Manuel Engesser et al. 2009) have been well developed and widely used in industrial and commercial applications. Recently, with the market expansion of electronic devices including automobiles, aerospace and portable electronics, great research effects have been motivated again to develop monolithic integrated silicon composite sensors that feature high reliability, low costs and mass fabrication capability (Wang et al. 2011(Wang et al. , 2012Xu et al. 2008;Roozeboom et al. 2013).This study aims at developing a novel monolithic composite MEMS sensor. The composite sensor integrated a piezoresistive pressure sensor and a piezoresistive accelerometer on one chip. It has a sandwich structure and is fabricated using bulk-micromachining process (Chen et al. 2009) and anodic wafer bonding technology (Liu et al. 2011;San et al. 2013). The accelerometer adopts double-cantilever-mass structure by which double cantilevers can lessen lateral sensitivity in insensitive direction and the mass can enlarge sensitivity in sensitive direction. The pressure sensor has rectangular diaphragm structure. The mass of accelerometer and the pressure-sensing diaphragm of pressure sensor are simultaneously wet anisotropic etched by using only one mask. Anodic bonding technology is used to seal the pressure-reference cavity for the pressure sensor and form the vacuum chamber for free motivation of accelerometer's cantilever-mass. Glass is bonded with the low pressure chemical vapor deposition (LPCVD) α-Si (amorphous silicon) layer in front side of wafer and with the silicon substrate in back side, respectively, to form sandwich structure. Around bonding areas in front side of wafer, trenches are designed and fabricated to ensure the electrical conduction between the LPCVD α-Si layer and the silicon substrate, which can protect the piezoresistors from p-n junction break-down during anodic bonding process in front side of wafer.Abstract A monolithic composite MEMS sensor with sandwich structure is designed, simulated, fabricated and characterized. It consists of a rectangular diaphragm piezoresistive pressure sensor and a double-cantilever-mass piezoresistive accelerometer. The professional MEMS software, Intellisuite 8.5, is used to simulate the performances of the composite sensor. The composite sensor is fabricated on a (100)-silicon wafer by using MEMS bulk-micromachining and anodic bonding technology. One-step wet anisotropic etching process on the backside of the wafer can form the main backside shape of the composite sensor including the mass of accelerometer and the pressure sensing diaphragm. The glass-silicon-glass sandwich structure is formed with α-Si (amorphous silicon)-glass anodic bonding on the top surface of the wafer and Siglass anodic bonding at the bottom. The fabricated composite sensor is measured, resulting in 33.0 μV/V kPa sensitivity for the 450 kPa-ranged pressure sensor, as well as, 11.2 μV/V g sensitivity for the 125 g-ranged accelerometer. The die size of the composite sensor chip is 2.5 mm × 2.5 mm × 1.4 mm. The...
Background Ductility of polymer-supported metal films is important for flexible electronic devices and it is strongly affected by the metal film, polymer substrate, and their interfacial properties. Objective In this paper, the effect of interfacial adhesion and substrate thickness on the metal film ductility was investigated. Methods Mechanical behavior of 500 nm-thick aluminum (Al) films deposited on polyethylene-terephthalate (PET) substrates with thickness of 12, 25, and 50 μm was studied by tensile testing with in-situ electrical resistance measurements and post-mortem scanning electron microscopy. In addition, plasma etching was applied to tailor the PET surface condition before Al film deposition. Subsequently, the Al/PET interfacial adhesion was quantitatively evaluated using the laser spallation approach.
ResultsThe tensile tests showed that plasma etching improved the ductility of the Al films, and that the apparent ductility of the Al film on the 50 μm-thick PET substrate was substantially lower than that on the 12 and 25 μm PET thickness. Laser spallation results revealed that the plasma etching increased the Al/PET interfacial adhesion. Conclusions The influence of plasma etching and substrate thickness on the Al film ductility can be explained by the interface adhesion and shear lag theory. Plasma etching improves the interfacial adhesion by inducing both chemical and physical changes on the PET surface, and substrate thickness contributes to interface shear stress upon strain localization. The competing effect of the interfacial adhesion and the interfacial shear stress leads to a limiting substrate thickness for the desired ductility at a given tensile strain.
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