Showing papers in "Journal of Micromechanics and Microengineering in 1997"
TL;DR: In this paper, the characterization of a home-made negative photoresist developed by IBM is described, called SU-8, which can be produced with commercially available materials and has an outstanding aspect ratio near 15 for lines and 10 for trenches, combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.
Abstract: This paper describes the characterization of a home-made negative photoresist developed by IBM. This resist, called SU-8, can be produced with commercially available materials. Three blends were prepared for this article and some of its optical and mechanical properties are presented. One of its numerous advantages is the broad range of thicknesses which can be obtained in one spin: from 750 nm to with a conventional spin coater. The resist is exposed with a standard UV aligner and has an outstanding aspect ratio near 15 for lines and 10 for trenches. These ratios combined with the electroplating of copper allow the fabrication of highly integrated electromagnetic coils.
1,045 citations
TL;DR: Polydimethylsiloxane (PDMS) is a commercially available physically and chemically stable silicone rubber as mentioned in this paper, which has a unique flexibility with a shear elastic modulus due to one of the lowest glass transition temperatures of any polymer.
Abstract: Polydimethylsiloxane (PDMS) is a commercially available physically and chemically stable silicone rubber. It has a unique flexibility with a shear elastic modulus due to one of the lowest glass transition temperatures of any polymer . Further properties of PDMS are a low change in the shear elastic modulus versus temperature , virtually no change in G versus frequency and a high compressibility. Because of its clean room processability, its low curing temperature, its high flexibility, the possibility to change its functional groups and the very low drift of its properties with time and temperature, PDMS is very well suited for micromachined mechanical and chemical sensors, such as accelerometers (as the spring material) and ISFETs (as the ion selective membrane). It can also be used as an adhesive in wafer bonding, as a cover material in tactile sensors and as the mechanical decoupling zone in sensor packagings.
868 citations
TL;DR: In this paper, an overview of the materials available in integrated circuit manufacturing is given, and the etch mechanism and sacrificial layer etch kinetics are reviewed, and selectivity issues important for the proper choice of layers and etchants are addressed.
Abstract: Silicon dioxide sacrificial layer etching has become a major surface micromachining method to fabricate microsensors and microactuators often made of polycrystalline silicon. An overview of the materials available in integrated circuit manufacturing is given, and the etch mechanism and sacrificial layer etch kinetics are reviewed. Selectivity issues important for the proper choice of layers and etchants are addressed discussing the chemical attack of aluminum during long sacrificial layer etching, as an example. Various etchants known from other studies are compared: concentrated and dilute HF, buffered HF (BHF), nitric acid based etchants known as P-etch, R-etch, S-etch, as well as mixtures of HF and HCl, and vapor HF. `Pad-etch', an acetic acid/ammonium fluoride/ethyleneglycole solution is shown to have an enhanced selectivity against aluminum. Some device examples such as arrays of deflectable micromirrors demonstrate the versatile application of sacrificial oxide etching in surface micromachining.
178 citations
TL;DR: In this article, micro enzyme reactors for applications in micro total analysis systems (mu TASs) require new methods to achieve structures with a large surface area onto a micro substrate.
Abstract: Miniaturization and silicon integration of micro enzyme reactors for applications in micro total analysis systems (mu TASs) require new methods to achieve structures with a large surface area onto ...
159 citations
TL;DR: A novel electrothermally and laterally driven microactuator made of polysilicon has been designed, fabricated, and tested in this article, where the operational principle is based on the asymmetrical thermal expansion of the microstructure with different lengths of two beams.
Abstract: A novel electro-thermally and laterally driven microactuator made of polysilicon has been designed, fabricated, and tested. The operational principle is based on the asymmetrical thermal expansion of the microstructure with different lengths of two beams, but not based on the variable cross sections of the microstructure. A microgripper to demonstrate one possible application of the microactuator is fabricated and characterized. The input voltage of this design is less than 10 dc to produce 20 m displacement with about 0.6 mJ heat dissipation, and the maximum temperature is less than 600C. A gripping force up to 2.8 N can be generated. Simulation results are compared with the experimental data and show good agreement. Some design parameters strongly influencing the performance of the microactuator are discussed also.
154 citations
TL;DR: In this paper, the design of a micropump employing only one valve is presented, which gives flow rates in the 10 - 100 range, which are very suitable for drug-delivery applications.
Abstract: The design of a micropump employing only one valve is presented. This device was simulated by means of a model based on electrical analogies and equivalent networks. With a total size of , and a working voltage of 10 V, the device sizing gives flow rates in the 10 - 100 range, which are very suitable for drug-delivery applications.
144 citations
TL;DR: In this paper, distributed-parameter transducers are examined theoretically with special regard to their dynamic electromechanical behaviour and equivalent circuits used to represent them, and the circuits are developed starting from basic EM-transduction principles and the electrical and mechanical equations of equilibrium.
Abstract: Distributed-parameter electromechanical transducers are examined theoretically with special regard to their dynamic electromechanical behaviour and equivalent circuits used to represent them. The circuits are developed starting from basic electromechanical transduction principles and the electrical and mechanical equations of equilibrium. Within the limits of the assumptions on boundary conditions, the theory presented is exact with no restrictions other than linearity. The link with lumped-parameter transducers, that were the subject of a previous publication will be indicated. Elementary electrostatic, electromagnetic, electrodynamic and piezoelectric transducers are used to illustrate the basic theory. Exemplary devices include a capacitive force (displacement) sensor, several types of a mechanical resonator, electromechanical filters, a piezoelectric thickness monitor and a piezoelectric acceleration sensor.
143 citations
TL;DR: A multilayering microelectrode technique has been developed to construct large-area travelling-wave dielectrophoresis (TWD) separators for separating cells, viruses and proteins as mentioned in this paper.
Abstract: Multilayering microelectrode techniques have been developed to construct large-area travelling-wave dielectrophoresis (TWD) separators. Novel electrode designs have enabled arrays with up to 25 000 electrodes to be constructed. The separation capacity of a 1000 electrode (20 mm) array has been demonstrated by separating components of whole blood. The development of sophisticated bio-particle separators capable of separating cells, viruses and proteins is discussed.
139 citations
TL;DR: In this paper, a computer code based on the shooting method was developed for calculating the induced tension, deflections and stresses in axially constrained doubly clamped microbeams.
Abstract: Stretching effects in axially constrained doubly clamped microbeams have been analysed for mechanical and electrostatic loads. A computer code based on the shooting method, a numerical integration procedure, has been developed for calculating the induced tension, deflections and stresses. Analytic solutions for concentrated force, distributed pressure and electrostatic loading were derived and verified by numerical simulation. Typical dimensions for microbeams considered are . Various cases have been evaluated, with and without induced tension and/or residual strain. Displacements and stresses are reduced when induced tension is included and are considerably smaller with intrinsic tension.
106 citations
TL;DR: In this paper, a new procedure for the production of smooth and defect-free surfaces in the anisotropic etching of silicon in alkaline solutions is described, and it is found that etching in an ultrasonic bath results in the facilitated detachment of hydrogen bubbles at the surface which is suggested to be one of the causes for surface roughening.
Abstract: A new procedure for the production of smooth and defect-free surfaces in the anisotropic etching of silicon in alkaline solutions is described It has been found that etching in an ultrasonic bath results in the facilitated detachment of hydrogen bubbles at the surface which is suggested to be one of the causes for surface roughening In the presence of mild ultrasound radiation a significant improvement in surface finish of the orientation has been observed The inclusion in the bath of oxygen and/or isopropanol results in root mean square roughness values smaller than 20 nm The effectiveness of bath additives has been related to changes of the contact angle between the liquid/gas/etching interface Quantitative determination of roughness and surface imaging have been obtained by atomic force microscopy; dissolution rates were studied by profilometry Etching under ultrasound conditions and the use of additives does not change the etch kinetics, indicating that additional convection only changes hydrogen bubble detachment
88 citations
TL;DR: In this paper, gear pumps using micro gear wheels with diameters of 596 and and a height of have been realized at IMM by means of a combination of LIGA technology and precision engineering.
Abstract: Gear pumps using micro gear wheels with diameters of 596 and and a height of have been realized at IMM by means of a combination of LIGA technology and precision engineering. Using oil as pumping medium the pumps achieve back pressures of more than 1200 hPa and flow rates of up to . The self-filling pumps tolerate air bubbles and particles contained in the working medium. The gear pumps displace 82 and 213 nl respectively per revolution, i.e. they offer the possibility of very precise dosing of viscous fluids, such as oil.
TL;DR: In this paper, the authors demonstrate the feasibility of using through-mask electrochemical etching for producing high-precision topographies on titanium using a methanol-based electrolyte.
Abstract: Well defined three-dimensional structures on titanium were fabricated by electrochemical micromachining. An optimum electrolyte composition and electrochemical parameters were determined for obtaining controlled cavity shapes and a smooth surface finish. Using a methanol based electrolyte, mass transport controlled dissolution conditions were identified and subsequently applied to the fabrication of arrays of hemispherical cavities in diameter. The results of the present study demonstrate the feasibility of using through-mask electrochemical etching for producing high-precision topographies on titanium.
TL;DR: In this article, the internal stress and stress gradient of thin polysilicon films were evaluated with surface micromachined test structures, and the structure that measured internal stress consisted of actuator beams rotating an indicator through an angle corresponding to the stress.
Abstract: The internal stress and stress gradient of thick () and thin () polysilicon films were evaluated with surface micromachined test structures. The structure that measured internal stress consisted of actuator beams rotating an indicator through an angle corresponding to the stress. The indicator deflection was measured in an SEM. Finite element analysis (FEA) was used both to optimize the design and to calibrate the structure. A folded beam design was used to minimize the total area the structure occupied so that it could be incorporated in the wafer layout of other surface micromachined details, and used for online process diagnostics. The indicator was provided with a Vernier scale to facilitate quick evaluation in an optimal microscope. The stress gradient was measured from the deflection of long () cantilever beams. The deflection was measured in an optical microscope and the output was calibrated with FEA calculations.
TL;DR: An electrostatically actuated polymer microvalve with a movable membrane electrode is presented, which is made by thermal injection molding of conductive polyamide with two insulating layers with a conductive layer in between.
Abstract: An electrostatically actuated polymer microvalve with a movable membrane electrode is presented. The microvalve cases are made by thermal injection molding of conductive polyamide. The movable membrane acting as an electrode consists of two insulating layers with a conductive layer in between. The three layers are patterned differently and transferred from a silicon wafer to the valve case in a batch process. The case of the microvalve and the three-layer membrane are joined by adhesive injected into cavities in the case. The three-layer membrane is moved electrostatically by a suitable voltage applied between the case and the membrane. The membrane of thickness is attracted to the upper or the lower valve chamber, thus opening or closing the inlet of the microvalve. The microvalve has an outer diameter of 5 mm and is 3 mm thick. The membrane electrode is moved when the voltage applied is approximately 60 - 150 V. Volume flows of up to 0.2 are attained at a differential pressure of 1100 hPa.
TL;DR: In this article, thermal isolation is achieved by locating the sensitive element on thin free-standing membranes fabricated by means of micromachining of silicon, and the results have been correlated with extensive FEM studies.
Abstract: Metal oxide gas sensors have to be heated during operation. Ideally they should have low power consumption and a uniform temperature distribution over the sensitive area. Thermal isolation is achieved by locating the sensitive element on thin free-standing membranes fabricated by means of micromachining of silicon. Uniformity of the temperature is helpful for discriminating different gases and, thus, increasing the selectivity. This can be achieved by careful design of the heater or by additional structures. Micromachined test structures have been fabricated, their mechanical strength and thermal behaviour have been determined and the results have been correlated with extensive FEM studies.
TL;DR: In this paper, a mechanical law with a simple elementary model of membrane deflection is used to demonstrate the static instability of such a system under electrostatic actuation and provide an analytical solution for the membrane position.
Abstract: Having developed a mechanical law with a simple elementary model of membrane deflection, we demonstrate the static instability of such a system under electrostatic actuation and provide an analytical solution for the membrane position. This allows us to highlight the sticking effect and the hysteresis phenomenon of the pump strike volume due to the nonlinearity of such excitation. We determine a parameter optimization procedure for the dimensions of the electrostatic actuated membrane in order to achieve maximum volume displacement.
TL;DR: In this article, a computer program was developed to investigate the significance of various physical effects to the dose distribution in the resist material, which in turn determined the lateral structure resolution and the quality of the resist structures.
Abstract: Deep x-ray lithography with synchrotron radiation is the key microfabrication process in the LIGA technology. Micro-components with a height of some up to several mm can be manufactured with sub- precision. The pattern transfer accuracy is governed by technological constraints like thermal deformation of the mask as well as by various physical effects, e.g. diffraction, emission of photo- and Auger electrons, fluorescence radiation, radiation scattering and divergence of the synchrotron radiation beam. A computer program has been developed to investigate the significance of these effects to the dose distribution in the resist material, which in turn determines the lateral structure resolution and the quality of the resist structures. In this paper the models used for the calculation and the calculation procedure are introduced and the weight of the different contributions with respect to transfer accuracy is investigated. It is shown that beam divergence and diffraction are much less important than the image blur caused by photoelectrons. Fluorescence radiation emitted from the mask membrane or the substrate contributes to the dose deposition in the resist if mask membrane or substrate consists of high-atomic-number material. Scattering of radiation is negligible for resist layers which are less than some mm thick. The calculations are compared with measurement results for different substrate materials, synchrotron radiation sources and resist heights. A good agreement was found between calculated dose distributions and measured resist side wall profiles. This allows a partial compensation of the above-mentioned accuracy limiting effects early in the mask design phase.
TL;DR: In this paper, the authors describe the simulation, design and fabrication of acceleration switches for automotive applications, and a simulation model is introduced which describes the dynamical behaviour of the sensor, such as the switching time, the overload protection, the self-test feature and the damping behavior.
Abstract: This paper describes the simulation, design and fabrication of acceleration switches for automotive applications. A simulation model is introduced which describes the dynamical behaviour of the sensor. The main focus of the development is on the specifications of the accelerometer, such as the switching time, the overload protection, the self-test feature and the damping behaviour. The simulated acceleration switches are fabricated with the use of a sacrificial layer technique and electroplated moulding of microforms. The 3D-UV Microform technology was preferred because it enables high aspect ratio patterning of commercially available thick photoresists. First devices of the microswitch sensors were characterized by means of optical measurement facilities for the determination of resonance frequencies and of the dynamical behaviour during test pulses. Measurements on a shaker were carried out to confirm the validity of the model.
TL;DR: In this article, the authors compared the stress measurement techniques using micromachined structures with the wafer curvature technique and simulated buckling bridges and rotating indicator structures using thin polysilicon films.
Abstract: Stress measurement techniques using micromachined structures are compared with the wafer curvature technique. Buckling bridges and rotating indicator structures are simulated, designed and fabricated using thin polysilicon films. Stress ranging from the high compressive to the high tensile state can be detected using appropriate indicator designs.
TL;DR: A simple and reliable technology for the fabrication of micromachined micropumps is presented in this article, where the assembling of different wafers to produce valves and cavities is usually the critical step regarding final yield.
Abstract: A simple and reliable technology for the fabrication of micromachined micropumps is presented The assembling of different wafers to produce valves and cavities is usually the critical step regarding final yield Our technology uses exclusively the well known anodic bonding technique for this purpose The prospective performance of the devices has been evaluated by finite element methods and system level simulations
TL;DR: In this article, a photoresist sacrificial layer was used to fabricate microactuators and micromotors, and the photoresists used in the new process are easy to coat, easy to dissolve and less process steps are involved.
Abstract: A new process using photoresists as sacrificial layers has been developed to fabricate micromechanical components and systems. Commonly used photoresists are spun on a substrate as a sacrificial layer and patterned by a mask aligner. Free-standing metal structures are built by patterning a second layer of thick photoresist and electroplating on top of the photoresist sacrificial layer. Electrostatic microactuators and micromotors have been fabricated using the new photoresist sacrificial layer technique. Compared with all the existing sacrificial layer techniques, the photoresists used in the new process are easy to coat, easy to dissolve and less process steps are involved. The process is compatible with most of the materials and processes used in existing microfabrication technology. The fabrication of micromechanical systems becomes much simpler and cheaper with the use of a photoresist as a sacrificial layer.
TL;DR: In this paper, a new compensation layout for the protection of convex corners during anisotropic etching resulting in almost perfectly square corners is presented, and the compensation mask design is tested in KOH etching and compared to other compensation designs presented earlier.
Abstract: A new compensation layout for the protection of convex corners during anisotropic etching resulting in almost perfectly square corners is presented. The compensation mask design is tested in KOH etching and compared to other compensation designs presented earlier. Advantageous new features are that etching to half of the designed depth of the new corner compensation is geometrically defined and not dependent on KOH concentration - a unique feature - and a high space efficiency, about 20% better than earlier designs for perfect square corners.
TL;DR: In this paper, a chemical - mechanical polishing treatment was used to reduce the surface roughness of the nitride before bonding and the measured surface energies of the room-temperature bond were comparable to values found for Si-Si hydrophilic bonding.
Abstract: Wafers with LPCVD silicon-rich nitride layers have been successfully direct bonded to silicon-rich nitride and boron-doped silicon surfaces. A chemical - mechanical polishing treatment was necessary to reduce the surface roughness of the nitride before bonding. The measured surface energies of the room-temperature bond were comparable to values found for Si - Si hydrophilic bonding. A mechanism similar to this bonding is suggested for silicon nitride bonding.
TL;DR: In this paper, a refinement of the anodization process commonly used for the formation of porous silicon is described, which allows the fabrication of arrays of very high aspect ratio sub-micron pores and free-standing pillars.
Abstract: We describe a refinement of the anodization process commonly used for the formation of porous silicon, which allows the fabrication of arrays of very high aspect ratio sub-micron pores and free-standing pillars. These structures are shown to possess a wide photonic band gap in the near infra red.
TL;DR: In this article, the fabrication and simulation of micromachined cantilever valves is described. Butler et al. report the fabrication of these valves can be subdivided into the generation of cantilevers and ducts via KOH etching and a final fusion bonding step to join them.
Abstract: This paper reports the fabrication and simulation of micromachined cantilever valves. For quasi-static fluid-structural simulations, the FEM package ANSYS and the CFD package Flow3D are coupled with a control programme to yield the flow rate for the cantilever valve. The results are compared with micromachined cantilever valves. The fabrication of these valves can be subdivided into the generation of cantilevers and ducts via KOH etching and a final fusion bonding step to join them. For the release of the cantilever, toluene is used to avoid stiction while drying the chips. Agreement between measured and simulated flow rates is shown to be good and gives confidence in the use of this simulator for valve development. Dynamic simulations are established with an impact model of the cantilever sitting on top of the duct. This allows the prediction of the dynamic behaviour of cantilever valves.
TL;DR: In this paper, a capacitive differential pressure sensor has been developed, which can be monolithically integrated on one chip with a suitable signal conditioning circuit, and a nominal sensitivity of 18% has been measured for a positive differential pressure of 1 bar.
Abstract: A capacitive differential pressure sensor has been developed. The process used for the fabrication of the sensor is IC-compatible, meaning that the device can potentially be monolithically integrated on one chip with a suitable signal conditioning circuit. A sensor for a differential pressure range of was fabricated and tested with a frequency modulated detection circuit, and good agreement was found with the theoretical model of the sensor. A nominal sensitivity of 18% has been measured for a positive differential pressure of 1 bar.
TL;DR: In this article, the simulation and characterization of a low-cost IR source is described, where the IR emission is obtained from heated thin film resistors which are either self-suspended or deposited on a membrane.
Abstract: The simulation and characterization of a low-cost IR source are described. The IR emission is obtained from heated thin film resistors which are either self-suspended or deposited on a membrane. The simulation, performed with a finite difference method, shows that a reasonably good modulation can be obtained at 50 Hz and higher. Such specifications meet the requirements of various IR gas sensors such as photoacoustic sensors.
TL;DR: The importance of early consideration in the design cycle of packaging, and the environment in which the microsystem will be placed, is stressed in this article, where the authors describe some of the issues associated with the packaging of microsystems and how packaging can influence their reliability and performance.
Abstract: This paper describes some of the issues associated with the packaging of microsystems and how packaging can influence their reliability and performance. The importance of early consideration in the design cycle of packaging, and the environment in which the microsystem will be placed, is stressed. It illustrates how the IC packaging industry has striven to overcome the problems of residual stress, stress minimization, hermeticity, and improved thermal performance in their packages and how this can be applied to microsystem packaging. Packaging problems specific to microsystems are identified.
TL;DR: In this paper, a cantilever with integrated tip and piezoelectric layer (zinc oxide, ZnO) for actuation and detection has been microfabricated using monocrystalline silicon as the bulk material.
Abstract: Cantilevers with integrated tip and piezoelectric layer (zinc oxide, ZnO) for actuation and detection have been microfabricated using monocrystalline silicon as the bulk material. Arrays of five levers and cantilevers with two independent ZnO layers have also been obtained. The levers have been mechanically and electrically characterized. Dynamic mode and contact mode atomic force microscopy (AFM) images were achieved using the integrated piezoelectric layer of these levers as a vertical deflection sensor.
TL;DR: In this article, the fluid mechanics and operating characteristics of micro bearing that support rotating surfaces in micromachines are analyzed and an infinite-series solution is obtained for the two-dimensional governing equations.
Abstract: The fluid mechanics and operating characteristics of bearings that support rotating surfaces in micromachines are different from their larger cousins. The present study analyzes microbearings represented as an eccentric cylinder rotating in a stationary housing. The flow Reynolds number is assumed small, the clearance between shaft and housing is not small relative to the overall bearing dimensions, and there is slip at the walls due to non-continuum effects. The two-dimensional governing equations are written in terms of the streamfunction in bipolar coordinates and an infinite-series solution is obtained. For high values of the eccentricity and low slip factors the flow may develop a recirculation region. The force and torque on the load-bearing inner cylinder increase with increasing eccentricity and decrease with increasing slip.