Thermally-based transducer microsystems can be made by using CMOS IC technology, post-CMOS micromachining or deposition, and flip-chip packaging. Technology steps, materials, and physical effects pertinent to thermal microtransducers are summarized together with microheater, thermistor, thermopile, thermal isolation, and heat sink structures. An infrared intrusion detector, a thermal air flow sensor, and thermally excited microresonators for acoustic and chemical sensing serve as demonstrators. We discuss the characterization of process-dependent properties of CMOS materials crucial for thermal microtransducer CAD.

A cost-effective process with short fabrication time for making x-ray masks for research and development purposes is described here for fabricating high-aspect ratio microelectromechanical structures using synchrotron based x- ray lithography. Microscope cover glass slides as membrane material is described. Slides with an initial thickness of 175 micrometers are etched to a thickness in the range of 10 - 25 micrometers using a diluted HF and buffered hydrofluoric acid solutions. The thinned slides are glued on supportive mask frames and sputtered with a chromium/silver sandwich layer which acts as a plating base layer for the deposition of the gold absorber. The judicial choice of glue and mask frame material are significant parameters in a successful fabrication process. Gold absorber structures are electroplated on the membrane. Calculations are done for contrast and dose ratio obtained in the photoresist after synchrotron radiation as a function of the mask design parameters. Exposure experiments are performed to prove the applicability of the fabricated x-ray mask.

Systematic design methods for MicroElectroMechanical Systems (MEMS) have been lacking and typical design procedures encompass trial and error approaches. This paper discusses the application of the topology optimization method as a systematic tool for MEMS design. The topology optimization method distributes one or more passive or active materials in a design domain, such that some output performance is optimized. Here, the method is applied to the design of thermal or electrothermal micro actuators where the output work performed on a workpiece of given stiffness is to be maximized. It is shown that actuators with either large output displacement or large output force can be designed by specifying low or high stiffness of the workpiece, respectively. The optimal topologies are strongly dependent on the stiffness of the workpiece as well.

This paper describes a design rule checking (DRC) tool developed as an aid for designing microelectromechanical structures (MEMS) using AutoCAD^TM running on a Windows NT workstation. The application suite, MEMSdrc, consists of a graphical user interface integrated into AutoCAD^TM to invoke DRC, translation and interface software to communicate with a commercial IC layout design checking software package, and routines to interactively display and review the results. The user interface provides the capability to select a checking window area and specific DRC rules to be applied to the design. The MEMS structures, defined as 2D AutoCAD^TM geometry are translated first into DXF format, then to GDSII format. A remote process transfers the files to a Unix workstation where Mentor Graphics ICverify is invoked to perform the layout design rule checks. Upon completion, the results are translated into DXF geometry and returned back to the Windows NT workstation to be overlaid onto the original design. A set of icons are provided for the user to interactively review the results inside of AutoCAD^TM using a first/next/previous technique.

Although MEMS device designers currently make use of process simulation, 3D visualization and finite element/boundary element analysis tools, MEMS systems designers lack the design and verification tools enjoyed by electronic circuit and systems designers. System level and circuit level simulation tools for MEMS are beginning to become available, but an important issue is the availability of macromodels. This paper discusses an integrated CAD tool suite based on extensions to VLSI electronic circuit and systems tools to handle signals in multiple energy domains. These tools maintain synchronized physical, structural and behavioral design views and work in conjunction with a library of MEMS schematic symbols, layout generators, and behavioral models. Integration of electronic circuit and systems tools and MEMS systems tools allow designers to address the important problems of ensuring system performance goals are met, system partitioning and determining the degree of integration of sensing/actuating devices and interface/calibration electronics. These new physical design and simulation tools are applied to fabricated design examples and the results are critiqued. Discussions of the merits and limitations of our tools and other design tools is also included. Links between system level tools and MEMS device design tools are also described.

IDT (Interdigital Transducers) offer significant potential for detecting ice formation on rotorcraft applications. Sensing of flex beam deflection and acceleration, ice formation and deicing are major candidate areas where smart conformal IDT and MEMS based sensors can be exploited by the rotorcraft community. The major technical barrier of the present day smart structures technology is the need for wired communication between sensors and actuators in the rotating system and controllers, data storage units, and cockpit avionics. Many proposed sensors and actuators are commonly distributed either along the blade length or, in the active flap devices, out near the 75% blade radial station. Also they are not conformal to the airfoil shape of the rotor blades. The communication between rotating and fixed systems is typically accomplished using complex slip ring assemblies transferring electronic information down through the rotor shaft. Although advances have been made in wired communication, these complex assemblies are essentially similar to test hardware and present numerous reliability and maintainability limitations when implemented on a production scale. Considering these limitations, development of a wireless means of communication through a new generation of conformal sensors with built-in antenna, akin to telemetry, could have a dramatic beneficial payoff for rotorcraft applications. In this paper, an integration of IDT microsensors and MEMS sensors is presented.

In the fabrication of fully integrated sensors, which combine sensor and electronics on a single chip, it is essential to ensure that any additional process steps introduced for the sensor do not adversely affect the electronics. Where possible it is desirable to use existing processes or layers to fabricate the sensor. This is not always possible and therefore additional processing steps must be added to that of the electronic circuitry. In the fabrication of MEMS the additional processing is usually one of the forms of micromachining. Many processing steps are not compatible with the electronics and therefore they have to be adjusted which may lay considerable constraints on both materials and processing steps. In this paper the range of options to designer will be discussed.

Five micrometers silica particles can be arranged on CaTiO₃ substrates by drawing an electrified pattern on the substrate (drawing step) and then dipping it in a suspension of the particles (arranging step). The fixing treatment of the arranged particles is necessary in order to repeat the above two steps and to fabricate 3D micro-structures. A thin film of the fluoride polymer is formed on the substrate after the particle arrangement to fix the arranged particles. The effect of the coating film on the drawing step and arranging step was studied. It was found that the coating film improved both steps rather than cause interference. The drawing, arranging and fixing are the elemental techniques of the particle arrangement process, and 3D micro-structures can be constructed by repeating these steps in order. Application of the process to a gas sensor was discussed.

A new process for the fabrication of piezoelectric quartz thin films on silicon is investigated. With this process, new silicon-implemented acoustic wave delay lines for sensor applications can be realized. An acoustic-wave delay-line consists of two interdigital thin film metal transducers fabricated on a piezoelectric crystal. In order to realize acoustic-wave devices on (non-piezoelectric) silicon, the use of piezoelectric thin films such as zinc oxide, aluminum nitride or PZT has been reported. However, these films often exhibit stress, aging, pinholes, or poor reproducibility which affects the performance of the device. The bonding of piezoelectric quartz (with its known and fixed mechanical and piezoelectric properties) to silicon improves the performance of silicon-implemented acoustic-wave devices. The process used, consists of a wet chemical treatment after which the wafers are prebonded at room temperature. Annealing at 140 degree(s)C for 3 hours yields a sufficient high bond strength.

The quality of surface finish and precise height of LIGA components produced by electroplating has been studied. Planarization is often required to meet specifications for both basic LIGA processing (single level) and extended LIGA processing (multi-level). The HI-MEMS Alliance has successfully developed such a planarization process.

MEMS fabrication faces multiple technological challenges before it can become a commercially viable technology. One key fabrication process required is the deep silicon etching for forming high aspect ratio structures. There is an increasing interest in the use of dry plasma etching for this application because of its anisotropic (i.e. independent of silicon crystal orientation) etching behavior, high etch rate, and its compatibility with traditional IC processing. Alcatel has developed a patented inductively coupled high density plasma source which delivers high etch rate, uniform, anisotropic silicon etching to depths as deep as 500 micrometers . This plasma source has been used for fabricating devices such as accelerometers, yaw rate sensors etc. Etch process performance data on some of these devices will be presented. Thus the Alcatel deep etching system provides the enabling technology requires for deep silicon micromachining of microsensors.

This work describes the determination of mechanical properties of sputtered piezoelectric zinc oxide (ZnO) films. The residual stress of the thin ZnO films was measured using the wafer curvature and the sputter parameters for growth of films with low tensile stress determined. Tensile films are often preferred in membrane structures because, e.g. buckling is avoided. A membrane deflection method was applied to measure the plane-strain modulus of ZnO films on SiN_x. A new model which includes the flexural rigidity of a multilayered membrane was used to calculate the residual stress and plane-strain modulus of the membrane layers. The measured plane-strain modulus for ZnO on SiN_x is 115 GPa. Nano indenter experiments on a ZnO film deposited on a Al-SiO₂-Si substrate revealed a similar value of 122 GPa for the plane-strain modulus. These results can be used for more accurate modeling of ZnO based microsensors and actuators, such as Lamb wave sensors.

Selectively coated cantilevers are being developed at ORNL for chemical and biological sensing. The sensitivity can exceed that of other electro-mechanical devices as parts- per-trillion detection can be demonstrated for certain species. We are now proceeding to develop systems that employ electrically readable microcantilevers in a standard MEMS process and standard CMOS processes. One of our primary areas of interest is chemical sensing for environmental applications. Towards this end, we are presently developing electronic readout of a mercury-sensitive coated cantilever. In order to field arrays of distributed sensors, a wireless network for data reporting is needed. For this, we are developing on-chip spread-spectrum encoding and modulation circuitry to improve the robustness and security of sensor data in typical interference- and multipath-impaired environments. We have also provided for a selection of distinct spreading codes to serve groups of sensors in a common environment by the application of code-division multiple-access techniques. Most of the RF circuity we have designed and fabricated in 0.5 micrometers CMOS has been tested and verified operational to above 1 GHz. Our initial intended operation is for use in the 915 MHz Industrial, Scientific, and Medical band. This paper presents measured data on the microcantilever-based mercury detector. We will also present design data and measurements of the RF telemetry chip.

Sensors embedded in structural composites have been a topic of research in recent years. Embedded sensors can be used to monitor and optimize the manufacturing process, to monitor performance during use, and for structural health monitoring in high-performance applications. For several years, embedded optical fibers were the predominant type of sensor. There are well-known reasons that optical fiber sensors have not yet been fully embraced in industry including primarily the cost of equipment and sensors, the fragility of the optical fiber itself, and the need to provide ingress and egress from the structure. Recent work by the authors and others has produced prototype wireless electronic sensors of various types that address these shortcomings. The US Office of Naval Research is funding a multi-disciplinary team to consolidate progress made in earlier programs towards self- contained microsensors to be embedded in a composite structure and queried using methods that do not require physical connections. The sensors are to be left in place for the lifetime of the structure, are powered by the querying apparatus, and require no penetrations through the surface of the structure. This paper describes the integrated approach taken to realize the goal of an interrogatable strain rosette that is embedded 0.25' into a graphite composite plate. It also describes the progress to date of the sensor system itself.

This paper presents the basic principles of operation and experimental investigations of a novel multi-layer microstrip antenna element for applications in integrated smart structures. The device is configured in a multilayer piezoelectric-dielectric-strip grating environment, integrating dual functions of wireless sensing as well as actuation in a single, compact device. The device employs microwave radiation and reception for the wireless remote operations. The sensing function is electrically discriminated from the actuation function in the single Simultaneous Sensing and Actuating Smart Antenna Element device by making use of two orthogonal E-field polarizations of microwave radiation for the two separate functions. This is possible by using a novel `polarization grating' arrangement, which allows selective transmission and interactions of the microwave signals in the two orthogonal polarization modes. Alternate methods using two distinct frequency bands, instead of the two polarizations, may also be effectively employed for discrimination of the separate sensing and actuation functions.

The major drawback of a microstrip patch antenna is it's narrow bandwidth characteristics. One method that has been investigated to increase bandwidth is the addition of a parasitic element to the microstrip patch antenna. In an active microstrip patch antenna, variable bandwidth can be achieved by varying the spacing between the antenna and the parasitic element, which is fixed to a dielectric plate. In this study, an actuator is developed, tested and employed on an actual microstrip patch antenna and it's parasite. Since a relatively large displacement (1 cm) is needed, this mesoscale actuator is comprised of stacked Rainbow actuators. This study takes advantage of the fact that, for antennas operating at higher frequencies, smaller absolute displacements will result in significant percentage changes in antenna bandwidth. The use of the parasite and the active system accounted for up to a factor of five increase in antenna bandwidth. Various control techniques were employed to counteract the effects of hysteresis and creep on the actuator. Because the use of metal components can degrade antenna performance, emphasis was placed on synergy in the design process.

Recently, it has been demonstrated that aperture antennas can have their performance improved by utilizing PVDF as a shape controlling actuator. Since PVDF is a polymer with limited control authority, these antennas can only be employed in space based applications. This study examines more robust antenna structures devised of a thick metalized substrate with surface bonded piezoceramic (PZT) actuators. In this work, PZT-actuated adaptive antennas of cylindrical- cut shape are studied. First, the PZT-actuated antenna surface is modeled based on the classical curved beam theory and Newton's method. Second the Voltage vs. Deflection relationship is experimentally verified. Third, the resulting far field radiation pattern is simulated on computer.

Now that the technology for Integrated sensor and MEMS devices has become sufficiently mature to allow mass production, it is expected that the prices of bare chips will drop dramatically. This means that the package prices will become a limiting factor in market penetration, unless low cost packaging solutions become available. This paper will discuss the developments in packaging technology. Both single-chip and multi-chip packaging solutions will be addressed. It first starts with a discussion on the different requirements that have to be met; both from a device point of view (open access paths to the environment, vacuum cavities, etc.) and from the application point of view (e.g. environmental hostility). Subsequently current technologies are judged on their applicability for MEMS and sensor packaging and a forecast is given for future trends. It is expected that the large majority of sensing devices will be applied in relative friendly environments for which plastic packages would suffice. Therefore, on the short term an important role is foreseen for recently developed plastic packaging techniques such as precision molding and precision dispensing. Just like in standard electronic packaging, complete wafer level packaging methods for sensing devices still have a long way to go before they can compete with the highly optimized and automated plastic packaging processes.

A new interconnection technique has been developed that allows versatile multiple strand connections between microsensors, sensor arrays, and chips designed for wire bonding. The new technique has been termed `microflex interconnects' (MFI). Conventional wire bonding technique is commonly restricted to planar interconnects with a limited degree of freedom for placing microsystem components. The MFI technique has overcome this limitation by interconnecting microsystem components through custom designed flexible foils with embedded metallized conductors. The MFI foils may also serve as circuit substrates. This basic foil material is polyimide (Du Pont PI 2611) or BCB which are patterned photolithographically. Platinum, gold or either conductive metals are sputtered or evaporated on the foil and patterned using lift-off technique. Several metallization layers can be embedded in the material. Pitch and shape of the MFI contact pads correspond to the one of the chips to be interconnected. A via hole is placed in the center of the MFI contact pads. MFI pads and chip pads are adjusted. Metal balls or wedges generate the electrical and mechanical contact through the vias between the chips and the MFI substrate. An commercial wire bonder is the only equipment needed to perform the MFI method. The MFI technique was applied to bond standard CMOS integrated circuit bond pads with a width of 30 micrometers and a pitch of 70 micrometers to a 10 micrometers thick MFI foil. The integration density of the of the MFI technique correspond to one of the flip- chip technology. Special advantages of the MFI technique are 3D interconnects, the flexibility in design and shape, and easy visual inspection of alignment qualities. The MFI method is also suited for biomedical applications because all materials used are biocompatible.

The cointegration of IC microsensors, actuators and readout circuit leads to smart Micro Electro Mechanical Systems (MEMS) which are superior in many aspects to their conventional discrete counterparts. However, the packaging of such device is still a challenge and a major factor of the overall production cost. On one hand MEMS need protection against mechanical contact and media. On the other hand, the encapsulation of the transducer must be partially permeable to the environment. We developed a packaging method which successfully addresses these challenges. Thereby the number of steps needed to electrically contact and partially seal the MEMS are reduced by combining them using flip-chip technology. An opening in the substrate is aligned with the transducer, and enables the interaction with external media. Concurrently with the electrical connections, a frame plated onto the microsystem is soldered to a corresponding structure on the substrate. This frame seals the rest of the chip from the medium interacting with the transducer. Using passive test chips we evaluate the performance of the new packaging method. Various underbump metal and solder deposition techniques were investigated. Both ceramic and flexible organic substrate materials were used. The combination Ni/Au bumps/InPb₄₀ solder/ceramic substrate showed the following mechanical and electrical parameters: For 98% of the tested chips, the helium leakage rate of the sealing frame surrounding the sensor is below the threshold of the used mass spectrometer (5 X 10^-7 Pa l s^-1). For flip-chip pads ranging from 200 to 300 mm square, the bump resistances are smaller than 2 m(Omega) . The approach, is illustrated with three successfully packaged MEMS for the measurement of humidity, gas flow, and volatile organic compounds, respectively. They all contain integrated readout circuitry providing digital output.

In this paper we present a silicon micromachined wet cell for use with a Love-wave liquid sensor. The Love-wave sensor is composed of an electronic amplifier and an acoustic Love- wave delay-line on a piezoelectric substrate. Together they form an oscillator. Liquid is placed in intimate contact with the Love-wave sensor; corresponding to its viscosity the acoustic wave velocity changes, which is observed through a change in the oscillation frequency. An issue that arises in a sensor of this type is that the input impedance of the interdigital transducers (IDTs) of the delay-line changes dramatically due to the dielectric properties of the liquid above them. This adds electrical load to the amplifier and affects the oscillator's performance by reducing its resolution and sensitivity. The electric loading of the IDTs by the liquid also leads to unwanted sensitivity with respect to the electrical properties of the liquid. The wet cell was designed to overcome this disadvantage. By virtue of this cell the liquid is directed only over the wave propagation path, and so the transducers are protected from the liquid's influence. In designing the cell, bubble formation in the liquid, chemical inertness, bonding aspects and temperature effects were all considered. The design utilizes a silicon micromachined channel that guides the liquid between the transducers. Furthermore a heater for controlling the temperature of the liquid has been incorporated. Experiments have shown that placing thin side walls of a silicon micromachined channel in the propagation path of the wave adds little to the insertion loss. Losses of only 6 dB or less were recorded, which confirms the suitability of this configuration. In addition to viscosity sensors this design can be applied to a broad range of Love-wave liquid sensors, including those in the biochemical area.

As the workhorse of the integrated circuit (IC) industry, the capabilities of CMOS have been expanded well beyond the original applications. The full spectrum of analog circuits from switched-capacitor filters to microwave circuit blocks, and from general-purpose operational amplifiers to sub- nanosecond analog timing circuits for nuclear physics experiments have been implemented in CMOS. This technology has also made in-roads into the growing area of monolithic sensors with devices such as active-pixel sensors and other electro-optical detection devices. While many of the processes used for MEMS fabrication are not compatible with the CMOS IC process, depositing a sensor material onto a previously fabricated CMOS circuit can create a very useful category of sensors. In this work we report a chemical sensor composed of bioluminescent bioreporters (genetically engineered bacteria) deposited onto a micro-luminometer fabricated in a standard CMOS IC process. The bioreporter used for this work emitted 490-nm light when exposed to toluene. This luminescence was detected by the micro- luminometer giving an indication of the concentration of toluene. Other bioluminescent bioreporters sensitive to explosives, mercury, and other organic chemicals and heavy metals have been reported. These could be incorporated (individually or in combination) with the micro-luminometer reported here to form a variety of chemical sensors.

Microacoustic sensors feature a number of benefits like real-time electronic readout, small size, robustness, high sensitivity, and cost-effective fabrication. For liquid sensing applications Love wave devices utilizing a surface bound shear mode are particularly well-suited. In this paper we discuss the crucial issues in the design of a Love wave device for the utilization in a smart liquid-sensor system, where special attention is paid to the interaction of the sensing device with the associated electronics and the influence of the adsorbing film used for biosensing applications.

We present a packaged single-chip microsystem for the detection of organic vapors. The sensor is fabricated using a 0.8 micrometers CMOS IC process provided by AMS Austria Mikro Systeme. Volatile organic compounds are detected by measuring the capacitance change of three polymer coated interdigitated capacitors due to analyte absorption. To protect the read-out circuitry from the organic vapors, the device is packaged using flip-chip technology. This technology allows for openings in the ceramic substrate for the sensing capacitors while hermetically sealing the remaining chip area. Measurements for different volatile organic compounds and chemically sensitive polymer layers are presented. The packaged microsensor array is a first step towards the realization of a small, low cost electronic nose on a single chip.

We present a chemical gas sensor based on a resonating cantilever beam in CMOS MEMS technology. The sensor is actuated employing electrothermal actuation. Thus, for a 300 micrometers long beam vibration amplitudes of 6.5 nm per mW heating power are achieved. The vibrations are detected with piezoresistors in a Wheatstone bridge scheme. Detection sensitivities above 200 (mu) V per mW heating power are measured with the bridge biased at 5 V. The beams have quality factors of up to 600. The static power dissipation that goes along with the electrothermal actuation scheme leads to a small temperature elevation of 0.3 K/mW of the sensitive area. The beams are coated with poly(etherurethane) as the sensitive layer. The layer thickness was determined by the change of the initial resonance frequency. Concentrations of octane, ethanol and toluene in synthetic air were measured. For toluene, concentrations as low as 250 ppm can be detected.

The paper reviews the architecture and design of low-cost high-performance sensor systems. These systems consist of a number of multiplexed sensor elements, sensor-specific front-ends, modifies and microcontroller or digital signal processors (DSPs). Important properties that act as focus points for the system design are: adaptability, accuracy, dynamic range, speed, power consumption, reliability and costs. To enable low-cost design and implementation, a universal set-up, using universal components, is used. Universal sensor interfaces with front-ends for resistive, capacitive, resistive-bridge sensing elements, as well as voltage-, current- and charge-generating sensing elements are discussed. The analog sensor signals are converted to analog signals in the time domain using period-modulated oscillators. The A/D conversion of the time-domain signal can be implemented in the microcontroller or DSP. It is shown that, also in this case, the principles of the sigma- delta converters can be applied. As an example the paper deals with a systematic approach to the design of reliable, high-performance low-cost capacitive sensors. The problems and their solutions of both the physical- and the electrical-signal processing are discussed. The examples consider the application of capacitive sensors in position detectors, liquid-level detectors and personnel detectors.

A low-cost smart measurement system for resistive (bridge) and capacitive sensors is presented and demonstrated. The measurement system consists of three main parts: the sensor element, a universal transducer interface (UTI) and a microcontroller. The UTI is a sensor-signal-to-time converter, based on a period-modulated oscillator, which is equipped with front-ends for many types of resistive (bridge) and capacitive sensors, and which generates a microcontroller-compatible output signal. The microcontroller performs data acquisition of the output signals from the interface UTI, controls the working status of the UTI for a specified application and communicates with a personal computer. Continuous auto-calibration of the offset and the gain of the complete system is applied to eliminate many nonidealities. Experimental results show that the accuracy and resolution are 14 bits and 16 bits, respectively, for a measurement time of about 100 ms.

Every oscillator contains an element which determines the frequency of the oscillator. A delay-line can be such an element. An oscillator which uses a delay-line puts specific demands on the electrical circuits needed in this oscillator. In this paper we look systematically at the parameters involved in the design of the electronic circuitry. In order to be able to do this properly we first determine the electrical behavior of an acoustical delay- line with the help of an equivalent circuit. Consequently we look at the parameters of the electronic circuit which are important for realization of a highly stable oscillator with special attention for the fact that the frequency determining element is a delay-line. With the help of this analysis we were able to find design criteria. According to this criteria we built actual circuits by using monolithic integration and measured them. The result of these measurements are given.

A digital readout electronics scheme in CMOS technology is described for integration with microelectromechanical sensors on the same chip. The readout criteria is general in nature and can be employed with a variety of analog sensors. The presented scheme in CMOS technology is fully integrable with the multiple sensor outputs either in a chain or an array format and is capable of detecting low analog output signals from a few (mu) V to mV range. The CMOS circuit design is compatible with +/- 1.5 V operation for low power consumption.

This paper describes a high-temperature (250 degree(s)C) pressure-transducer interface for resistive Wheatstone bridges. The long-term drift of the smart sensor, i.e., the (pressure) sensor plus its interface electronics, will be determined by the drift of the sensor only. A continuous three-signal auto-calibration sequence of the interface electronics keeps the transducer interface virtually free of long-term drift. A patented low-drift pre-amplifier forms an essential element in this system. The high-temperature operation of the transducer interface has been investigated from both an electronic and a packaging point of view. The system has been realized by combining CMOS ASICs with a thick-film packaging technology. The pressure-transducer interface works up to 250 - 275 degree(s)C with 15 - 16 bits accuracy.

Implementation issues represent an unfamiliar challenge to most control engineers, and many techniques for controller design ignore these issues outright. Consequently, the design of controllers for smart structural systems usually proceeds without regard for their eventual implementation, thus resulting either in serious performance degradation or in hardware requirements that squander power, complicate integration, and drive up cost. This paper summarizes previously reported results in the application of FPGAs to the realization of digital controllers for smart structures and reports ongoing effort to extend these results to multiple input, multiple output systems.

The MOSIS Service (located at the University of Southern California's Information Sciences Institute) offers a route to obtain custom designed, prototype quantities of ASICs, Multichip Modules (MCMs) and MEMs devices. Over the last few years the service added MIDAS (MCM Interconnect Designers Access Service) for MCM fabrication to the list of standard offerings. Thus a designer can now access domestic, high- volume IC and MCM production lines to obtain low-cost, prototype quantities of both. In addition custom MEMs fabrication is now supported in conjunction with the Microelectronics Center of North Carolina. This unique resource is available to all users including commercial, government and university. The low-cost environment exists via a multi-project environment, where users share the cost of NRE, masks, and fabrication. MOSIS takes care of front end foundry tasks such as data preparation and obtaining masks as well as placing the orders and delivering the finished product. This paper gives a brief overview of the MOSIS service. In addition, it provides an update of the technologies available including, flip-chip MCM fabrication and assembly, 0.35 micron CMOS, bare die bumping, and MEMs technologies.

Polarizers and polarization beam splitters are the most important devices in magneto-optical readout system. With a commercially available foundry polysilicon surface micromachining process (Multi-User Means ProcesS, or MUMPS) offered by MCNC (Mems Center at North Carolina), we have realized, on a single Si chip, an integrated polarization beam splitting system with a binary phase Fresnel lens for collimation. Polarization extinction ratios of 10 dB for the transmitted light and over 20 dB for the reflected light have been achieved. The whole system is prealigned using Computer-Aided Design on a Si substrate and is then lifted up perpendicular to the substrate after structure release.

This paper describes the design of a low-power photo-voltaic power converter which will be used in a directional hearing aid. It is argued, that the use of a switched-capacitor converter is needed when integration on a chip is demanded. This converter combined with a parallel power converter has an efficiency that lies between 70% and 85%. This efficiency depends on the charging voltage of the implemented rechargeable thin-film lithium-ion battery. This battery will be glued at the back side of the power-converter chip. The converter is controlled by a maximum-power-point-tracker to perform maximum charging of the battery under the varying conditions of the solar cell. The controller is adapted to operate with a switched-capacitor converter. This paper also shows a structured derivation of the necessary solar cell area. The complete power converter has been designed in a custom CMOS process and the major part of the circuit operates in the sub-threshold area.

An acoustic emission (AE) sensor has been developed by Honeywell Technology Center for avionics, industrial control, and military applications. The AE sensor design is based on an integrated silicon microstructure, a resonant microbeam with micron-level feature size, and frequency sensitivity up to 500 kHz. The AE sensor has been demonstrated successfully in the laboratory test environment to sense and characterize a simulated AE even for structural fatigue crack monitoring applications. The technical design approach and laboratory test results are presented.

The integration of MEMS, SAW devices and required microelectronics and conformal antenna to realize a programmable wireless accelerometer is presented in this paper. This unique combination of technologies results in a novel accelerometer that can be remotely sensed by a microwave system with the advantage of no power requirements at the sensor site. The microaccelerometer presented is simple in construction and easy to manufacture with existing silicon micromachining techniques. Programmable accelerometers can be achieved with splitfinger interdigital transducers (IDTs) as reflecting structures. If IDTs are short circuited or capacitively loaded, the wave propagates without any reflection whereas in an open circuit configuration, the IDTs reflect the incoming SAW signal. The programmable accelerometers can thus be achieved by using an external circuitry on a semiconductor chip using hybrid technology. The relatively small size of the sensor makes it an ideal conformal sensor. The accelerometer finds application as air bag deployment sensors, vibration sensors for noise control, deflection and strain sensors, inertial and dimensional positioning systems, ABS/traction control, smart suspension, active roll stabilization and four wheel steering. The wireless accelerometer is very attractive to study the response of a `dummy' in automobile crash test.

In this paper we present a stacking technology for an integrated packaging of an intelligent transducer which is formed by a micromachined silicon transducer and an integrated circuit chip. Transducer and circuitry are stacked on top of each other with an intermediate chip in between. The bonding of the transducer and the intermediate chip is done by flip chip solder bump bonding. The bonding between the above two-layer stack and the circuit chip is done by conductive adhesive bonding combined with gold studs. We demonstrate the stacking technologies on passive test chips rather than real devices and report on technological details.

We propose the utilization of a Smart In-Package [Micro] ALigner (SIMPAL) to enable fiber optical sensors for thick walled composite structures. Fiber optic coupling is the barrier preventing single mode and multimode fiber optical sensors systems from being incorporated into composite structures. A fiber optic connector that has a MEMS in-package micro aligner, integrated optical detectors, and control electronics is proposed to overcome the incompatibility between structural manufacturing tolerances and fiber optic alignment tolerances. The SIMPAL technology will enable affordable optical connection with sub-micron alignment tolerances to be made after the fiber optics are machined off at the egress point during a standard trimming process. We have demonstrated and described the MEMS actuator part of the SIMPAL. This active part is a 3-axis active fiber optic micro-aligner small enough to fit into current electro-optical packages. The micro-aligner is fabricated on a silicon wafer with the high aspect MEMS/LIGA process technology. The electrically controllable actuators demonstrate the high force and displacements necessary for in-package alignment of a micro-optics. The integration of lenses, optical sensors and control electronics is proposed to realize a smart optical backplane interconnect system.

This paper discusses the design, fabrication and testing of a surface micromachined Counter-Meshing Gears discrimination device which functions as a mechanically coded lock. A 24 bit code is input to unlock the device. Once unlocked, the device provides a path for an energy or information signal to pass through the device. The device is designed to immediately lock up if any portion of the 24 bit code is incorrect. The motivation for the development of this device is based on occurrences referred to as High Consequence Events. A High Consequence Even is an event where an inadvertent operation of a system could result in the catastrophic loss of life, property, or damage to the environment.

Optically/electrically operable flexible film microactuators that can offer up to two orders high efficiency of photonic to mechanical conversion compared to ceramic actuators are conceptualized. A polarized ceramic wafer of non- centrosymmetric perovskite ferroelectric ABO₃ compounds, such as lead lanthanum zirconate titanate (PLZT), when exposed to an illumination (approximately 350 to 400 nm wavelength) close to the bandgap energy, can generate a large photovoltage (approximately 1.0 kV/mm) across its length, and by the inverse piezoelectric effect cause the piezoceramic wafer to deflect in the direction away from the illumination. The optical actuation effect in piezoceramic wafers is investigated as a function of thickness, composition, and surface roughness. Such flexible microactuators would enable a new generation of micro- electro-mechanical and micro-opto-mechanical systems where the actuation will not be restricted by the clamping effect due to the rigid substrate as in the current silicon based micromachined structures. To deposit the piezoceramic film directly onto a flexible substrate, the substrate must have high temperature stability, high strength (Young's Modulus approximately 4.9 X 10¹⁰ N/m²), a close match of thermal coefficients of expansion with the piezoceramic film, and a tailorable crystal orientation in order to provide a desired template for growth of oriented PLZT. This paper also presents a comparison of a variety of flexible substrate films and fibers and our recent results on polybenzoxazole (PBO), a polymeric candidate for a flexible high temperature substrate. Variation of the properties of PBO as a function of temperature are also presented.

The accuracy of piezoresistive based silicon sensors is partially determined by the uncertainty in the piezoresistive coefficients. In the production of sensors it is therefore desirable to measure the coefficients for the used technological process to avoid costly calibration of the sensors after production. A practical measurement method consists of bending a three-element rosette. The resulting resistance changes are used to calculate the independent piezoresistive coefficients (pi) ₁₁, (pi) ₁₂, and (pi) ₄₄. A recognized problem of this method are the large uncertainties in the smallest calculated coefficients. These uncertainties arise partially from errors in the resistance measurements. This paper shows that the calculation of the coefficients is very sensitive to the measurement errors. This sensitivity is especially pronounced if there are large differences in magnitude between (pi) ₁₁, (pi) ₁₂, and (pi) ₄₄, such as in p-type silicon. It appears, however, that the error sensitivity can be greatly reduced by optimizing the rosette orientation in the (001) crystal plane. For a p-type silicon rosette the optimum orientation is k*(pi) /2 (k equals 0, 1, 2,...) with respect to the [100] axis. Orientation along these angles may result in a reduction of the uncertainties up to a factor 48.

The LIGA process is being further developed to fabricate large surfaces covered with high aspect ratio microstructures (HARMs). A HARM is defined as a structure hundreds of micrometers in height and with a height and with a height/characteristic lateral dimension which is five or greater. The molding step of the LIGA process provides one method to rapidly and inexpensively fabricate HARM-covered sheets. Molding experiments were performed to determine combinations of processing parameters which produce high quality, high density polyethylene HARMs. In addition to developing an inexpensive process to manufacture HARMs, uses for HARM-covered sheets are being investigated. One example is heat transfer enhancement. Microfins were added to the surface of a cylinder and experiments quantified their effect on the rate of convective heat transfer for a cylinder in crossflow.

For the production of conductive structures in insulating ceramics UV excimer laser radiation is often used in two- step processes first to activate alumina, while the metal deposition is carried out subsequently from special solutions for electroless metal plating. An alternative process for obtaining conductive traces in alumina surface has been reported recently. However, the resulting conductivity is still far from the values required by fast progresses in packaging technology. In this paper the modification process is investigated with respect to the ability of the selectively laser-modified, alumina to promote electroless metal deposition. This is of basic interest because sources of CO₂ radiation are more stable and easier to handle in comparison to sources of excimer radiation. Moreover the described process can be considered as an alternative way of alumina activation. It is shown that alumina treated with cw CO₂ laser radiation under an ethanol layer takes on the ability to reduce Cu from its electroless plating bath which permits to significantly increase the conductivity of the laser- modified conductive tracers.

The sensitivity of the chemical sensor, based on the resistance change of Al₂O₃-doped and SnO₂-doped ZnO (ZnO:Al and ZnO:SnO₂) thin film, is studied for exposure to various gases. It is found that the ZnO:Al and ZnO:Sn thin film chemical sensor has a high sensitivity and excellent selectivity for amine (TMA and DMA) gas and ethanol gas, respectively. The ZnO:Al (5.0 wt%) thin film chemical sensor which exhibit a high sensitivity for exposure to odors from rotten sea foods, such as salmon, sea bream, oyster, squid and sardine, responds to the freshness change of these sea foods. The ZnO:SnO₂ (78 wt%) thin film chemical sensor which exhibit a high sensitivity for exposure to aroma from alcohols, such as wine, Japanese sake, and whisky, responds to the freshness change of these alcohols.