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LAB4MEMS II
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Introduction

Building on the established foundation and successes of the first Lab4MEMS project, Lab4MEMS II has been launched by the European Nanoelectronics Initiative Advisory Council with the aim of developing a pilot line for innovative key enabling technologies on advanced Micro-Opto-Electro-Mechanical Systems (MOEMS). MOEMS, which merge MEMS and Micro-optics are designed to sense and manipulate optical signals on a very small scale, using integrated mechanical, optical and electrical systems. Such multi-technology integration make MOEMS an ideal platform for many industrial demonstrators and future commercial products such as pico-projectors, IR scanners and spectrometers actuated electrostatically or electromagnetically or piezo-electrically. The project will therefore aim in demonstrating the successful implementation of innovative MOEMS micro-mirror technologies enabling 3D IR scanning (Fig. 1a) and video projection though pico-projectors integrated with low-power portable electronics (Fig. 1b).


             

Fig. 1: Micro-mirror technologies for (a) pico-projectors (b) micro-scanners


The €20.5 million Lab4MEMS II project involves 20 industrial, academic and research partners, including the University of Malta and is in line with the European Community’s target of establishing Europe at the fore-front of micro and nanotechnology. The project will promote investment in the manufacturing and characterisation facilities currently located in each participating country while the main MOEMS industrial pilot line being located at ST-Microelectronics, the project’s coordinating partner.
 

UoM Contributions

The University of Malta (UoM) is actively involved in a number of work packages (WP) within Lab4MEMS II. In WP2, UoM is contributing in the design and optimisation of single and dual-axis micro-mirrors, utilising different actuation methodologies which are targeted for pico-projector and micro-scanner applications. As part of WP3, UoM is focusing on the finite element (FE) numerical techniques enabling the simulation of electrostatic and electromagnetic micro-mirror actuation with a focus on fluid damping mechanisms. UoM is also involved in WP4, where the design and construction of an in-house MOEMS characterisation facility is undertaken, in order to enable the scanning and dynamic display performance measurements of the fabricated micro-mirror prototypes. UoM is also involved in WP6, whose aim is to elaborate and coordinate a plan of dissemination, exploitation and standardisation. The following sections provide more details on the on-going tasks undertaken by UoM as part of the project.

Design Optimisation of a Single-axis Resonating Micromirror

UoM, in collaboration with ST, is engaged in the performance analysis of an electrostatically actuated single-axis micro-mirror designs operating in a resonant torsional mode as part of a raster scanning optical system. The aim of this work is to increase the resonant frequency, scan angle and mirror diameter while limiting the actuation bias voltage, mirror dynamic deformation (Fig. 2) and torsional spring stresses. Parametric design optimisation will be carried out by performing coupled structural-electrostatic-fluidic simulations using ANSYS FE software, the results from which will be experimentally validated.
  
Fig. 2: Dynamic deformation of a rectangular micromirror oscillating at 25 kHz and max θ of 12°


Design of a Gimbal-less Electrostatic Micromirror


The two axis gimbal-less MEMS mirror consists of a structure that can resonate along two different rotational axis at two separate frequencies. Since the difference in resonant frequencies can only be very small, the 2D Lissajous scanning pattern is produced. The maximum resolution obtainable with these patterns is dependent on the ratio of the two frequencies therefore precise tuning of these two frequencies is required. UoM is also working on the development of a new actuation method that utilises a vertical comb drive instead of rotational comb drive. This allows the manufacturing of a more compact mirror (Fig. 3). Analysis is also being carried out on the mirror deformation introduced by this new actuation mechanism.

 
                                           

Fig. 3: Modal analysis of a bidirectional gimbal-less micromirror design 


Design of an Electromagnetic Micromirror


Among the actuation mechanisms for MOEMS devices, electromagnetic technology can result in relatively large static torque and displacements at low voltages. The investigated design for the electromagnetic micro-mirror exploits the Lorentz force between an external magnetic field and the current flowing into properly modelled micro-coils. The numerical analysis of the proposed electromagnetically actuated micromirror has been performed using COMSOL in order to explore and demonstrate the actual feasibility of this actuation technology and to obtain preliminary results on the micro-mirror rotation range.



Fig. 4: Torsional mode shape 3-axis micro-mirror preliminary design with electromagnetic actuation


MOEMS Characterisation Setup

UoM is also setting up a MOEMS testing facility in order to characterize optical devices developed by various partners. The facility consists of three setups: The first setup uses a position sensitive detector to measure the angle of a scanning micro-mirror. The second setup (Fig. 5a) is compact version of to the first setup, which allows it to be mounted on a force shaker in order to analyze the performance of a scanning micro-mirror in a vibrating environment. The last setup uses a global shutter camera to analyze the quality of a pixel projected by a MOEMS projector. As part of the Lab4MEMS II project, UoM also procured a micromechanical testing station (Fig. 5b). This device applies a mechanical force on the micro-mirrors in order to measure the spring stiffness and other mechanical properties.