Boyin Chen

Applications on MEMS packaging and micro-reactors using wafer-level glass cavities by a low-cost glass blowing method

Micro cavities including channels and bubbles play an important role in micro-reactors, micro total analysis systems (μTAS), analytical and bio-analytical applications, and microelectromechanical systems (MEMS) packaging. Materials including polymers, metals, silicon and glass have been used in fabrication processes of micro cavities. Compared with plastics, glass is inert and has excellent chemical stability towards organic solvents, strong acids. However, glass is notoriously difficult to machine. In this study, we presented a novel blowing process to fabricate wafer-level micro glass cavities including micro-channels and bubbles. At first, cavities were formed by wet etching on the surface of a silicon wafer. Then, the silicon cavities were sealed with a glass wafer by anodic bonding under high pressure. The bonded wafers were then heated up to above the softening point of the glass and baked for several minutes. The gas included in the sealed cavities to foam the softened glass into cylindrical channels or spherical bubbles. Results show that the wafer level micro glass cavities including cylindrical glass channels and spherical glass bubbles with smooth internal surface have been achieved successfully by the this way. The model of preparing micro glass cavities was also discussed. As examples, applications for wafer-level MEMS packaging and micro-reactors using micro glass bubbles and channels prepared by glass blowing methods will also be presented. This blowing method provides a low-cost avenue to prepare micro glass cavities of high quality for applications of micro-reactors, micro total analysis systems (μTAS), analytical and bio-analytical applications, and MEMS packaging.

A novel wafer level hermetic packaging for MEMS devices using micro glass cavities fabricated by a hot forming process

Hermetic or vacuum packaging to maintain a controllable cavity pressure and low costs are required by many MEMS devices having moving parts. A novel fabrication technology using micro glass cavities for wafer level hermetic MEMS packaging including accelerometer or gyroscope will be presented.

A novel approach to fabricate glass micro-objects for MEMS application

A novel foaming process to fabricate wafer-level micro glass objects including bubbles and runners for MEMS packaging was studied. Firstly shallow cavities were wet etched fast on the surface of a silicon wafer. CaCO3 powders were placed in the silicon cavities. Then the cavities were sealed with a glass wafer by anodic bonding. The bonded wafers were then heated up, and the gas released by CaCO3 foamed the glass into cylindrical channels or spherical bubbles according to the pattern in silicon substrate. Results show that the wafer level glass spherical cavities and glass channels by hot forming process are fabricated successfully. The objects on silicon wafer are from 2000 µ m to 100 µ m in diameter. After hot-forming process the diameter of micro glass spherical objects are approximately from 3500 µ m to 130 µ m in diameter. A theoretical model of the foaming process was discussed as well as the potential applications of the micro glass objects. This process was used to fabricate low-cost micro glass cavities including channels and bubbles with a cylindrical or spherical shape and a smooth internal surface for applications of micro reactors, analytical and bioanalytical applications, and MEMS packaging.

Preparation of packaging cap with binary glass microlenses for wafer level packaging of Focal Plane Arrays (FPAs)

To improve the image resolution of thermal imagers, which image objects by uncooled Focal Plane Arrays (FPAs) made up of two-dimension Infra-red (IR) detector arrays, detector size is decreased, and this results in the reduction of detector IR absorber area . However, reduction of IR absorber area may affect IR detectors sensitivity accordingly. In order to reduce the detector size without reducing the detectors sensitivity, the microlenses which can focus the infrared ray on the IR absorber area need to be prepared. A hot forming process of fabricating binary-optics microlenses for wafer-level-packaging of IR FPAs using Pyrex7740 glass is introduced in the paper. Pyrex7740 glass is a widely-used material in the field of packaging of micro system due to its coefficient of thermal expansion is similar to that of silicon and good optical performance for optical devices. The process is based on etching stepwise structures in silicon, and binary-optics silicon-mold wafer is fabricated by a multilevel reactive-ion etching (RIE), followed by anodic bonding of a thin glass wafer to the etched silicon wafer under vacuum. The bonded wafers are then heated inside a furnace at a temperature above the softening point of the glass, and the glass is blown into the stepwise structure due to the atmospheric pressure. Besides, the filling rate of glass into the silicon cavity mold is also discussed. After the silicon mold is removed, glass packaging caps with wafer-level binary-optics microlenses for vacuum packaging are fabricated. Results show that packaging caps, which are of 620um×620um with focal lengths ranging from 1mm to 100 mm at 2.2 um wavelength, are prepared. While the FPAs are encapsulated by the packaging glass caps, the microlenses combined with the detector concentrate light sufficiently to increase the effective collection area, and IR detectors sensitivity is improved. Due to the excellent transmission efficiency in visible and near IR light of the Pyrex 7740 glass, the binary-optics microlenses may have potential application in the other optic devices including Light Emitting Diode (LED).

Preparation of micro glass channels for micro-reactors by a chemical foaming process

A micro glass micro-reactor prepared by a chemical foaming process (CFP) is presented in this paper. By the CFP process, micro glass channels were simultaneously shaped on a glass wafer which consists of the following steps. First, shallow micro channels were etched in a silicon wafer followed by placing foaming agents in the silicon channels. Second, these silicon channels were sealed with a thin glass wafer by bonding a glass wafer. Third, the bonded wafers were heated to a temperature above the softening point of the glass and held for several minutes. The gas released by the foaming agents in the silicon cavities blew the softened glass to form a glass channel followed by cooling and annealing. Then, the hot-formed glass channels decorated by nano-sized catalysis, Ti02, were used as photocatalytic microfluidic reactors to exploit the application of the CFP-made micro glass channels. Methylene blue was filled into the micro glass channels followed by UV exposure to test the photocatalytic properties. Results showed that micro channels were prepared successfully. Results also indicate that the photocatalytic properties of nano-sized Ti02 were improved by using micro glass channels for their high specific area.