We are developing a phase-modulating micro mirror-array spatial light modulator to be used for real holography within the EU-funded project REALHOLO, featuring millions of pixels that can be individually positioned in a piston mode at a large frame rate. We found earlier that an electrostatic comb-drive array offers the best performance for the actuators: sufficient yoke forces for fast switching even at low voltages compatible with the CMOS addressing backplane. In our first design, the well-known electrostatic cross-talk issue had already been much smaller than would have been possible for parallel-plate actuators, but it was still larger than the precision requirements for high-image-quality holography. In this paper, we report on our analysis of the crucial regions for the electrostatic cross-talk and ways to reduce it while observing manufacturing constraints as well as avoiding excessively high field strengths that might lead to electrical breakdown. Finally, we present a solution that, in FEM simulations, reduces the remaining cross-talk to well below the required specification limit. This solution can be manufactured without any additional processing steps and suffers only a very small reduction of the yoke forces.

Earth observation (EO) is crucial for addressing environmental and societal challenges, but it struggles with revisit times and spatial resolution. The EU-funded SURPRISE project aims to improve EO capabilities by studying space instrumentation using compressive sensing (CS) implemented through spatial light modulators (SLMs) based on micromirror arrays (MMAs) to improve the ground sampling distance. In the SURPRISE project, we studied the development of an MMA that meets the requirements of a CS-based geostationary instrument working in the visible (VIS) and mid-infrared (MIR) spectral ranges. This paper describes the optical simulation procedure and the results obtained for analyzing the performance of such an MMA with the goal of identifying a mirror design that would allow the device to meet the optical requirements of this specific application.

The need of high-resolution Earth Observation (EO) images for scientific and commercial exploitation has led to the generation of an increasing amount of data with a material impact on the resources needed to handle data on board of satellites. In this respect, Compressive Sensing (CS) can offer interesting features in terms of native compression, onboard processing and instrumental architecture. In CS instruments the data are acquired natively compressed by leveraging on the concept of sparsity, while on-board processing is offered at low computational cost by information extraction directly from CS data. In addition, instrument's architecture can enjoy super-resolution capabilities that ensure a higher number of pixels in the reconstructed image with respect to that natively provided by the detector. In this paper, we present the working principle and main features of a CS demonstrator of a super-resolved instrument for EO applications with ten channels in the visible and two channels in the medium infrared. Besides the feature of merging in a single step the acquisition and compression phases of the image generation, its architecture allows to reach a super-resolution factor of at least 4x4 in the images reconstructed at the end of process. The outcome of the research can open the way to the development of a novel class of EO instruments with improved Ground Sampling Distance (GSD) - with respect to that one provided natively by the number of sensing elements of the detector - and impact EO applications thanks to native compression, on-board processing capabilities and increased GSD.

The Fraunhofer Institute for Photonic Microsystems (IPMS) has been developing and manufacturing micromirror arrays for more than 20 years. While originally focusing on applications related to microlithography and therefore mainly for light in the deep ultraviolet range, the range of applications has been expanded since, including applications in the visible and near-infrared range. This paper gives an overview of the devices and their designs, fabrication, and characterization.

Fraunhofer IPMS has developed a linear micro mirror array (ASLM8k) for use as fast intensity modulator in the DUVUV spectral range (190-410nm). Its 2.2 Million mirrors are grouped to 8192 pixels. Framerates of about 1MHz enable parallel high speed exposure at rates of >10.10⁹ Pixel/s (greyscale). Large pixels serve to provide a comparably high laser energy in the partial beams while keeping the fluence at the MMA below damage threshold. The ASLM8k is a perfect match for powerful high repetition rate lasers and allows to address applications like laser direct imaging (LDI), i.e. maskless exposure of photoresists, and laser direct writing (LDW), e.g. laser patterning of thin films. The ASLM8k has been successfully used in prototypes of a LDI tool developed by an industrial partner. Fraunhofer IPMS aims to contiue the development of the ASLM8k with further industrial partners to utilize the MMA for additional applications.

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.

The Fraunhofer Institute for Photonic Microsystems (IPMS) develops and fabricates MOEMS micro-mirror arrays for a variety of applications in image generation, wave-front correction and pulse shaping. In an effort to extent the application range, mirrors are being developed that withstand higher light intensities. The absorbed light generates heat. Being suspended on thin hinges, and isolated from the bulk by an air gap, the mirrors heat up. Their temperature can be significantly higher than that of their substrate. In this paper we describe an experiment carried out to verify simulations on the temperature within the mirror plates during irradiation. We created a structure out of electrically connected mirror plates forming a four-point electrical resistor, and calibrated the thermal coefficient of the resistor in a temperature chamber. We irradiated the resistor and calculated the mirror temperature. In the experiment, the temperature in the mirror plates increased by up to 180 °C. The mirrors did not show significant damage despite the high temperatures. Also, the experiment confirms the choice of heat transport mechanisms used in the simulations. The experiment was done on 48 μm x 48 μm mirrors suspended over a 5 μm air gap, using a 355 nm solid-state laser (4 W, up to 500 W/cm2).

The Fraunhofer IPMS, in cooperation with Micronic Laser Systems, develops and fabricates micromirror arrays used as spatial light modulators (SLM) for image generation in microlithography. The SLMs used consist of 2048x512 individually addressable micromirrors of 16x16 mu m(2) and can be operated in an analog mode at a frame rate of up to 2 kHz. There are continued efforts to improve the performance of the mask writers with respect to stability and CD uniformity, which include measures to improve the SLMs used, especially with respect to the optical quality and the stability.Therefore, a new technology has been introduced which allows to use different materials for the mechanical suspension and the mirror, thus optimizing them separately. The hinges are made of a thin layer of a material with very good creep resistance, while the mirrors consist of a thick aluminium alloy with high reflectivity in DUV. Furthermore, the same inorganic material is used for the planarization of the electrodes (by means of chemical mechanical polishing) and as sacrificial layer for the actuator fabrication. Thus, at the end of the process, all sacrificial material, including that between the electrodes is removed. In this way, the charging effects caused by dielectrics between the electrodes (as seen in the previous devices) are eliminated.The first devices using the technology described above have been fabricated and tested. The first tests in a lithography machine show that considerable improvements in machine performance can be expected. The next steps are to stabilize and optimize the process.

Micro-machined spatial light modulators (SLMs) can be used in various applications such as micro lithography and adaptive optics. Fraunhofer IPMS has a very long experience in developing such devices. Ideally, the optically active surface area of the SLMs would be completely flat when not actuated. In reality, the SLM chip might be slightly bent and/or warped and the surface might show hills and valleys on various lateral length-scales due to fabrication imperfections. This surface profile is very hard to avoid in typical fabrication and mounting processes and can degrade the overall performance of the SLM in critical applications. Adjusting the shape by piezo-actuator arrays, would be a possible solution, but a very complex and expensive one. An array of screws acting on the SLM is too coarse to be a suitable method for adjusting the flatness properly for optical surface quality. An additional drawback of both above ways to improve the planarity is that it is difficult to get rid of the heat generated in the SLM during operation.

We describe charging effects on spatial light modulators (SLM). These light modulators consist of up to one million mirrors that can be addressed individually and are operated at a frame rate of up to 2 kHz. They are used for deep ultraviolet (DUV) mask writing where they have to meet very high requirements with respect to accuracy. To be usable in a mask-writing tool, the chips have to be able to work under DUV light and maintain their performance with high accuracy over a long period of time. Charging effects are a problem frequently encountered with MEMS, especially when they are operated in an analog mode. In this work, the issue of charging effects in SLMs used for microlithography, their causes and methods of their reduction or elimination, by means of addressing methods as well as technological changes, is discussed. The first method deals with the way charges can accumulate within the actuator. It is a simple method that requires no technological changes but cannot always be implemented. The second involves the removal of the materials within the actuator where charges can accumulate. (c) 2008 Society of Photo-Optical Instrumentation Engineers.

This paper describes charging effects on spatial light modulators (SLM). These light modulators consist of up to one million mirrors that can be addressed individually and are operated at a frame rate of up to 2 kHz. They are used for DUV mask writing where they have to meet very high requirements with respect to accuracy.In order to be usable in a mask-writing tool, the chips have to be able to work under DUV light and maintain their performance with high accuracy over a long time. Charging effects are a problem frequently encountered with MEMS, especially when they are operated in an analog mode.In this paper, the issue of charging effects in SLMs used for microlithography, their causes and methods of their reduction or elimination, by means of addressing methods as well as technological changes, will be discussed. The first method deals with the way charges can accumulate within the actuator, it is a simple method that requires no technological changes but cannot always be implemented. The second involves the removal of the materials within the actuator where charges can accumulate.

Electrostatic Micro-actuators are being increasingly used for a wide variety of applications such as spatial light modulators, scanning mirrors, optical cross connects, micro-valves, and others. Usually the electrical forces operate in one direction and are balanced by a mechanical spring. The resulting deflection is then either defined by a mechanical stop, or it is only a meta-stable equilibrium position: at an additional external force or deflection it will snap to a different position, frequently again defined by a mechanical stop. This issue is well known and is often called 'pull-in'. In the often used parallel-plate capacitor actuator, the instability already begins at a deflection of only on third of the original capacitor plate separation. For safety reasons and due to the steep response-curve one can only use an even smaller fraction of the mechanically possible movement. This means, that the gap below the actuator has to be designed very much larger than the required maximum deflection. To get the pre-described force and deflection, a much higher voltage is needed than for potential smaller gap widths. The useable range of deflection for many types of micro-actuators can be extended without the penalty of large drive voltage or low shock resistivity, by employing springs with steeper-than-linear restoring force. Alternatively, the voltage needed for a given range of deflection may be reduced. This paper shows the benefits and how to design and dimension these types of springs.

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-programmable 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.