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.

The development of devices that are based on MEMS-on-CMOS technology becomes increasingly time-consuming since System-on-a-Chip (SoC) solutions for highly integrated and miniaturized devices are approaching smaller feature sizes. In order to reduce the development costs and shorten the time-to-market periods, the combination of commercially available CMOS processes from foundries with the subsequent processing in a dedicated MEMS facility is beneficial. This concept offers the possibility to separate the different technological requirements of conventional CMOS manufacturing and MEMS actor processing, which may follow different design rules and process specifications. As a representative of the dedicated MEMS foundries, Fraunhofer IPMS performs surface micromachining on 200 mm wafers for a variety of MEMS devices, in particular for spatial light modulators (SLM). Over the past decade, much experience was gained in development activities for customer specific applications like micro mirror arrays. In this paper, we will discuss essential requirements and upcoming challenges for the monolithic integration of surface micro-machined optical MEMS on foundry-fabricated CMOS backplanes, as conventional (i-Line) lithography is approaching patterning limits. We will present approaches of tuning the planarization of the CMOS chip surface to achieve an excellent mirror array flatness with CMOS compatible inorganic sacrificial layer techniques. Concepts like Mix&Match lithography for achieving high overlay accuracy and the litho stitching technique for the patterning of large chips will be reviewed and a brief outline of our roadmap for the implementation of DUV lithography will be presented.

We developed a novel 512 x 320 tip-tilt micro mirror array (MMA) together with the entire related technology platform, including mirror fabrication process, integrated CMOS address circuitry and external drive electronics. The MMA itself consists of 2axis-tip-tilt actuators at 48 mu m pixel size, allowing a continuous pure tip-tilt motion up to 3.5 degrees in arbitrary directions, fully calibratable at standard deviations of better than 0.025 degrees. The mirrors are realized within a 2-level architecture defined by three structural layers, two for hinge and reinforcement suspension and one for the overlying mirror. They are fabricated by surface-micromachining within a fully CMOS compatible process. MMA programming is accomplished by an underlying CMOS backplane supporting drive voltages up to 27V and frame rates up to 3.6kHz.

We have developed a novel 512 x 320 micro mirror array consisting of 2axis-tip-tilt actuators with 48 mu m pixel size, allowing a continuous, pure tip-tilt motion up to 3.5 degrees in arbitrary directions, fully calibratable with standard deviations of better than 0.025 degrees. The device is realized in a fully CMOS compatible process with an underlying integrated address circuitry.

We have developed a novel 512 × 320 micro mirror array consisting of 2axis-tip-tilt actuators with 48μm pixel size, allowing a continuous, pure tip-tilt motion up to 3.5° in arbitrary directions, fully calibratable with standard deviations of better than 0.025°. The device is realized in a fully CMOS compatible process with an underlying integrated address circuitry.

We present a complementary metal-oxide-semiconductor (CMOS) compatible heterogeneous 3D integration process that allows the integration of two monocrystalline silicon layers on top of CMOS control electronics. With this process we demonstrate the fabrication of hidden hinge micromirror arrays from monocrystalline silicon for adaptive optics applications. The piston-type micromirror arrays have the flexures underneath the mirror plates on separate silicon layers. Arrays of 48 x 48 mirror elements with an air-gap between mirror and address electrode of 10 mu m were fabricated. The mirrors were found to be drift free and showed no imprinting. A maximum electrostatic mirror displacement of 3 mu m is demonstrated.

In this paper, we report on the heterogeneous integration of monocrystalline silicon membranes for the fabrication of large segmented micromirror arrays for adaptive optics applications. The design relies on a one-level architecture with mirrors and suspension formed within the same material, employing a large actuator gap height of up to 5.1 μm to allow for a piston-type mirror deflection of up to 1600 nm. Choosing monocrystalline silicon as actuator and mirror material, we demonstrate a completely drift-free operation capability. Furthermore, we investigate stress effects that degrade the mirror topography, and we show that the stress originates from the donor silicon-on-insulator wafer. The novel heterogeneous integration strategy used in this work is capable of reducing this stress to a large extent.

In this paper we present wafer-level heterogeneous integrated hidden-hinge micro-mirror arrays for adaptive optics applications. The micro-mirrors are made of mono-crystalline silicon and fabricated by two cycles of adhesive wafer bonding on fan-out substrates with addressing electrodes. The fabrication scheme allows the down-scaling of the micro-mirrors in size, the up-scaling of the array size and the implementation of additional material layers. Furthermore, large distances of the micro-mirrors to the electrodes can be achieved and hence a large deflection of the mirrors is possible. The micro-mirrors exhibit excellent deflection stability; no drift or hysteresis can be observed.

Thispaperpresents a novelCMOS-compatible fabrication process andevaluations ofamicromirror array (MMA)madeofmono-crystalline silicon (m-Si) for adaptive optic (AO)applications. Them-Simirror layer is transfer bonded fromasilicon-on-insul ator (SOI) donor waferwithadhesive waferbonding towards aninter- mediate patterned polymer spacer layer andclamped with metalplating. We present a CMOS compatible, bond alignment-free fabrication schemeoffering thepotential forhighairgapdistances between substrate andmirrors andweshowfirst measurements ofthefabricated mirrors. INTRODUCTION Micro-mirrors havefounda widerangeof applications inthepastdecades, e.g. inprojection systems (1), optical scanners (2), optical switches (3)andmaskless

This paper presents a novel CMOS-compatible fabrication process and evaluations of a micro mirror array (MMA) made of mono-crystalline silicon (m-Si) for adaptive optic (AO) applications. The m-Si mirror layer is transfer bonded from a silicon-on-insulator (SOI) donor wafer with adhesive wafer bonding towards an intermediate patterned polymer spacer layer and clamped with metal plating. We present a CMOS compatible, bond alignment-free fabrication scheme offering the potential for high air gap distances between substrate and mirrors and we show first measurements of the fabricated mirrors.

Large micromechanical mirror arrays (MMA) with analog pixel deflection integrated onto active CMOS address circuitry require both high-quality planar reflective optical surfaces and a stable deflection versus voltage characteristic. However, for implementing a CMOS-compatible surface-micromachining process, certain obstacles such as a restricted thermal budget and a limited selection of suitable materials must be overcome. Amorphous TiAl is presented as a new actuator material for monolithical MEMS integration onto CMOS circuitry. TiAl films may be sputter deposited at room temperature, have an x-ray amorphous structure, and a low stress gradient. The glassy structure and high melting point make TiAl less vulnerable to stress relaxation, which makes TiAl an ideal spring material. One-level actuators with TiAl or Al-TiAl-Al structural layers and two-level actuators with separate TiAl spring and Al-alloy mirror layers were fabricated and tested with respect to their drift stability. The stability of TiAl-based actuators was found to be superior in comparison to one-level Al-alloy actuators. Two-level actuators with TiAl hinges emerge as the most promising design. (c) 2008 Society Photo-Optical Instrumentation Engineers.

The large-scale integration of analog operable MEMS micro-mirrors onto active CMOS address circuitry requires high quality planar reflective optical surfaces but also a stable deflection vs. voltage characteristic. However, for implementing a CMOS compatible surface micromachining process, certain obstacles like a restricted thermal budget and a limited selection of suitable materials must be overcome. In this paper, amorphous TiAl is presented as a new actuator material for monolithical MEMS integration onto CMOS circuitry at room temperature. Sputter deposited TiAl has an x-ray amorphous structure and a low stress gradient. The missing long range order and the high melting point help to virtually eliminate stress relaxation effects, i.e. TiAl hinges behave almost perfectly elastic. In a first study, 40 &mgr;m wide piston mirrors have been implemented onto substrates with fixed wired address electrode arrays. The actuators had a 300 nm TiAl core sandwiched between two layers of 25 nm Al. The devices reach a maximum deflection of about 500 nm at a dc voltage of about 23V. The drift-stability of the deflection has been tested at "worst case" conditions close to the deflection limit. During 30 min of continuous deflection near 500 nm a mechanical drift below 25nm has been observed. TiAl offers the perspective for actuators capable of a stable analog operation, which is essential to many applications, such as adaptive optics.

The large-scale integration of analog operable MEMS micromirrors onto active CMOS address circuitry involves several challenges. Mirror actuators must be fabricated using CMOS compatible technology, exhibit highly reflecting planar optical surfaces, and stable analog deflection-voltage characteristics not compromised by drift or creep effects. CMOS integration imposes strict limits depending on the range of available materials and the restricted temperature budget. Highly elastic materials such as single-crystalline Si or poly-SiGe have been integrated by layer transfer bonding or PECVD deposition, respectively. In this paper, a novel approach, i.e., the low-temperature monolithic integration of creep-resistant all-sputtered glassy TiAl mirror actuators with Al reflective coating is presented.

Various applications in modem optics are demanding for Spatial Light Modulators (SLM) with a true analog light processing capability, e.g. the generation of arbitrary analog phase patterns for an adaptive optical phase control. For that purpose the Fraunhofer IPMS has developed a high-resolution MEMS Micro Mirror Array (MMA) with an integrated active-matrix CMOS address circuitry. The device provides 240 x 200 piston-type mirror elements with 40 pin pixel size, where each of them can be addressed and deflected independently at an 8bit height resolution with a vertical analog deflection range of up to 400 mn suitable for a 271 phase modulation in the visible. Full user programmability and control is provided by a newly developed comfortable driver software for Windows XP (R) based PCs supporting both a Graphical User Interface (GUI) for stand-alone operation with pre-defined data patterns as well as an open ActiveX (R) programming interface for a direct data feed-through within a closed-loop environment. High-speed data communication is established by an IEEE 1394a FireWire interface together with an electronic driving board performing the actual MMA programming and control at a maximum frame rate of up to 500 Hz. Successful application demonstrations have been given in eye aberration correction, coupling efficiency optimization into a monomode fiber, ultra-short laser pulse modulation and diffractive beam shaping. Besides a presentation of the basic device concept the paper will give an overview of the obtained results from these applications.

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.

Light and electricity are two major sources leading technology advances into the future. Micro-opto-electro-mechanical-systems (MOEMS) devices combine these two sources in an ideal manner: they are electronically addressable devices comprising optical elements to modulate light temporally and/or spatially. Further, MOEMS devices take advantage of high integration density, high reliability, high bandwidth, and low cost fabrication for mass production. While in some cases MOEMS technology focuses on the replacement of conventional devices, the majority of developments uses the unique potential of this technology to create devices based on novel principles with extended or even new functionality for advanced applications. Products based on MOEMS technology have already entered or are only a few steps away from entering the market in various fields, e. g., in consumer, information, and communication technology, medicine, biology, and metrology. This work gives an overview of MOEMS development activities with special emphasis on devices for light beam deflection and modulation. Single micromirrors, e. g., for scanning or laser beam positioning, are also presented and discussed as micromirror arrays and membrane mirrors for image generation and phase modulation. Technology trends are derived from the current development activities and an outlook to future work is given. (c) 2005 Society of Photo-Optical Instrumentation Engineers.

The MEMS Phase Former Kit developed by the Fraunhofer IPMS is a complete Spatial Light Modulator system based on a piston-type Micro Mirror Array (MMA) for the use in high-resolution, high-speed optical phase control. It has been designed for an easy system integration into an user-specific environment to offer a platform for first practical investigations to open up new applications in Adaptive Optics. The key component is a fine segmented 240 x 200 array of 40 μm piston-type mirror elements capable of 400 nm analog deflection for a 2pi phase modulation in the visible. Each mirror can be addressed and deflected independently by means of an integrated CMOS backplane address circuitry at an 8bit height resolution. Full user programmability and control is provided by a newly developed comfortable driver software for Windows XP based PCs supporting both a Graphical User Interface (GUI) for stand-alone operation with pre-defined data patterns as well as an open ActiveX programming interface for a closed-loop operation with real-time data from an external source. An IEEE1394a FireWire interface is used for high-speed data communication with an electronic driving board performing the actual MMA programming and control allowing for an overall frame rate of up to 500 Hz. Successful proof-of-concept demonstrations already have been given for eye aberration correction in ophthalmology, for error compensation of leightweight primary mirrors of future space telescopes and for ultra-short laser pulse shaping. Besides a presentation of the basic device concept and system architecture the paper will give an overview of the obtained results from these applications.

Electrostatically driven Micro Scanning Mirrors and Micro Mirror Arrays were designed and fabricated. This paper gives an overview of the device properties and shows by means of examples the large potential of these MOEMS-devices. The single crystal silicon Micro Scanning Mirrors achieve an optical scan range of up to 60degrees at less than 20 V High shock resistivity and excellent long run behaviour allowed to build a scan engine for bar code reading. Micro Mirror Arrays with up to 1 million individually addressable pixels were fabricated. The DRAM-like architecture of the circuitry allows us to achieve frame rates up to 2 kHz. The device serves as a high dynamic programmable mask for DUV-microlithography. Patterns meeting the requirements for the 130 nm node were successfully written. A similar device with piston like elements was fabricated for wave front correction in ophthalmology. Arrays with up to 200 * 240 pixels were fabricated.

Light and electricity are said to be the all purpose tools for the next decades. Photonic Microsystems combine this tools in an ideal manner: They are electronically addressable devices with an optical functionality allowing to modulate light temporally and/or spatially. Further., they take advantage of high integration density, high reliability. high bandwidth and low cost fabrication for serial production.While in some cases Photonic Microsystem Technology is focused on the replacement of conventional devices, the majority of developments uses the unique potential of this technology to create devices based on novel principles with extended or even new functionality for advanced applications. Products based on Photonic Microsystem Technology have already entered or are only a few steps away from entering the market in various fields e. g. in information and communication technology, medicine, biology and metrology.This paper gives an overview of the Photonic Microsystems development activities with special emphasis on devices for light deflection and light modulation. Single micro mirrors e. g. for scanning or laser beam positioning are as well presented and discussed as micro mirror arrays and membrane mirrors for image generation and phase modulation. Technology trends are derived from the current development activities and an outlook to future work is given.