Gerhard Mader

Simulation, design and fabrication of electroplated acceleration switches

This paper describes the simulation, design and fabrication of acceleration switches for automotive applications. A simulation model is introduced which describes the dynamical behaviour of the sensor. The main focus of the development is on the specifications of the accelerometer, such as the switching time, the overload protection, the self-test feature and the damping behaviour. The simulated acceleration switches are fabricated with the use of a sacrificial layer technique and electroplated moulding of microforms. The 3D-UV Microform technology was preferred because it enables high aspect ratio patterning of commercially available thick photoresists. First devices of the microswitch sensors were characterized by means of optical measurement facilities for the determination of resonance frequencies and of the dynamical behaviour during test pulses. Measurements on a shaker were carried out to confirm the validity of the model.

Temperature and stress dependence of Young’s modulus in semiconducting barium titanate ceramics

In order to study the temperature and stress dependence of Young’s modulus in semiconducting barium titanate ceramics, the longitudinal sound velocity was measured at a frequency of 5 MHz in the temperature range of 20–180 °C. It is striking that at temperatures above the Curie point (Tc=120 °C) the sound velocity reaches values that are 10–20% higher than those at room temperature. Furthermore, a shift of the Curie point of about 2×10−8 K/Pa is observed if uniaxial stress is applied perpendicular to the sound propagation. Both effects can be understood by means of the phenomenological theory of Devonshire.

Quasianalog accelerometer using microswitch array

Abstract This paper describes the development of a quasianalog accelerometer which uses an array of acceleration switches. The investigations are based on results of fabricated and evaluated single-microswitch sensors. The new acceleration sensor concept combines the advantage of high EMI immunity and simple signal pre-conditioning circuitry. Important characteristics of the laterally moving cantilevers, such as resonance frequency and switching time, can be determined by a single mask. First test devices have been fabricated by the use of a special sacrificial-layer additive technology. This Microform technology combines UV patterning of very thick photoresist layers and moulding of the resulting patterns by electroplated metals. This technology is used for the fabrication of laterally driven microswitches, each having a different acceleration threshold. Under an applied acceleration, the cantilever beam deflects laterally and closes a contact with an electrode. With an electrode on each side of the cantilever, two directions of acceleration can be measured. A simulation model has been developed which enables the design of quasianalog sensors for different applications. Different layouts are created to investigate the basic characteristics. The simulation results are verified on a shaker using the fabricated test structures of a single-microswitch sensor.

Study of microscopic heat sources in semiconducting barium titanate ceramics

If high electric fields are applied to semiconducting barium titanate ceramics, the rapid temperature rise caused by power dissipation makes it difficult to separate the field dependence of the resistance from its temperature dependence. For that reason the microscopic temperature rise during a voltage pulse was calculated by a theoretical model for the heat production and the heat flow inside a single grain. In addition, the local temperature behavior was measured experimentally by means of an infrared radiometric microscope. The fast temperature rise during a voltage pulse (350 V/mm; 400 μs) and the cooling off immediately after the end of the pulse prove that there are significant heat sources at the grain boundaries. In ceramics with relatively large grains (30–60 μm) temperature differences up to 50 K within a single grain were measured.

Pyroelectric infrared sensor arrays based on the polymer PVDF

Abstract Within the group of pyroelectric materials, PVDF (polyvinylidene fluoride) not only has the advantages of a polymer (cheap, easy to process), it also yields a signal voltage of the same order of magnitude as conventional single-crystal lithium tantalate. Because of their low thermal conductivity, self-supporting PVDF films show a high spatial resolution which is important for sensor arrays. A four-element array and its directive diagram and measurements of signals produced by a moving human body are used to illustrate the directional selectivity of the various sensor elements. By evaluating directional motion, such arrays allow traffic monitoring and area supervision.

Physically Different Sensor Concepts for Reliable Detection of Side-Impact Collisions

This paper describes new concepts in order to detect side impact collisions. Based on the specific system requirements for side impact detection, two physically different concepts are described and compared to each other.Acceleration sensing principles, applied in todays single point sensing systems, were adapted to cope with the unique requirements for side collision detection. A more advanced and completely new concept is based on the sensing of the pressure change within the cavity of the impacted door. Based on these sensing principles, different system configurations are illustrated. The performance of both sensing principles is compared on the basis of available crash and misuse test conditions. It can be stated that the sensing principles support the rigid firing requirements of a timely airbag deployment. However, the selection of the system configuration and the physical sensing principle has to account for the individual deformation behaviour of the vehicles side structure. (A) For the covering abstract of the conference see IRRD 875833.

Photocapacitance characteristics of amorphous‐silicon Schottky diode sensor arrays and their changes due to the Staebler–Wronski effect

The capacitancemeasurements on a‐Si:H Schottky diodes reported in the literature refer to large‐area (some 10‐mm2) specimens and were carried out in the dark at frequencies typically around 10 Hz. The main interest in these publications is the determination of the density of states in the band gap. For linear photodetector array applications, however, interest centers around the voltage and frequency characteristics of the capacitance of small‐area back‐to‐back Schottky diodes under illumination and at frequencies typically around 1 kHz. But photoinduced changes in the capacitance are also of significance with a view to possible read‐out circuits and their long‐term stability. The capacitance was therefore measured over the frequency range 0.2–20 kHz and over the voltage range −5 to +5 V. Whereas the dark capacitance exhibited no changes due to photoinduced degradation, significant differences between degraded and nondegraded states were observed in the voltage and frequency characteristics of the photocapacitance. During degradation under high bias voltage (−5 V), the maximum of the capacitance shifted from −0.1 to +0.4 V indiumtin oxide bias voltage and the capacitance showed a distinct increase. The photoinduced changes observed for the photocapacitance characteristics could be minimized by ensuring that the elements adjacent to the sensor were at equipotential with the sensor. Full reversibility of the photoinduced changes due to thermal annealing could be verified. The changes of the C‐V and C‐ω characteristics can be explained by the occurence of the well‐known Staebler–Wronski effect.

Photoinduced degradation of reverse‐biased small‐area a‐Si:H Schottky barriers

Photoinduced changes (Staebler–Wronski effect) in the photocurrent and dark current of a reverse‐biased small‐area Schottky barrier made from amorphous silicon are investigated. The well‐known, small reductions in the photocurrent are contrasted with the large increases in the dark bias current. This behavior of the dark bias current is a new phenomenon and cannot be explained on the basis of a bulk mechanism. The indications are that even under high bias voltages recombination processes take place close to the interface and give rise to thermally reversible changes of the gap density‐of‐states. Special attention is paid to the bias voltage and wavelength dependence of the degradation effect. The results are discussed in qualitative terms.