We present a novel resonantly excited 2D-micro-scanning-mirror which makes use of an electrostatic driving principle. To achieve large deflection angles, the driving electrodes are located in the chip plane. With that, small electrode gaps can be used without restricting the deflection angle geometrically. The mirror plate, with an area up to 1.5 mm×1.5 mm, is suspended by a gimbal mounting and can, therefore, be deflected along two axes. The base material for the fabrication of the device is a SOI-wafer with a top layer thickness of 30 μm. A special isolation technique which is based on open and filled isolation trenches is suitable to seperate the electrical potentials on the fixed and movable parts. In particular, the filled trenches allow to excite the two oscillations independently. The influence of the surrounding gas on the coupling of the oscillations is examined. No significant influence is observed. The investigations of the mechanical performance show that the devices have a shock resistivity of about 3.4×10 3 × g . Results of long run tests with a duration of 7×10 9 periods at a torsional angel of ±10° show that the change of the eigenfrequency is smaller than 0.01%. The performance of the novel 2D-micro-scanning-mirror is demonstrated by the generation of various Lissajous patterns by the reflected laser beam. Frequency ratios of 1:1 up to 13:1 are obtained with the presented devices.

A resonantly excited 2D-micro-scanning-mirror with large deflection

Machine intelligence has become a driving factor in modern society. However, its demand outpaces the underlying electronic technology due to limitations given by fundamental physics, such as capacitive charging of wires, but also by system architecture of storing and handling data, both driving recent trends toward processor heterogeneity. Task-specific accelerators based on free-space optics bear fundamental homomorphism for massively parallel and real-time information processing given the wave nature of light. However, initial results are frustrated by data handling challenges and slow optical programmability. Here we introduce a novel amplitude-only Fourier-optical processor paradigm capable of processing large-scale ∼(1000×1000) matrices in a single time step and 100 µs-short latency. Conceptually, the information flow direction is orthogonal to the two-dimensional programmable network, which leverages 106 parallel channels of display technology, and enables a prototype demonstration performing convolutions as pixelwise multiplications in the Fourier domain reaching peta operations per second throughputs. The required real-to-Fourier domain transformations are performed passively by optical lenses at zero-static power. We exemplary realize a convolutional neural network (CNN) performing classification tasks on 2 megapixel large matrices at 10 kHz rates, which latency-outperforms current graphic processing unit and phase-based display technology by 1 and 2 orders of magnitude, respectively. Training this optical convolutional layer on image classification tasks and utilizing it in a hybrid optical-electronic CNN, shows classification accuracy of 98% (Modified National Institute of Standards and Technology) and 54% (CIFAR-10). Interestingly, the amplitude-only CNN is inherently robust against coherence noise in contrast to phase-based paradigms and features a delay over 2 orders of magnitude lower than liquid-crystal-based systems. Such an amplitude-only massively parallel optical compute paradigm shows that the lack of phase information can be accounted for via training, thus opening opportunities for high-throughput accelerator technology for machine intelligence with applications in network-edge processing, in data centers, or in pre-processing information or filtering toward near-real-time decision making.

Massively parallel amplitude-only Fourier neural network

Scanned displays have potential for achieving high brightness and see-through configurations in many display applications. A MEMS- based solution based on these tradeoffs for SVGA level performance is presented, with test data illustrating optical, mechanical, and electrical performance. Comparison of this scanner against video requirements and other scanners previously reported are illustrated. The feasibility of MEMS-based scanners for Retinal Scanning Displays and other applications is discussed, with extension to higher video performance standards.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Performance of a biaxial MEMS-based scanner for microdisplay applications

Micro scanning mirrors are quite versatile MEMS devices for the deflection of a laser beam or a shaped beam from another light source. The most exciting application is certainly in laser-scanned displays. Laser television, home cinema and data projectors will display the most brilliant colors exceeding even plasma, OLED and CRT. Devices for front and rear projection will have advantages in size, weight and price. These advantages will be even more important in near-eye virtual displays like head-mounted displays or viewfinders in digital cameras and potentially in UMTS handsets.
Optical pattern generation by scanning a modulated beam over an area can be used also in a number of other applications: laser printers, direct writing of photo resist for printed circuit boards or laser marking and with higher laser power laser ablation or material processing.
Scanning a continuous laser beam over a printed pattern and analyzing the scattered reflection is the principle of barcode reading in 1D and 2D. This principle works also for identification of signatures, coins, bank notes, vehicles and other objects. With a focused white-light or RGB beam even full color imaging with high resolution is possible from an amazingly small device. The form factor is also very interesting for the application in endoscopes. 
Further applications are light curtains for intrusion control and the generation of arbitrary line patterns for triangulation. Scanning a measurement beam extends point measurements to 1D or 2D scans. Automotive LIDAR (laser RADAR) or scanning confocal microscopy are just two examples. Last but not least there is the field of beam steering. E.g. for all-optical fiber switches or positioning of read-/write heads in optical storage devices. The variety of possible applications also brings a variety of specifications. This publication discusses various applications and their requirements.

Applications and requirements for MEMS scanner mirrors

A novel resonantly excited 2D-Micro-Scanning-Mirror is presented which makes use of an electrostatic driving principle allowing to locate the driving electrodes in the chip plane. The mechanical elements and the mirror plate consist of a 30 /spl mu/m thick single crystal silicon layer. The mirror plate is suspended by a gimbal mounting and can therefore be deflected along two axes. It is shown that a special isolation technique is suitable to separate the electrical potentials on the movable elements and therefore allows to excite the two oscillations independently. The isolation technique is based on the oxidation and polysilicon filling of 1 /spl mu/m wide trenches in the 30 /spl mu/m thick layer of silicon. The influence of the surrounding gas on the coupling of the oscillations is examined. No significant influence is observed. The performance of the novel 2D-Micro-Scanning-Mirror is demonstrated by the generation of various Lissajous patterns by the reflected laser beam. Frequency ratios of 1:1 up to 13:1 are obtained with the presented devices.

An electrostatically excited 2D-micro-scanning-mirror with an in-plane configuration of the driving electrodes

Modern UV-lithography is searching for new highly parallel writing concepts. Spatial light modulation (SLM) offers such possibilities but special emphasis must be put on the ability of SLM devices to handle ultraviolet light (UV). We designed and fabricated micromirror arrays which fulfill these requirements. Possible applications for such UV-SLMs are direct writing systems for semiconductor and printing, and UV-stimulated biochemistry. For deep UV laser pattern generation (248 nm) e.g. we designed and fabricated a 2048x512 pixel UV-SLM with individually addressable aluminum micromirrors. They are illuminated by an excimer laser pulse and imaged onto a photomask substrate. A complete pattern is stitched together at a rate of 1 kHz. The minimum feature size is 320 nm and analog modulation of the pixels allows to realize an address grid of only 1.6 nm. The design of the array is modular so that other array sizes can be tailor made to customers needs. Design and fabrication aspects for a CMOS compatible realization of these micromirror arrays are addressed as well as their performance in lithography applications.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design and fabrication of micromirror arrays for UV lithography

Design and modeling aspects of torsional 1D and 2D Micro Scanning Mirrors are presented. During the oscillation of the mirror plate the inertial moment gives rise to a deformation of the plate. This dynamic deformation results in a defocusing of the reflected laser beam. Therefore, the scan frequency of a device with a given size of the mirror plate and deflection angle is limited. Further restrictions arise from the demanded mechanical robustness like resistivity against shock and torsional stress. This leads to a minimum eignefrequency of the device which in the case of a rectangular shaped is proportional to the width of the spring. To enable a single mode operation it is advantageous that the torsion around the springs is the lowest mode sufficiently separated from all others. A FEM-analysis has been carried out to determine the mode sequence of a 1D and a 2D Micro Scanner respectively. The analytical calculated eigenfrequencies agree well with the numerical determined. Taken into account the result of the analytical and numerical investigations 1D and 2D Micro Scanning Mirrors have been designed and fabricated. The mirror and the springs are defined in a 20 to 30 micrometers thick single crystal silicon layer. The results of the experimental investigations with respect to the shock resistivity and the long run behavior probe the suitability of the modeling.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Design and modeling of large deflection micromechanical 1D and 2D scanning mirrors

The Fraunhofer IPMS and Micronic Laser Systems AB have developed a technology for the maskless DUV microlithography using spatial light modulation (SLM). This technology uses an array of micromirrors as a pro-programable mask, which allows writing up to 1 million pixels with a framerate of up to 2 kHz. The SLM is fabricated at the IPMS using its high-voltage CMOS process. The mirrors are fabricated by surface micromachining using a polymer as sacrificial layer. The mirrors are operated in an analog mode to allow sub-pixel placement of the features.

Application of spatial light modulators for microlithography

Fraunhofer IPMS has developed a one-dimensional high-speed spatial light modulator in cooperation with Micronic
Mydata AB. This SLM is the core element of the Swedish company’s new LDI 5sp series of Laser-Direct-Imaging
systems optimized for processing of advanced substrates for semiconductor packaging. This paper reports on design,
technology, characterization and application results of the new SLM. With a resolution of 8192 pixels that can be
modulated in the MHz range and the capability to generate intensity gray-levels instantly without time multiplexing, the
SLM is applicable also in many other fields, wherever modulation of ultraviolet light needs to be combined with high
throughput and high precision.

/pdf/high-speed-one-dimensional-spatial-light-modulator-for-laser-47rh6kcf3j.pdf

High-speed one-dimensional spatial light modulator for Laser Direct Imaging and other patterning applications

Three different types of deformable mirror Spatial Light Modulators (SLMs) based on device concepts like Viscoelastic Control Layer (VCL), Cantilever Beam Mirror (CBM), and Moving Liquid Mirror (MLM) have been developed. All of them allow to create deformation profiles which act as phase gratings whose period is defined by the pitch of the pixel electrodes. The diffraction of the incident light is used to achieve spatial light modulation. The operation principles of the different types of SLMs are outlined in detail. All the mentioned SLMs can be manufactured on top of a high voltage CMOS circuitry. SLMs with up to 2 million pixels in analog operation mode have been realized up to now. The benefits of the different approaches with respect to fabrication aspects and respect to different applications will be addressed. For the angular deflection of light a new type of resonant microscanner mirror was developed. The device is based on a silicon micromechanical torsional actuator. The new approach for the configuration of the electrodes and the resulting driving principle allows to achieve large scanning angles (plus or minus 30 degree optically at atmospheric pressure) at low driving voltages (20 V max.) and low power consumption (less than 1 (mu) W). The operation principle of the new device enables the realization of 2D scanners as well.

Peter Duerr

Papers

Design and fabrication of micromirror arrays for UV lithography

Design and modeling of large deflection micromechanical 1D and 2D scanning mirrors

Application of spatial light modulators for microlithography

High-speed one-dimensional spatial light modulator for Laser Direct Imaging and other patterning applications

Micromirrors for direct writing systems and scanners