Showing papers in "Sensors and Actuators A-physical in 1999"

Micro-stereolithography of polymeric and ceramic microstructures

Abstract: Micro-stereolithography (μSL) is a novel micro-manufacturing process which builds the truly 3D microstructures by solidifying the liquid monomer in a layer by layer fashion. In this work, an advanced μSL apparatus is designed and developed which includes an Ar + laser, the beam delivery system, computer-controlled precision x–y–z stages and CAD design tool, and in situ process monitoring systems. The 1.2 μm resolution of μSL fabrication has been achieved with this apparatus. The microtubes with high aspect ratio of 16 and real 3D microchannels and microcones are fabricated on silicon substrate. For the first time, μSL of ceramic microgears has been successfully demonstrated.

Measurement of the effective transverse piezoelectric coefficient e31,f of AlN and Pb(Zrx,Ti1−x)O3 thin films

Abstract: The effective piezoelectric transverse coefficient e(31,f) was measured on various lead zirconate-titanate (PZT) and aluminum nitride thin films. The measurement set-up is based on the collection of the electric charges created by the forced deflection of a Si cantilever coated with a piezoelectric material. The maximum value was obtained from a tetragonal composition of PZT (45/55 Zr/Ti ratio) and was equal to 8.3 C/m(2). The ALN layer exhibited 97% of the theoretical value calculated from single crystal data, i.e., e(31,f)- = 1.02 C/m(2) (C) 1999 Elsevier Science S.A. All rights reserved.

Laminar fluid behavior in microchannels using micropolar fluid theory

Abstract: In this paper, we describe microchannel fluid behavior using a numerical model based on micropolar fluid theory and experimentally verify the model using micromachined channels. The micropolar fluid theory augments the laws of classical continuum mechanics by incorporating the effects of fluid molecules on the continuum. The behavior of fluids was studied using surface micromachined rectangular metallic pipette arrays. Each array consisted of 5 or 7 pipettes with widths varying from 50 to 600 μm and heights ranging from 20 to 30 μm. A downstream port for static pressure measurement was used to eliminate entrance effects. A controllable syringe pump was used to provide flow while a differential pressure transducer was used to record pressure drop. The experimental data obtained for water showed an increase in the Darcy friction factor when compared to traditional macroscale theory, especially at the lower Reynolds number flows. The numerical model of the micropolar fluid theory predicted experimental data better than the classical Navier–Stokes theory and the model compares favorably with the currently available experimental data.

Novel interconnection technologies for integrated microfluidic systems

Abstract: A new approach to realize silicon based integrated microfluidic systems is presented By using a combination of silicon fusion bonding (SFB) and deep reactive ion etching (DRIE), multi-level fluidic `circuit boards' are fabricated and used to integrate microfluidic components into hybrid systems A multi-level laminating mixer and a manifold with multiple pressure sensors are presented as application examples To interface the microfluidic system to the macroscopic world, three types of DRIE-fabricated, tight-fitting fluidic couplers for standard capillary tubes are described One type of coupler is designed for minimal dead space, while another type reduces the risk of blocking capillaries with adhesive A third design demonstrates for the first time a silicon/plastic coupler combining DRIE coupler technology with injection-molded press fittings

A plastic micropump constructed with conventional techniques and materials

Abstract: A plastic micropump which can be produced using conventional production techniques and materials is presented. By applying well-known techniques and materials, economic fabrication of micropumps for various applications is feasible even at low production volumes. The micropump is capable of pumping both liquid and gas at a considerable high pump rate and is self-priming, which means that it can start pumping gas in a dry state and automatically fills with liquid. Pump rates, at actuation frequencies between 2 and 500 Hz, were around 2 ml/min for water and up to 50 ml/min for air. A differential pressure of 1.25×104 Pa (125 cm water column) was reached. Basically, the micropump consists of two parts, a flat valve assembly with two passive membrane valves and an actuator placed on top. The valves were made by sandwiching a punched thin polymer film between two plastic valve parts containing the valve seats. The latter parts are made by reactive injection molding of an epoxy resin. Two types of actuators have been applied to drive the pump; an electromagnetic actuator consisting of a magnet placed in a coil and secondly a disk. The first actuator, when combined with a flexible polymer pump membrane, showed a very large pump rate for gas, up to 40 ml/min at the resonant frequency of the actuator system. A disadvantage of the electromagnetic actuator was the relatively large volume occupied by the coil giving the micropump final dimensions of 10×10×8 mm3. Application of the piezoelectric actuator reduced these dimensions down to 12×12×2 mm3 with comparable performance.

Touch mode capacitive pressure sensors

Abstract: Touch mode capacitive pressure sensors offer better performance in industrial applications than other devices. In touch mode operation, the diaphragm of the capacitive pressure sensor touches the substrate structure in operation range. The advantages of this mode of operation are near-linear output characteristics, large over-range pressure and robust structure that make it capable to withstand harsh industrial field environment. The principle, design, and characteristics of touch mode capacitive pressure sensors using various materials and technologies are discussed in this paper.

A micro cell lysis device

Abstract: A new micromachined cell lysis device is developed. It is designed for miniature bio-analysis systems where cell lysing is needed to obtain intracellular materials for further analysis such as DNA identification. It consists of multi-electrode pairs to apply electric fields to cells. We adopt the means of using electric field lysing because it can greatly simplify purification steps for preparation of biological samples compared to conventional chemical methods. Yeast, Chinese cabbage, radish cells and Escherichia coli are tested with the device. The lysis of yeast, Chinese cabbage and radish cells is observed by a microscope. The experimental observation suggests that E. coli are also lysed by the pulsed electric field. The range of electric field for the lysis is on the order of 1 kV/cm to 10 kV/cm. The Teflon coated on the electrodes can protect the electrodes during the pulsing period. In addition, for practical reasons, we reduce the voltage required for lysing to less than 10 V by making the electrode gap on the order of microns.

Recent advances in silicon etching for MEMS using the ASE™ process

Abstract: In the ongoing enhancement of MEMS applications, the STS Advanced Silicon Etch, ASE™, process satisfies the demanding requirements of the industry. Typically, highly anisotropic, high aspect ratios profiles with fine CD control are required. Selectivities to photoresist of 150:1 with Si etch rates of up to 7 μm/min are achievable. Applications range from shallow etched optical devices to through wafer membrane etches. This paper details some of the fundamental trends of the ASE™ process and goes on to discuss how the process has been enhanced to meet product specifications. Parameter ramping is a powerful technique used to achieve the often conflicting requirements of high etch rate with good profile/CD control. The results are presented in this paper.

Thermal flow sensor for liquids and gases based on combinations of two principles

Abstract: A new type of a flow sensor is presented which is based on a thermal principle. The combination of two detecting methods results both in a considerable increase in measuring range (0.1 to 150 mm/s) and in a shorter reaction time of less than 2 ms. Furthermore, the sensor is relatively insensitive to pollution. Devices were manufactured and successfully tested for liquids and gases.

3D microfabrication by combining microstereolithography and thick resist UV lithography

Abstract: A new approach for the realization of true 3D polymer structures is presented in this paper. It consists in adding, in a post-processing microstereolithography step, 3D polymer microstructures on top of a micropart patterned by means of planar processes such as thin films, bulk silicon etching or high aspect ratio structuration (LIGA, RIE, thick resist). In this way, some shape limitations of the planar technologies can be overcome for new functional applications. Moreover, the direct processing of microstereolithography on predefined structures eliminates manipulations which are associated with micro-assembly of separated parts. To demonstrate this combination of microstructuration processes, an example showing a conical axle added by microstereolithography on a SU-8 piece of gearing is presented.

Fabrication of glassy carbon microstructures by soft lithography

Abstract: This paper describes fabrication techniques for the fabrication of glassy carbon microstructures. Molding of a resin of poly furfuryl . alcohol using elastomeric molds yields polymeric microstructures, which are converted to free-standing glassy carbon microstructures by . 2 . heating T ; 500-11008C under argon. This approach allows the preparation of macroscopic structures several mm with microscopic . features ; 2 mm . Deformation of the molds during molding of the resin allows preparation of curved microstructures. The paper also presents a method of incorporating these structures on a chip by masking and electroplating. q 1999 Elsevier Science S.A. All rights reserved.

Anisotropic etching rates of single-crystal silicon for TMAH water solution as a function of crystallographic orientation

Abstract: We evaluated orientation dependence in the etching rate of single-crystal silicon for tetramethyl-ammonium-hydroxide (TMAH) water solutions. Etching rates for a number of crystallographic orientations were measured for a wide range of etching conditions, including TMAH concentrations of 10–25% and temperatures of 70–90°C. We found significantly different characteristics from those for KOH water solutions. Firstly, different types of orientation dependence in etching rate were found around (111) between TMAH and KOH. This means the bonding energy of the silicon crystal lattice is not a single factor that dominates orientation dependence, and there exist different etching mechanisms for the two etchants. Secondly, effects of the circulation of etchants on the etching rates were not negligible in TMAH in contrast to KOH system.

Self-excited piezoelectric PZT microcantilevers for dynamic SFM—with inherent sensing and actuating capabilities

Abstract: Currently three crucial components are necessary for the dynamic SFM, they are the microcantilever, oscillator, and cantilever deflection sensor. We demonstrate a piezoelectric microcantilever made of PZT thin films for SFM. This PZT microcantilever can perform the same functions which have to be done by the three crucial components. It is able to excite itself when an ac voltage is applied to it, and actuate itself in z -directional displacement by a superimposed dc voltage, while force sensing is executed concurrently. Since the motional admittance can be derived from the piezoelectric current output when the PZT microcantilever is vibrated at resonance frequency, the motional admittance will vary as the change of vibrational amplitude. Thus the topography of the sample can be recorded as the trace of the difference between output signals of motional admittance. The piezoelectric coefficient d 31 of the PZT layer is about −58 pC/N. The dimensions of piezoelectric microcantilevers used are 125×50×3.8 μm. The actuating ability is estimated as 75 nm/V. The vertical resolution of the self-excited PZT microcantilever can be derived as 1.2 A at the bandwidth of 125 Hz. Very clear images of a 1.0 μm pitch Au coated SiO 2 grating and an evaporated gold film on a smooth glass plate are obtained by an SFM using this self-excited force sensing PZT microcantilever. The invention of this smart PZT microcantilever endows the possibility of constructing a stand-alone micro SFM system and a multiprobe SFM system.

External control of dissipation in a nanometer-scale radiofrequency mechanical resonator

Abstract: We demonstrate a technique by which the quality factor of a magnetically-actuated mechanical resonator is controlled by an external electrical circuit. Modulation of this parameter is achieved by local variation of the electrical impedance presented to the resonator at its resonance frequency. We describe a theory that explains this result as arising from eddy currents in the external electrical circuit, which are driven by electromotive forces generated through motion of the resonator in the applied magnetic field. The theory is in good agreement with the induced variation in quality factor that we observe.

Photopatterning of thermally sensitive hydrogels useful for microactuators

Abstract: Hydrogels based on PNIPAAm [poly-(N-isopropylacrylamide)] are an attractive working material for microactuators because of their swelling with thermally induced phase transitions leading to a very high volume expansion. By the employment of co-polymerization with a chromophore, a specially designed polymer has been developed that can be photocrosslinked to a gel and by this photopatterned. The focal point of this work is the preparation and characterization of mircopatterns using this co-polymer. The efficiency of the photochemical reaction is quite good and patterning results down to 20 μm spaces have been achieved. The swelling of dot-like patterned hydrogel films on Si/SiO2 substrates in water occurs with similar temperature dependency and a swelling ratio of 3 to 3.5 in the same order of magnitude compared to bulk PNIPAAm-based gels, but the transition time of 2 to 8 s measured at the gelous dots is much shorter than that of macroscopic objects, making the material interesting for microactuator performance. The transition temperature decreases from 32 to 34°C at pure PNIPAAm to 18 to 20°C at the photopatterned gels of the copolymer.

A new technology for fluidic microsystems based on PCB technology

Abstract: A new technology for fluidic microsystems has been developed at Rostock University. This new technology is based on the manufacturing principles of printed circuit boards (PCB). The same manufacturing steps closely connect fluidic and electric components. Unlike the requirements for other technologies, e.g., silicon technology, only moderately complex equipment is necessary. The microsystems fabricated by this new technology can handle fluids (transport, mix, flow control, heating) and can measure properties such as temperature, viscosity, density, colour and pH-values. Various applications are possible in chemistry, biology, medicine and many other technical fields. Compatibility with electronic technologies is the main objective of this development. The technology allows low production costs even for small quantities, so it is suitable for small companies and for special applications.

Solder self-assembly for three-dimensional microelectromechanical systems

Abstract: A solder technology has been developed that utilizes molten solder surface tension forces to self-assemble MEMS 3-D structures. Using solder, a single batch reflow process can be used to accomplish hundreds or thousands of precision assemblies, and the cost per assembly can be reduced considerably. A model, based on surface energy minimization of molten liquids, has been developed for predicting assembly motion. The modeling, combined with experimental studies, have demonstrated ±2° assembly angle control is possible when the MEMS structures are assembled by solder alone. To improve the self-assembly angle precision, a self-locking mechanism can be added, which reduces the assembly angle variation down to ±0.3°.

Plasma enhanced chemical vapor deposition silicon oxynitride optimized for application in integrated optics

Abstract: Silicon Oxynitride (SiON) layers are grown from SiH4/N2, NH3 and N2O by Plasma Enhanced Chemical Vapor Deposition (PECVD) The process is optimized with respect to deposition of layers with excellent uniformity in the layer thickness (δd<1%), high homogeneity of the refractive index (Δn=2–7×10−4) and good reproducibility of the layer parameters The optical losses of slab-type waveguides is determined to be as low as 02 dB/cm at 6328 nm wavelength Due to absorption of N–H and Si–H vibrational overtones, the optical losses in the third telecommunication window, around 1550 nm, is increased to about 2 dB/cm for low index layers By an anneal step, however, the hydrogen content of the films can be reduced as is confirmed by IR-spectroscopy and the optical losses decrease to below 02 dB/cm Based on the optimized PECVD SiON technology, a layer structure fulfilling the strong requirements of telecommunication devices, is designed for operation at 1550 nm wavelength This structure, consisting of a SiON core layer (n=14857) surrounded by thick oxide cladding layers (n=14637), has the potential for realization of channel waveguides allowing for low-loss bends with a small bending radius and high fiber-to-chip coupling efficiency

A highly selective ammonia gas sensor using surface-ruthenated zinc oxide

Abstract: Preparation and characterisation of a highly selective surface-ruthenated zinc oxide sensor for ammonia in trace levels is demonstrated. The introduction of some RuO linkages on the surface of ZnO leads to a dramatic enhancement in the sensitivity (S) to 1000 ppm level of ammonia at 300°C (S=440) as compared to the similar response obtained for pure ZnO (S=1.5). A systematic study using various characterisation techniques such as EDAX, SEM, CV and XPS indicates the key role played by the amount and distribution of Ru species on the surface.

Roughening of single-crystal silicon surface etched by KOH water solution

Abstract: We investigated roughening of single-crystal silicon surface during chemical anisotropic etching using KOH water solution. The change in roughness strongly depends on the crystallographic orientation of the silicon. We plotted a map showing roughness distribution as a function of orientation. A smooth surface appears in a region including the (100), (211), and (311) planes. A very rough surface appears in a region including the (320) and (210) planes. It was observed that the roughened surface shows facet textures composed of certain crystallographic planes. We further studied the effects of KOH concentration and etching temperature. The roughness of (110) plane decreases with an increase in KOH concentration and is independent of the etching temperature.

A micromachined pressure/flow-sensor

Abstract: The micromechanical equivalent of a differential pressure flow-sensor, well known in macro mechanics, is discussed. Two separate pressure sensors are used for the device, enabling to measure both, pressure as well as volume flow-rate. An integrated sensor with capacitive read-out as well as a hybrid, piezo-resistive variant is made. The fabrication processes are described, using silicon and glass processing techniques. Based on the sensor layout, equations are derived to describe the sensor behavior both statically as well as dynamically. With the derived equations, the working range of the sensor and the thermal and time stability is estimated. The computed results of the stationary behavior are verified with the measured data. A good similarity in linearity of the pressure/flow relation is found. The computed hydraulic resistance, however, differs from the measured value for water with 21%. This difference can be explained by the high sensitivity of the resistance to the resistor channel cross-section parameter in combination with the difference between the rounded etched shape and the rectangular approximation. From fluid dynamics simulations, a working range bandwidth of about 1 kHz is expected. Thermal influences on the sensor signal due to viscosity changes are in the order of 2% flow signal variation per Kelvin. From these results, it can be concluded that the sensor can be used as a low cost, low power consuming flow and pressure-sensing device, for clean fluids without particles and without the tendency to coat the channel walls. If a high accuracy is wanted, an accurate temperature sensing or controlling system is needed.

Novel C-MOS compatible monolithic silicon gas flow sensor with porous silicon thermal isolation

Abstract: A novel C-MOS compatible silicon gas flow sensor using porous silicon for thermal isolation has been designed and fabricated. The small sensor size combined with the very good thermal isolation by porous silicon assure fast response, with a time constant of the order of 1.5 ms. The principle of operation is based on heat transfer from a polysilicon resistor to the fluid and the detection of the flow-induced temperature difference by Al/polysilicon thermopiles, integrated at both sides of the heater. The sensor has been evaluated in nitrogen flows from 0 to 0.4 m/s. The sensitivity per heating power is 6.0 mV/(m/s)W and the responsivity is 0.65 V/W. The noise equivalent power and the minimum detectable velocity are 1.5×10 −8 W/Hz 1/2 and 4.1×10 −3 m/s, respectively. The chip size is 1.1 mm×1.5 mm.

A micro-fluxgate magnetic sensor using micromachined planar solenoid coils

Abstract: This paper presents a new micro-fluxgate magnetic sensor based on micromachined 3-dimensional toroidal type planar coils used as excitation and sensing elements. A rectangular-ring shaped magnetic core and the `second harmonic' operation principle are adopted in this fluxgate sensor. With the use of a newly developed UV-LIGA thick photoresist process and electroplating techniques, excitation and sensing coils as well as permalloy magnetic cores were fabricated to realize a planar three-dimensional magnetic fluxgate sensor on silicon wafers. Excellent linear response over the range of −500 μT to +500 μT, with a system sensitivity of 8360 V T−1 and a resolution of 60 nT was achieved from the sensor realized in this work. The total response range of the sensor is −1.3 to +1.3 mT. The electroplated thick, Cu coil windings result in low coil resistance and a low power consumption of ∼100 mW for an operational frequency range of 1–100 kHz. The small size, the high sensitivity and resolution, and lower power consumption, make this integratable magnetic fluxgate sensor suitable for various applications such as: portable navigation systems, space research, and proximity sensors and detectors.

The utilization of low temperature co-fired ceramics (LTCC-ML) technology for meso-scale EMS, a simple thermistor based flow sensor

Abstract: For certain applications the small size characteristics of MEMS structures can be traded off for low cost production and high manufacturing yields. This is the realm of meso-scale (intermediate scale) electromechanical systems. Low temperature co-fired ceramic tape materials offers the potential of emulating a great deal of silicon MEMS technology at the meso scale level. In this article we show the design, construction, characterization and modeling of a thermistor based flow sensor totally constructed using LTCC tapes and the hybrid microelectronics technology.

5×5 2D AFM cantilever arrays a first step towards a Terabit storage device

Abstract: In this paper we report on the microfabrication of a 5×5 2D cantilever array and its successful application to parallel imaging. The 5×5 array with integrated force sensing and tip heating has been fabricated using a recently developed, all dry, silicon backside etching process. The levers on the array have integrated piezoresistive sensing, and are placed on a constriction in the lever to improve sensitivity. The array is scanned in x and y directions using voice coil actuators. Three additional voice coil z actuators are used in a triangular arrangement to approach the sample with the array chip. The system is thus leveled in the same way as an air table. We report details of the array fabrication, the x – y scanning and approach system as well as images taken with the system. The results are encouraging for the development of large-scale VLSI-Nano EMS, allowing the fabrication and operation of large AFM cantilever arrays to achieve high-data-rate Terabit storage systems.

Chemical tapering of polymer optical fibre

Abstract: We introduce a novel method of chemically removing the cladding of PMMA based polymer optical fibre (POF) using organic solvents which can also be used to create etched tapers of any profile within lengths of POF or at fibre ends. The process is simple, inexpensive, low in chemical hazard and operator skill and has application to both improve the performance of numerous POF devices and allow conversion of silica devices to polymer. We give details of the etching processes involved and optical properties of the devices produced. We believe that this is the first application of this chemical process to the tapering of POF cores and suggest possible future applications of the technique.

A thermoelectric converter for energy supply

Abstract: A thermoelectric power generator in silicon technology is used for the energy supply of low power systems. An application is described generating an electrical power of 1.5 μW with a temperature difference of 10°C. With the generated electrical power it is possible to operate a small preamplifier and a sensor control system. For complexer applications a generator with a power in the region of 20 μW would be desirable.

Micromachined membrane particle filters

Abstract: Particle membrane filters (8×8 mm2) with circular, hexagonal and rectangular through holes are designed, fabricated and tested. By varying hole dimensions from 6 to 12 μm, opening factors from 4 to 45% are achieved. In order to improve the filter robustness, a composite silicon nitride/Parylene membrane technology is developed, and the burst pressure of the filters is increased more than 4 times. More importantly, fluid dynamic performance of the filters is also studied by both experiments and numerical simulations. It is found that the gaseous flow through the filters depends strongly on opening factors, and the measured pressure drops are much lower than that from numerical calculation using the Navier–Stokes equation. Interestingly, surface velocity slip can only account for a minor part of the discrepancy. This suggests that a very interesting topic for micro fluid mechanics research is identified.

Capacitive detection scheme for space accelerometers applications

Abstract: This paper presents the design and performance of an ultra-sensitive position sensor dedicated to future space accelerometers. The electromechanical transducer is based on a capacitive scheme and aims at detecting the motion of a proof-mass in an electrostatic accelerometer. A new design called “area variation capacitance” is investigated to minimize back-action forces exerted on the proof mass. The resolution of that position sensor is a few tenths of picometer in the 0–1 Hz bandwidth. The position is digitized with a sigma–delta converter to feed the control laws of the accelerometer.

Thermally actuated optical microscanner with large angle and low consumption

Abstract: A monolithic silicon integrated optical micro-scanner is presented. The device consists of a mirror located on the tip of a thermal bimorph actuator beam. The fabrication process is very simple and compatible with IC fabrication techniques. The device is excited electrothermally at its resonance frequency, enabling large angular deflections at low power consumption. The technological process consists of basic frontside silicon micromachining steps requiring only three mask levels. The moving part is defined by selective silicon bulk etching. The bimorph beam is made of silicon dioxide and a thin film conductor. The residual stress in the two layers is used to achieve a 45 degrees out-of-plane rest position of the mirror. This allows optical components (e.g., laser diode, collimating lens) to be placed directly on the silicon substrate. Mirrors of 500 x 300 to 800 x 800 mu m(2) with resonant frequencies varying from 600 to 100 Hz were realized. Mechanical scan angles of above 90 degrees were achieved. The devices are very robust and have run through fatigue tests of billions of cycles at 300 Hz and 90 degrees deflection. The power consumption of the device is typically 1 mW for 30 degrees mirror deflection. (C) 1999 Elsevier Science S.A. All rights reserved.