Werner Langheinrich

Application of oxygen plasma processing to silicon direct bonding

Abstract R.f. plasma oxidation of silicon in the reactive ion etching (RIE) mode is investigated as a pretreatment for silicon direct bonding (SDB). An ‘active oxide’ is formed on the surface, which can be wetted by water rinsing. The result is good adhesion of the wafer pairs to be bonded. A bond strength of 1.3–2.7 J/m2, sufficient for assembling purposes, is already obtained at temperatures of 450 °C.

An analytical model of MAGFET sensitivity including secondary effects using a continuous description of the geometric correction factor G

An analytical model of the sensitivity of magnetic field-effect transistors (MAGFETs) is presented. The model includes secondary and parasitic geometric effects as well as operating point dependencies. In order to get a continuous mathematical description for the sensitivity, we introduce a continuous function for the geometric correction factor G. This description of G is not limited to MAGFETs and can be used for any magnetic device.

Measurement and modelling of sensitivity and noise of MOS magnetic field-effect transistors

Abstract The characteristics of magnetic field-sensitive split-drain MOSFETs (MAGFETs) have been experimentally measured. The sensitivity depends on the geometry and the operating point of the MAGFET. Particular attention is paid to the lateral parasitic conductance between the split drains. The equivalent spectral noise density of the magnetic flux density is measured. Additionally, a macro-model of the MAGFET has been developed for SPICE.

Contactless measurement of torque

This paper describes a micromechanical sensor for contactless detection of torque at rotating shafts. The sensor consists of a silicon chip and uses a magnetoelastic principle for measurement. A closed magnetic loop is formed by the sensor chip and a magnetoelastic layer which is applied to the shaft. The coil which generates the magnetic field and magnetic field sensors are part of the sensorchip. The general measurement concept as well as the optimization of the system using finite-element-modeling are presented together with details about the fabrication of the coils, the magnetic sensors and an analysis of measuring results of the first laboratory samples of the complete sensor.

Simulation of thermally induced package effects with regard to piezoresistive pressure sensors

Abstract Microsystems are on their way out of laboratories into production. One of these microsystems, a piezoresistive pressure sensor developed by Robert Bosch GmbH, is examined within this paper. Obviously, one can detect undesirable temperature effects resulting from the sensor package, which influence the electrical characteristics of the sensor. By means of finite-element modelling (FEM), a simulation of the temperature effects can be managed. It is also possible to search for alternative designs of the sensor package.

Signal processing for magnetic micro torque sensors

A novel type of signal processing for a magnetic micro torque sensor is described and simulated. The sensor principles are based on a soft magnetic core shaped as a yoke, two current-carrying coils, a soft magnetic amorphous ribbon with strong magnetostrictive properties that is fixed on a shaft, and at least two magnetic flux-density sensors. The sensor determines directly the change of permeability of the amorphous ribbon on the shaft. Nevertheless, the variation of the air gap between the sensor and the rotating shaft affects the measurement principle. Therefore, the magnetic flux density is measured at two positions, one at the face of the soft magnetic core and the other beside the face of the core in the area of the stray flux. The evaluation of these two flux densities yields the distance between the sensor and the shaft as well as the permeability of the amorphous ribbon. The problem arising with this practice is the determination of the sensitivity of the flux-density sensors. As the current-carrying coils are alternately operated in a common and a push-pull mode, the unknown sensitivities of the flux-density sensors do not affect the evaluation of the permeability of the amorphous ribbon on the shaft.

Contactless Measurement of Torque

Abstract This paper describes a micromechanical sensor for contactless detection of torque at rotating shafts. The sensor consists of a silicon chip and uses a magnetoelastic principle for measurement. A closed magnetic loop is formed by the sensor chip and a magnetoelastic layer which is applied to the shaft. The coil which generates the magnetic field and magnetic field sensors are part of the sensorchip. The general measurement concept as well as the optimization of the system using finite-element-modeling are presented together with details about the fabrication of the coils, the magnetic sensors and an analysis of measuring results of the first laboratory samples of the complete sensor.

Modelling of a micromachined torque sensor

Abstract A micromachined torque sensor head is presented. The torque is evaluated by using an amorphous ribbon fixed on a shaft and an NiFe yoke with exciting coils and CMOS MAGFETs underneath the pole pieces to detect the change in magnetic flux density caused by a torque applied to the shaft. The CMOS MAGFETs are positioned in the centre field and in the stray field. The magnetic circuit is modelled by transferring it into an electrical equivalent circuit. From the equivalent circuit two equations are derived for the magnetic flux density in the centre and stray fields. The coefficients of the polynomials are a function of the magnetic resistors. The magnetic resistors depend on the relative permeability μ r , the air gap d and the temperature T . For the thermal dependence of the sensor a first-order approximation for the ferromagnetic materials NiFe, Co 75 Si 15 B 10 and the CMOS MAGFETs has been used. Progress in the construction of the integrated yoke and coils is documented.