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Design example: Variable Optical Attenuator (VOA) MEMS Device VOAs play an important role in fibre optic networks. They are widely used in Dense Wavelength Division Multiplexing (DWDM) for signal intensity control at the transmission and reception nodes. The micro mirror based VOAs use an actuator to tilt the mirror and control the misalignment between the input optical beam and output fibre. The optical attenuation is set by the amount of misalignment.

The VOA chip shown in figure 2 is a uni-directional (1D) tilting micro mirror fabricated with the aforementioned platform. The vertical comb drive actuator in this design significantly reduces the voltage requirement to achieve maximum tilt and has a linear voltage-theta curve within its designed operating range. The result is shown in figure 3. With the low-stress gold metallisation on the top surface, the radius of curvature of the mirror is greater than 1.5 µm.

Technology Prototyping: Multi Project Wafer Runs Researchers and designers benefit by being able to access the common process platform for MEMS SOI technology through the use of multi-project wafer fabrication. This allows multiple designs to co-inhabit the same fabrication run and share costs associated with setup, mask development and fabrication, reducing the prototyping costs for the individual designer. Moreover, the repeated runs of the same process flow increases the yield of fabrication, thus provides further reduction in cost. Additionally, by virtue of process standardisation, use of this platform provides a predictable and faster path to prototyping, as well as a direct path to larger volume production for commercial applications. Micralyne has partnered with CMC Microsystems to make this process available to companies and researchers as part of a cost effective Multi-Project Wafer (MPW) prototyping service.

Another virtue of a standard process platform is enabling development of a robust process design kit, or PDK. This allows enhanced use of design software, thereby improving and expediting the design and simulation phase, which will lead to reducing manufacturing risk. The PDK for this platform is based on the Tanner L-Edit/MEMS Pro interface, which allows for layout development and design rule checking. Additionally, by utilizing the information of the design process, 3D models of the device can be generated for physical modelling and optimisation through a number of software tools, such as ANSYS or COMSOL.

Summary The presented MicraGEM-Si process platform incorporate novel process options, enabling design of vertical comb drive actuators and other key MEMS structures supporting applications including optical based MEMS devices and inertial sensors. The MPW prototyping service will allow MEMS researchers to design and manufacture devices within defined design rules, greatly reducing the initial cost and risk of development, while speeding the time to market for MEMS-based devices.


CMC Microsystems

<< Figure 3:

MEMS for VOA — mirror tilt

response to an

applied voltage. >>

45 | commercial micro manufacturing international Vol 7 No.3

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