 MPa (bonding temperature: 100 °C). It was
sufficient for use in optical applications. These results show the potential for producing highly functional optical
devices and for low-cost packaging of LiNbO3 devices.
This paper describes the low-temperature bonding of a lithium niobate (LiNbO3) waveguide chip to a silicon (Si) substrate for integrated optical systems. The bonding was achieved by introducing the surface activation by plasma irradiation into the flip-chip bonding process. After the surfaces of the Au thin films (thickness: 100 nm) of the
LiNbO3 chip and the Si substrate were cleaned using an Ar radio frequency (RF) plasma, Au-Au bonding was carried out only by contact in ambient air with applied static pressure. The bonded chips fractured at bonding temperature higher than 150°C because of the coefficient of thermal expansion (CTE) mismatch. The LiNbO3 chips were successfully bonded to the Si substrates at relatively low temperature (100°C). The die-shear strength of the LiNbO3 chip was estimated to be more than 12 kg (3.8 MPa), the upper limit of our shear testing equipment.
Tensile and fatigue testing using miniature specimen was proposed to compare the mechanical behaviors of Sn-3.0%Ag-0.5%Cu alloy in small and large volumes respectively. It was found that the tensile strength data of the miniature specimen was not similar with clear inferiority to that of the large volume under all test conditions. The differences in their mechanical properties are attributed to dendrite morphology and intermetallic compounds size. Thus, the mechanical behavior and the solidification microstructure strongly depend on specimen volume, which suggests that small size be used to measure mechanical behaviors of solder alloys.
Flip-chip bonding of various optical components on a silicon substrate by passive optical alignment, which eliminates complicated optical axis precise alignment, has opened up many new possibilities in constructing highly functional, reliable, and low-cost optical micro-systems. Using this technique several micro-sensors have been developed. Moreover, for future optical micro-systems, a novel method of a low temperature flip-chip bonding using surface activated bonding process has been introduced.
Fine needle-like crystals of C60, “C60 nanowhiskers”, were found in 2001 in a colloidal solution of PZT ceramics with added C60. Not only the C60 nanowhiskers but also nanowhiskers composed of C70 and C60 derivatives can be synthesized at room temperature by using the liquid-liquid interfacial precipitation method (LLIP method). Tubular nanowhiskers composed of C60 and C70 molecules have been successfully fabricated by using the LLIP method as well. The tubular fullerene nanowhiskers are named “fullerene nanotubes” here. The tubular fullerene nanowhisker is a new form of single crystalline needle-like crystal whose wall is composed of fullerene molecules. In this paper, structural, electrical and mechanical properties of the fullerene nanowhiskers and fullerene nanotubes are discussed.
Resonant-typed microscanners based on a silicon diaphragm and actuated by PZT was designed and fabricated on purpose to improve the deformed microstructure while resonating at high frequency. In order to yield large actuating force, hybrid PZT deposition process: sol-gel method and laser ablation was developed to manufacture thick PZT films with well-crystallized perovskite phase for the applications of microscanners. In our previous study, a sol-gel derived PZT was used due to the high film quality, large deposition area and easy composition control. However, to make a thick and crack-free PZT film, several times of coating and thermal treatment is not only time consumption, but increases the risk of contamination and leads the complicated problem of thermal residual stress. In this paper, the hybrid-derived PZT film with thickness of 3 μm was prepared with simplified steps and reduced processing time. Regarding to the performance of microscanners, 1D scan motion with straight patterns and scan angle of 8±1° has been demonstrated, while resonating with 7 Vp at resonance frequency (2325 Hz). The 2D scan pattern with area of (8±1°)×(5±1°) and less deformed edged was also obtained successfully due to the improvement of the silicon-based flat mirror surface.
In order to deal with problems in SFM-based data storage, such as low data rate and tip stabilities, we designed and fabricated a micro cantilevers array based on Pb(Zr, Ti)O3 (PZT) thin films. The data rate can be improved by parallel operation using the cantilevers array. And the tip wearing can be slowed down by a thermal mechanical writing mechanism using micro-heaters integrated on the tips, also taking advantage of the independent active tip-sampling spacing control by applying different DV bias to each PZT cantilever. The PZT film was prepared by a modified sol-gel process and electrostatic-spray coating method. The prototype of cantilevers array has been fabricated and characterized. With such a device, data bits with size of about 50nm was recorded and readout in the experiments.
The emerging MEMS technologies are entering in an active phase of high volume production and successful commercial applications. The expertise and the qualification for space application of such devices have already begun. But these technologies are still recent and important efforts on the reliability issue have to be done. This paper defines the role of technological analysis in the actual MEMS design process. Afterwards, it presents MEMS technological analysis techniques developed at CNES applied to an open MEMS technology. In particular, it is shown how these technological analyses response to designer needs and that the designer and the founder still need a strong interaction. We also present the MEMS reliability issue at CNES and replace it in the current world's one.
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