Microscanner

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A microscanner, or micro scanning mirror, is a microoptoelectromechanical system (MOEMS) in the category of micromirror actuators for dynamic light modulation. Depending upon the type of microscanner, the modulatory movement of a single mirror can be either translatory or rotational, on one or two axes. In the first case, a phase shifting effect takes place. In the second case, the incident light wave is deflected.

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Resonant translational mirror in pantograph design with a deflection of +-500 mm Translatmsm.jpg
Resonant translational mirror in pantograph design with a deflection of ±500 μm

Microscanners are different from spatial light modulators and other micromirror actuators which need a matrix of individually addressable mirrors in order to accomplish the desired modulation at any yield. If a single array mirror accomplishes the desired modulation but is operated in parallel with other array mirrors to increase light yield, then the term microscanner array is used.

Characteristics

Common chip dimensions are 4 mm × 5 mm for mirror diameters between 1 and 3 mm. [1] Larger mirror apertures with side measurements of up to approx. 10 mm × 3 mm can also be produced. [2] The scan frequencies depend upon the design and mirror size and range between 0.1 and 50 kHz. The deflection movement is either resonant or quasi-static. [3] With microscanners that are capable of tilting movement, light can be directed over a projection plane.

Many applications requires that a surface is addressed instead of only a single line. For these applications, actuation using a Lissajous pattern can accomplish sinusoidal scan motion, or double resonant operation. Mechanical deflection angles of micro scanning devices reach up to ±30°. [4] Translational (piston type) microscanners, can attain a mechanical stroke of up to approx. ±500 μm. [5] This configuration is energy efficient, but requires complicated control electronics. For high end display applications the common choice is raster scanning, where a resonant scanner (for the longer display dimension) is paired with quasi-static scanner (for the shorter dimension). [3]

Drive principles

The required drive forces for the mirror movement can be provided by various physical principles. In practice, the relevant principles for driving such a mirror are the electromagnetic, electrostatic, thermoelectric, and piezoelectric effects. [3] Because the physical principles differ in their advantages and disadvantages, the driving principle is chosen according to the application. Specifically, the mechanical solutions required for resonant scanning are very different for those of quasi-static scanning. Thermoelectric actuators are not applicable for high-frequency resonant scanners, but the other three principles can be applied to the full spectrum of applications.

For resonant scanners, one often employed configuration is the indirect drive. In an indirect drive, a small motion in a larger mass is coupled to a large motion in a smaller mass (the mirror) through mechanical amplification at a favorable mode shape. This is in contrast to the more common direct drive, where the actuator mechanism moves the mirror directly. Indirect drives have been implemented for electromagnetic, [6] electrostatic, [7] as well as piezoelectric actuators. [8] [9] Existing piezoelectric scanners are more efficient using direct drive. [3]

Electrostatic actuators offer high power similar to electromagnetic drives. In contrast to an electromagnetic drive, the resulting drive force between the drive structures cannot be reversed in polarity. For the realization of quasi-static components with positive and negative effective direction, two drives with positive and negative polarity are required. [10] As a rule of thumb, vertical comb drives are utilized here. Nevertheless, the highly non-linear drive characteristics in some parts of the deflection area can be hindering for controlling the mirror properly. For that reason many highly developed microscanners today utilize a resonant mode of operation, where an eigenmode is activated. Resonant operation is the most energy-efficient. For beam positioning and applications which are to be static-actuated or linearized-scanned, quasi-static drives are required and therefore of great interest.

Magnetic actuators offer very good linearity of the tilt angle versus the applied signal amplitude, both in static and dynamic operation. The working principle is that a metallic coil is placed on the moving MEMS mirror itself and as the mirror is placed in a magnetic field, the alternating current flowing in the coil generates Lorentz force that tilts the mirror. Magnetic actuation can either be used for actuating 1D or 2D MEMS mirrors. Another characteristic of the magnetically actuated MEMS mirror is the fact that low voltage is required (below 5V) making this actuation compatible with standard CMOS voltage. An advantage of such an actuation type is that MEMS behaviour does not present hysteresis, as opposed to electrostatic actuated MEMS mirrors, which make it very simple to control. Power consumption of magnetically actuated MEMS mirrors can be as low as 0.04 mW. [11]

Thermoelectric drives produce high driving forces, but they present a few technical drawbacks inherent to their fundamental principle. The actuator has to be thermally well insulated from the environment, as well as being preheated in order to prevent thermal drift due to environmental influences. That is why the necessary heat output and power consumption for a thermal bimorph actuator is relatively high. One further disadvantage is the comparably low displacement which needs to be leveraged to reach usable mechanical deflections. Also thermal actuators are not suitable for high frequency operation due to significant low pass behaviour.

Piezoelectric drives produce high force, but as with electrothermal actuators the stroke length is short. Piezoelectric drives are, however, less susceptible to thermal environmental influences and can also transmit high-frequency drive signals well. To achieve the desired angle some mechanism utilizing mechanical amplification will be required for most applications. This has proven to be difficult for quasi-static scanners, although there are promising approaches in the literature using long meandering flexures for deflection amplification. [12] [13] For resonant rotational scanners, on the other hand, scanners using piezoelectric actuation combined with an indirect drive are the highest performer in terms of scan angle and working frequency. [8] [9] [14] However, the technology is newer than electrostatic and electromagnetic drives and remains to be implemented in commercial products. [3]

Fields of Application

LDC module with 1D microscanner and integrated optical position sensor on the back side Fraunhofer IPMS 1D-Mikroscanner-Module.jpg
LDC module with 1D microscanner and integrated optical position sensor on the back side
An electrostatic 2D microscanner in a DIL20 casing Fraunhofer IPMS 2D-Mikroscanner-Modul.jpg
An electrostatic 2D microscanner in a DIL20 casing
MEMS scanner module for 3D distance measurement (LIDAR) with a single sending mirror (mirror dimensions approx. (9.5 x 2.5 mm)) and a synchronized microscanner array (2 x 7) as receiver unit. Fraunhofer IPMS 3D-Mikroscanner-Modul.jpg
MEMS scanner module for 3D distance measurement (LIDAR) with a single sending mirror (mirror dimensions approx. (9.5 × 2.5 mm)) and a synchronized microscanner array (2 × 7) as receiver unit.

Applications for tilting microscanners are numerous and include:

Some of the applications for piston type microscanners are:

Manufacture

Wafer with resonant microscanners, ready-processed with the Fraunhofer AME75 process (based on blank BSOI wafers), before dicing the devices. Fraunhofer IPMS Im AME75-Prozess gefertigte Mikroscanner auf einem BSOI-Wafer.jpg
Wafer with resonant microscanners, ready-processed with the Fraunhofer AME75 process (based on blank BSOI wafers), before dicing the devices.
Detail of a wafer with VarioS microscanners, developed and produced based on a modular fabrication system at Fraunhofer IPMS. Fraunhofer IPMS VarioS-Mikroscanner auf einem BSOI-Wafer.jpg
Detail of a wafer with VarioS microscanners, developed and produced based on a modular fabrication system at Fraunhofer IPMS.

Microscanners are usually manufactured with surface or bulk micromechanic processes. As a rule, silicon or BSOI (bonded silicon on insulator) are used.

Advantages and disadvantages of microscanners

Microscanners are smaller, lower mass, and consume smaller amounts of power compared to macroscopic light modulators such as galvanometer scanners. Additionally, microscanners can be integrated with other electronic components such as position sensors. [17] Microscanners are resistant to environmental influences, and can tolerate humidity, dust, physical shocks in some models up to 2500g, and can operate in temperatures from -20 °C to +80 °C.

With current manufacturing technology microscanners can suffer from high costs and long lead times to delivery. This is an active area of process improvement

Related Research Articles

<span class="mw-page-title-main">MEMS</span> Very small devices that incorporate moving components

MEMS is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size, and MEMS devices generally range in size from 20 micrometres to a millimetre, although components arranged in arrays can be more than 1000 mm2. They usually consist of a central unit that processes data and several components that interact with the surroundings.

<span class="mw-page-title-main">Atomic force microscopy</span> Type of microscopy

Atomic force microscopy (AFM) or scanning force microscopy (SFM) is a very-high-resolution type of scanning probe microscopy (SPM), with demonstrated resolution on the order of fractions of a nanometer, more than 1000 times better than the optical diffraction limit.

Laser scanning is the controlled deflection of laser beams, visible or invisible. Scanned laser beams are used in some 3-D printers, in rapid prototyping, in machines for material processing, in laser engraving machines, in ophthalmological laser systems for the treatment of presbyopia, in confocal microscopy, in laser printers, in laser shows, in Laser TV, and in barcode scanners. Applications specific to mapping and 3D object reconstruction are known as 3D laser scanner.

<span class="mw-page-title-main">Deformable mirror</span> Mirror whose surface can be deformed

Deformable mirrors (DM) are mirrors whose surface can be deformed, in order to achieve wavefront control and correction of optical aberrations. Deformable mirrors are used in combination with wavefront sensors and real-time control systems in adaptive optics. In 2006 they found a new use in femtosecond pulse shaping.

<span class="mw-page-title-main">Bimorph</span>

A bimorph is a cantilever used for actuation or sensing which consists of two active layers. It can also have a passive layer between the two active layers. In contrast, a piezoelectric unimorph has only one active layer and one passive layer.

A MEMS thermal actuator is a microelectromechanical device that typically generates motion by thermal expansion amplification. A small amount of thermal expansion of one part of the device translates to a large amount of deflection of the overall device. Usually fabricated out of doped single crystal silicon or polysilicon as a complex compliant member, the increase in temperature can be achieved internally by electrical resistive heating or by a heat source capable of locally introducing heat. Microfabricated thermal actuators can be integrated into micromotors.

Microoptoelectromechanical systems (MOEMS), also known as optical MEMS, are integrations of mechanical, optical, and electrical systems that involve sensing or manipulating optical signals at a very small size. MOEMS includes a wide variety of devices, for example optical switch, optical cross-connect, tunable VCSEL, microbolometers. These devices are usually fabricated using micro-optics and standard micromachining technologies using materials like silicon, silicon dioxide, silicon nitride and gallium arsenide.

<span class="mw-page-title-main">Digital micromirror device</span>

The digital micromirror device, or DMD, is the microoptoelectromechanical system (MOEMS) that is the core of the trademarked DLP projection technology from Texas Instruments (TI). Texas Instrument's DMD was created by solid-state physicist and TI Fellow Emeritus Dr. Larry Hornbeck in 1987. However, the technology goes back to 1973 with Harvey C. Nathanson's use of millions of microscopically small moving mirrors to create a video display of the type now found in digital projectors.

Micromirror devices are devices based on microscopically small mirrors. The mirrors are microelectromechanical systems (MEMS), which means that their states are controlled by applying a voltage between the two electrodes around the mirror arrays. Digital micromirror devices are used in video projectors and optics and micromirror devices for light deflection and control.

<span class="mw-page-title-main">Digital holographic microscopy</span>

Digital holographic microscopy (DHM) is digital holography applied to microscopy. Digital holographic microscopy distinguishes itself from other microscopy methods by not recording the projected image of the object. Instead, the light wave front information originating from the object is digitally recorded as a hologram, from which a computer calculates the object image by using a numerical reconstruction algorithm. The image forming lens in traditional microscopy is thus replaced by a computer algorithm. Other closely related microscopy methods to digital holographic microscopy are interferometric microscopy, optical coherence tomography and diffraction phase microscopy. Common to all methods is the use of a reference wave front to obtain amplitude (intensity) and phase information. The information is recorded on a digital image sensor or by a photodetector from which an image of the object is created (reconstructed) by a computer. In traditional microscopy, which do not use a reference wave front, only intensity information is recorded and essential information about the object is lost.

<span class="mw-page-title-main">MEMS magnetic field sensor</span>

A MEMSmagnetic field sensor is a small-scale microelectromechanical systems (MEMS) device for detecting and measuring magnetic fields (Magnetometer). Many of these operate by detecting effects of the Lorentz force: a change in voltage or resonant frequency may be measured electronically, or a mechanical displacement may be measured optically. Compensation for temperature effects is necessary. Its use as a miniaturized compass may be one such simple example application.

A MEMS magnetic actuator is a device that uses the microelectromechanical systems (MEMS) to convert an electric current into a mechanical output by employing the well-known Lorentz Force Equation or the theory of Magnetism.

MEMS for in situ mechanical characterization refers to microelectromechanical systems (MEMS) used to measure the mechanical properties of nanoscale specimens such as nanowires, nanorods, whiskers, nanotubes and thin films. They distinguish themselves from other methods of nanomechanical testing because the sensing and actuation mechanisms are embedded and/or co-fabricated in the microsystem, providing—in the majority of cases—greater sensitivity and precision.

Microelectromechanical system oscillators are devices that generate highly stable reference frequencies to measure time. The core technologies used in MEMS oscillators have been in development since the mid-1960s, but have only been sufficiently advanced for commercial applications since 2006. MEMS oscillators incorporate MEMS resonators, which are microelectromechanical structures that define stable frequencies. MEMS clock generators are MEMS timing devices with multiple outputs for systems that need more than a single reference frequency. MEMS oscillators are a valid alternative to older, more established quartz crystal oscillators, offering better resilience against vibration and mechanical shock, and reliability with respect to temperature variation.

Electrostatic–pneumatic activation is an actuation method for shaping thin membranes for microelectromechanical and microoptoelectromechanical systems. This method benefits from operation at high speed and low power consumption. It can also cause large deflection on thin membranes. Electrostatic-pneumatic MEMS devices usually consist of two membranes with a sealed cavity in between. One membrane-calling actuator deflects into the cavity by electrostatic pressure to compress air and increase air pressure. Elevated pressure pushes the other membrane and causes a dome shape. With direct electrostatic actuation on the membrane, a concave shape is achieved.

A nanoelectromechanical (NEM) relay is an electrically actuatedswitch that is built on the nanometer scale using semiconductor fabrication techniques. They are designed to operate in replacement of, or in conjunction with, traditional semiconductor logic. While the mechanical nature of NEM relays makes them switch much slower than solid-state relays, they have many advantageous properties, such as zero current leakage and low power consumption, which make them potentially useful in next generation computing.

A microvalve is a microscale valve, i.e. a microfluidic two-port component that regulates the flow between two fluidic ports. Microvalves are basic components in microfluidic devices, such as labs-on-a-chip, where they are used to control the fluidic transport. During the period from 1995 to 2005, many microelectromechanical systems-based microvalves were developed.

A piezoelectric microelectromechanical system (piezoMEMS) is a miniature or microscopic device that uses piezoelectricity to generate motion and carry out its tasks. It is a microelectromechanical system that takes advantage of an electrical potential that appears under mechanical stress. PiezoMEMS can be found in a variety of applications, such as switches, inkjet printer heads, sensors, micropumps, and energy harvesters.

<span class="mw-page-title-main">Niels Quack</span> Swiss and German engineer

Niels Quack is a Swiss and German engineer specialized in optical micro engineering. He is a SNSF professor at EPFL and director of the Photonic Micro- and Nanosystems Laboratory at its school of engineering.

<span class="mw-page-title-main">Wibool Piyawattanametha</span> Professor

Wibool Piyawattanametha is the head of Advanced Imaging Research (AIR) Center, King Mongkut's Institute of Technology Ladkrabang, Thailand.

References

  1. ↑ VarioS Mikroscanner Construction Kit. Fraunhofer Institute for Photonic Microsystems IPMS (Product Description).
  2. 1 2 Sandner, T.; Grasshoff, T.; Wildenhain, M.; Schenk, H. (2010). Schenk, Harald; Piyawattanametha, Wibool (eds.). "Synchronized micro scanner array for large aperture receiver optics of LIDAR systems". Proc. SPIE. MOEMS and Miniaturized Systems IX. 7594 – MOEMS and Miniaturized Systems IX: 75940C. Bibcode:2010SPIE.7594E..0CS. doi:10.1117/12.844923. S2CID   108647803.
  3. 1 2 3 4 5 6 Holmstrom, S.T.S.; Baran, U.; Urey, H. (2014). "MEMS Laser Scanners: A Review". Journal of Microelectromechanical System. 23 (2): 259–275. doi:10.1109/JMEMS.2013.2295470. S2CID   23257771.
  4. 1 2 Drabe, C.; James, R.; Schenk, H.; Sandner, T. (2010). Schenk, Harald; Piyawattanametha, Wibool (eds.). "MEMS-Devices for Laser Camera Systems for Endoscopic Applications". Proc. SPIE. MOEMS and Miniaturized Systems IX. 7594 – MOEMS and Miniaturized Systems IX: 759404. Bibcode:2010SPIE.7594E..04D. doi:10.1117/12.846855. S2CID   111072386.
  5. ↑ Sandner, T.; Grasshoff, T.; Schenk, H.; Kenda, A. (2011). Schenk, Harald; Piyawattanametha, Wibool (eds.). "Out-Of-Plane Translatory MEMS actuator with extraordinary large stroke for optical path length modulation". Proc. SPIE. MOEMS and Miniaturized Systems X. 7930 – MOEMS and Miniaturized Systems X: 79300I. Bibcode:2011SPIE.7930E..0IS. CiteSeerX   10.1.1.1001.2433 . doi:10.1117/12.879069. S2CID   42065927.
  6. 1 2 Yalcinkaya, A.D.; Urey, H.; Brown, D.; Montague, T.; Sprague, R. (2006). "Two-Axis Electromagnetic Microscanner for High Resolution Displays". Journal of Microelectromechanical Systems. 15 (4): 786–794. doi:10.1109/JMEMS.2006.879380. S2CID   43694721.
  7. ↑ Arslan, A.; Brown, D.; Davis, W.O.; Holmstrom, S.; Gokce, S.K.; Urey, H. (2010). "Comb-Actuated Resonant Torsional Microscanner With Mechanical Amplification". Journal of Microelectromechanical System. 19 (4): 936–943. doi:10.1109/JMEMS.2010.2048095. S2CID   9521896.
  8. 1 2 Baran, U.; Brown, D.; Holmstrom, S.; Balma, D.; Davis, W.O.; Muralt, P.; Urey, H. (2012). "Resonant PZT MEMS Scanner for High-resolution Displays". Journal of Microelectromechanical System. 21 (6): 1303–1310. doi:10.1109/JMEMS.2012.2209405. S2CID   19273731.
  9. 1 2 Gu-Stoppel, S.; Janes, J.; Kaden, D.; Quenzer, H.; Hofmann, U.; Benecke, W. (2013). Piezoelectric resonant micromirror with high frequency and large deflection applying mechanical leverage amplification. Proc. SPIE Micromachining and Microfabrication Process Technology XVIII. San Francisco, CA, USA. pp. 86120I–1–86120I–8. doi:10.1117/12.2001620.
  10. ↑ D. Jung; T. Sandner; D. Kallweit; T. Grasshoff; H. Schenk (2012), Schenk, Harald; Piyawattanametha, Wibool; Noell, Wilfried (eds.), "Vertical comb drive microscanners for beam steering, linear scanning and laser projection applications", MOEMS and Miniaturized Systems XI, MOEMS and Miniaturized Systems XI (in German), vol. 8252, pp. 82520U–1–10, Bibcode:2012SPIE.8252E..0UJ, doi:10.1117/12.906690, S2CID   109410879
  11. ↑ "Lemoptix - LSCAN Micromirror". Archived from the original on 2012-02-06. Retrieved 2012-02-07.
  12. ↑ Tani, M.; Akamatsu, M.; Yasuda, Y.; Toshiyoshi, H. (2007). A two Axis Piezoelectric Tilting Micromirror with a Newly Developed PZTmeandering Actuator. Proc. IEEE 20th Int. Conf. MEMS. Kobe, Japan. pp. 699–702. doi:10.1109/MEMSYS.2007.4432994.
  13. ↑ Kobayashi, T.; Maeda, R.; Itoh, T. (2009). "Low Speed Piezoelectric Optical Microscanner Actuated by Piezoelectric Microcantilevers Using LaNiO3 Buffered Pb(Zr, Ti)O3 Thin Film". Smart Materials and Structures. 18 (6): 065008–1–065008–6. Bibcode:2009SMaS...18f5008K. CiteSeerX   10.1.1.710.550 . doi:10.1109/JMEMS.2012.2209405. S2CID   19273731.
  14. ↑ Baran, U.; Holmstrom, S.; Brown, D.; Davis, W.O.; Cakmak, O.; Urey, H. (2014). Resonant PZT MEMS Scanners with Integrated Angle Sensors. 2014 International Conference on Optical MEMS and Nanophotonics (OMN). Journal of Microelectromechanical System. Glasgow, Scotland. pp. 99–100. doi:10.1109/OMN.2014.6924612.
  15. ↑ Scholles, Michael; Bräuer, Andreas; Frommhagen, Klaus; Gerwig, Christian; Lakner, Hubert; Schenk, Harald; Schwarzenberg, Markus (2008). "Ultracompact laser projection systems based on two-dimensional resonant microscanning mirrors". Journal of Micro/Nanolithography, MEMS, and MOEMS. 7 (2): 021001. doi:10.1117/1.2911643.
  16. ↑ Wolter, A.; Schenk, H.; Gaumont, E.; Lakner, H. (2004). Urey, Hakan; Dickensheets, David L (eds.). "MEMS microscanning mirror for barcode reading: from development to production". Proc. SPIE. MOEMS Display and Imaging Systems II. 5348 – MOEMS Display and Imaging Systems II: 32–39. Bibcode:2004SPIE.5348...32W. doi:10.1117/12.530795. S2CID   120908834.
  17. ↑ Grahmann, J.; Grasshoff, T.; Conrad, H.; Sandner, T.; Schenk, H. (2011). Schenk, Harald; Piyawattanametha, Wibool (eds.). "Integrated piezoresistive position detection for electrostatic driven micro scanning mirrors". Proc. SPIE. MOEMS and Miniaturized Systems X. 7930 – MOEMS and Miniaturized Systems X: 79300V. Bibcode:2011SPIE.7930E..0VG. doi:10.1117/12.874979. S2CID   109599620.
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