Showing papers in "Sensors and Actuators A-physical in 1994"
TL;DR: In this article, the design, modelling and performance characteristics of electrostatically driven vacuum-encapsulated polysilicon resonators are addressed, and an expression for the pull-in voltage of a beam is given.
Abstract: In this paper, the design, modelling and performance characteristics of electrostatically driven vacuum-encapsulated polysilicon resonators are addressed. A one-port configuration is preferably employed for excitation and detection of the vibration. Mechanical instability (pull-in) is discussed on the basis of the energy minimum principle. An expression for the pull-in voltage of a beam is given. The electromechanical behaviour in a limited frequency regime around the fundamental resonance is accurately modelled by an electric circuit consisting of a (static) capacitor shunted by a series (dynamic) RLC branch. The d.c. bias dependence of the circuit components and of the series resonance frequency has been experimentally investigated and is compared with the theory. The large-amplitude behaviour is discussed as well. The plate modulus and residual strain of boron-doped polysilicon are estimated from the resonance frequencies of microbridges of varying lengths. The feasibility of their application as resonant strain gauges is investigated. The 210 m long beams typically have an unloaded fundamental frequency of 324 kHz, a gauge factor of 2400 and an uncompensated temperature coefficient of -135 ppm 0C-1.
417 citations
TL;DR: In this paper, it was shown that integration of a capacitive microphone and a preamplifier will result in a further reduction of the noise level of the FET microphone.
Abstract: Silicon micromachining has successfully been applied to fabricate piezoelectric, piezoresistive and capactive microphones. The use of silicon has allowed the fabrication of microphones with integrated electronic circuitry and the development of the new FET microphone. The introduction of lithographic techniques has resulted in microphones with very small (1 mm2) diaphragms and with specially shaped backplates. The application of corrugated diaphragms seems a promising future development for silicon microphones. It is concluded from a noise consideration that the FET microphone shows a high noise level, which is mainly due to the small sensor capacitance. From this noise consideration, it can be shown that integration of a capacitive microphone and a preamplifier will result in a further reduction of the noise.
374 citations
TL;DR: In this paper, a single-crystal slhcon, high aspect ratlo, low-temperature process sequence for the fabelfcatlon of suspended movable smgle-crystals s&on (SCS) beam structures is presented.
Abstract: A single-crystal slhcon, high aspect ratlo, low-temperature process sequence for the fabrlcatlon of suspended rmcroelectromechamcal structures (MEMS) usmg a smgle hthography step and reactwe Ion etching (RIE) IS presented The process IS called SCRJZAM I (single-crystal reactwe etchmg and metalhzatmn) SCREAM I IS a bulk mlcromachmmg process that uses RIE of a s~hcon substrate to fabricate suspended movable smgle-crystal s&on (SCS) beam structures Beam elements wth aspect ratios of 10 to 1 and widths rangmg from 0 5 to 4 0 Frn have been fabricated All process steps are low temperature (<3OO “C), and only conventronal sd~con fabrlcation tools are used photohthography, RIE, MIE, plasma-enhanced chemxal-vapor deposrtlon (PECVD) and sputter deposlhon SCREAM I IS a self-ahgned process and uses a smgle lithography step to define beams and structures srmultaneously as well as all necessary contact pads, electrIcal mterconnects and lateral capaators SCREAM I has been specifically deslgned for integration with standard Integrated cmxnt (IC) processes, so MEM deuces can be fabricated adjacent to prefabricated analog and dIgItal carcuitry In this paper we present process parameters for the fabncatlon of discrete SCREAM I devices We also discuss mask design rules and show micrographs of fabncated deuces
295 citations
TL;DR: In this paper, a monolithically integrated acceleration sensor is presented, which contains the complete detection circuitry on the same chip, and the output signal of the accelerometer is fed back to the sensor element, so that an overall electromechanical closed loop is built.
Abstract: A monolithically integrated acceleration sensor is presented, which contains the complete detection circuitry on the same chip. It is fabricated by means of polysilicon surface micromachining. This design represents the first fully integrated accelerometer that completely meets the requirements of the automotive industry. The sensor structure itself consists of a differential capacitor, whose interdigitated fingers translate parallel to the chip surface. The detection circuitry works at high frequency with a 1 MHz carrier. The output signal of the accelerometer is fed back to the sensor element, so that an overall electromechanical closed loop is built. This allows the sensor to work in a forced-balance mode, reducing the sensor deflection and thus noise and distortion. Additionally, an electrostatic activated self-test function of the sensor element is implemented. The overall sensitivity is 20 mV g−1 with an acceleration range of ±50g. Fundamentals of the fabrication process of the sensor element and basic theoretical considerations are presented. Measurement results of the complete 'sensor and circuit' system are given.
256 citations
TL;DR: In this paper, the residual gas generated during the anodic binding process and that desobed from the silicon and glass surface increase the pressure in a sealed cavity, and two methods are proposed to eliminate residual gas; (i) the residual gases are evacuated through a small opening after bonding, and then the opening is plugged by depositing a material in vacuum, and (ii) a non-evaporable getter (NEG) is used for the second method.
Abstract: Vacuum packaging by the glass-silicon anodic process is studied. The residual gas generated during the anodic binding process and that desobed from the silicon and glass surface increase the pressure in a sealed cavity. In order to fabricate a vacuum sealed cavity, two methods are proposed to eliminate the residual gas; (i) the residual gases are evacuated through a small opening after bonding and then the opening is plugged by depositing a material in vacuum, (ii) the residual gases are absorbed by a getter inside the sealed cavity. A non-evaporable getter (NEG) is used for the second method. A vacuum sealing of tens of Torr is obtained by the firat method. The second method and a combnation of the two methids enables vacuum sealing at a pressure lower than 10-5Torr. A prototype of a capacitive vacuum sensor is fabricated by using the second method.
247 citations
TL;DR: In this article, a surface micromachining process, using an oxide sacrificial layer and poly/nitride/poly membranes, has been developed for light modulators integrated on the same chip as the signal processing.
Abstract: The development of compact light modulators integrated on the same chip as the signal processing opens many opportunities for combining inter-chip optical communications with standard silicon circuitry. The use of surface micromachining allows high speed of operation and small size integration with other circuitry. The optical and mechanical requirements for the devices also have to be considered, to ensure compatability with standard silicon processing. A surface micromachining process, using an oxide sacrificial layer and poly/nitride/poly membranes, has been developed. This paper presents the optical and mechanical considerations in the development of a compact micromachined silicon Fabry-Perot interferometer. Initial tests have shown that these micromachined membranes represent a compact and effective light modulating method.
239 citations
TL;DR: In this article, a probe with four anemometric sensors and four gas sensors has been developed so that the direction of an odor source can be determined using a wind tunnel environment.
Abstract: A new method for localization of an odor source is proposed. A probe with four anemometric sensors and four gas sensors has been developed so that the direction of an odor source can be determined. The anemometric sensors are used for measuring the direction of the air flow carrying odor molecules, and the gas sensors are used for detecting the gas-concentration gradient. Moreover, mounting the probe on a mobile stage with the probe under the control of a personal computer makes it possible to realize an autonomous mobile sensing system. An odor source has been successfully localized using this system in a wind tunnel.
236 citations
TL;DR: In this article, the authors investigated the mechanisms causing stiction of polysilicon structures fabricated by surface micromachining techniques and found that during drying from rinse liquids attractive dynamic capillary forces are responsible for bringing micromechanical structures into contact with the underlying substrate.
Abstract: The mechanisms causing stiction of polysilicon structures fabricated by surface micromachining techniques have been investigated. It is found that during drying from rinse liquids attractive dynamic capillary forces are responsible for bringing micromechanical structures into contact with the underlying substrate. Measured adhesion energies of sticking microbridges indicate that van der Waals forces are responsible for the stiction of hydrophobic surfaces and that hydrogen bridging is an additional adhesion mechanism for hydrophilic surfaces. Methods to reduce the stiction problem are indicated.
218 citations
TL;DR: In this article, the responses of smooth and textured surface thickness-shear mode (TSM) resonators in liquid are examined, and the results show that smooth devices, which viscously entrain a layer of contacting liquid, exhibit a response that depends on the product of liquid density and viscosity.
Abstract: The responses of smooth- and textured-surface thickness-shear mode (TSM) resonators in liquid are examined. Smooth devices, which viscously entrain a layer of contacting liquid, exhibit a response that depends on the product of liquid density and viscosity. Textured-surface devices, which also trap liquid in surface crevices, pores, etc., exhibit an additional response that depends on liquid density alone. Combining smooth- and textured-surface resonators in a monolithic sensor enables the liquid density and viscosity to be extracted simultaneously.
213 citations
TL;DR: In this paper, a fabrication process based on surface-micromachining techniques for electrostatically driven vacuum-encapsulated polysilicon resonators is presented, and a novel freeze-drying method that does not require vacuum equipment is presented.
Abstract: Basic design issues and a fabrication process based on surface-micromachining techniques for electrostatically driven vacuum-encapsulated polysilicon resonators are presented. A novel freeze-drying method that does not require vacuum equipment is presented. Reactive sealing with LPCVD silicon nitride is used to create the evacuated cavity, resulting in cavity pressures close to the deposition pressure. Design issues regarding choice of materials, technology and layout are discussed. First experimental results, including an admittance plot of the one-port resonator and a plot indicating the dependence of the Q-factor on the resonator geometry and ambient pressure, are presented.
202 citations
TL;DR: In this article, low-temperature wafer-to-wafer bonding and throughwafer interconnect Au/Si eutectic bonding has been investigated as it can conveniently be combined with bulk-micromachined through-wire interconnect, provided that the processes involved comply with the constraints imposed by the proper operation of active electrical and micromechanical subsystems.
Abstract: Micromechanical smart sensor and actuator systems of high complexity become commercially viable when realized as a multi-wafer device in which the mechanical functions are distributed over different wafers and one of the wafers is dedicated to contain the readout circuits The individually-processed wafers can be assembled using wafer-to-wafer bonding and can be combined to one single functional electro-mechanical unit using through-wafer interconnect, provided that the processes involved comply with the constraints imposed by the proper operation of the active electrical and micromechanical subsystems This implies low-temperature wafer-to-wafer bonding and through-wafer interconnect Au/Si eutectic bonding has been investigated as it can conveniently be combined with bulk-micromachined through-wafer interconnect The temperature control in eutectic bonding has been shown to be critical
TL;DR: In this article, an optical fiber deformation sensor with a resolution of 10 μm and an operational range of 60 mm has been realized for the monitoring of large structures over several months without noticeable drift.
Abstract: An optical-fiber deformation sensor with a resolution of 10 μm and an operational range of 60 mm has been realized. The system is based on low-coherence interferometry in standard single-mode telecommunication fibers. It allows the monitoring of large structures over several months without noticeable drift. No continuous measurement is needed and the system is insensitive to variations of the fiber losses. This technique has been applied to the monitoring of a 20 m × 5 m × 0.5 m, 120 ton concrete slab over six months. It is possible to measure the shrinkage of concrete and its elastic coefficient during pre-straining, giving reproducible results in good agreement with theoretical calculations and measurements performed on small concrete samples. This paper describes the optical arrangement and the procedures used to install optical fibers in concrete.
TL;DR: In this paper, a theoretical and experimental study of this viscous fluid loading is presented, where a Love wave has a pure shear horizontal polarization and therefore no elastic interaction with an ideal liquid.
Abstract: It has been shown recently that a properly designed Love wave sensor is very promising for (bio)chemical sensing because of its high sensitivity. Furthermore, it is well known that a Love wave has a pure shear horizontal polarization and therefore no elastic interaction with an ideal liquid. This property makes it particularly interesting for (bio)chemical sensing in a liquid environment. However, interaction with a viscous fluid can never be avoided. It causes a small frequency shift which slightly distorts the sensor response and increases the insertion loss of the device. A theoretical and experimental study of this viscous fluid loading is presented here.
TL;DR: In this article, the authors introduce a new concept in vibrating quartz sensors, where the vibrational characteristics of such a compound resonator, namely the nominal frequency and vibrational amplitude, are correlated to the physical characteristics of the medium vibrating synchronously with the quartz resonator as a compound Resonator.
Abstract: This paper reviews the original contributions in the development of vibrating quartz sensors, loaded with whatever medium: solid, liquid or gas. The common feature of such a loading is its ability to vibrate synchronously with the quartz resonator as a compound resonator. The paper introduces a new concept in vibrating quartz sensors, where the vibrational characteristics of such a compound resonator, namely the nominal frequency and vibrational amplitude, are correlated to the physical characteristics of the medium vibrating synchronously with the quartz resonator as a compound resonator. The energy transfer model is introduced to explain the microweighing capability of quartz resonators. Further, it is proved that microweighing is a common feature of all quartz resonators, whatever their vibrational mode. It is also proved that other piezoelectric resonators exhibit the same capability. Damping of quartz-resonator vibrations at certain temperatures during a temperature sweep is correlated with the deposited film morphology. Resonance of the gas within a cavity is used for the development of tunable gas sensors. Examples are given for hydrogen and methane detection without using a catalyst. An experiment called ‘Nanobalance’ is also presented, which was performed in outer space.
TL;DR: In this article, an electromagnetic microrelay is proposed as a practical application of microelectrochemical system (MEMS) technology and the basic performance of its key components is evaluated.
Abstract: An electromagnetic microrelay is proposed as a practical application of microelectrochemical system (MEMS) technology and the basic performance of its key components is evaluated. The contact resistance and breakdown voltage of contact electrodes are measured for very small loads and gaps. The static and dynamic deflection of the contact springs is measured for very small movements. Based on these experimental results, design guidelines for key components are proposed. Two prototypes that partly use MEMS technology are produced and their switching performance is demonstrated. One prototype uses a flat microspring with a length and width of 0.3 mm; its switching speed is more than ten times that of a conventional relay. The other is a 2×2 matrix relay, with four self-latching switches; each switch has two stable positions, open and closed, and is driven by a current pulse. This component study and prototype development verify the suitability of MEMS technology for mechanical relays.
TL;DR: By combining the LIGA technique with processes used in the manufacture of micromembranes, micronembrane pumps have been built with pump chambers 100 μm in height and with pump membrane diameters between 2 and 5 mm.
Abstract: By combining the LIGA technique with processes used in the manufacture of micromembranes, micromembrane pumps have been built with pump chambers 100 μm in height and with pump membrane diameters between 2 and 5 mm. The pump case is made of gold, whereas the 2.7 μm thin pump membrane consists of titanium. The passive microvalves of the pump consist of patterned micromembranes arranged one over the other and made of titanium and polyimide by use of thin-film techniques. The micropump has been tested so far with an external pneumatic drive. Both air and water have been pumped.
TL;DR: In this paper, a survey of SAW sensor systems is given, where three categories of sensors are defined as transit-time, resonator and chirp-type devices and each category is subdivided into active and passive signal processing systems.
Abstract: A survey is given of SAW sensor systems. Three categories of sensors are defined as transit-time, resonator and chirp-type devices and each category is subdivided into active and passive signal-processing systems. In these, the mechanical change of the SAW device is evaluated by difference measurements of the transit time, phase or resonance frequency, which are described quantitatively. To show the high resolution of active sensor systems, an electronic spirit level (based on SAW resonators) is described. New SAW chirp sensors allow the dispersive interdigital transducer or reflector geometry to be adjusted to the sensor system resolution and measurement range. In passive systems the sensor device is connected to an antenna. The SAW is excited by an interrogating radio impulse. After a SAW transit time, the sensor radiates back to the interrogator an impulse containing the sensor's information. The time and frequency response of all sensor categories and the possibilities of temperature compensation are discussed.
TL;DR: In this article, a closed-loop controller is used to control the output flow of a piezoelectric silicon micropump with a controlled output flow, which can maintain a constant output flow when the pressure difference between the pump's output and input varies.
Abstract: A piezoelectric silicon micropump with a controlled output flow is presented. A closed-loop controller regulates the liquid's flow. The system can maintain a constant output flow when the pressure difference between the pump's output and input varies. This regulation has been demonstrated for flow rates from 10 to 100 μl/min, and for pressure differences up to 100 mbar. The main components of the system as well as the results obtained are discussed.
TL;DR: In this article, a wide range of bulk and surface-generated acoustic waves are described and prototype sensing-element geometries are presented and results obtained using several candidate acoustic wave biosensors are also discussed.
Abstract: Acoustic waves excited in a piezoelectric medium provide an attractive technology for realizing a family of biosensors that are sensitive, portable, cheap and small. In this paper a wide range of bulk and surface-generated acoustic waves are described and prototype sensing-element geometries are presented. Results obtained using several candidate acoustic wave biosensors are also discussed.
TL;DR: In this article, the authors investigated the sensitivity and dynamic range of a fiber optic based surface plasmon resonance sensor with a set of aqueous refractive index standards and found that the sensitivity was between 5.0×10−4 and 5.5 × 10−5 index of refraction units.
Abstract: The refractive index sensitivity and dynamic range of a recently developed fiber optic based surface plasmon resonance sensor have been investigated. The sensor response was studied using a set of aqueous refractive index standards. The sensitivity to refractive index was found to be between 5.0×10−4 and 5.0×10−5 index of refraction units. The dynamic range of an unmodified sensor was between 1.25 and 1.40 index of refraction units. The dynamic range was tuned for ranges between 1.00 and 1.40 index of refraction units with the addition of thin high refractive index overlayer films. This range is significant since it includes both gas and aqueous chemical sample refractive indices. The upper limit of the refractive index dynamic range was extended to 1.70 by use of a sapphire fiber core material.
TL;DR: In this paper, a single chip pressure and tenperature sensor system with on chip electronics is presented, where the capacitive pressure sensor is fabricated using a CMOS process with additional surface micromachining steps to form a membranes.
Abstract: In this paper a single chip pressure and tenperature sensor system with on chip electronics is presented. The capacitive pressure sensor is fabricated using a CMOS process with additional surface micromachining steps to form a membranes. The membrane dimensions have been optimized for a pressure range of 2, 3.5, 10 and 35 bars, respectively. The temperature sensor shows a straight linear output signal in a temperature range of 0 to 70 °C. For the signal processing switched capacitor circuits are used. The sensor signals are converted to a pulse width modulated output signal. The silicon chip has an active area of 3.5 mm 2 . Between 0 and 80 °C a temperature dependence of the pressure segnal of less than 200 ppm/°C referring to full scale was found.
TL;DR: Several thin-film deposition and etching techniques of the polymer fluorocarbon are investigated and the resulting thinfilm properties will be compared with those of commercially available bulk polytetrafluoroethylene.
Abstract: Several thin-film deposition and etching techniques of the polymer fluorocarbon are investigated and the resulting thin-film properties will be compared with those of commercially available bulk polytetrafluoroethylene. The most promising deposition technique is performed in a conventional reactive ion etcher using a carbonhydrotrifluoride (CHF3) plasma. By changing the deposition parameters, control of the properties and step coverage of the deposited thin films within a certain range is possible, eg., uni-directional and conformal step coverage of deposited thin films can be obtained. Etching is performed with the help of an evaporated aluminium oxide mask using an oxygen, nitrogen, or sulfurhexafluoride plasma for isotropic etching, or a CHF3 plasma giving a directional etch profile. The combination of the unique properties, deposition and etching techniques make fluorocarbon thin films a promising tool for micromachining; a number of applications will be discussed and demonstrated.
TL;DR: In this article, an assembly method for three-dimensional microelements is presented, where the assembly is done in situ with a micromanipulator in an SEM using Au-Si eutectic bonding.
Abstract: An assembly method for three-dimensional microelements is presented. The assembly is done in situ with a micromanipulator in an SEM using Au-Si eutectic bonding. Microblocks bonded to larger silicon substrates are used for evaluation of the mechanical strength and a microarch is presented to demonstrate the possibilities of the technique. The microelements are fabricated by bulk micromachining, and sputter deposited with chromium and gold. Etched (111) faces have been successfully bonded. TEM investigation of samples from vacuum furnace experiments show large gold grains with smaller chromium silicide grains in the bonded region. The silicon in the eutectic liquid precipitates epitaxially on both silicon faces. Mechanical bending tests on the microblocks give sufficiently high fracture stresses for the intended applications in microrobotic systems. Average fracture stresses of 65 MPa are measured for one set of parameters. Problems encountered are misalignments of the microelements during processing and void formation in the bonds. It is believed this is connected to the experimental equipment and set-up. The microarch, which consists of three assembled microblocks, reaches a tensile stress of 16 MPa, encouraging further development. In conclusion, strong microbonds are achieved using a solidified gold-silicon eutectic melt as an adhesive, and it is demonstrated for the first time that three-dimensional microassembly by means of eutectic bonding of micromachined elements can be performed by manipulation and processing on a locally heated specimen table.
TL;DR: In this paper, anisotropic chemical etching of crystalline silicon in aqueous KOH is simulated at the atomic level using a cellular automata model, where experimental etch-rate ratios as well as the influence of temperature and concentration of the etchant are taken into account by introducing a stochastic component.
Abstract: Anisotropic chemical etching of crystalline silicon in aqueous KOH is simulated at the atomic level using a cellular automata model. Experimental etch-rate ratios as well as the influence of temperature and concentration of the etchant are taken into account by introducing a stochastic component. With the help of two examples, the underetching of a convex mask corner and mask-corner compensation for mesa-type corners, the capabilities of this model are demonstrated.
TL;DR: In this paper, a new physical model has been proposed for the characterization of slide film damping, where two parallel plates are in relative tangential motion and viscous energy dissipation in the fluid between the two plates becomes a representative damping mechanism.
Abstract: Slide film damping occurs when two parallel plates are in relative tangential motion. Viscous energy dissipation in the fluid between the two plates becomes a representative damping mechanism in laterally driven microdevices. In this paper, we investigate the slide film damping both theoretically and experimentally. A new physical model has been proposed for the characterization of slide film damping. Dynamic characteristics of a fluid film have been described in terms of velocity profiles, damping mechanisms, and levels of viscous energy dissipation. Simplified analytical damping formulae have been developed for practical Q estimation. The theoretical Q compares well with the experimental Q. Data reported by previous investigators are also analyzed and compared with the Q value estimated in the present study. It is concluded that our theoretical model offers simple and reasonably good quantitative prediction of Q. Possible sources of error in the theoretical Q prediction are discussed. The effects of fluid-film thickness and microstructure geometry on Q are investigated, so that the results can be used in the damping design for laterally driven microtransducers.
TL;DR: In this paper, the authors present an overview of recent developments in the SiC field, including the commercial availability of bulk SiC crystals, which is likely to establish SiC as a new wafer technology which allows many devices to be fabricated in analogy to known Si ones, in which the high-temperature limit for the operation of sensors and electronic circuits can be significantly extended.
Abstract: The paper presents an overview of recent developments in the SiC field. Within this field, two main streams are emerging: on the one hand, the commercial availability of bulk SiC crystals is likely to establish SiC as a new wafer technology which allows many devices to be fabricated in analogy to known Si ones. In this way, the high-temperature limit for the operation of sensors and electronic circuits can be significantly extended. Thin films of SiC, on the other hand, can be used as an add-on to the existing Si technology. Using such films, new possibilities emerge with regard to the fabrication of microsensors. Applications of thin-film SiC in optics, optoelectronics and micromachining are demonstrated.
TL;DR: In this paper, the authors present the SAMLAB-ARTICLE-1994-010 Record created on 2009-05-12, modified on 2016-08-08, and used for this purpose.
Abstract: Note: 116 Reference SAMLAB-ARTICLE-1994-010 Record created on 2009-05-12, modified on 2016-08-08
TL;DR: In this article, a microrobot is modelled as a damped three-degree-of-freedom system driven by displacement excitation, and its design is determined from simulation results based on this model.
Abstract: A vibration energy field generated by a piezoelectric vibrator can supply a microrobot with power without using wires, by exciting resonant actuators mechanically. Furthermore, this energy field implicitly contains control signals that make it possible to activate actuators selectively. A microrobot measuring 1.5 mm×0.7 mm has been fabricated using silicon micromachining technology and a folding process to make three-dimensional structures. The microrobot is modelled as a damped three-degree-of-freedom system driven by displacement excitation. The microrobot's design is determined from simulation results based on this model.
TL;DR: In this paper, a monolithic single-chip sensor array for measuring chemical and biochemical parameters has been developed and fabricated in a modified standard CMOS process, which is used for amperometric or potentiometric measurements in order to get a concentration-dependent spatial profile of the detected analyte.
Abstract: A monolithic single-chip sensor array for measuring chemical and biochemical parameters has been developed and fabricated in a modified standard CMOS process. The array can be used for amperometric or potentiometric measurements in order to get a concentration-dependent spatial profile of the detected analyte. In addition to 400 working electrodes and two reference electrodes, the chip contains integrated read-out amplifiers, digital circuits for addressing the individual components and test circuits. The on-chip signal processing allows detection of chemical or biochemical analytes without any interference by the external measurement equipment. High electrode impedances and low power consumption have been achieved by using CMOS technology. Chemical modification of the electrodes is possible by applying an external voltage to the electrodes. In advantage to non-integrated solutions, the system can be used in a wide field of applications, especially for measurements in narrow passages because of the total chip size of only 14×14 mm.
TL;DR: A combination of different technologies is used for the realization of smart acoustic-wave-based microsensors, where electronic circuitry and an acoustic delay line are integrated on a single silicon chip as discussed by the authors.
Abstract: A combination of different technologies is used for the realization of smart acoustic-wave-based microsensors, where electronic circuitry and an acoustic delay line are integrated on a single silicon chip. For a monolithic Lamb wave oscillator, the three required technologies are described: bipolar IC technology, thin-film piezoelectric zinc oxide technology, and micromachining technology. The last two technologies have to be IC compatible and are not allowed to affect the IC processing in order to prevent malfunction of the electronic circuitry. The realized monolithic Lamb wave sensor has several applications. Examples are the determination of the density, viscosity and sound speed of liquids, and (bio)chemical applications, where mass adsorption at the sensor surface is monitored. The sensor described in this paper demonstrates the determination of the weight percentage of water in water—ethanol solutions.