This paper discusses issues related to transitioning a company from the advanced technology development phase (with a particular focus on MEMS) to a profitable business, with emphasis on start-up companies. It includes several case studies from (primarily) NovaSensor MEMS development history. These case studies illustrate strategic problems with which advanced MEMS technology developers have to be concerned. Conclusions from these case studies could be used as checkpoints for future MEMS developers to increase probability of profitable operations. The objective for this paper is to share the author's experience from multiple MEMS start-ups to accelerate development of the MEMS market by focusing state- of-the-art technologists on marketing issues.

The application of laser technology has shown great advantages in the fast growing area where electronic and mechanical components are combined to form miniature structures. Use of laser-induced polymerization (LIP) in making microstructures has drawn increasing attention. A focused laser beam can be guided directly to write three-dimensional patterns. The advantages are high cure speed, constant intensity along the curing distance and uniform exposure over the curing area. It will result in more efficient absorption by selecting an appropriate photoinitiator and reduce the unwanted reactions, which are common in conventional UV light curing. This also leads to a more precise control of the penetration profile. This paper will report on fabrication of three-dimensional microstructures on a laser microfabricating system using the principle of UV LIP. Laser curing parameters were optimized to make micro-sized primitives, including cubes, cylinders, annuluses, and pyramids. By combining primitives, more complicated structures were obtained. A scanning electron microscope and a roughness step tester gave the feature size and surface roughness. The polymerized objects had lateral dimensions of about 200 micrometers and were typically be 300 micrometers in height. The best average surface roughness was 385 nanometers.

Micromachining performed by Excimer Lasers in conjunction with NC-controlled machines offer flexible production possibilities for 3-D-surfaces. Due to the limitations of conventional micromachining technology for brittle transparent materials in the micro range, a new laser machining beam guiding and data handling system was designed and built. The data handling starts with the mathematical description of the surface shape to be machined. The contour can be derived from a mathematical function or individual xyz-data point information from any CAD-program. A pre-processor calculates the nc-data for laser triggering, xyz-motion and the nc-mask control. Each laser pulse leads to a material removal, defined by the illuminated surface on the work piece as well as the energy density. The principal of superposition of pulses allows the creation of the desired contour. The chosen ablation strategy determines the surface roughness and the process speed. To achieve best results, it has to be carefully adjusted for a specific material. This technique does not require prefabricated tools such as semiconductor masks. This is a sufficient method for structuring grooves in ceramics, diamonds or glass as well as aspherical transparent optical surfaces or micro lens arrays. The excellent absorption of 193 nm compared to 248 nm or larger wavelengths leads to damage free structuring of most brittle materials. The optimized surface ablation process requires spot sizes and energy densities on the work piece which can not be realized with a mirror based beam guidance system. To eliminate these restrictions, a new mirror free machining concept with a gas flushed beam guiding system mounted on a granite vibration reduction table with air bearing positioning system was build. This paper describes the potential of 193 nm treatment of 3-D micro surfaces with a process optimized machine and data handling system.

A novel technique to fabricate binary microlens on polymer substrates by 248 nm KrF excimer laser micromachining is proposed. A successfully fabricated eight-level binary microlens with diameter 1.25 mm and focal length 43 mm on polycarbonate (PC) sheet is also reported. Using this technique, microlens patterns are mask-projected on the polymer materials via the laser ablation effect instead of complicated multi-stepped lithography and etching processes. Moreover, the precise ablated depth of microlens can be achieved by adequately controlling the number of laser pulses. In order to reduce alignment complexity and offset, multiple mask patterns are produced in one quartz plate and the mask holder is loaded by a servo-controlled x-y stage. SEM pictures and optical interference inspections show that the etched surface and sidewall have roughness deviation less than 30 nm, which is compatible with those results obtained by other techniques. This technique can fabricate a 2 X 2 array of eight-level binary microlens in about several seconds. He-Ne laser and proper optics arrangements are used to measure the diffraction efficiency of the fabricated devices. Experimental results show that the unique technique can produce the multi- level microlens with submicrometer feature size, high-quality surface morphology, and satisfactory optical characteristics.

A highly ordered nanochannel array structure with high aspect ratios was fabricated based on the anodization of aluminum. A texturing treatment of the Al surface was carried out by nanoindentation process using the SiC mold initiated the development of an ideally-arranged-hole-array structure of anodic porous alumina. The hole-array has ideal hexagonal arrangement over millimeter dimensions, and the aspect ratio of the channel was over 150. In this report, the fabrication of the highly ordered nanochannel array and the application of the obtained structure to the preparation of nanostructures are described.

Electrochemical etching of silicon is commonly used for sensor fabrication processes. In fluoride-containing solutions porous silicon can be formed while in alkaline solutions silicon can be passivated by passing an anodic current through the silicon. For batch fabrication it is more convenient to have a contactless etch method. Galvanic etching can be used for this purpose. In this paper some general aspects of galvanic etching are considered. Examples of galvanically etched structures are presented.

Boron-doped silicon layers with sufficiently high doping levels become effective stop-layers during the chemical etching of silicon in alkaline type solutions (KOH, NaOH, LiOH) or in EDP (ethylene-diamine-pyrocatechol). An advantageous chemical solution consisting in tetramethyl ammonium hydroxide (TMAH) with isopropyl alcohol (IPA), showing similar etching properties was also proposed. The property as a stop layer of the boron-doped silicon is currently used as the most convenient etch-stop technique, because it is easy to define the thickness of the structure by the depth of boron diffusion in silicon. However, the boron diffusion profile in silicon is not a step-like distribution, but it presents a continuous decrease of the concentration from the silicon surface to the bulk, that depending on the diffusion conditions, i.e. diffusion time, temperature and doping technique. It is therefore expected that such a decrease will result to a continuous variation of the etching rate and a consequently variation of the etching time with the diffusion depth. In this paper we present firstly the doping properties of the silicon layers doped by the termo-chemical method using chemical sources. It is shown that the doping properties vary within the boron-doped layers. Boron diffusion profiles determined by SIMS method and electrical method are presented in order show the specific behavior of the concentration distribution in the silicon bulk. Misfit dislocations are induced by the boron diffusion in silicon at high concentrations. The conditions of the generation of the misfit dislocations in the boron-doped layers depends on the processing conditions, especially on the diffusion time and temperature. We show that the density distribution of the misfit dislocations in the silicon bulk is not uniform after the boron prediffusion and diffusion processes. From the point of view of the micromechanical applications, the inhomogeneity of the structural and doping properties of the silicon layer can influence the stress properties of such silicon-doped layers. Therefore, in order to reduce the stress gradient in the silicon membranes and micromechanical elements, it is necessary to obtain layers with uniform material properties. Both the doping and structural properties of the boron doped layers are to be therefore better knowledged and controlled. However, the doping properties obtained after the boron doping by termo-chemical method or by implantation doping technique cannot provide uniformly doped silicon layers. Therefore, a careful chemical etching during the self-limitation process of the boron-doped silicon layers offers such a possibility, as it will be presented in the paper. In order to eliminate from the silicon doped layers the regions were the properties of the silicon layers are not uniform, it is necessary to control the chemical etching process which is the next important step in the bulk micromachining technology useful to prepare the micromechanical elements. These key parameters of the chemical etching process are the chemical etching rate and the chemical etching time. It is shown that it is possible to calculate the chemical etching rate and the chemical etching time for some specified etching conditions. Such a possibility allows to control the thickness of the micromechanical elements and to eliminate the stress gradient induced by the non-uniform doping and by the misfit dislocations in the silicon micromechanical elements.

A high performance silicon dry etch process (STS Advanced Silicon Etch ASE) which in many cases is a beneficial replacement for the usual anisotropic wet etch methods like KOH etching is presented. During fabrication of Micro-Electro- Mechanical Systems (MEMS) the patterning of silicon is an essential step. Conventional wet or dry etching processes used up to now cannot meet the majority of future MEMS patterning needs. The process described in this paper allows a wide range of possible geometries and freedom of design and mask layout for novel MEMS applications. The installed etch system is working with an inductively coupled plasma source (ICP) which produces high plasma densities at low pressure to achieve deep silicon etching (greater than 200 micrometer) with high etch rates up to 5 micrometer/min and a high passivation layer selectivity. The new ASE process uses only fluorine based chemistry and operates at room temperature. ASE uses photoresists and silicon oxid layers as an etch passivation and allows the manufacturing of silicon structures with nearly vertical side walls in bulk and surface micromachining illustrated by several MEMS applications carried out at the Fraunhofer Institute for Solid State Technology. With depths up to 100 micrometer realized at the institute now and an excellent anisotropic profile control ASE is obviously the tool, useful from device development to volume production of microsystems.

Adhesion, friction, and wear are prevalent problems in a majority of MEMS devices. Understanding of surface interactions in MEMS is of paramount importance for controlling stiction phenomena. This paper will discuss various surface treatments employed to reduce adhesion and friction in polysilicon-based MEMS, their successes and their limitations.

This work presents film properties and initial reliability studies for thin Teflon-like films applied to a unique test vehicle, the Sandia-designed and fabricated microengine. Results on microengines coated with the film show a factor of three improvement in their lifetime and an order of magnitude reduction in the coefficient of friction when compared to uncoated samples. Coefficients Of Friction (COF) of 0.07 for the Teflon-like film and 1.0 for uncoated samples are extracted from models which match the measured behavior of working microengines. These films, deposited from a plasma source, exhibit the ability to penetrate into very narrow, deep channels common to many MEMS devices. For as-deposited film, both the refractive index at 1.4 and the contact angle with water at 108 degrees show the film to be very similar to bulk Teflon PTFE. Film stability as a function of temperature has been examined using Fourier Transform Infrared (FTIR) spectroscopy. The film structure as observed by the fluorine- carbon (F-C) peak is stable up to 200 C, but starts decomposing above 250 C. Film composition has been examined using X-ray photoelectron spectroscopy (XPS) and is quite different for directly exposed surfaces compared with deep, narrow channels where the deposition process is diffusion limited.

We have developed a new magnetic actuation process for hinged, surface micromachined structures to assemble three-dimensional optical devices with high efficiency and high yield. Electroplated magnetic material (Permalloy) is integrated with two types of hinged microstructures and the magnetic actuation process has been experimentally characterized. Under a given external magnetic field, the angular displacement of a hinged structure is determined by the volume of the magnetic material or by the stiffness of an auxiliary flexural loading spring. Preliminary design rules for achieving asynchronous actuation of hinged microstructures have been established to enable effective parallel assembly of three-dimensional devices. We have demonstrated parallel actuation of arrays of individual microstructures and three-dimensional assemblies under a globally applied external magnetic field.

For the assembly of miniaturized radar distance sensors vacuum gripers for handling touch sensitive and very small millimeter wave monolithic integrated circuits (M³IC's) have been developed. The grippers are designed modularly to allow different combinations of gripper heads, chip-specific gripper plates and gripper exchange interfaces. The manufacture of the gripper components by (mu) -EDM and the batch processing of photoetchable glass is presented. In addition, a solution for the removal of M³IC's from adhesive carriers, such as VR Gel-Paks and bluetape with vacuum support has been developed which is suitable for automatic pick & place machine routines.

In silicon surface micromachining, the newly developed GPE (gas-phase etching) process was verified as a very effective method for the release of highly compliant microstructure. The developed GPE system with anhydrous HF (hydrogen fluoride) gas and CH₃OH (methanol) vapor was characterized and its selective etching properties were discussed. P-doped polysilicon and SOI (silicon on insulator) substrate were used as a structural layer and TEOS (tetraethylorthosilicate) oxide and thermal oxide as a sacrificial layer. The etch rates of HF GPE were 400 angstrom/min for sacrificial TEOS oxide and 1000 angstrom/min for bulk TEOS oxide. For SOI structures, we adopted two step process of wet etch and HF GPE process to reduce the process time and confirmed relatively low etch rate of 55 angstrom/min for 1.8 micrometer-thick thermal oxide after 6:1 BHF etching for 15 minutes.

We report a comprehensive approach to design, fabricate and characterize silicon microlenses for applications in IR image sensors. ZEMAX design tool was used to assist in the design of the lenses. Conventional photolithography and thermal reflow of melting resist technique were deployed to achieve spherical resist patterns. Reactive ion etching (RIE) was utilized for transfer of resist patterns to the substrate in O₂ and C₂F₆ environment. The shape of the fabricated lenses, i.e. radii of curvature and focal length were controlled within a wide range, by controlling the etch rates of resist and substrate, which were further controlled by varying the flow of gases, selectivity and power. Optical methods such as ray analysis and profilometry were used to obtain lens properties. Scanning electron microscopy was performed to analyze the morphology of the fabricated lenses.

This process combines the best features of bulk and surface micromachining. It enables the production of stress free, thick, virtually arbitrarily shaped structures with well defined, thick or thin sacrificial layers, high sacrificial layer selectivity and large undercuts using IC compatible, processes. The basis of this approach is the use of readily available {111} oriented substrates, anisotropic Si trench etching, SiN masking and KOH etching.

In this paper, the fabrication process of polycrystalline diamond film micro-resonators was first reported. Silicon was used as substrate, LPCVD polysilicon films were used as diamond-growth-compatible sacrificial layer, and doped diamond films were grown and patterned by oxygen ion beam dry etching to be the resonators. The flexural beam resonator was vibrated in air under electrostatic excitation with AC voltage of 45 V.

We have investigated the growth of TiNi shape memory alloy thin films at relatively low temperatures (below 150 degrees Celsius) by an ion beam sputter deposition process which is compatible with integrated circuit microfabrication technology. Films of thickness less than 5 micrometer have been deposited onto various substrates including silicon, glass and Kapton and generally exhibit shape memory characteristics without requiring high temperature annealing. Films covering areas up to 5 cm² have been grown and also TiNi microstructures having a range of minimum lateral dimensions down to approximately 100 micrometer have been fabricated. Temperature-time profiles measured during direct electrical Joule heating have been used to derive thermal parameters and monitor phase changes indicative of the two-way shape memory effect. The implications for speed of response by scaling shape memory alloy structures to micrometer dimensions are considered.

A bulk-micromachined interdigitated comb actuator supported by surface-micromachined polysilicon springs is proposed and fabricated for excitation of resonating momentum. The excitation force electrically generated by the interdigitated comb pair with a 420 height of (110) wafer is more effective than that obtained using a comb pair with a few height fabricated by a surface micromachining technique. The geometry of the interdigitated comb finger pair is 420 high, 20 wide, 5 apart from the neighboring interdigitated comb finger, respectively. A (110) oriented 420-thick Si wafer is used to fabricate the interdigitated comb electrode array using the technique of anisotropic bulk etching in KOH aqueous solution. A 5-thick phosphorous-doped LPCVD polysilicon film is used for fabrication of the flexures of the comb actuator using the technique of reactive ion etching. Repetition of the LPCVD Si₃N₄ film deposition and reactive ion etching process builds a Si₃N₄ structure, which envelopes and protects the released polysilicon structure from KOH aqueous etchant without an additional mask for passivation patterning. Using a double-sided aligned fabrication technique realizes not only polysilicon flexures formation on both sides of the actuator but also removal of two slant (111) planes in concave corners of the interdigitated comb finger array, which appear during (110) Si orientation-dependent etching and limit the interdigitated comb actuator design.

The establishment of a process to allow planarization of deep x-ray lithography based microfabricated metal components via diamond lapping has enabled examination of three additional microfabrication issues. The areas of improvement that are discussed include materials, microassembly and packaging, and multilevel fabrication. New materials work has centered on magnetic materials including precision micromagnets and surface treatments of electrodeposited materials. Assembly and packaging has been aided by deep silicon etch processing and the use of conventional precision milling equipment combined with press-fit assembly. Diffusion bonding is shown to be a particularly important approach to achieving multilevel metal mechanisms and furthermore shows promise for achieving batch assembled and packaged high aspect-ratio metal micromechanics.

In recent years a number of microfabrication technologies have been developed suitable for the realization of micro products on industrial scale. One field that demands for miniaturization is the field of molecular biotechnology. In order to handle thousands of different substances within a short limit of time and minimum consumption of valuable biomolecules microstructured tools for synthesis, separation and analysis are required. Most current developments in this field are based on bulk and surface micromachining of silicon and are therefore limited to one material. Micromolding technologies permit the cost effective mass production of microstructures from a wide variety of modern high-performance polymers. This paper is focused on the development and fabrication of miniaturized devices for biotechnical applications: a self-filling micropump suited for liquid transport and dosage, nanotiterplates for combinatorial chemistry, fluidic chips suited for DNA-sequencing and chips for biosensors. For micromolding these structures conventional molding techniques have to be adapted. This comprises the mold insert fabrication either by LIGA-technique or by advanced methods of precision engineering, process adaptation to enable high density packaging, the screening of polymer materials to meet demands for optical transparency or stability towards particular solvents, and quality control for high process reproducibility.

We have fabricated a unified Orifice Plate Assembly (OPA) for high-resolution inkjet printheads, which has orifices, ink flow channels, and reservoirs three-dimensionally in a single body, using single-step 3D photolithography followed by single-step electroplating. These three components are the core in inkjet printheads because they determine almost all of ink fluidics, especially the size and trajectory of an ink drop. Therefore, for high-resolution beyond 600 dpi, a unified and high-precision orifice plate assembly is strongly needed. By newly devised 3D patterning technique, namely Multi- Exposure and Single Development (MESD), we form the 3D photoresist mold for the unified OPA. Once the 3D unified OPA mold is fabricated, nickel electroplating is performed on it until the roof of the channel molds is fully covered by the overplated Ni, and until all the plating fronts around orifices in the entire wafer converge to their salient orifice molds. This converging margin in the electroplating step, which is originated from the salient orifice mold, excellently enhanced the wafer-level uniformity of the orifice size and shape. We neatly demonstrated both the unified OPA of various orifice size and shape, and one corresponding to a 2400 dpi- inkjet printhead, using MESD method with a single-coated 41 micrometer-thick photoresist of Hoechst AZ9262.

A simple electroplating surface micromachining process for fabricating freestanding microstructures using UV lithography of thick photoresist and double electroplating has been developed. Compared with the conventional surface micromachining process, this process can be used to fabricate various shapes of freestanding 'out-of-plane' microstructure. In this process, two different materials electroplated continuously in a single mould are used as a sacrificial and a structural layer respectively. Fabrication of different shapes of 3D microstructures using controlled overplating on the patterned plate base electrode array has been reported, and this method was applied to form a 3D sacrificial layer. Shape of the sacrificial layer can be varied by changing width and space of the patterned plating base electrodes. After selective etching of the sacrificial layer we can obtain a released structure, the shape of which is automatically determined by that of sacrificial layer. Released gap and thickness of the structure are easily controlled by only changing electroplating time. Using this process, a simple microactuator that is able to move in the vertical direction and have inclined side-support beams is successfully fabricated. This technique can be applied to fabricate a novel type of surface micromachined actuating component.

A novel and high-yield process is presented to fabricate electroplated 3D micro-coils for MEMS and microelectronics. The 3D Solenoid-type Integrated Inductor (SI²) is decomposed into two parts, bottom conductor lines and air bridges. The bridges are formed by only one electroplating step. This single-step fabrication of the electroplated air bridges is possible by forming the 3D photoresist mold with a Multi-Exposure and Single Development method (MESD). We have successfully demonstrated 3D micro-coils with or without a core. This method is so easy and simple that we can dramatically improve the fabrication yield, which is the hardest obstacle in the various 3D micro-coil fabrication methods. Also, this method has good IC process compatibility owing to low process temperature and the monolithic feature.

A review of fabrication techniques and testing of single crystal Si resonant devices with high aspect ratio capacitive transduction mechanisms has been presented. Deep trenches have been etched in single crystal Si using a Cl₂ plasma generated by an electron cyclotron resonance (ECR) and an inductively coupled plasma (ICP) source. This etching has been extended to the fabrication of resonant devices thicker than 50 micrometer using a frontside-release process and these devices have been electrically tested. The thick devices allow larger capacitance between drive and sense plates, which in turn reduces required driving voltage and increases sensing current. In addition, an etching condition has been developed which can etch trenches as narrow as 0.1 micrometer to depths greater than 3 micrometer. This etch has been used to fabricate comb driven resonators with high aspect ratio gaps (greater than 30) between comb fingers. Finally, a fabrication method to integrate these single crystal Si mechanical devices with a conventional circuit process with only one additional masking step has been developed. Eleven micrometer thick clamped-clamped beam comb driven resonators have been fabricated and tested on the same chip with working CMOS transimpedance amplifiers. The resonator had a resonant frequency of 28.9 kHz and a maximum amplitude of vibration of 4.6 micrometer, while the amplifier had a 3-dB frequency of 150 kHz and a power dissipation of 1.25 (mu) W.

The recent development of a high-aspect ratio Si etch (HARSE) process has enabled the fabrication of a variety of Si structures where deep trench etching is necessary. The HARSE process relies on the formation of a sidewall etch inhibitor to prevent lateral etching of the Si structures during exposure to an aggressive SF₆/Ar plasma etch chemistry. The process yields highly anisotropic profiles with excellent dimensional control for high aspect ratio features. In this study, Si etch rates and etch selectivities to photoresist are reported as a function of chamber pressure, cathode rf-power, ICP source power, and gas flow. Si etch rates greater than 3 micrometer/min with etch selectivities to resist greater than 75:1 were obtained. Lateral dimensional control, etch selectivities to SiO₂ and Si₃N₄, and aspect ratio dependent etching (ARDE) will also be discussed.

Using both wet and plasma etching, we have fabricated micro- channels in silicon substrates suitable for use as gas chromatography (GC) columns. Micro-channel dimensions range from 10 to 80 micrometer wide, 200 to 400 micrometer deep, and 10 cm to 100 cm long. Micro-channels 100 cm long take up as little as 1 cm² on the substrate when fabricated with a high aspect ratio silicon etch (HARSE) process. Channels are sealed by anodically bonding Pyrex lids to the Si substrates. We have studied micro-channel flow characteristics to establish model parameters for system optimization. We have also coated these micro-channels with stationary phases and demonstrated GC separations. We believe separation performance can be improved by increasing stationary phase coating uniformity through micro-channel surface treatment prior to stationary phase deposition. To this end, we have developed microfabrication techniques to etch through silicon wafers using the HARSE process. Etching completely through the Si substrate facilitates the treatment and characterization of the micro-channel sidewalls, which dominate the GC physico- chemical interaction. With this approach, we separately treat the Pyrex lid surfaces that form the top and bottom surfaces of the GC flow channel.

Deep-reactive ion etching (DRIE) of silicon, also known as high-aspect-ratio silicon etching (HARSE), is distinguished by fast etch rates (approximately 3 micrometer/min), crystal orientation independence, anisotropy, vertical sidewall profiles and CMOS compatibility. By using through-wafer HARSE and stopping on a dielectric film placed on the opposite side of the wafer, freestanding dielectric membranes were produced. Dielectric membrane-based sensors and actuators fabricated in this way include microhotplates, flow sensors, valves and magnetically-actuated flexural plate wave (FPW) devices. Unfortunately, low-stress silicon nitride, a common membrane material, has an appreciable DRI etch rate. To overcome this problem HARSE can be followed by a brief wet chemical etch. This approach has been demonstrated using KOH or HF/Nitric/Acetic etchants, both of which have significantly smaller etch rates on silicon nitride than does DRIE. Composite membranes consisting of silicon dioxide and silicon nitride layers are also under evaluation due to the higher DRIE selectivity to silicon dioxide.

In this paper, we review work on a novel low temperature SOI HARM process at the Defence Evaluation and Research Agency (DERA) and its integration with on-chip CMOS electronics -- as part of a fully integrated MEMS process or as 'value-added' post-processing on commercial CMOS wafers. BSOI material was designed for micromachining applications. The SOI layer acted as a device layer while the insulating dielectric acted as an etch stop and as a sacrificial layer. This resulted in a low stress material that was optimized for the sacrificial release process. Trench isolation was achieved by deep dry etching to the buried dielectric. These trenches could be refilled to allow metallization to reach isolated components. Higher temperature refill material could also act as a lateral mechanical anchor for structures that would otherwise be completely undercut and float off during the sacrificial process. Structures with aspect ratios of up to 50:1 have been defined using combinations of photolithography, deposition and dry etching. CMOS transistor and capacitor characteristics were measured before and after SOI HARM processing. No detectable change in their characteristics was found. This process is attractive for many micromachining applications. Prototype micro-inertial devices fabricated in this technology are also presented in this paper.

According to the fabrication processes, the thin film materials are normally under residual stresses. Unlike the microelectronics devices, the micromechanical structures are no longer constrained by the silicon substrate underneath after anisotropic etch undercutting. Therefore the residual stresses may lead to bending and buckling deformations of micromechanical structures. The buckling behavior has been exploited to measure the residual stresses of thin films. This characteristic can also be applied to fabricate out-of-plane three dimensional micromechanical structures, if their deflections are controllable. Buckling of microbridges is difficult to be predicted since it is strongly dominated by the fabrication processes and boundary conditions. Presently the information regarding the buckling of micromachined structures is still not complete yet. Therefore the application of this characteristic is limited. In this research, the effect of boundary conditions on the buckling of microbridges is studied through analytical and experimental approach. In addition, the effects of the thickness and length of the microbridges on buckling are also discussed. During the experiment, silicon dioxide microbridges are fabricated through standard micromachining fabrication processes. The contribution of this paper is to provide a useful information in designing microbridges. Therefore the buckling behavior can be predicted and then exploited to fabricate useful micromechanical structures. The potential application of this research is in preventing leakage of the micro valves.

We have examined a simple and low-cost method to achieve planarization and trench filling on a severe surface topography for MEMS. The method simply uses a single-layer coating of a thick photoresist or polyimide, where the coating thickness is much greater than the severe surface topography. From extensive experiments, we extracted simple empirical formulae for the planarization factor (beta) of the thick photoresist AZ4562 and polyimide PI2611, which let us know the minimum film thickness required to obtain a certain (beta) on a given surface step height and pattern density. We could compare the planarization capability of AZ4562 and PI2611 by this method. Moreover, after the planarization with a thick photoresist, we have shown a new way, other than the plasma etching, to remove the upper photoresist layer conformally. Therefore, we could remain the photoresist only in trenches and fill up very deep and wide trenches with the photoresist. Also, we have shown the etch-back result of PI2611 using conventional O₂ plasma RIE. Using these methods, we obtained the (beta) of 98% on the surface of 20 micrometer-deep and 200 micrometer-wide lines and spaces with a single-coated 70 micrometer-thick photoresist. And 10-micrometer-deep and 200 micrometer-wide trenches as well as 2 micrometer-deep and 50 micrometer-wide trenches were neatly filled up with the photoresist. As applications for MEMS, we fabricated microchannels by metal coating after the trench fill-up process, and even multilevel microchannels by controlling the height of the photoresist remaining in the trench and repeating the trench fill-up process.

MUMPS (Multi-User MEMS Process) is receiving increasingly wide use in micro optics. We have investigated the optical properties of the polysilicon reflective surface in a typical MUMPS chip within the visible light spectrum. The effect of etching holes on the reflected laser beam is studied. The reflectivity and diffraction patterns at five different wavelengths have been measured. The optical properties of the polysilicon reflective surface are greatly affected by the surface roughness, the etching holes, as well as the material. The etching holes contribute to diffraction and reduction of reflectivity. This study provides a basis for optimal design of micromachined free-space optical systems.

One of the limiting factors in fabrication of surface micromachined structures is the residual stress formed in the film during deposition. In order to fabricate the microstructure using the polysilicon layers deposited in a conventional LPCVD furnace, we used the multi-stacked polysilicon films and reported a method of stress control in that films. In the multi-stacked polysilicon film there exist the polysilicon/polysilicon interfaces, at which oxidized layers are formed during film stacking and dopant atoms are segregated. These facts made the multi-stacked film difficult to be used as structural layers for microstructure fabrication. In order to control the stress profile, we investigated the effects of dopant distribution and oxidized layers on the stress profile in the multi-stacked film using micromachined test structures. The stress profile could be modified considerably by multi-steps doping process and the residual stress was reduced to 15 MPa for 5 micrometer thick film. The contribution of the oxidized layer to the stress profile was also studied extensively and we could reduce the effect of the oxidized layer by the symmetrical stacking of films. Using the simple model, the dopant-induced stress profile was calculated theoretically from the dopant concentration profile and it suggested an improved method for estimating the stress profile of doped polysilicon films. Using the method developed in this study, the microstructure made of the multi-stacked polysilicon film was successfully fabricated with a low stress gradient of 0.5 MPa/micrometer. The conventional LPCVD equipment without any modification can fabricate the polysilicon structural layer for the microstructure fabrication by the multi-stacking process, which offered the convenient method of stress control.

To meet the MEMS assembly requirement, we have developed an assembly apparatus. This apparatus consists of a stereo microscope, a CCD camera incorporated with a video monitor, an X-Y translation precision stage, and a specifically fabricated suction glass needle. The suction glass needle is the core component in this apparatus, which is mounted on a micromanipulator, and used to suck up the microelements to be assembled. The assembly operation is carried out under the observation of a stereo microscope with a video camera. As a result, an electro-static micromotor with a 300 micrometer diameter rotor is accurately assembled by this assembly apparatus.

Recently, the focus is on microforming of three-dimensional products, and many products are being produced in this way. We have investigated the microforming technique and forming machine that exclusively fits for making of medical micro tool as medical forceps. In the forming, both the freedom of the forming shape and productivity are important conditions to a process. To answer to these requirements, it was considered valuable to study methods combining various machining processes. From such viewpoint, we developed the new microforming system by using pressing and cutting and its functions were investigated through the forming experiment.

Anisotropic etching characteristics of (111)-oriented silicon in alkaline solutions was studied. Through a spoke pattern, it was found that (110) planes have the highest etching rate rather than high-index ones such as (211) or (331). With a round open, the final emergent periphery is hexagonal. The six sidewalls are defined by other (111) facets from its crystal geometry with three inclining angles of 70.5 degrees and another three declining angles of 109.5 degrees. The etched bottom surface morphology was also investigated by SEM pictures observation. Results show that aqueous KOH solution results in smooth surface due to its higher etching rate of residual oxide existed in the silicon, while the other etchants such as hydrazine (N₂H₄) and tetramethyl ammonium hydroxide (TMAH) induce seriously wavy roughness. As an application example, floating single-crystal silicon (c-Si) structures were fabricated with some potential functions as thermopile, silicon bolometer, mass flow transducer and other force microsensors.

PMMA (polymethyl methacrylate) has been widely used as x-ray LIGA material for its good features of electrical acid plating of all common metals to industrial applications. Unlike the tough characteristics of polyimide in almost all alkaline and acid solutions, PMMA is easily removed in chemical etchants after electroplating process. For this reason, ablation- etching characteristics of PMMA material for 3D microstructures fabrication using a 248 nm KrF excimer laser were investigated. Moreover, the uses of the laminated dry film were also studied in this work. Experimental results show that PMMA microstructures can produce the near-vertical side- wall profile as the laser fluence up to 2.5 J/cm². PMMA templates with high aspect ratio of around 25 were demonstrated, and the sequential electroplating processes have realized the metallic microstructures. Moreover, the microstructures fabricated in dry film show the perfect side- wall quality, and no residues of debris were found.

Described in this paper are a novel composite beam-mass structure and a micro gyroscope based on the structure. The composite beam consists of two sections: a section of vertical beam with a cross-section vertical to the wafer surface and a section of horizontal beam near the wafer surface. As the two sections have two orthogonal compliant directions, the structure has two orthogonal vibration modes: a vertical vibration mode decided by the horizontal beam and a lateral vibration mode decided by the vertical beam. Therefore, a vibratory gyroscope can be developed by this composite beam structure with a mass attached. As the composite beam is a multilevel structure that can hardly be fabricated by a conventional anisotropic etching technology, a novel 'maskless etching' technology for <100> vertical steps has been developed for the structure. Piezoresistive bridges on the surfaces of the horizontal and the vertical beams are used to monitor the driving vibration and to sense the output signal. Testing shows that the sensitivity from the piezoresistive bridge is 0.22 (mu) V/(degrees/sec) under a 6V AC driving with a DC bias. The special advantage of the sensor is the ability of working in an atmospheric environment.

This study is aimed at making metallic fine lines characterized with high aspect ratio. There are two methods we have developed. One is the trilevel lift-off method with submicron lithography, and the other is the lift-off method by using the commercial negative photoresist SU-8 made by IBM. First, the trilevel lift-off method is described. A pre- imidized, soluble polyimide layer of OCG Probimide 293 A is spun on a wafer with thickness 4 micrometer. A 120 nm thick layer of silicon oxynitride was formed on the polyimide by PECVD. A layer photoresist layer was applied and patterned. This photoresist layer is used as the etching mask of silicon oxynitride by RIE with the gas CF₄ plasma. Similarly, the silicon oxynitride is used as the etching mask of the thick polyimide layers by RIE with the gas O₂ plasma. After metallization the pre-imidized polyimide is dissolved in methylene chloride lifting off the oxynitride and metal layers. Following this way, the submicron lithography, such as silylation technology, is suitable to make the aspect ratio up to 10 and the metal line will still have 3 micrometer height. The other is the lift-off method by using negative photoresist SU-8. This SU-8 is originally used as high aspect ratio molding. The linewidth of SU-8 is reduced to 2 micrometer linewidth with 12 micrometer height, and used as the remover to lift off after metallization. This SU-8 makes the fine-line metallization of 2 micrometer linewidth to achieve the aspect- ratio up to 5.

To better understand and to help optimize the electroforming portion of the LIGA process, we have developed one and two- dimensional numerical models describing electrodeposition of metal into high aspect-ratio molds. The one-dimensional model addresses dissociation, diffusion, electromigration, and deposition of multiple ion species. The two-dimensional model is limited to a single species, but includes transport induced by forced flow of electrolyte outside the mold and by buoyancy associated with metal ion depletion within the mold. To guide model development and to validate these models, we have also conducted a series of laboratory experiments using a sulfamate bath to deposit nickel in cylindrical molds having aspect ratios up to twenty-five. The experimental results indicate that current densities well in excess of diffusion-limited currents may still yield acceptable morphologies in the deposited metal. However, the numerical models demonstrate that such large ion fluxes cannot be sustained by convection within the mold resulting from flow across the mold top. Instead, calculations suggest that the observed hundred-fold enhancement of transport probably results from natural convection within the molds and that buoyancy-driven flows may be critical to metal ion transport even in micron-scale features having very large aspect ratios. Taking advantage of this enhanced ion transport may allow order-of-magnitude reductions in electroforming times for LIGA microdevice fabrication.

We describe the fabrication techniques of novel, compact optical elements for collimating and/or focusing beams of X- rays or thermal neutrons. These optical elements are solid composite arrays consisting of regular stacks of alternating micro-foils, analogous in action to Soller slit collimators, but up to three orders of magnitude smaller. The arrays are made of alternating metals with suitable refractive indices for reflection and/or absorption of the specific radiation. In one implementation, the arrays are made of stacked micro-foils of transmissive elements (Al, Cu) coated and/or electroplated with absorbing elements (Gd, Cd), which are repeatedly rolled or drawn and restacked to achieve the required collimation parameters. We present results of these collimators using both X-rays and neutrons. The performance of the collimating element is limited only by the choice of micro-foil materials and the uniformity of their interfaces.

A photographic method using silver halide emulsions as photoresist medium has been used for the fabrication of relief blazed diffractive elements. The fabrication method comprises the design of half tone masks in the computer and the recording of a reduced image of the mask on the emulsion. After development a thin film of aluminum is laid over the emulsion to obtain a high reflective zone plate.

Conditioning neutron and X-ray beams is best achieved with glancing-incidence reflective optics. Square micro-channel arrays offer an increasingly practical geometry for this implementation. We present results for focussing neutrons with two such arrays, one with channel size of 32 micrometer, which places us truly in the microscopic regime. These two arrays, designed for soft X-rays, perform comparably with neutrons.

Microassembly promises to extend MEMS beyond the confines of silicon micromachining. This paper surveys research in both serial and parallel microassembly. The former extends conventional 'pick and place' assembly into the micro-domain, where surface forces play a dominant role. Parallel assembly involves the simultaneous precise organization of an ensemble of micro components. This can be achieved by microstructure transfer between aligned wafers or arrays of binding sites that trap an initially random collection of parts. Binding sites can be micromachined cavities or electrostatic traps; short-range attractive forces and random agitation of the parts serve to fill the sites. Microassembly strategies should furnish reliable mechanical bonds and electrical interconnection between the micropart and the target substrate or subassembly.

Silicon became well known as the base material for high performance microstructures on the basis of cost, performance, durability, and excellent mechanical as well as electrical properties. Numerous market surveys and projections have identified a myriad of high volume opportunities over the past two decades. Yet true commercial success has remained in isolated pockets. The appeal of mechanical and electrical on the same miniature device combined with the photogenic resulting structures has resulted in a general hype of the technology. In concept, microstructures in silicon can fill just about any role as a small scale physical to electrical interface. However, the danger lies in assuming that these applications justify the cost. These costs of ownership include infrastructure cost, cost of compensating for performance limits, time to market, and hidden manufacturing costs. Many technically elegant microstructure solutions become solutions looking for problems. This presentation looks first at the opportunity and characteristics of silicon microstructures that make it an enabling technology, followed by examples where the technology has found markets. A summary of the industry characteristics and a comparison and contrast with the traditional electronics industry follows. A profile of successful microstructure applications and future trends leads to insight on how to structure a commercially viable approach. Finally, a summary of the market drivers and requirements and the true cost of ownership provides guidance on markets where a microstructure solution makes sense.

An overview of the key micromachining technologies that enable communications applications for MEMS is presented with a focus on frequency-selective devices. In particular, micromechanical filters are briefly reviewed and key technologies needed to extend their frequencies into the high VHF and UHF ranges are anticipated. Series resistance in interconnect or structural materials is shown to be a common concern for virtually all RF MEMS components, from mechanical vibrating beams, to high-Q inductors and tunable capacitors, to switches and antennas. Environmental parasites -- such as feedthrough capacitance, eddy currents, and molecular contaminants -- are identified as major performance limiters for RF MEMS. Strategies for eliminating them via combinations of monolithic integration and encapsulation packaging are described.