Showing papers in "Sensors and Actuators A-physical in 1992"
TL;DR: In this article, the tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) was used for silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C.
Abstract: Detailed characteristics of tetramethyl ammonium hydroxide (TMAH, (CH3)4NOH) as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C have been studied. The etch rates of (100) and (110) crystal planes decrease with increasing concentration. The etched (100) planes are covered by pyramidal hillocks below 15 wt.%, but very smooth surfaces are obtained above 22 wt.%. Etch rates of 1.0 μ/min for the (100) plane and 1.4 μ/min for the (110) plane at 90 °C are obtained using a 22 wt.% solution. The etch-rate ratio of (111)/(100) varies from 0.02 to 0.08. The etch rate of thermally oxidized SiO2 is almost four orders of magnitude lower than that for (100) and (110) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Etch-stop techniques using a heavily boron-doped layer or p—n junction prove to be applicable to TMAH solutions.
448 citations
TL;DR: Fluxgate sensors have been used for measuring d.c. magnetic fields up to 1 mT with a maximum resolution of 10 pT as mentioned in this paper, where the flux is gated by the excitation field, and both crystalline and amorphous ferromagnetic materials can be used for the core.
Abstract: Since the 1930s, fluxgate sensors have been used for measuring d.c. magnetic fields up to 1 mT with a maximum resolution of 10 pT. In the sensor core the flux is gated by the excitation field. The preferable sensor geometry is a ring-core; both crystalline and amorphous ferromagnetic materials can be used for the core. Although a lot of fluxgate magnetometer types have appeared, the classical type with detection of the second harmonics by a phase-sensitive detector is the most popular. Fluxgate sensors are reliable and rugged and their applications range from space research to submarine detection.
338 citations
TL;DR: A review of micro resonant force gauges is presented in this article, where a theoretical description is given of gauges operating in a flexural mode of vibration, including a discussion of non-linear effects.
Abstract: A review of micro resonant force gauges is presented. A theoretical description is given of gauges operating in a flexural mode of vibration, including a discussion of non-linear effects. Gauge factor and quality factor are defined and their relevance is discussed. Performance issues such as sensitivity, stability and resolution are addressed. Design aspects, including the means for excitation and detection of the vibration, and examples of silicon microfabrication technologies are described.
272 citations
TL;DR: In this paper, the authors describe the development of a new type of tactile sensor which is designed to operate with a piezoelectric element employed as the sensor, which is able to detect hardness and/or softness of an object.
Abstract: This paper describes the development of a new type of tactile sensor which is designed to operate with a piezoelectric element employed as the sensor. Conventional tactile sensors, which consist of a strain gauge, conductive elastomer and piezoelectric polymer film, are confined solely to data acquisition relating to pressure or force. However, the new sensor proposed here is able to detect, very much like the human hand, the hardness and/or softness of an object. Several experiments have been carried out to investigate its possible applications in robotics and medicine. It is demonstrated that the visualization of tactile sensory performance using the new sensor is most useful in a robotics application; the sensor is also able to detect the hardness of an extraneous substance and that of skin.
249 citations
TL;DR: In this paper, the one-dimensional (1D) differential equation of motion of a doubly clamped single-span beam with an axial load was solved analytically for lateral natural frequencies and mode shapes.
Abstract: Polysilicon resonant microbeams can be used as strain-sensitive elements to replace conventional silicon piezoresistors in precision sensor applications, such as pressure sensors and accelerometers. These elements are combined with conventional silicon diaphragms or flexures with a proof mass to convert pressure or acceleration directly into a frequency output. Vacuum-enclosed resonant microbeam elements 200 or 400 μm long, 45 μm wide and 1.8 μm thick have been fabricated using LPCVD mechanical-grade polysilicon at the University of Wisconsin. Q-values determined using gain/phase analysis are typically over 25 000. Lower Q-values are primarily the result of residual gas in the cavity. Closed-loop operation from −60 to 180°C using piezoresistive sensor and electrostatic drive has been achieved with automatic gain control (AGC) to prevent overdrive. The characteristic resonance frequencies of the beams have been measured, with 550 kHz, 1.2, 2.2 and 5.2 MHz being typical of the frequencies of the one-dimensional bending modes for the 200 μm length. These measurements of the multiple resonance frequencies of a single beam provide a means of testing mathematical models of the dynamic behavior as well as determining the residual beam stress. The one-dimensional (1D) differential equation of motion of a doubly clamped single-span beam with an axial load can be solved analytically for lateral natural frequencies and mode shapes. These 1D solutions have been verified by 3D finite-element methods. In addition, the finite-element models are used to identify both lateral and torsional modes. The closed-form solutions agree closely with the numerical results and the experimental data.
212 citations
TL;DR: In this article, the design and application of silicon thermal flow sensors is discussed and it is shown how the transduction path in the complete measurement system, going from flow variable to electrical signal, results in three fundamental problems, which can be associated with, respectively, the mechanical, thermal and electrical signal domains.
Abstract: This paper discusses the design and application of silicon thermal flow sensors. It is shown how the transduction path in the complete measurement system, going from flow variable to electrical signal, results in three fundamental problems, which can be associated with, respectively, the mechanical, thermal and electrical signal domains. These aspects are further discussed in relation to the silicon flow-sensor research performed at the Electronic Instrumentation Laboratory.
165 citations
TL;DR: In this article, the Young's modulus of 0.54 μm low-stress LPCVD SiXN y films was determined using a single-layer cantilever.
Abstract: The resonance method has been used to determine the Young's modulus of 0.54 μm low-stress LPCVD Si x N y films. The films are prepared as thin single-layer cantilevers using standard silicon micromachining techniques. By using different excitation methods, including photothermal, acoustic and mechanical, the thin-beam resonating structures can be forced to vibrate. The influences of air damping and cantilever deflection, produced during preparation, on the cantilever resonance behavior are discussed.
158 citations
TL;DR: In this paper, a pressure sensor utilizing polysilicon piezoresistors with a measurement range of 1 bar and a sensitivity of roughly 11 mV/V FS, a laser-trimmed poly-silicon temperature sensor with an accuracy of −3.4 × 10 −3 K −1 and non-linearity of less than 0.5% and an on-chip calibration and temperature compensation are described.
Abstract: Important characteristics of boron-doped LPCVD polysilicon layers with regard to sensor applications are presented. Properties such as the resistivity, temperature coefficient of the resistance, gauge factor and long-term stability are described. A pressure sensor utilizing polysilicon piezoresistors with a measurement range of 1 bar and a sensitivity of roughly 11 mV/V FS, a laser-trimmed polysilicon temperature sensor with a sensitivity of −3.4 × 10 −3 K −1 and non-linearity of less than 0.5% and a pressure sensor with polysilicon-based on-chip calibration and temperature compensation are described.
126 citations
TL;DR: In this paper, the authors describe the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm.
Abstract: The paper describes the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm. The piezoelectric properties of these layers have been exploited to excite (with low voltage signals) and detect oscillations of the diaphragm. The layer configurations and associated vibrational modes of the diaphragm have been designed and a phase-locked loop (PLL) technique implemented in electronic circuits able to keep the resonant condition, despite the change of resonance frequency due to variation of the applied differential pressure. It is shown that for an adequate choice of operating frequency (i.e. of the vibrational mode) a good sensitivity and thermal stability of the sensor can be obtained; in this device, operating at frequency around 57.8 kHz, corresponding to the third-mode frequency ⨍ 0.3 , a shift Δ⨍ 0.3 = 650 Hz is found by changing the pressure from 0 to 900 mmHg. We found also that ⨍ 0.3 changes less than 6 × 10 −3 by changing the temperature from 23 to 100 °C. Moreover the sensor allows long-term measurements of static pressures without significant hysteresis effects.
107 citations
TL;DR: In this paper, three methods for their deposition have been investigated: thin metallic films, platinum black deposited by a galvanic process, and highly porous metals deposited by evaporation in nitrogen.
Abstract: Infrared absorbing layers are used to transform radiation into heat. They must combine high absorption with low film thickness. Three methods for their deposition have been investigated: thin metallic films; platinum black deposited by a galvanic process; highly porous metals deposited by evaporation in nitrogen.
101 citations
TL;DR: In this article, a single-element approach for the electrostatic excitation and capacitive detection of the vibrational motion of the resonators is described, and the behavior of the air-gap capacitor is modeled as a lumped spring-mass system and its limitations are discussed.
Abstract: This paper deals with the theory of an air-gap capacitor used as a micromechanical resonator. Both static and dynamic aspects are discussed. A single-element approach for the electrostatic excitation and capacitive detection of the vibrational motion of the resonators is described. The non-linear character of the electrostatic force is accounted for in the static analysis. The behaviour of the air-gap capacitor is modelled as a lumped spring-mass system and its limitations are discussed. Also an equivalent electrical one-port network is derived, which can be used in a circuit simulation to account for the mechanical behaviour of the resonator. The results obtained from the spring-mass system are compared with the results obtained from a more elaborate numerical analysis of the air-gap capacitor. The lumped spring-mass system is adequate for modelling the air-gap capacitor.
TL;DR: In this paper, it was shown that magnetically generated forces can be made much larger than electrostatic forces even for 1 μm air gaps, and that efficiency arguments are moot unless microfabricated actuators shrink further in size (in which case heat dissipation is a problem).
Abstract: There has been a growing interest in microactuation, which we define as the ability to achieve motions with micron-level precision, and in microfabricated actuators, which we define as actuators which are themselves micron scale in size. Recent articles on microfabricated actuators have suggested that electrostatic approaches are more favorable than magnetic approaches. This article revisits these issues from the perspective of microactuation with application to microfabricated actuators. We show that magnetically generated forces can be made much larger than electrostatic forces even for 1 μm air gaps, that efficiency arguments are moot unless microfabricated actuators shrink further in size (in which case heat dissipation is a problem), and that the benefits of integration of electronics with a microactuator are questionable. We also show, by direct comparison of a magnetic and an electrostatic microfabricated actuator, that magnetic approaches which are wholly compatible with microelectronics fabrication can produce forces comparable to those from electrostatic approaches. From these arguments we conclude that the case for magnetic microactuation and magnetically driven microfabricated actuators is compelling, and that the advantages of microfabrication of actuators are not clear.
TL;DR: In this paper, a silicon subminiature microphone based on the piezoresistive effect in polysilicon using only one chip is proposed, which is fabricated by a technique that is compatible with a slightly modified CMOS process also using a standard micromechanical fabrication technology.
Abstract: A silicon subminiature microphone, based on the piezoresistive effect in polysilicon using only one chip, is proposed. The acoustic sensor is fabricated by a technique that is compatible with a slightly modified CMOS process also using a standard micromechanical fabrication technology. The main production steps will be described, including the design and the fabrication of the sensor. Experimental results of the piezoresistive coupling factors and the temperature dependence of the polysilicon resistors are given. Measured results of the airborne sound sensitivity are about −92 dB/Pa. The frequency response is nearly flat with deviations of about ± 3 dB from 100 Hz to 5 kHz and with a resonance at 10 kHz.
TL;DR: In this article, several different cantilever designs have been fabricated: a simple beam with various cross sections as well as a folded meander shape with square cross section, and high-aspect-ratio silicon tips with variable geometries.
Abstract: Monocrystalline silicon cantilevers with integrated silicon tips for scanning force microscopy are fabricated by means of micromachining techniques. Theoretical considerations including finite element modelling have been carried out in order to find a suitable shape and dimensions according to the mechanical requirements. Several different cantilever designs have been fabricated: a simple beam with various cross sections as well as a folded meander shape with square cross section. Special attention has been paid to the application of these silicon microprobes to measure friction. Moreover, high-aspect-ratio silicon tips with variable geometries are presented and their integration onto cantilevers is demonstrated. Finally, the fabrication of an array of such microprobes is described, which enables multiple parallel or serial surface profiling to be achieved. These integrated micromachined cantilevers have been successfully applied in standard atomic force microscope measurement systems.
TL;DR: In this paper, different prototype organic coatings were used for three different transducers with the aim of optimizing the selective detection of organic molecules, and different thermodynamically and kinetically controlled sensor parameters were obtained from capacitance, quartz microbalance and calorimetric transducers.
Abstract: Different ‘prototype’ organic coatings were used for three different transducers with the aim of optimizing the selective detection of organic molecules. The different thermodynamically and kinetically controlled sensor parameters were obtained from capacitance, quartz microbalance and calorimetric transducers. The results are discussed in the framework of different interaction mechanisms which occur in the detection of one organic gas component with its specific molecular weight, dielectric constant or heat of interaction.
TL;DR: The fabrication process of a silicon condenser microphone and experimental results of the acoustic measurements are described in this article, where the back-electrode area is either structured with grooves by a plasma etching technique or with holes by anisotropic etching.
Abstract: The fabrication process of a silicon condenser microphone and experimental results of the acoustic measurements are described. The microphone consists of two chips. One chip carries the 150 nm thick silicon nitride membrane, which has an area of 0.8 mm × 0.8 mm. The second chip contains the back electrode, the spacer and the contact pads of the microphone. In order to reduce the streaming resistances in the air gap, the back-electrode area is either structured with grooves by a plasma etching technique or with holes by an anisotropic etching technique. A frequency-independent sensitivity of 10 mV/Pa (open circuit, 1.8 mV/Pa measured) up to 30 kHz is obtained as a result of this structuring of the back-electrode area. Since the air-gap height is only 2 μm, the capacitance of the transducers ranges from 1 to 1.3 pF. The total size of the silicon microphone is 1.6 mm × 2 mm × 0.56 mm.
TL;DR: In this paper, two wafers are machined in such a way that an optical path of about 4 mm in length is obtained in which dispersed light from a 32-slit diffraction grating is projected onto an array of photodiodes.
Abstract: Silicon bulk micromachining techniques have been employed to fabricate an integrated grating and detector array in silicon for operation in the visible and near-infrared spectral range. Two wafers are machined in such a way that an optical path of about 4 mm in length is obtained in which dispersed light from a 32-slit diffraction grating is projected onto an array of photodiodes. The wafers are subjected to an electrochemically controlled etch. The interior of one of the wafers is subsequently coated with a reflective film. The grating and the array of photodetectors are integrated in the second wafer, which remains uncoated. The wafers can be bonded using the direct silicon-to-silicon fusion bonding technique. The functional division into a reflective wafer and a grating/readout wafer greatly simplifies the integration of the complete device in a smart silicon sensor.
TL;DR: In this paper, the authors used wet anisotropic etching of silicon with KOH and the electrochemical etch-stop at p-n junctions to realize smart mechanical sensors and actuators using a standard CMOS process.
Abstract: Piezoresistive accelerometers with a monolithically integrated operational amplifier were produced, the fabrication process based on a commercial 3 μm CMOS process. The mechanical structures were realized using wet anisotropic etching of silicon with KOH and the electrochemical etch-stop at p—n junctions. Measurements show that the integration of these necessary micromachining process steps into the IC process do not influence the parameters of the electronic devices. Also, the parameters of the mechanical structures are comparable to discrete devices. The realization of application-specific smart mechanical sensors and actuators using a standard CMOS process is now possible.
TL;DR: In this paper, a new capacitive tactile sensor for shear and normal force measurements is described. But the sensor is not suitable for the measurement of the shear or normal forces, and its performance is limited to a range of 0.05 N over the range of 10 N.
Abstract: This paper describes a new capacitive tactile sensor for shear and normal force measurements. The spatial sampling principle has been applied to measure the capacitance values efficiently and to transfer the spatial capacitance distribution into the time domain. The shear and normal forces are determined by measuring variations in the phase and amplitude of the output signal, respectively. A first experimental model of the sensor shows a resolution of 0.05 N over the range of 10 N for both shear and normal force measurements.
TL;DR: In this article, the drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane, which represents the first suspended-gate sensor with deflection control.
Abstract: Silicon subminiature microphones can be manufactured with the methods of micromachining technology. Several condenser-type microphones have been designed and fabricated at our institute. Capacitive microphones are described, which have a structured back electrode and a membrane of silicon nitride. A smooth frequency response up to 30 kHz with a maximum open-circuit sensitivity of 10 mV/Pa is obtained. A special design of a capacitive sensor has been realized with the FET microphone. The drain current of a field-effect transistor with a suspended gate is modulated by the vibrations of the membrane. This design represents the first suspended-gate sensor, the drain current of which is deflection controlled. Design, construction and experimental results of sensitivity and frequency response are given.
TL;DR: In this article, the authors present the results of investigations which have led to the batch fabrication of a new condenser microphone and subsequent measurement of its characteristics, which is achieved with a very simple IC-compatible process comprising only five photolithography steps.
Abstract: This paper presents the results of investigations which have led to the batch fabrication of a new condenser microphone and the subsequent measurement of its characteristics. With an overall size of 3 × 4 × 0.8 mm 3 including an hybrid JFET, the microphone has an integrated back-chamber and is achieved with a very simple IC-compatible process comprising only five photolithography steps. The diaphragm has a thickness of 1 μm. It is fabricated with the classical EDP boron etch-stop technique. Frequency responses of the microphone with a bias voltage of 20 V show sensitivities of 3.5 and 0.4 mV/Pa, depending on the fabrication parameters; the corresponding bandwidths are 2.5 and 20 kHz, respectively. Two methods of measurement have been set up in order to determine the built-in tension of heavily boron-doped silicon and have led to the same value of 70 MPa.
TL;DR: In this article, general ideas for the systematic design of smart sensors and processors are presented, and their consequent and systematic application has been shown to result in novel, simple and accurate processors.
Abstract: In this paper, general ideas for the systematic design of smart sensors and processors are presented. Although the ideas are based on classical theory, their consequent and systematic application has been shown to result in novel, simple and accurate processors. The concept is demonstrated by a new design for a position-sensitive detector (PSD) displacement transducer. With a simple low-cost circuit, based on the use of opamps, the processor inaccuracy is less than 10 −4 for a displacement range of 3 mm, which is ten times better than that of the PSD itself. Besides the opamp version, a BICMOS design for operation at a single supply voltage of 5 V has also been presented.
TL;DR: In this article, a simulation model for batch fabrication of piezoresistive pressure sensors is presented, where an error band for the sensor response is determined in terms of processing variations for a temperature range of −40 to 130 °C over a pressure range of 0 to 45 psi.
Abstract: A major problem associated with piezoresistive pressure sensors is their cross sensitivity to temperature. The influence of temperature is manifested as a change in the span and offset of the sensor output. Moreover, in batch fabrication, minor process variations change the temperature characteristics for individual units. In this paper, a simulation model for the batch fabrication of piezoresistive pressure sensors is presented. An error band for the sensor response is determined in terms of processing variations for a temperature range of −40 to 130 °C over a pressure range of 0 to 45 psi. Utilizing this information, a new temperature-compensation technique, especially suited for batch fabrication, is described. This technique shows very encouraging results in removing the zero pressure offset and significantly reduces the errors caused by processing variations on the same wafer.
TL;DR: In this paper, two types of pyroelectric sensor set-ups using the polypropylene polysilicon (PVDF) are discussed, and a MOSFET is used to read out the pyroelectrically generated signal.
Abstract: In this paper two types of pyroelectric sensor set-ups using the pyroelectric polymer PVDF are discussed. In the first a PVDF membrane is mounted on a support ring. As a result, the material is thermally well isolated and the thermal sensitivity of this configuration is high. On the other hand, this set-up is not very robust as the wires (which can be numerous in the case of a matrix sensor) connecting the PVDF sensor to the readout electronics are vulnerable. The second set-up discussed solves this problem. Now the PVDF foil is glued to a silicon substrate containing the readout circuitry. A MOSFET is used to read out the pyroelectrically generated signal.
TL;DR: In this article, a flowmeter based on a monolithic integrated flow sensor has been developed for measuring liquid flows as small as 0.1 ml/min in microchannels.
Abstract: A flowmeter based on a monolithic integrated flow sensor has been developed for measuring liquid flows as small as 0.1 ml/min in microchannels. The flowmeter is able to operate in thermal transit-time mode and thermal dilution mode. Diodes on the silicon chip are used both as the heating device and as the temperature detectors. When operating in thermal transit-time mode, the flowmeter has an accuracy better than 0.2% (at a flow rate of 0.2 ml/min) and a 90% response time less than 1 s. While operating in thermal dilution mode, the flowmeter has an accuracy of about 1%, but features an excellent dynamic performance with a —3 dB frequency cutoff up to 5 Hz. A dynamic model has also been developed for the interpretation of the mechanism of the flow sensor and for the calibration of the flowmeter. Simulation based on the model shows good agreement with the experimental results. The flowmeter will be used to monitor and control the liquid flow in FIA (flow injection analysis) systems.
TL;DR: In this paper, a photo-ASIC consisting of light-sensitive structures, light-emitting devices and analog and digital circuits is integrated on a single chip, achieving an external quantum efficiency of 50-80% in the visible spectrum.
Abstract: With ‘photo-ASICs’ comprising light-sensitive structures, light-emitting devices and analog and digital circuits, complete optical metrology systems can be integrated on a single chip. We report the realization of key components of such photo-ASICs using an industrual IC CMOS process. We achieve photodiodes with an external quantum efficiency of 50–80% in the visible spectrum and position-sensitive devices (PSDs) with a spatial non-linearity of around 0.3%. We demonstrate surface-channel CCDs with a charge-transfer efficiency of 99.8% at room temperature, as well as bucket-brigade devices (BBDs) with a lower charge-transfer efficiency of 96%. Light-emitting diodes (LEDs) are realized, emitting infrared light at 1160 nm (forward biased) and broadband visible yellow light with a spectral maximum at 640 nm (reverse biased). We discuss simple applications of passive photo-ASICs, such as a centroid detector, a 3-D camera, a motion detector and a focus sensor, used to obtain a relative measure for the local focus of an optically imaged scene, for example, in a photographic camera.
TL;DR: In this article, the results of AC photocurrent measurements with insulated semiconductor LAPS devices where the semiconductor either is illuminated through the insulator (frontside) or alternatively from the opposite side (backside) were reported.
Abstract: Alternating photocurrent measurements with light-addressable potentiometric sensors (LAPSs) have been used to monitor pH, redox potential, and ionic concentrations at discrete locations in an electrolyte in contact with LAPS devices. We report here the results of AC photocurrent measurements with insulated semiconductor LAPS devices where the semiconductor either is illuminated through the insulator (frontside) or alternatively from the opposite side (backside). Such comparative AC photocurrent measurements were made with semiconductors of varied thickness, at varied frequency of light intensity modulation, and at several different photoexcitation wavelengths. The results are fit to a theoretical expression which predicts the dependence of photocurrent on modulation frequency, wafer thickness, bulk minority carrier lifetime, and surface recombination velocity. The results are useful to optimize the design of LAPS devices with regard to these parameters. The results also predict optimal conditions for minimal lateral spacing of adjacent sensing areas in LAPS devices.
TL;DR: In this paper, the authors report on the operational characteristics of LOCOS-based microfabricated radial-gap electric motors through lifetime tests, transient measurements, modeling, and parameter extraction, and find that the reduction of static friction in the bearings by the incorporation of a silicon nitride film permits these micromotors to spin in normal air ambients.
Abstract: We report on the operational characteristics of LOCOS-based microfabricated radial-gap electric motors through lifetime tests, transient measurements, modeling, and parameter extraction. We have found that the reduction of static friction (stiction) in the bearings by the incorporation of a silicon nitride film permits these micromotors to spin in normal air ambients. Frictional drag from the bearing, which results from the electric-based side-pull of the rotor, is found to be the dominant rotor-retarding force and to lead to motor wearout after approximately 10 000 rotor revolutions. Furthermore, the frictional coefficient of the nitride-on-polysilicon micromotor bearing is determined to be 0.36 ± 0.04.
TL;DR: In this article, the most important types of attractive forces are discussed with respect to their possible influence on the performance of micromachined structures, and it is concluded that the main reason for sticking of PECVD silicon nitride micromechined structures is adsorption of water molecules, attracted each other as soon as the surfaces come into contact.
Abstract: A troublesome phenomenon encountered during the realization of free-standing microstructures, for example, beams, diaphragms and micromotors, is that initially released structures afterwards stick to the substrate. This effect may occur during wafer drying after the etching process has been completed, as well as during normal operation as soon as released structures come into contact with the substrate. In this paper the most important types of attractive forces are discussed with respect to their possible influence on the performance of micromachined structures. It is concluded that the main reason for sticking of PECVD silicon nitride micromachined structures is adsorption of water molecules. The water molecules, adsorbed on both surfaces, attract each other as soon as the surfaces come into contact. It is shown that a chemical surface modification, in order to achieve hydrophobic surfaces, is an effective method for avoiding adsorption of water, and therefore reduces sticking. Sticking of micromachined structures during drying is reduced by rinsing with a non-polar liquid before wafer drying.
TL;DR: In this paper, a feasibility study on the possibility of combining sensors and circuits into a single microelectronic integrated smart sensor is presented, and it is to be expected that these sensors will become available within the next five years.
Abstract: Progress in the automation of industrial production machines, such as robots, and of consumer products, such as cars, kitchen and household machines, has hitherto been constrained by the lack of inexpensive sensor systems. Large-scale sensor applications can only be made economically feasible if sensors and circuits are combined in microelectronic chips with standardized digital bus output. This is the concept of integrated smart sensors (ISS). This paper first discusses the industrial relevance of sensors in automated production machines and consumer products. Secondly, the inevitable evolution of sensors into integrated smart sensors is shown. Thirdly, a feasibility study on the possibility of combining sensors and circuits into single microelectronic integrated smart sensors is presented. Though integrated smart sensors with a digital bus output are not yet on the market, it is to be expected that these sensors will become available within the next five years.