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9 January 2008 Specialized hybrid batch fabrication process for MEMS RF voltage sensors
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RF voltage measurement based on electrostatic RMS voltage-to-force conversion is an alternative method in comparison to the classical thermal power dissipation method. It is based on a parallel-plate capacitor with one elastically hinged plate. By applying an AC voltage, a force proportional to its RMS value is generated between the plates, and consequently the movable plate swings to the equilibrium position between spring force and electrostatic force. For a theoretically adequate resolution and precision, the necessary geometrical dimensions of the sensor practically require the use of advanced micromachining techniques. In this contribution, we discuss a unique batch fabrication process to meet the challenge of having two very large plane-parallel surfaces separated by only a few microns. The basic design consists of an actuator made of silicon embedded between two glass wafers for electrical contacting and sealing. Each step of this hybrid process has been optimized to prevent residual liquids leading to stiction and breaking of the fragile parts of the micro-structures. Flat grooves in the silicon define the gap between the capacitor electrodes, and an anisotropic dry-etch step releases the actuator. A second glass wafer builds the top of the stack and is fixated using a patterned photo-resist. Bumpers on the bottom layer and ridges in the top wafer improve the robustness of the structure. In this paper, we present a detailed analysis of the production process, pointing out critical as well as alternative design steps towards the optimized sensor. Finally, results of working devices are shown.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Jan Dittmer, Rolf Judaschke, and Stephanus Büttgenbach "Specialized hybrid batch fabrication process for MEMS RF voltage sensors", Proc. SPIE 6800, Device and Process Technologies for Microelectronics, MEMS, Photonics, and Nanotechnology IV, 68000P (9 January 2008);


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