Stephan Voss

Anode Design Variation in 1200-V Trench Field-stop Reverse-conducting IGBTs

Reverse-conducting (RC) IGBTs with a monolithically integrated reverse diode are meanwhile available for soft-switching applications such as lamp ballast or inductive cooking as well as for hard-switching applications such as inverters in refrigerators, air conditioners or general purpose drives. In this paper, we present results on the electrical behavior of 1200-V RC-IGBTs designed predominantly for soft switching applications. Miscellaneous parameters of the RC- IGBT, namely its thickness, the field-stop profile and the p-emitter dose were varied under the additional constraint to improve the behavior also for more severe switching conditions.

Ionic transport in 0.2[XNa2O·(1−X)Rb2O]·0.8B2O3 mixed-alkali glasses

Mixed sodium–rubidium borate glasses with compositions 0.2[XNa2O·(1-X)Rb2O]·0.8B2O3 (X = 1.0; 0.8; 0.6; 0.4; 0.2; 0.0) were prepared from alkali-metal carbonates and diboron trioxide. The density ρ and the molar volume Vmol of the prepared glasses vary almost linearly with composition whereas the glass-transition temperature Tg shows a minimum between X = 0.2 and X = 0.4. Measurements of the electrical conductivity using an ac complex impedance technique have been performed between 5 Hz and 1.3 MHz over the entire composition range. The conductivity diffusion coefficient, Dσ, of the mobile alkali-metal ions was deduced from the electrical dc conductivity via the Nernst–Einstein relation. The diffusivity has a minimum and the activation enthalpy a maximum at X ≈ 0.4 indicating the mixed-alkali effect. Supposing an Arrhenius-type temperature dependence the activation parameters and pre-exponential factors were determined. The deviations from the Arrhenius function were also studied and found to be most pronounced around X = 0.2 to 0.4. The time-dependent isotherm of the diffusivity of 0.2Na2O·0.8B2O3 glass was investigated at about 40 K below Tg and attributed to the relaxation of the glass network.

Mixed-alkali effect in Na–Rb borate glasses: A tracer diffusion and electrical conductivity study

The ionic transport in a series of 0.2 [X Na2O·(1 − X)Rb2O]·0.8B2O3 glasses has been studied by measuring both the electrical conductivity of these glasses and the tracer diffusivities of 22Na and 86Rb as functions of composition and temperature. At constant temperature (380 °C) the tracer diffusivities of 22Na and 86Rb decrease monotonically with decreasing Na- or Rb-content, respectively. The tracer diffusivities as functions of the composition parameter X intersect near X = 0.2 (‘crossover composition’). This behaviour gives rise to a minimum in the conductivity which appears near X = 0.4. At the crossover composition X = 0.2 the diffusivities of 22Na and 86Rb are practically the same within the measured temperature range resulting in similar Arrhenius parameters. For each other investigated composition the Arrhenius parameters for 22Na and 86Rb diffusion differ significantly. Comparing the 22Na-diffusivity in the pure Na-borate glass with the corresponding conductivity diffusion coefficient calculated via the Nernst–Einstein equation from the measured conductivity yields a temperature-independent Haven ratio. In contrast, a temperature-dependent Haven ratio was found in the pure Rb-borate glass. In order to compare the tracer diffusivities in mixed-alkali glasses with their ionic conductivity we introduce a ‘common Haven ratio’ for the mixed-alkali glasses which coincides with the conventional definition of the Haven ratio for single-alkali glasses. On the Rb-rich side the common Haven ratio decreases with temperature for Na–Rb borate glasses (X = 0.2 and X = 0.4) similar to the Haven ratio in the pure Rb borate glass.

Mixed-alkali effect of tracer diffusion and ionic conduction in Na-Rb borate glasses as a function of total alkali content

Abstract The mixed-alkali effect is studied in Y [X Na2O · (1−X) Rb2O] · (1−Y) B2O3 glasses as a function of the total alkali content Y. To this aim the ionic transport in glasses with Y = 0.3 was investigated by impedance spectroscopy and by the radiotracer diffusion technique. The results are compared with data obtained earlier by our group on a glass system with Y = 0.2. In both systems the relative compositions X = Na/(Na + Rb) are varied from 0.0 to 1.0 in steps of 0.2. The dc electrical conductivity is higher in Y = 0.3 glasses than in Y = 0.2 glasses and exhibits a minimum in each system near X = 0.4. Also near X = 0.4 a pertaining maximum in activation enthalpy occurs being more pronounced for Y = 0.3 as compared to Y = 0.2. The glass-transition temperature Tg is almost identical for glasses with Y = 0.2 and 0.3 with a minimum near X = 0.2. The diffusivities of 22Na and 86Rb measured at a constant temperature (380 °C) show in both glass systems (Y = 0.3 and Y = 0.2) a similar dependence on the composition parameter X. The 86Rb diffusivity decreases exponentially with decreasing Rb content. The 22Na diffusivity decreases with decreasing Na content but reaches an almost constant plateau on the Rb-rich side. For each relative composition X the diffusivities of the two isotopes increase by nearly the same constant factor, when Y is increased from 0.2 to 0.3. In both systems 22Na- and 86Rb-diffusivities as functions of the composition parameter X intersect near X = 0.2 explaining the minimum in dc-conductivity. Composition dependent common Haven ratios were obtained by comparing the conductivity with the diffusion data.

Reduction of the temperature dependence of leakage current of IGBTs by field-stop design

In this paper we propose a new method to reduce the temperature dependence of the leakage current of IGBTs by reducing the temperature dependence of the anode-side current gain αpnp. The temperature dependence of αpnp can be reduced by using field-stop zones that contain doping atoms with deep levels in the band gap of silicon. We demonstrate how the temperature dependence of the leakage current is influenced when using deep-level donors instead of shallow-level donors in the field-stop zone.

Reverse Conducting IGBT - A new Technology to Increase the Energy Efficiency of Induction Cookers

This paper discusses the usage of reverse conducting IGBTs in resonant converters of single plated induction cooker appliances. At first, the technology of such IGBTs is introduced. In order to provide insight into the IGBT and to enable predictions of the IGBTs behavior in applications, a virtual prototype for SPICE simulators and a procedure to set up simulations of the induction cooker converter is presented. Measurements confirm the benefits of reverse conducting IGBTs in this application. It is shown that the latest generation of these IGBTs increases the efficiency of the system. This leads to a lower temperature increase during operation and allows the use of smaller heat sink for example.

Spreading-resistance profiling of silicon and germanium at variable temperature

We have developed the concept of variable-temperature spreading-resistance profiling (VT-SRP) for the characterization of electrical active impurities or defects in semiconductor crystals. Unlike conventional SRP systems, which are exclusively operated at room temperature, our home-built VT-SRP device allows for measurements at different temperatures typically ranging from 150 to 400 K. VT-SRP is able to combine the accurate resolution of an impurity depth profile with a determination of the predominant impurity-related electronic level in the semiconductor band gap. This feature was exploited on germanium crystals with diffusion-induced gold distributions. Another application concerns the depth profile analysis of foreign elements that occur in various defect configurations. This was demonstrated on Si samples diffused with sulfur or selenium since these impurities may be present as isolated atoms as well as pairs. Given the well-known energy levels of the two S or Se configurations in Si we were able to...

Use of 300 mm magnetic Czochralski wafers for the fabrication of IGBTs

As in other semiconductor industries, there is a strong trend to use larger wafer diameters for the fabrication of power devices. However, for wafer diameters above 200 mm float-zone (FZ) silicon which is traditionally used for IGBTs is not available. Therefore, there is a need to use silicon material which has been fabricated by the magnetic Czochralski (Cz) method to make use of 300 mm wafers for IGBT-production. As this material contains a relatively high concentration of oxygen, the influence of carbon/oxygen-complexes has to be taken into account. CIOI-complexes can be decorated with hydrogen atoms resulting in donor-like complexes. Particularly, the application of proton-irradiation for the doping of the field-stop zone results in a relatively high concentration of interstitial carbon which is continuatively associated with the generation of undesired donors.

High-temperature spreading-resistance profiling for the characterization of impurity distributions in n-type silicon

Abstract We have developed the technique of high-temperature spreading-resistance profiling (HT-SRP) for the characterization of electrically active impurities or defects in semiconductors. As a major feature, HT-SRP together with the well-established SRP method at room temperature combines the accurate resolution of an impurity profile with a determination of the defect states that control the electronic properties of the semiconductor. Some basic aspects of this technique are demonstrated on Si samples diffused with sulfur or selenium.