To fabricate arbitrarily shaped microrelief surfaces you should be able to design and control beside the X- and Y- direction also the Z-direction. With common micromachining technologies this could not be obtained. The surface micro machining technology, with sacrificial layer etching as a key process, is a planar technology, which offers no degree of freedom to design the surface in Z-direction. The bulk micro machining technology, with anisotropic KOH etching of silicon as a key process, offers only restricted possibilities for 3D design. To overcome this limitation binary optical elements have been fabricated using multi-mask processes or multidose e-beam or laser writing. For refractive optical lenses resist melting is a good compromise. This paper reports on a new methodology to fabricate the above discussed arbitrarily shaped structures using a one step lithography process. This technique is called one-level gray-tone lithography, which is common to standard IC manufacturing processes, supplemented by some processes like spincoating and developing of thick resist layer, electroplating of thick metal layers and dry etching. This group of processes has been collected into a new technology category with free design capabilities in Z- direction up to 20 micrometer: relief micro machining. Particular emphasis is put on the design of the halftone transmission masks. The algorithms to transfer an initial height profile into a design representation in the common data format GDSII are discussed. The great data amount of a reticle layout is reduced significantly by a first order data compaction. The specific parameters for the mask making and the resist process are determined. Several components like shaped gratings or lenses are shown in resist up to 15 micrometers thick. In the field of transferring the pattern into a substrate material like silicon or glass, a dry etching process is evaluated.

The SAMPLE (Sandia agile MEMS prototyping, layout tools, and education) service makes Sandia's state-of-the-art surface micromachining fabrication process, known as SUMMiT, available to U.S. industry for the first time. The service provides a short course and customized computer-aided design (CAD) tools to assist customers in designing micromachine prototypes to be fabricated in SUMMiT. Frequent small-scale manufacturing runs then provide SAMPLE designers with hundreds of sophisticated MEMS (microelectromechanical systems) chips. SUMMiT (Sandia ultra-planar, multi-level MEMS technology) offers unique surface-micromachining capabilities, including four levels of polycrystalline silicon (including the ground layer), flanged hubs, substrate contacts, one-micron design rules, and chemical-mechanical polishing (CMP) planarization. This paper describes the SUMMiT process, design tools, and other information relevant to the SAMPLE service and SUMMiT process.

A new approach has been proposed to realize suspended microstructures such as cantilevers, diaphragms, springs, spirals, etc. over pits of controlled depth in bulk silicon micromachining process using direct wafer bonding technology. The structures have been realized in heavily boron doped silicon and dielectric layers. The electrostatic actuation voltage of the cantilever beams have been computed as a function of physical parameters and compared with experimentally measured values. LPCVD polysilicon has been investigated with a view to obtain low stress films for use in surface micromachining technology. The effect of deposition parameters on stress in the polysilicon films has been studied. Post deposition annealing is shown to have profound effect on the stress properties of the polysilicon films. Rapid thermal annealing is found to be much more effective in reducing the stress compared to conventional furnace annealing. The advantage of direct wafer bonding technology for electrostatically actuated microstructures have been presented. The application of this technology for MEMS have been discussed.

We report on our activities in the design, fabrication and characterization of refractive and diffractive micro-optical elements and their integration into micro-systems. Various fabrication techniques like interferometric recording, mask projection steps, or direct writing are used to generate high resolution surface-relief profiles in photoresist. The transfer of the surface profile into glass or quartz is possible using reactive ion etching (RIE). Low-cost micro- optical elements can be fabricated in organic polymers using various replication techniques. Different types of micro- optical elements can be integrated on a substrate together with other opto-electronic components. We present selected applications in the field of laser beam shaping, space communications and blood gas sensors.

We report on the fabrication of lens components, based on diffractive optical elements, for the purpose of imaging laser-diode emission onto fibers or photodetectors, or for collimation applications. The miniature optical elements are arranged in arrays with 250 micrometer pitch which make them well suited for applications with fiber ribbons. Test optical plates were made of polycarbonate using hot stamper replication technology. The imaging properties of these optical plates from single-mode fibers onto single-mode fibers or from lasers onto single-mode fibers are discussed. The addition of 3D-marker structures to the outline borders of such plates made them suitable for use in micro-optical benches with built-in mechanical registration structures. We fabricated the optical bench inserts with built-in passive alignment elements using deep x-ray LIGA technology (LIGA is a German acronym for 'lithographie, galvanik und abformung' meaning lithography, electroforming and molding). This technology offers high mechanical precision even for the 500 micrometer thick optical bench inserts which we fabricated by injection molding out of transparent and thermally stable polycarbonate. We report on first arrangements of plastic optical bench inserts into micro-optical benches. With the aim towards a fully replicated micro-optical bench made out of plastic we also report on a mounting concept for laser-didoes with built-in alignment trenches. The fabrication process and important properties of these special lasers which we recently developed for transceiver applications are described. We use these lasers for imaging onto single-mode fibers applying the diffractive optical element plates already mentioned.

Planar integrated free-space optics has been suggested and demonstrated as a micro-optical systems technology for optical interconnection and processing. It is based on the integration of micro-optical elements on a single glass substrate. Active optoelectronic components are mounted onto the substrate using hybrid integration techniques. An important problem related to the packaging is the heat removal from these active device arrays. A high interconnection density -- which is desirable from an architectural point of view -- can cause a dissipated power on the order of 100 W/cm². This may compromise the performance of individual devices and the system as a whole. As cooling mechanisms, we consider convection which requires sufficiently large surfaces and conduction in an intermediate layer of high thermal conductivity between the passive optics and the optoelectronics. Both, structured silicon coolers and diamond layers are of interest for a practical realization. Here, we discuss material and design aspects of heat spreaders. Both, theoretical modeling and experimental results are presented. A test setup including an array of vertical cavity surface emitting lasers (VCSELs) is analyzed. The temperature distribution on the array is determined experimentally by the shift of the optical wavelength. Computer simulations are used to evaluate the experimental data.

We report the experimental g-performance characterization of surface-micromachined FDDI (fiber distributed data interface) optical bypass switches. Novel surface-micromachined FDDI optical bypass switch consists of an out-of-plane micromirror is driven by integrated scratch drive actuators, and balanced by a spring. A pull-back spring is integrated with the switch in order to satisfy the requirements for the fail-safe feature of the FDDI optical bypass switch. We have performed the vibration test of the switch in collaboration with Rockwell Science Center. The purpose of this test is to investigate the robustness of the surface-micromachined fib optic switch against external vibrations. Error-free operation up to 89s (equipment-limited) was observed for vibration frequencies from 200 Hz to 10 kHz. Comparison of the receiving sensitivity with and without vibration shows that there is virtually no effect of vibration of this scale. No mechanical failure observed throughout the entire test.

Opto-mechanical fiber-optic attenuators are bulky and slow. The MARS (mechanical anti-reflection switch) modulator offers a high-speed alternative, with less than 10 microsecond response and 30 dB analog dynamic range. This talk describes a compact low-loss package with separate input and output fibers held in a single ceramic ferrule, a tiny (0.5 X 1 mm) gradient index lens, and a reflective MARS modulator in the collimated beam plane. This component has applications in telecommunications for line build out and dynamic amplifier gain control.

Fiber-optic switches become more and more appealing components not only in the field of optical communication, but also in measurements systems, sensors and data storage. We have developed a number of concepts for fiber-optic switches, all based on different types of special micro-optical components, actuated by miniaturized mechanical systems, primarily piezoelectric actuators. We present micro-optical configurations and discuss their potential for the creation of different-types of miniaturized switches. Keywords: micro-optics, micro-optical switches, piezoelectric actuators

Two different applications of micro-opto-electro-mechanical systems (MOEMs) are described in this paper. The first one is a Q-switched fiber laser using a micro-mirror as switching element. We present the general concept, the latest experimental setup with results and simulations on the behavior of the pulsed laser. The second application is an opto-mechanical switch for telecommunication ring networks. We describe a free-space optical switch using a micro-mirror, micro-optical elements and a fiber bundle.

This paper presents the design, modeling, and verification of a MEMS silicon torsion mirror for applications in laser printing. It begins with a description of the torsion mirror design, followed by detailed discussions of modeling and verification of the design. A coupled electro-mechanical computer-aided-design software package MEMCAD is used to perform both electrical and mechanical analysis of the mirror under different applied voltages. The MEMCAD modeling results are then post-processed through a program, which retrieves the displacement components of nodes from MEMCAD output and fits a quadratic surface to the deformed reflecting mirror surface. This approximated surface is to be used later in an optical modeling package to analyze the optical performance of the device. The post-processed results are verified by experiential measurements. The first six natural modes of the mirror are determined and are given to help understand the mechanical response of the mirror to different excitation frequencies, Finally, with the aid of MEMCAD, sensitivity analysis for translation versus rotation is performed in order to optimize the mirror design for a raster output scanner (ROS) optical system.

This paper describes how nonlinear force flexures can be used to increase the stable deflection distance of an electrostatically operated micromirror. Traditional micromirrors have flexures that provide linear force as a function of deflection. Electrostatic attraction is a nonlinear force, so after a traditional micromirror has deflected one-third of the initial separation distance between the top and bottom electrode, the mirror's position becomes unstable, and the mirror quickly jumps down to the bottom electrode. This phenomenon is called 'snap-through,' and it has been well-documented. A nonlinear second order flexure has a restorative force that is proportional to the square of the deflection distance. A second order flexure does not exhibit snap-through until the micromirror is deflected one-half the initial separation between the top and bottom electrode. Higher order flexures are capable of traveling a larger distance before snap-through. This paper presents a theoretical simulation of traditional and higher order flexures. Specific nonlinear flexure designs have been constructed and demonstrated.

This paper presents novel micro-opto-electro-mechanical (MOEM) applications employing vertical thermal actuators. The high force and large deflection of backbent vertical thermal actuators are useful in many applications, particularly when a single large deflection is required for device setup. For example, backbending two actuators driven in parallel flips a 250 micrometer square mirror to 45 degrees off the substrate. The actuators can then be driven to permit scanning over 45 degrees. In another example, 3 backbent actuators are used to position an electrostatically actuated optical beam steering mirror 10 micrometer off the substrate thereby increasing the maximum steering angle by a factor of 5. Critical to applications like these is predictable and repeatable operation of the actuators. The actuators are comprised of a polysilicon cantilever bar mechanically coupled to two expansion arms. If sufficient current is driven through the expansion arms they deform, bowing upward. Upon removal of the drive current the expansion arms shrink, backbending the actuator by pulling the tip of the actuator upward. Test actuators of three different sizes were carefully backbent. After backbending, the deflection of each actuator was measured on an interferometric microscope with plus or minus 5 nm precision. Although nonlinear, the relationship of backbending deflection to drive power is well behaved, and repeatable.

The mechanical anti-reflection switch is an optical modulator based on the electrostatically induced vertical movement of a membrane above the substrate. Two basic types may exist, one where the membrane is insulating, wherein an electrode with an optical window is placed upon the membrane, and a second where the membrane is conducting, requiring no separate electrode. The first has the advantage that the region in the optical window is flat, but the disadvantage that since the window has no force applied to it, higher voltages are required for the same speed. We examine here the effects of membrane curvature on the optical performance of the second type.

We present two monolithically integrated optical sensor systems based on semiconductor photonic integrated circuits. These compact, robust and highly functional transducers perform all necessary optical and electro-optical functions on-chip; extension to multi-sensor arrays is easily envisaged. A monolithic Michelson interferometer for high-resolution displacement measurement and a monolithic Mach-Zehnder interferometer for refractometry are discussed.

The use of integrated optical components can be highly beneficial in the realization of displacement sensors. To affront efficiently the problems related with fringe counting and signal fading, the configuration of the optical interferometer is particularly important. Passive interferometer configurations are preferred, with the phase shifted output signals being directly available optically, since they allow a simplified electronic processing for fringe counting and phase demodulation. This article reviews the contributions integrated optics can make in the realization of efficient, compact and reliable displacement sensors. Special emphasis is made in comparing passive interferometer configurations to obtain the phase diversity. The different possibilities in the realization and integration of the optical, optoelectronical and electronical elements are mentioned.

In this work several different approaches designed to produce an opto-electronic chemical sensor based on light-emitting porous Si are described, all of which entail modification of the as-formed porous Si surface in order to alter device characteristics. The issue of selectivity and sensitivity of a given porous Si sensor can be modified by coating the porous Si surface with 'basket'-shaped molecules known as calixarenes; the ability of such a structure to detect copper ions and organonitrogen compounds is reported. Surface modification of porous Si through etching and deposition of conducting polymers in order to alter Si light emission color and intensity is also discussed. The fabrication of porous Si- based waveguides on Si and the impact of surface modification with erbium ions are also described.

Despite their almost universal application in science and technology, optical microscopes with submicron spatial resolution remain large, expensive pieces of laboratory equipment. In this paper, we report on our construction of a near-field scanning optical microscope (NSOM) using the MCNC MUMPs technology. The construction of our microscope required the solution of a number of technological challenges including the assembly of an XYZ stage capable of moving the sample out of the plane of the silicon wafer, the macro alignment of the fiber used as the optical probe and efficient collection of the scattered light. In this paper we describe how the NSOM was built and show some preliminary images taken with it.

A tristimulus color sensitive photo-detector consisting of three buried p-n junctions, implemented in a BiCMOS technology is presented. The three buried junctions give three band-pass- like spectral responses, which peak respectively in the blue, green and red areas. Simulated results obtained with a 1-D analytic model fit well the experimental curves obtained by measuring the sensing arrays in the test chip, designed and fabricated in a 1.2 micrometer BiCMOS process. The colorimetric characterization of the device is performed. A mean color difference of 2.15 is obtained.

The results of a design study for the development of an eye- safe (near-infrared wavelength), compact, multichannel optical interconnect system appropriate for integration with electronics and to be used for short distance communication are discussed. There are potential advantages to using optical interconnects instead of current hardwire interconnections for data transmission over short distances. This technology also has potential applications to data transmission for computing applications. This design study focused on the development of an optical interconnect module to function much like a conventional data cable. The module must be rugged, small, easily integrated into current data transfer, and must have the potential to be produced in volume and at lost cost. The desired system level performance of the optical interconnects was evaluated and design specifications were determined for the optical design. Trade studies involving current technologies were performed to determine suitable hardware configurations. These requirements pointed toward the application of microfabrication technology and micro-optics in order to accomplish the design goals. A pseudo-monolithic silicon-based optical system has been proposed involving diffractive and microrefractive optics along with integrated sensors and emitters. The device emphasizes the use of existing technologies gathered from different disciplines and integrated into one system.

Buried double p-n junction (BDJ) structure designed and fabricated in a standard CMOS process is presented. Under reverse-biasing conditions, it provides two measurable photo- generated junction currents I₁ and I₂, which have a linear dependence on the incident photon flux. Over the visible range, the ratio I₂/I₁ is a monotone- increasing function of the wavelength, which can serve as a reference curve for wavelength determination. The reference curve r((lambda) ) can be obtained by measurement or by calculation. A physically-based model is suggested for the simulation of photocurrents and the computation of the curve r((lambda) ). Two application examples of the BDJ detector are presented. For the development of microspectrophotometry, replacing photodiodes by BDJ detectors offers a solution to problems of wavelength calibration. In the case of colorimetric pH measurement, the BDJ detector is used to detect spectral changes of absorption.