Jintang Shang

Microwave makes carbon nanotubes less defective.

An ultrafast microwave annealing process has been developed to reduce the defect density in vertically aligned carbon nanotubes (CNTs). Raman and thermogravimetric analyses have shown a distinct defect reduction in the CNTs annealed in microwave for 3 min. Fibers spun from the as-annealed CNTs, in comparison with those from the pristine CNTs, show increases of approximately 35% and approximately 65%, respectively, in tensile strength ( approximately 0.8 GPa) and modulus (approximately 90 GPa) during tensile testing; an approximately 20% improvement in electrical conductivity (approximately 80000 S m(-1)) was also reported. The mechanism of the microwave response of CNTs was discussed.

Micromachining of Pyrex 7740 Glass by Silicon Molding and Vacuum Anodic Bonding

A wafer-level processing technology that is used to precisely fabricate regular arrays of deep cavities in a Pyrex 7740 glass wafer is presented by silicon molding and vacuum anodic bonding. The fabrication process is based on etching cavities in silicon, followed by vacuum anodic bonding of a glass wafer to the etched silicon wafer. The bonded wafers are then heated inside a furnace at a temperature above the softening point of the glass, and the glass is shaped into cavities. The processing parameters are obtained by a series of experiments. The array of square glass cavities with 10-μm side length is accurately fabricated. Finally, a wafer-level hermetic packaging process is demonstrated after the second anodic bonding process. A diced single chip has been tested for leakage rate and bonding strength, which shows that the presented fabrication process is appropriate for the wafer-level packaging of MEMS devices.

Micromachining of Pyrex7740 glass and their applications to wafer-level hermetic packaging of MEMS devices

A new wafer-level process to precisely fabricate regular arrays of deep cavities on the Pyrex7740 glass wafer as well as applications to wafer-level hermetic packaging of MEMS devices are presented. The process is based on the anodic bonding, and the Si substrate is employed as a mold layer to form the shape of the cavity. The appropriate processing parameter is obtained from a series of experiments. Finally, the wafer-level hermetic packaging process of MEMS devices is completed by the second anodic bonding process. The whole process has been carried out with dew point sensors in wafer-level and illustrated in detail.

Hot-forming of micro glass cavities for MEMS wafer level hermetic packaging

Hermetic or vacuum packaging to maintain a controllable cavity pressure and low costs are required by many MEMS devices having moving parts. In this paper we propose a hot-forming process of fabricating micro glass cavity arrays for wafer-level and hermetic packaging of MEMS. First, the principle of the hot-forming process was discussed. Then, the hot-forming process for preparing cavity arrays in Pyrex7740 glass wafer was studied experimentally. After that, edge wrinkling of hot-formed wafers, hermetic wafer-level packaging, singulation of the wafer level cavity arrays were discussed. Results show that wafer-level packaged cavities were prepared, whose diameter was controllably between 200 microns and 2000 microns. It is also found that the hot-forming temperature and the processing time affect the filling rate of the glass. Results also show that edge wrinkling of hot-formed wafer could be removed by lowering the hot-forming temperature. It is then revealed that singulation of bonded wafers was achieved by low-cost laser drilling. Results show that the leakage rate of the packaged cavity is below 5Χ10−9 Pa. m / s.

Fabrication of Micro-Polymer Lenses With Spacers Using Low-Cost Wafer-Level Glass-Silicon Molds

A novel low-cost molding process to prepare polymer-based micro-lens arrays with spacers for optical applications was investigated in this paper. The process consists of the following steps: 1) hemispherical glass bubble arrays, used as the upper part of the molds, was prepared by combining a hot-forming process and a chemical-foaming process; 2) the silicon mold, used as the lower part of the molds, was fabricated by etching; 3) an anti-stick layer was coated on the concave surface of the glass mold; and 4) the lens material, UV-curable glue, was dispensed into the concave molds, followed by curing and de-molding. The optical properties of the lens were characterized by a profile meter and a beam analyzer. The results showed that the micro-polymer lens arrays with spacers were successfully prepared using the low-cost wafer-level glass-silicon mold. The results indicate that the micro-lenses have hemispherical structures and smooth surface.

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.

Chip-on-board (COB) wafer level packaging of LEDs using silicon substrates and chemical foaming process(CFP)-made glass-bubble caps

In this paper, we investigate a novel Chip-On-Board (COB) process for wafer level LED packaging using micro glass-bubble caps and silicon substrates. The COB packaging process is firstly studied experimentally, which consists of the following steps. First, a silicon substrate with lead lines is prepared. Second, LEDs are mounted on the silicon substrate followed by wire-bonding. Third, phosphor is distributed uniformly onto the spherical inner wall surface of glass bubbles. Fourth, the spherical glass bubbles are filled with silica gel. Finally the LEDs on the silicon substrate are encapsulated by the spherical glass-bubble caps. The thermal performance of the LEDs using the COB technology is then simulated by ANSYS and tested. Results show that the COB process is demonstrated successfully and the packaged LED chip has a good thermal and optical performance. Results also indicate that the wafer level COB LED packaging technology using silicon substrates and CFP-made spherical glass-bubble caps would improve the reliability and optical performance of high power white light LEDs greatly.

A new approach to fabricate deep cavities in Pyrex7740 glass for vacuum packaging of sensors

In the field of manufacturing of micro-system, the Pyrex7740 glass is a widely-used material since its coefficient of thermal expansion is similar to that of silicon and it has good optical performance for optical sensors and actuators. The use of Pyrex7740 glass is limited by its isotropic etching characteristic. In this paper, a new wafer-level process to precisely fabricate deep cavities on the Pyrex7740 glass is presented. The process is based on the anodic bonding, and the Si substrate is employed as a mold layer to form the shape of the cavity. Finally the cavities were formed by the atmospheric pressure after the special heat treatment. The Pyrex7740 glass substrate with cavities could be used for high density packaging of micro-system by anodic bonding or adhesive bonding, and may also benefit the application in the micro flow channel system. This new micro-machining process could be described as a basic wafer-level process to the MEMS technology.

Fabrication of low cost wafer-level micro-lens arrays with spacers using glass molds by combining a Chemical Foaming Process (CFP) and a Hot Forming Process (HFP)

This paper reports an innovative molding process for the fabrication of low cost wafer-level micro-lens array with spacers of optical applications. The concave mold for the micro-lens includes two parts: the upper glass mold and the under silicon mold. The upper glass mold was prepared by combining the Hot Forming Process (HFP) and the Chemical Foaming Process (CFP). The under silicon mold was prepared by etching. Specially designed concave structures were prepared on both parts. An anti-adhesion layer was formed on the surface of the concave mold. UV-light curable glue, the lens material, was injected into the concave mold and cured. Results show that wafer-level micro-lens arrays with spacers were successfully fabricated after de-molding the reusable mold. Samples of 6×6 micro-lens arrays with spacers, in diameter of 800μm and pitch of 2600μm, were prepared. Fabrication imperfection and design of micro-lens array was discussed.

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.