OP TI X SA FAQ on MEMS Mirrors What are Lemoptix MEMS mirrors

OP TI X SA FAQ on MEMS Mirrors What are Lemoptix MEMS mirrors - Description

What are the main characteristics of Lemoptix MEMS mirrors What is the difference between Mechanical and Opti ID: 30180 Download Pdf

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OP TI X SA FAQ on MEMS Mirrors What are Lemoptix MEMS mirrors

What are the main characteristics of Lemoptix MEMS mirrors What is the difference between Mechanical and Opti

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OP TI X SA FAQ on MEMS Mirrors What are Lemoptix MEMS mirrors




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OP TI X SA FAQ on MEMS Mirrors What are Lemoptix MEMS mirrors? ................................ ................................ ................................ ........ What are the main characteristics of Lemoptix MEMS mirrors? ................................ ............................ What is the difference between Mechanical and Optical Tilt Angle ................................ ....................... What is the difference between Magnetically and Electrostatically actuated MEMS mirror? ............... What is th e resonance frequency?

................................ ................................ ................................ ......... What is the difference between Static actuation mode and Resonant actuation mode? ...................... Can a MEMS mirror designed to be actuated in Static mode can also be actuated in Resonant mode? Can a MEMS mirror designed to be actuated in Resonant mode can also be actuated in Static mode? Does Lemoptix design custom MEMS mirrors: 1D and 2D? ................................ ................................ .... What are the tradeoffs when designing a MEMS mirror?

................................ ................................ ...... What is the minimum Lemoptix MEMS mirror module size? ................................ ................................ What is the Lemoptix MEMS shock resistance? ................................ ................................ ...................... What is the Lemoptix MEMS mirror lifetime? ................................ ................................ ........................ Is there any handling care with MEMS mirrors? ................................ ................................ ..................... What

is the reflectivity level over the wavelength range? ................................ ................................ .....
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OP TI X SA Lemoptix MEMS (Micro Electro Mechanical System) mirror, also called MOEMS, are mechanical suspended and movable structure , made of pure monocrystalline silicon, well known for having very high long term reliability and very good mechanical performance. d MEMS devices such as accelerometer are used as sensing device in automotive airbags, probably the m ost stringent application where reliability is simply essential. MEMS devices can also be

found in mobile device in the form of gyroscopes and accelerometers. Lemoptix has developed a new generation of MEMS device suitable for optical scanning application s including barcode scanners, endoscopy/confocal microscopy, optical spectrometers, medical imaging, microprojectors, head up displays, scanners, laser printers, fiber optics telecommunication etc... Responding to industry requests to significantly reduce size, power consumption and increased performance of micromirror devices, Lemoptix has developed a bottom up approach of manufacturing by using semi conductor equipment to build

highly innov ative products that feature: Monocrystalline silicon based and magnetically actuated micromirrors Static also called steering or DC, ( KHz 70KHz) mirrors 1D or 2D types 1 mm to 5mm overall size Up to +/ 50  optical degrees scanning angle (+/ 5 mechanical degrees scanning angle) Very low power , 0.2V 5V control voltage Close loop or open loop control (embedded position sensor to control both scanning angle and frequency) Off the shelf available or through custom services The optical angle is twice the mechanical angle , as see in the drawing below.
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OP TI X SA Magnetic and electrostatic actuation of MEMS mirrors are the two main actuation techniques. Electrostatic actuation works by applying a voltage potential difference between the MEMS mirror and the fixed part of the MEMS chip. Magnetic actuation works by the Lorentz force, when the MEMS mirror is placed under a permanent magnetic field. Both techniques can be used in principle but it has been demonstrated that the magnetic actuation technique brings significant advant ages as can be seen in the table below . Applications such as laser printer, confocal microscopy and laser

microprojection benefit from these inherent advantages. Electrostatic actuation Lemoptix Magnetic actuation Actuation voltage Very high (> 50V to 150V) Low (< 5V) Actuation linearity Very bad (hysteresis behavior) Very good Mirror control Very difficult (see linearity) Very good Power consumption Low Low Module size Small Small (patented architecture) Achievable scanning angle Large Very large Sensitivity to dust Very high (short circuit) None Mirror position sensing Indirect and low precision Direct and very precise Sensitivity to radiation Very high None Static actuation mode Very limited

(low angle) Very high angle achievable Resonant frequency is a frequency at which a body shows a very large reaction (amplitude motion or oscillation) for a low excitation level. For the MEMS mirror, it is the frequency at which the scanning amplitude is maximal for a given actuation level. Therefore t o achieve large scanning amplitude at very low power, the MEMS mirror should be actuated with an actuation signal equal to the mechanical resonant frequency for the mirror.
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OP TI X SA Normally , a MEMS mirror is mechanical ly design ed to work in either static or resonant mode.

Static also called steering mode means that the mirror is actuated far from its mechanical resonant frequency, and therefore the relation between the scanning angle and the actuation signal is linear and the mirror can be driven to hold a specific position by applying a certain continuous actuation signal. Typically the static mode operation goes from static (tilt the mirror and hold a position ) up to several hundreds of Hz. In this frequency range, the mirror will follow the actuation signal shape. The Resonant actuation mode is the mode where the MEMS mirror is actuated with a signal freq

uency equal to the resonant frequency of the mirror. Because the mirror scanning amplitude is amplified at mechanical resonant frequency (this amplification factor is called the Quality Factor), the mirror motion will act as a mechanical oscillator and then will follow a sinusoidal motion (and not a linear m otion which is the case for Static actuation mode) Yes. Indeed, each moving body has an intrinsic resonant frequency. A MEMS mirror designed to be actuated in Static mode will typically have a low mechanical stiffness to enable large Static motion will minimum signal amplitude. These types

of mirrors can a lso be actuated at their mechanical resonant frequency (typically lower than the resonant frequency of the designed Resonant mode MEMS mirrors). Note that if actuating the Static designed MEMS mirror at their resonant frequency, the required actuation sign al amplitude will have to be greatly reduce , to avoid having too large a scanning angle (due to the amplification factor at mechanical resonant frequency). See below the amplitude response of the MEMS mirror if actuated at a frequency far from the resonant frequency (left) and if actuated at the resonant frequency (right).

Note the difference in actuation signal amplitude: +/ 2.5V to achieve +/ 15 optical degrees on the left and only +/ 0.2V to achieve the same scanning amplitude on the right. 20 15 10 10 15 20 Optical scanning angle ( Applied DC voltage (V) 10 12 14 16 300 350 400 450 500 Optical angle [+/ ] ( Frequency (Hz)
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OP TI X SA Yes, but it is not optimized for such operation . MEMS mirror designed for Resonant mode are very stiff therefore actuating the MEMS mirror with a frequency far from the mechanical frequency will create very little motion of the mirror. Indeed at resonant

frequency, the MEMS mirror motion benefi ts from an amplification factor, called the Quality Factor. This me ans that for the same actuation signal amplitude, the MEMS mirror can show more than 500 times the scanning amplitude when actuated at its resonant frequency, than when actuated far from it. However once the actuation signal frequency becomes cl oser and closer to the mechanical resonant frequency of the mirror, the scanning amplitude becomes larger and larger, reaching its maximum at the MEMS resonant frequency. Lemoptix offers both off the shelf and custom solutions. I n the past 12

years, with over 300 different MEMS mirror designed, manufactured and tested, Lemoptix developed a unique expertise in designing 1D and 2D MEMS mirror. The design experience covers: 1D Static mode MEMS mir ror 1D Resonant mode MEMS mirror 2D MEMS mirror with 1 axis in Static mode and the other axis in Resonant mode 2D MEMS mirror with both axis in Static mode 2D MEMS mirror with both axis in Resonant mode Off the shelf 1D mirrors are presented in the genera l datasheet : http://www.lemoptix.com/technology/products/lscanmicromirror A MEMS mirror is a mechanical moving structure with optical

properties and related specifications, and a MEMS design mu t considering all these aspects . n general the main tradeoffs are: A high frequency mirror means the mirror size must be reduced in size to minimize the impact of the air damping A large scanning amplitude will require a smaller mirror size and lower mirror stiffness (then resulting in lower resonant frequency A large mirror size therefore require lower scanning a mplitude and resonant frequency, to maintain a good mirror flatness even during mirror motion To ensure mechanical assembly stability of the MEMS mirror chip (composed of

the moving part and fixed part of the MEMS) , a 1mm exclusion area around the moving part of the MEMS has to be considered. Therefore the Lemoptix minimum MEMS mirror module size can be calculated as follow: Module size (MEMS & magnet) = moving mirror size + 2mm
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OP TI X SA When designing a MEMS mirror, Lemoptix takes into account all parameters which are usually left aside , but which are key when designing products of high reliability . Shock resistance is one of these parameters, and for example F series mirror are designed to sustain shock above 4000g, which therefore fit

even the most stringent application. Because Lemoptix MEMS mirror are made of pure monocrytalline silicon and due to the ir specific mechanical desig , mirrors that have been tested above 10 12 cycles in continuous operation, day and night, do not show any performance degradation. MEMS mirrors are designed for high shock resistance but can break if a mass is directly applied to the unit. The uncovered mirror could be mishandled and broken simply with fingers or tweezers or other tools. Also, as a permanent magnet is employed to actuate the mirror, non magnetic tools should be used when

handling the mirror chip. Lemoptix MEMS mirrors are coated with high reflective aluminum coating, covered by a protective layer to avoid any corrosion. Typical reflectivity level in the visible range is above 85% and this value is greater in the UV and in the IR wavelengths (see http://en.wikipedia.org/wiki/Reflectivity