Abstract. RF transmission properties of human tissues were investigated in the frequency range from 50 MHz to 1 GHz. This work was motivated by the increasing interest in communication links between medically active implants and external interrogator units. We investigated theoretically and experimentally the transmission loss between an implant and an external interrogator unit. We assumed that due to the size of the implant a maximum area of only 1 cm2 is available for the printed circuit antenna. The size of the external interrogator antenna is less restricted. The maximum depth of the implant beneath the surface of the body was assumed to be 10 cm. For the simulations we took the dielectric properties of skin, fat and muscle as published in the literature. For the measurements, an artificial muscle dielectric proposed in the literature was used consisting mainly of a mixture of water, sugar and salt. In simulation and measurements the reactive part of the impedance of the antennas was compensated numerically. In simulations and measurements we obtained a transmission loss between 30 dB around 100 MHz and 65 dB around 900 MHz.

A reverse conducting IGBT in trench technology is presented. By this approach no carrier life time means are necessary to balance static and dynamic losses of the diode. The diode's p-emitter efficiency can be dynamically tailored by the applied gate voltage due to inversion charge carriers in the vicinity of the gate trench. This opens up the opportunity for a variety of gate control schemes with the aim of a charge carrier reduction before commutation thus reducing the recovery and the corresponding IGBT turn-on losses while the on-state diode losses remain low. A simple substitution of the IGBT and diode dies by the RCDC chips in the industry standard packages enables a significant increase of the power density (e.g. up to 30% for typical traction application) due to a thermal benefit given by lower thermal resistances as well as by a reduction of the dynamic losses due to special gate control.

The interpretation and evaluation of free carrier absorption experiments on SiC devices is essentially supported by computer simulations of the measurement process, which exploits the physical effect that the light absorption coefficient in a semiconductor depends on the electron and hole concentrations. Hence, the attenuation of a laser beam transmitted through a sample is an integral function of the local charge carrier density along the optical path. We investigated time-resolved absorption profiles in 4H-SiC pin-diodes in the high-injection regime at current densities of 100 A/cm². Based on "virtual experiments" we studied the factors limiting the spatial resolution or disturbing the absorption signal such as Fabry-Perot interferences.

We present an experimental equipment for studying the charge carrier distribution in the interior of bipolar 4H-SiC high power devices by means of laser absorption measurements. Since the light absorption coefficient in a semiconductor depends on the electron and hole concentration, the attenuation of a laser beam transmitted through a sample is an integral function of the local charge carrier density. In order to detect the tiny changes in the light intensity caused by the plasma-optical effect, a highly sensitive measurement set-up has been developed. Its crucial components are a low-noise blue laser and a high-speed and broad-band photo-diode amplifier circuit. Sample preparation is sophisticated and requires special care. We investigated charge carrier profiles in 4H-SiC pin-diodes in the high-injection regime at current densities between 175 A/cm² and 350 A/cm². The measured charge carrier profiles are in good agreement with computer simulations.

We simulated and measured the forward characteristics of 4H-SiC pin diodes in a wide temperature range from 300K to 700K. Our simulations are based on the stationary drift-diffusion model including a model for incomplete ionization of the dopants. Physically based models for Auger recombination and Shockley-Read-Hall recombination are used as well. For the mobility model the empirical relation of Caughey-Thomas is used. The model parameters to be calibrated in the simulation are the electron and hole minority lifetimes and the electron and hole bulk mobilities. Employing temperature-dependent carrier lifetimes we achieved very good agreement between simulations and measured data. For the temperature- and doping-dependent carrier mobilities we found that the best fit is obtained for a bulk mobility value much smaller than that suggested by standard parameters for 4H-SiC. With the calibrated parameters we simulated the internal carrier distributions for temperatures up to 700 K and for different carrier lifetimes.