M.F.K. Holm

Relaxation effects in high-voltage barium titanate nonlinear ceramic disk capacitors

Room-temperature capacitance-voltage-frequency measurements are reported for an 85-nF barium titanate high-voltage ceramic-disk nonlinear capacitor, intended for use in a power electronics turnoff snubber circuit. Bias-voltage excursions are from 0 to 1500 V DC, and the frequency responses are measured from quasi-DC to 1000 Hz. The observed C-V-frequency responses are modeled in terms of series-capacitance contributions from ferroelectric grains and p-n junction grain boundaries, involving 16 parameter variables. The ferroelectric capacitance terms are given by a modified Langevin function, and the grain-boundary capacitances are modeled by back-to-back p-n junction diodes on either side on an insulator boundary. The observed frequency dependence of the C-V response is attributed here to a Debye-type relaxation of the compensation regions at the grain boundaries, with time constant 15 ms. Good agreement between theory and experiment is obtained over the 0-1500-V bias range. >

High-permittivity ceramic dielectrics for tuning transmission in power electronic converters

The fabrication and application of high-permittivity ceramic materials for use in power electronic circuits are investigated. The ability to manufacture materials with a wide range of epsilon /sub r/ values and the influence of dielectric permittivity on the circuit behaviour of a converter employing planar connections are studied. It is shown conclusively that the circuit behavior of a power electronic circuit can be modified by only varying the properties of the materials used for supporting the connections. This mechanism can be used to improve the power transmission characteristics of the connections. Methods are described whereby the dielectric properties of BaTiO/sub 3/-based materials can be varied over a very wide range of 4<or= epsilon /sub r/<or=1300. The material is manufactured in the form of tiles that can be used to support connections, acting both as insulation and as a medium to help control circuit performance.<<ETX>>

Aspects of modeling of high voltage ferroelectric nonlinear ceramic capacitors

Experimental and theoretical studies are reported on the room temperature capacitance-voltage (CV) and (tan delta )-V response of a high-voltage barium titanate ceramic disc capacitor with prescribed nonlinear CV response, as fabricated for an intended power electronics application. The CV response was modeled in terms of a voltage-dependent series equivalent circuit incorporating grain-boundary junction capacitances and grain ferroelectric capacitances. A modified Langevin function was used to relate intergrain ferroelectric polarization, which yielded good agreement between theory and experiment for a 3-to-1 capacitance variation over the DC bias range up to 1000 V. >

High field capacitance-temperature behavior of BaTiO/sub 3/ ceramic disc capacitors

Experimental and theoretical studies are reported on the capacitance-temperature (CT) characteristics of an undoped BaTiO/sub 3/ high-voltage (1000 V) nonlinear ceramic disc capacitor with a 3.6:1 capacitance ratio over the DC bias voltage range, which has application to power electronics snubbers. CT responses for both the zero-bias and 1000-V-bias conditions are modeled in terms of the polarization of permanent dipole moments. High field modeling employed a modified Langevin function, incorporating an empirical domain sensitivity parameter together with a smeared Curie temperature. >

An integrated resonant DC-link converter, using planar ceramic capacitor technology

This paper presents a new approach to constructing an efficient integrated low profile DC/AC resonant link converter. The LC resonant circuit in the resonant DC-link converter is replaced by a planar integrated LC operating at high frequency and high power level, with an integrated passive voltage clamp. An extension of the capacitive bifilar winding of the integrated LC makes it possible to construct a very low impedance DC-link resonant busbar for the converter. Experimental results on a 3 kVA, 115 kHz prototype is presented.<<ETX>>

Development of large-area BaTi0/sub 3/ ceramics with optimized depletion regions as dielectrics for planar power electronics

High-voltage (500 V) barium titanate (BaTiO/sub 3/) ceramics are under development as compact high-permittivity dielectrics for planar structures in integrated power-electronic converters. Dielectric requirements include a high permittivity for meeting the dimensional constraints in converters, a high power-handling capability, low loss, and flat permittivity and tan/spl delta/ frequency responses up to 1 MHz. Dopant materials examined here focused on fine powders of Al/sub 2/0/sub 3/ and Al added during the sintering process. Best results were obtained by diffusion of externally-placed Al during the sintering cycle, with BaTiO/sub 3/ permittivities /spl epsiv//sub r//spl sim/1000, and loss tangents tan/spl delta/ </spl sim/4% over 1 kHz to 1 MHz. This paper describes fabrication and doping methods aimed at achieving such specifications. Electrical C-V testing up to 500 V on specimens of thickness 0.5-0.7 mm (with E-field intensities up to 10/sup 6/ V/m) was carried out using l-kHz bridge measurements, as well as in a power-electronic chopper circuit employing a BJT switch, and operating up to 500 V with pulse widths /spl sim/25 /spl mu/s and repetition rates /spl sim/4 kHz.

Manufacture, behaviour and modelling of BaTiO/sub 3/ nonlinear ceramic disc capacitors for high-voltage applications

The manufacturing and characterization of undoped, nonlinear barium titanate ceramic disc capacitors are discussed. The characterization of the capacitors includes the measurements of capacitance-voltage (C-V) response by means of a novel 1500-V quasi-DC charge/discharge circuit at room temperature and also as a function of temperature. Studies were made on the microstructure of the barium titanate ceramic material by means of scanning electron microscopy (SEM) analysis. The influence of oxygen flow during preparation on the density, capacitance, and nonlinearity of the ceramic material is reported. A model is proposed in which the high dielectric constant and nonlinearity of the ceramic material can be quantitatively explained by considering the material as containing an ensemble of randomly orientated domains. It is shown that temperature dependence of capacitance may also be explained with this model.<<ETX>>

Improving the frequency response of ceramic dielectrics for high power applications in power electronic converters

High-voltage (1000 V) distributed and lumped ceramic capacitors are under development for diverse applications in integrated power-electronics structures and systems for cost-efficient production. These applications range from systems involving new integrated packaging and manufacturing technologies such as for dc-dc converters, to optimal power-component designs such as in dissipative RCD turn-off snubber circuits for high-power transistor or thyristor switch protection. Their design requires an understanding of the interacting ferroelectric, grain-boundary, and space-charge mechanisms controlling the high-voltage and low-frequency response. This paper relates to an experimental and theoretical study of high-voltage (0 to 1000 VDC) acceptor-doped barium-titanate BaTiO/sub 3/ ceramic capacitors, for several possible uses in integrated power-electronic converters with flat voltage and frequency response up to 1 MHz. The paper includes interpretations, based on experiment, of the inter-dependence of (a) ferroelectric-grain, (b) semiconductor-compensation-insulator-compensation-semiconductor (n-c-i-c-n) grain-boundary, and (c) Debye space-charge contributions to capacitance, as functions of acceptor doping.

Observations on competing mechanisms governing the C-V responses of nonlinear ceramic capacitors

Ceramic capacitors with nonlinear C-V response find application in power-electronic snubber switching circuits at higher voltages. Here, the AC and in-situ switching C-V responses of commercial multilayer and high-voltage disc capacitors are compared in relation to their postulated ferroelectric grain and p-n junction grain-boundary contributions, with a view to optimizing component performance through an increased understanding of such interrelated mechanisms. >

Packaging of an integrated planar power passive module for a power electronics converter: a 1 MHz case study

Planar ferromagnetic and ceramic dielectric passive component-packaging technology can provide cost-effectiveness in the production of compact, efficient, structures for use in integrated power electronic modules operating at kW power levels. This paper describes the design of an innovative integrated planar passive module for use in a power electronic converter, for the transmission of 1 kW at 1 MHz. Here, the planar inductance in the design employed high-permeability (/spl mu//sub r/spl ap//1800) commercial type 3F3 ferrite E-core material. The planar constituent dielectric incorporated ceramic substrates of modified ferroelectric barium titanate (BaTiO/sub 3/), with relative permittivity /spl epsiv//sub r//spl ap/200. As described, this passive structure had an experimental power-handling capability of 1 kW (1.7 kVA), with a power density of 132 W/in/sup 3/ (8 W/cm/sup 3/) and operating efficiency of 87%.