R. Chabicovsky

Wide range semiconductor flow sensors

Abstract Micromachined flow sensors based on thin film germanium thermistors offer high flow sensitivities and short response times. Using the controlled overtemperature scheme, the measurable air flow velocity ranges from ±0.01 to ±200 m/s and the response time to large step changes of the air velocity is less than 20 ms. In the constant power mode, a signal rise time of 1.6 ms has been demonstrated by the application of shock waves. An air flow measuring range from 0.6 ml/h to at least 150 l/h has been achieved, e.g. with a rectangular flow channel of 0.54 mm 2 cross-sectional area. Using a lookup table transformation, a linearized output signal can be obtained within 25 μs.

Development of miniaturized semiconductor flow sensors

Abstract Miniaturized flow sensors based on thin film germanium thermistors were developed offering high flow sensitivities and short response times. The thermistors are placed on a silicon nitride diaphragm carried by a silicon frame. Using the controlled overtemperature scheme the measurable airflow rate ranges from 0.6 to 150 000 cm 3 /h. In this paper we mainly report on the dynamic properties of the sensor. The response of the sensor to step changes of the heater power will be compared with its response to shock waves for both the constant power mode and the constant overtemperature operating mode. A simple arrangement for the generation of acoustic shock waves will be presented.

A novel miniaturized sensor for carbon dioxide dissolved in liquids

Abstract In this paper, we report on a thin film sensor for the detection of carbon dioxide dissolved in liquids with the attention focused on its use for clinical blood gas analysis. Carbon dioxide from the analyte penetrates into a hydrogel electrolyte through a gas permeable membrane and is chemisorbed on a rhodium working electrode. The concentration of CO2 collected by this way is determined by an amperometric measurement technique based on the inverse voltammetry.

A Novel Transepidermal Water Loss Sensor

Recently, a novel microsensor to measure the transepidermal water loss (TEWL) of the human skin has been developed. The sensor is based on an interdigital electrode system covered with a highly hygroscopic salt film. It is mounted inside a closed chamber arrangement in a distance of about 1.4 mm away from the skin. In this paper, the authors present a new method to evaluate and calibrate the sensor device. Different TEWL values are imitated by a variable humidity source. Furthermore, the very high sensitivity of the TEWL sensor is demonstrated. The output signal represented by the conductance of the sensor varies over six orders of magnitude in the relevant TEWL range between 2 and 60 g/(m2middoth)

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.

Packaging of a thin-film sensor for transepidermal water loss measurements

The water content in the superficial part of the human skin is one index to evaluate the skin health. In the past we have developed a packaging concept which brings a sensor chip carrying a comb-shaped electrode system into intimate contact with the skin. The electrical impedance between these electrodes can be used as a measure for the water content of the skin. However, we have recently found that the same sensor chip used with a slightly altered packaging concept can measure the transepidermal water loss (TEWL), which is another indicator for the skin health. In our paper we report on the interconnection and packaging technique of this advanced measuring system for the evaluation of human skin. Furthermore, we present some first measurement results. The basic structure of the sensor consists of a thin film interdigital electrode system deposited on a ceramic substrate by rf-sputtering. Thin wires are guided through funnel-shaped holes arranged in the center of the contact pads. A CO/sub 2/ laser with a wavelength in the medium infrared range is used to produce these holes. The wires are bonded to the contact metallizations by using conductive adhesives. In the case of TEWL measurements the sensor chip does not touch the skin. The chip is placed in a distance of a few millimeters away from the skin. The electrical impedance of the electrode system depends on the stream of water molecules emitted from the skin. This kind of measurement does not suffer from pollution of the sensor chip by the oily substances of the skin surface. Therefore, the results are more reproducible compared to classical skin impedance measurements.

Partial discharge current measurement in high permittivity dielectrics and their meaning for quality control

Dielectric breakdown is one of the major problems of dielectrics with high permittivity. There are several intrinsic factors affecting breakdown strength of BaTiO/sub 3/ such as porosity, grain boundaries, and domain wall instability. But in general, the dielectric breakdown is caused by partial discharge within pores and cavities in the insulating ceramic body. The permittivity in these enclosures is usually much lower than the one of the BaTiO/sub 3/ matrix. Therefore, under operation of the ceramic capacitor the voltage across the pores may exceed the gas breakdown threshold and causes partial discharge in the pores according to the Paschens law. Although, the momentary effect of these discharges typically caused by currents in the microampere regime is little, their meaning for the long-term reliability of the component is crucial. In this paper we describe a new experimental set-up for determination of partial discharge phenomena in BaTiO/sub 3/ capacitors. The partial discharge current is monitored using a bridge circuit containing two branches with the same nonlinearity. In this way the basic harmonics of the bias current can be suppressed and the sensitivity of the interesting current peaks due to partial discharge is increased. Using this set-up we demonstrate the impact of mechanical defects on the partial discharge inception field strength. Moreover, the same capacitors were analyzed by means of metallographic cross sections. The ceramic-structure and fractures in the dielectric body due to unfavorable process parameters during manufacturing are analyzed. As a surprising result we show that capacitors even with significant fractures do not necessarily exhibit partial discharge even at an electrical field beyond 2 kV/mm. For this reason we conclude that conventionally applied electrical tests are insufficient for quality control.

Development trends in the field of sensors

Sensors play a major role in automation, analysis and monitoring of processes. The use of planar technology (IC-technology or IC-compatible technologies) caused a break-through in the field as it allows the realization of small, highly reliable, and cost-efficient sensor devices. The field of microelectromechanical systems (MEMS) technology has matured in the last decade and at the moment the further miniaturization into the nanoscale range attracts a lot of attention. In this contribution we give an overview on current trends in the field of sensors, where three different sensor fields are discussed in more detail: (bio)chemical sensors, automotive sensors and gas sensors.ZusammenfassungSensoren haben bei der Automatisierung, Analyse und Überwachung von Prozessen eine große Bedeutung. Durch die mögliche Realisierung von kleinen, zuverlässigen und kostengünstigen Sensoren führte die Anwendung der Planartechnologie (IC-Technologie oder IC-kompatible Technologien) zu einem Durchbruch in diesem Gebiet. In den letzten zehn Jahren ist das Gebiet der mikroelektromechanischen Systeme (MEMS) gereift und die Miniaturisierung schreitet weiter in den Nanometerbereich voran. Im vorliegenden Beitrag geben die Autoren einen Überblick über gegenwärtige Entwicklungstrends auf dem Gebiet der Sensorik, wobei drei Bereiche herausgegriffen werden: (bio)chemische Sensoren, Automobilsensorik und Gassensorik.

Evaluation of a novel transepidermal water loss sensor

Recently we have developed a novel microsensor to measure the transepidermal water loss (TEWL) of human skin. The sensor is based on an interdigital electrode system covered with a highly hygroscopic salt film. In this paper we present a new method to evaluate and calibrate the sensor device. Different TEWL values are imitated by a variable humidity source. We demonstrate the very high sensitivity of our TEWL sensor. The output signal represented by the conductance of the sensor varies over six orders of magnitude in the relevant TEWL range between 2 and 60 g/(m/sup 2/h). Our precise calibration method is very important for the reliable medical diagnosis of skin diseases.

Cathode sputtered permalloy films of high AMR effect and low coercivity

The anisotropic magnetoresistive (AMR) effect of dc sputtered Ni 81%-Fe 19% films has been increased up to /spl Delta//spl rho///spl rho/=3.93% at 50 nm thickness. Investigations have been concentrated on the influence of the target current, the target-substrate distance, and of the temperature of both target and substrate material. As a function of the applied magnetic bias field, the easy axis coercivity of the permalloy film is between 100 A/m and 200 A/m due to induced anisotropy. The dc magnetisation curves represents an almost ideal Stoner-Wohlfarth behaviour with a hard axis coercivity between 0 and 20 A/m.