We review selected micro- and nano-systems developed recently at the Physical Electronics Laboratory of ETH Zurich using industrial CMOS technology in combination with post-processing micromachining and film deposition: (1) an infrared sensor microsystem for presence detection of persons, (2) calorimetric, capacitive, and gravimetric chemical sensor microsystems for detection of volatile organic compounds in air, and (3) a parallel scanning AFM chip. The microsystems combine sensor structures and read- out circuitry on a single chip.

The military market drives the thrust for the development of robust, high performance MicroElectroMechanical Systems (MEMS) devices with applications such as: competent and smart munitions, aircraft and missile autopilots, tactical missile guidance, fire control systems, platform stabilization, smart structures with embedded inertial sensors, missile system health monitoring, aerodynamic flow control, and multiple intelligent small projectiles. Army missile applications will be a fertile market for MEMS products, such as MEMS-based inertial sensors. MEMS technology should significantly enhance performance and provide more robust mission capability in applications where arrays of MEMS devices are required. The Army Aviation and Missile Command Missile Research, Development, and Engineering Center is working diligently with other government agencies, academia, and industry to develop high performing MEMS devices to withstand shock, vibration, temperature, humidity, and long-term storage conditions often encountered by Army missile systems. The goals of the ongoing DARPA MEMS technology programs will meet a significant portion of the Army missile systems requirements. In lieu of presenting an all-inclusive review of Army MEMS applications, this paper addresses a number of opportunities and associated challenges for MEMS systems operating in military environments. Near term applications and the less mature, high-risk applications of MEMS devices are addressed.

Diaphragm pressure sensors based on silicon micro-machining have advantages of small size and integrability with control electronics to form efficient MEMS applications. In this paper analysis of diaphragm based pressure sensors are presented by deriving the displacement function. Governing equations for individual diaphragms are given followed by analysis of a systems of two coupled diaphragms. Coupled mode theory is used to analyze the two diaphragm pressure sensor by expanding the combined mode fields in terms of individual modes of the single diaphragms. Results are presented for typical diaphragm parameters. Results indicate that coupled diaphragm sensors can be more efficient than single diaphragm sensors.

A digital readout design in CMOS technology is described for monolithic integration with microelectromechanical capacitive sensors using on-chip variable sense capacitor arrays with resolutions of 2.5 fF, 10 fF and 40 fF, respectively. The designed circuit produces a 4-bit digital readout proportional to the capacitive difference between the sense and the reference capacitors. The CMOS digital readout is compatible with +/- 1.5 V operation for low power consumption, uses a +1.5 V reference voltage with a switching speed of approximately 100 kHz. The digital readout design presented here is quite general and can be used in a wide variety of analog microsensors on the chip.

Gas sensors fabricated using conventional silicon microtechnology can suffer from a number of significant disadvantages when compared with commercially available thick-film, screen-printed devices. For example, platinum gate MOSFET devices normally operate only at a temperature of up to 180 degree(s)C and this limits the catalyst activity, and hence their sensitivity and response time. In addition, the fabrication of an integrated, resistive heater poses interesting problems; thus whilst polysilicon heaters are CMOS compatible, they tend to suffer from non-linearity, poor reproducibility and stability; whereas platinum resistive heaters are incompatible with a CMOS process and thus difficult and expensive to manufacture. Here we propose the use of SOI technology leading to a new generation of high-temperature, silicon smart gas sensors (patent pending). Numerical simulations of an n-channel MOSFET structure on a thin SOI membrane have been performed in non- isothermal conditions using a MEDICI simulator. Our results demonstrate that SOI-based devices can operate at temperatures of up to 350 degree(s)C without causing a problem for neighboring CMOS I.C. circuitry. The power consumption of our SOI-based designs may be as low as ca. 10 mW at 300 degree(s)C and so compares favorably with previously reported values for non-SOI based silicon micromachined gas sensors. In conclusion, SOI technology may be used to fabricate novel high-temperature, micropower resistive and catalytic-gate MOSFET gas/odor sensors. These devices can be fabricated in a standard SOI CMOS process at low unit cost and should offer an excellent degree of reproducibility. Applications envisaged are in air quality sensors for the automotive industry and odor sensors for electronic noses.

In recent years Micro Electro mechanical systems (MEMS) and micro opto electro mechanical systems (MOEMS) have grown in importance, especially in smart structure applications. In this paper a theoretical comparative study is made analyzing three different types of micro pressure sensors. MEMS type pressure sensors of the piezo-resistive and capacitive type are considered along with MOEM pressure sensor of the Fabry- Perot interferometric type. It is found that piezo resistive and capacitive pressure sensors in the micro form attain improved noise performance as compared to their bulk counterparts. The opto-mechanical sensors shows better noise performance than the capacitive sensor, when the limiting noise is due to Brownian motion.

Compliant mechanisms are monolithic mechanical structures that rely on elastic deformation to generate sophisticated mechanical functions. This paper presents an overview of mathematical procedures employed for designing compliant mechanisms. The paper outlines: (1) topological synthesis-- which involves generation of a functional design in the form of a feasible topology starting from input/output force/motion specifications, and (2) size and shape optimization--to meet performance requirements. Some examples of compliant MEMS are also presented.

Nature provides many examples of organisms capable of attaching themselves to other organisms. Seeds and some parasitic insects, for example, have attachment mechanisms that allow them to remain undetected for long periods of time. Such properties may be useful in military and law enforcement tagging situations, where one desires the discrete placement of an active or passive device on an unwitting host. This paper describes the development of 3D micro-scale burrs, that can readily attach to clothing, and are capable of opening the door to new methods of tracking. With the development of bulk micro-machining techniques such as LIGA and MEMS the ability to develop such a carrier taggent has arisen. 3D micro-scale burrs, made of electrodeposited nickel, have been developed using the LIGA process and have been tested for use as carriers for micro- sensors and emitters both active and passive.

Processing technique for fabrication of high-aspect ratio structures in PZT is developed in this work using deep X-ray exposures at the CAMD synchrotron storage ring. Arrays of posts were successfully fabricated in PMMA mold as thick as 2700 micrometers and with aspect ratio as high as 15. This LIGA- like technique allows fabrication of structures of shapes and sizes not possible with standard techniques using bulk PZT material or by the existing thin film techniques for PZT deposition. The process shows promise for various applications including high resolution medical imaging and optical projection.

We propose a novel method to create various 3D arrangements of particles. In suspension such as an uncured polymer containing particles, the particles are aligned parallel to an imposed electric field, which are called particle chains, only on micro pillars of metal preformed at intended positions on a flat electrode due to an intensified electric field. The 2D arrangements of the 1D chains lead to the 3D arrangements of the particles. After the formation, the polymer is cured by heating in the electric field to stabilize the arrangements. According to this method, we succeed in making arrangements of glass beads with a diameter of 30 micrometers in silicone elastomer.

A new powder particle beam drawing apparatus is being developed in order to realize a solid free-form fabrication using a focused powder particle beam. The powder particle beam drawing apparatus was constructed of a powder particle injector, a powder particle beam gun, a beam deflector and focusing lenses. The powder particle injector supplies micro-sized powder particles of 0.1 to 100 micrometers gradually and continuously from a powder particle reservoir to a powder particle beam gun. The powder particle beam gun generates the beam of highly charged powder particles. The powder particles draws lines and figures on substrates through the beam deflector and focusing lenses. Preliminary experiments were carried out using carbon powder particles of 10 micrometers size. It was possible to focalize the beam size within 500 micrometers diameter and draw lines using the beam. These results suggests that the powder particle technology can be applied to fabrication processes of micro-electronics devices and micro-machines.

The development of improved implantable devices and materials require knowledge of their in vivo behavior. However, little is known about the actual loads borne by implanted devices in vivo. Direct load measurement would provide extremely valuable information, for the improvement of device designs, and for the rapid rehabilitation of individuals in which devices have been implanted. Multichannel telemetry systems, combined with strain gauges, can provide this information.

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 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' below the surface of a graphite composite plate. It also describes the progress to date of the sensor system itself.

The main objective of this paper is to demonstrate the capability of using wireless telemetry system for MEMS-IDT based sensors for sensing of various physical parameters. The system is based on a growing technology in the area of piezoelectric devices such as Surface Acoustic Wave (SAW) Devices. A wireless telemetry system is designed and developed to operate with the MEMS-IDT sensor. A miniature rectangular loop antenna is designed and constructed for integrating directly to the sensor. An impedance matching network is incorporated in the system to match the input and out put impedance and the performance is evaluated. It is observed that an improvement of 15 dB in signal strength due to the impedance matching network. This MEMS-IDT sensor is designed to provide quite complex signal processing functions within a very small package. This creates a great advantage in today's world where reduction in size is of utmost importance. Because SAW devices are most commonly fabricated on semiconductor substrates, microfabrication facilities are ideal for mass production can substantially reduce costs.

Recently, singly curved smart antennas that have the ability of changing their reflector shape through the use of piezoelectric actuators have been studied. The results show that those antennas have the ability to steer and shape radiation patterns in the far-field. As an extension of the previous work, this study examines the use of `doubly curved'--spherical--antenna structures to achieve better performance in controlling an antenna's coverage area. The spherical antenna is made of a thin plastic shell with a small hole at the apex for base mounting. As actuators, four PZT strip patches are attached along the meridians separated by 90 degrees respectively. The antenna structure is modeled following Reissner's shallow spherical shell theory, and the forces developed by the PZT actuators are applied as the boundary conditions at the outer edge. The deformed shape of the antenna is calculated with respect to the applied voltage and the far-field radiation pattern for the shape is simulated on the computer. Based on the theoretical work, an actual working model of the doubly curved antenna is built. Several experiments with the model verify that the beam steering and beam shaping mode can be achieved in the real situation.

Wireless Integrated Network Systems (WINS) provide distributed network and Internet access to sensors, controls, and processors that are deeply embedded in equipment, facilities, and the environment. The WINS network is a new monitoring and control capability for applications in transportation, manufacturing, health care, environmental monitoring, and safety and security. WINS combine microsensor technology, low power signal processing, low power computation, and low power, low cost wireless networking capability in a compact system. WINS networks will provide sensing, local control, and embedded intelligent systems in structures, materials, and environments. This paper describes the WINS architecture and WINS technology components including sensor interface and WINS event recognition systems.

With Q's in the tens to hundreds of thousands, micromachined vibrating resonators are proposed as IC-compatible tanks for use in the highly selective filters of communications subsystems. To date, bandpass filters consisting of spring- coupled micro-mechanical resonators have been demonstrated in a frequency range from HF to VHF. In particular, two- resonator micromechanical bandpass filters have been demonstrated with frequencies up to 35 MHz, percent bandwidths on the order of 0.2%, and insertion losses less than 2 dB. In addition, free-free beam, single-pole resonators have recently been realized with frequencies up to 92 MHz and Q's around 8,000. Evidence suggests that the ultimate frequency range of this high-Q tank technology depends upon material limitations, as well as design constraints--in particular, to the degree of electromechanical coupling achievable in micro-scale resonators.

The integration of MEMS, IDTs (Interdigital Transducers) and required microelectronics and conformal antenna to realize a programmable accelerometers and gyroscopes suitable for inertial navigation is presented in this paper. This unique combination of technologies results in novel conformal sensors that can be remotely sensed by a RF system with the advantage of no power requirements at the sensor site. The sensors presented are simple in construction and easy to manufacture with existing silicon micromachining and stereo lithography techniques. Programmable sensors 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 and gyroscopes can thus be achieved by using an external circuitry on a semiconductor chip using hybrid technology.

Prototype remotely queried embedded microsensor devices were installed on two US Navy platforms to verify the robustness of the transponder circuitry to survive in operational environments. Devices were installed on the Advanced Enclosed Mast/Sensor System aboard USS Radford in May 1998. These devices are in the high EMI environment of the SPS-40 radome. The devices were checked after deployment in October and were functioning normally. Devices were also installed on the Boeing AV-8B Harrier T1 aircraft and have successfully survived the vibration, temperature and acoustic noise environment of flight operations. These devices remain installed on these platforms and will be periodically checked to determine the suitability of the transponder circuitry for long term operation.

The design and experimental investigation on electronically tunable microstrip antenna is presented in this paper. These observations have been made as a first step towards the realization of an electronically tunable microstrip antenna taking advantage of the voltage tunable dielectric substrate. It is already established that the change in dielectric constant of Barium Strontium Titanate (BST) substrate material is more than 50% depending on the stoichiometric composition of BST and the biasing voltage. Microstrip patch antennas were printed on the tunable substrate and radiation performance was studied for different bias conditions and frequency tuning has been demonstrated. The operating frequency of the antenna is found to be changed by varying the applied dc voltage. Electronic steerability of the antenna array is possible by incorporating the BST phase shifters in antenna configuration.

This paper presents a new design of micromachined optical rotating sensor (ORS). The concept demonstration prototype shows that the sensor will be low cost, small and reliable. To obtain a micro ORS, a ring resonator was designed, based on the three-layer polysilicon surface micromachining process. The ring resonator is made up of three micro mirrors and a laser diode coated with an anti-reflective coating. The micro ORS relies on the Sagnac effect for its operation. The resolution analysis and sensor design is presented here, and the signal processing and control system design is discussed. The theoretical resolution is in the range of 1 - 6 deg/h.

A miniature ultrasound scanner has been constructed using a MEMS actuator called an Integrated Force Array. A second type of actuator called a Spiral Wound Transducer (SWT) is under development and shows significant promise for this application. Both the scanner and SWT will be discussed.

The surface micromachining process realized the dual-axis micro gyroscope. The 7.5 um-thick polysilicon layer deposited by LPCVD is used for the resonating structure. In this research, we report a new angularly actuated structure which detects the two-input angular rates simultaneously. One-chip is cheaper and smaller than using two gyro chips orthogonally-configured for the detection of two-input axis angular rate.

The main idea of the present work is to combine in the same film different enzymes and pH sensitive organic dyes in order to form an optical transducer. Decomposition of substrate molecules, catalyzed by enzymes, usually accompanied by pH changes in local surrounding, which can be registered by spectral transformations of indicator molecules. This idea was realized by using cyclo- tetrachromotropylene (Chromo1) as an indicator and an enzyme, such as Urease.

We present on-chip signal conditioning circuitry for the first parallel scanning Atomic Force Microscope sensors fabricated in industrial CMOS technology. The system combines, on a single chip, (1) two cantilevers for parallel scanning, (2) thermal actuators for independent deflection of the two cantilevers, (3) sensors to measure the deflection and (4) offset compensation and signal conditioning circuitry. It was fabricated using the 2.0 micrometers CMOS process of Austria Mikro Systeme and CMOS compatible post-processing micromachining. Scanning images were successfully acquired in contact and dynamic mode. The resolution of the recorded tapping mode images is better than 20 angstroms.

Smart structural systems require the electronic control systems which are integrated into the structures to be small, light weight and power-efficient. The Field Programmable Gate Array (FPGA) is a good platform to implement such controllers. In our previous work FPGA-based digital controllers were built and tested on a cantilevered beam. In order to implement multivariable controllers, the hardware resources for FPGA-based architecture need to be further reduced. Distributed Arithmetic (DA) has long been proven to be a very efficient means to mechanize computations that are dominated by inner products involving constant multiplicand. The computational requirements of the smart structural controllers match this type very well. In this paper various DA structure controllers are designed and results are compared with multiply-and-accumulate structure controllers. Single- and multi-variable controllers are implemented and tested on a cantilevered beam.

A design for an equivalent electric circuit of three-layered piezoelectric bimorph is presented. The piezoelectric bimorph is modeled as a beam in which only bending deformation can be induced; thus, its end deflections and rotations are considered the ports of the equivalent electric circuit. The electromechanical impedance parameters of the equivalent electric circuit, which has a single electrical and four mechanical ports, are found.

This paper describes an implementation of self-diagnosis and self-calibration strategies in a microcontroller-based distributed intelligent sensor system for environment monitoring. Two different areas of interest have been considered, namely water and air quality, where ion selective electrodes and thermal conductivity gas detectors, respectively, are used as the sensing elements.

This paper presents the conceptual design, fabrication and experimentation of a Love wave based acoustic ice sensor for sensing the phase change from liquid water to solid ice. The sensing of this transition is made possible by the shear horizontal nature of Love waves, utilizing it's damped to undamped nature during the transition from water to ice respectively.

This paper discusses sensor IC design and packaging approaches, sensor networks architecture and communication protocols, as well as current and future applications of a series of transducers which we have developed in order to address several of the unmet needs of sensing and closed loop control of smart structures and organism-like machines of the future. In particular, the approach described therein has been used to design and manufacture sensors tailored for the measurement of strain, rotation, displacement, pressure, vibration, flow, multi-axis fluid shear, multi-axis strain, tough, multi-axis acceleration, and sound. This paper describes a suite of networkable sensors designed to monitor the internal state of the system, such as strain and joint angle, as well as that of the environment and contact interface with the system, such as pressure, shear stress and contact forces and moments.

In this paper we review recent effort towards the development of both a smart tongue (the so-called `electronic tongue') and a smart nose (or so-called `electronic noise'). The difference being that the smart tongue operates within the solution under test, while the smart nose evaluates the nature of its headspace.

Conducting polymer films are employed as the active material in both resistive and acoustic waves gas sensors. Here we describe the use of an electroactive conducting polymer as the gate material in a gas-sensitive MOSFET sensor run at ambient temperature and compare it to a conventional catalytic metal gate MOSFET run at 180 degree(s)C.

We present a new method for discriminating organic vapors based on the variation of capacitance changes of an interdigitated CMOS capacitor with the thickness of the sensitive polymer layer. By carefully adjusting the thickness of the polymer layer, discrimination potential in addition to the chemical selectivity of the polymer is provided by the fact that the interdigitated capacitor signals depend on the layer thickness. At polymer thicknesses small compared to the center-to-center spacing of the electrodes, an increase in capacitance is observed for all analytes, whereas for thick layers, the direction of the capacitance changes depends on the dielectric constant of the analyte. Sensors can be designed to be insensitive towards a certain analyte by varying the polymer thickness. Measurements for volatile organic compounds using CMOS capacitors coated with different polymer thicknesses are presented to demonstrate the new way of increasing sensor selectivity.

Vapor detection has been realized by the shift of the whole surface plasmon resonance (SPR) curve under dynamic state of adsorption as well as by measuring SPR reflectivity signal at a fixed angle of incidence. Selective, fast and reversible adsorption of the vapor molecules has been observed. The increase of both film thickness and refractive index of spun films during adsorption are found to correspond to the calixarenes behavior and may be explained by capturing of guest molecules in the film matrix, followed by their condensation. A model of the vapor registration system has been established and we also report in this paper on the extent of the selectivity, thus leading to the establishment of a sensor array.

We present a novel composite sensing agent consist of calix[4]resorcinarene and the conducting polyorthomethoxyaniline and propose different sensing mechanisms that can take advantage of its nanoporosity and unique complexation reactions.

The Goodyear Tire & Rubber Company is evaluating the use of integrated MEMS (MicroElectroMechanical Systems) for tire pressure sensing applications in automotive, bus, truck, aircraft and military tire lines. This paper deals with the reasons for this and the vision we have of how this will be implemented.

Pressed PZT Piezoelectric disks were embedded in a range of materials and their properties monitored under a wide range of conditions. The output depends on the temperature and pressure exerted on the PZT by the surrounding material and by the mechanical impedance mismatch between the embedded PZT and the surroundings. By monitoring the `Q' of the PZT (the ratio of energy stored to energy dissipated) it was found that the PZT discs could be used as cure monitors, strain gauges, and as embedded dynamic mechanical property estimators. This latter property is a means of gauging the `health of the material', and its degradation with time. These sensors were part of the MTS/US Navy embedded sensor program, so the sensors could be addressed and read remotely. The techniques, the data and the applications are discussed in this paper.

Health monitoring of structural systems has gained a lot of interest in recent times. In this paper, we consider the wireless data acquisition for health monitoring of smart structures. Some of the work done towards development of micro sensors for wireless health monitoring of smart structures is presented. The concept of smart sensors is demonstrated with the help of commercially available micro controller and wireless Rx/Tx modules. Application of these smart sensors in health monitoring is also demonstrated on a laboratory set up. A subspace system identification method known as N4SID is used for getting the state space matrices of the nominal and the damaged systems. The concepts are demonstrated on simple test article. Finally, the future goals in the development of micro sensors are given.

Microsensors and Microelectromechanical Systems (MEMS) are currently being applied to the structural health monitoring of critical aircraft components. The approach integrates acoustic emission, strain gauges, MEMS accelerometers and vibration monitoring devices with signal processing electronics to provide real-time indicators of incipient failure of aircraft components with a known history of catastrophic failure due to fracture.

Fiber-reinforced composite materials are increasingly being used in the construction of advanced aircraft structures. The detection of damage in such materials is critical to ensure safe application. An in-situ structural health monitoring system, either embedded in the composite structure or surface-mounted, would permit the timely detection of damage in such structures. There has been much work reported on the application of, for example, piezoelectric and optical fiber sensing technology for the detection of composite damage. In this paper we outline our approach using silicon microsystem technology.