C.K. Campbell

Experimental and theoretical characterization of an antiferroelectric ceramic capacitor for power electronics

Capacitance-voltage (C-V) measurements up to 800 VDC were made on a modified lead-zirconate (PbZrO/sub 3/) 20-layer multilayer ceramic (MLC) antiferroelectric power-electronic capacitor, with large energy-density storage capability. For these a precision impedance analyzer was used, in conjunction with a high-voltage capacitor dc-bias circuit configured for voltage-isolation from the analyzer input. A peak effective permittivity /spl epsiv/ /spl sim/ 4300 was derived at the capacitance peak of 133 nF at 400-V dc-bias, yielding an energy density storage of /spl sim/0.5 J/cc in the device volume of 0.022 cc. Modeling of the experimental C-V response was applied to three conceptual series-connected capacitance regions within each grain and grain-boundary region of the MLC. The equivalent capacitance component for the first region was derived from the voltage-dependent polarizations within a ferroelectric and/or antiferroelectric grain. This involved application of differing Langevin functions for modeling the ferroelectric and antiferroelectric polarizations. That for the second region related to the voltage and frequency dependence of the equivalent p-n junction capacitance at opposite sides of a grain-boundary and compensation-region, with Debye-type relaxation constants relating its frequency dependence. The third capacitance region was associated with the insulator-barrier region itself. Agreement between experimental and theoretical C-V-f responses was considered to be good, in view of the number of modeling parameters and variables employed.

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. >

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. >

Technology for integrated RF-EMI transmission line filters for integrated power electronic modules

To complement the planar technologies being developed for integrated power electronic modules, new designs and the possibility of integration is needed in the area of high power conducted RF-EMI filters. A proposal for a planar design compatible with these technologies is investigated. A discussion on the construction of the filter and the processes used is presented as well as the performance of a prototype.

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. >

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. >

Improved transmission-line attenuators for integrated power filters in the RF band

Differential mode electromagnetic interference (EMI) at radio frequencies (RF) in compact integrated power electronic converter modules-as due in part to semiconductor switching and structural electromagnetic coupling-can be suppressed by the use of lossy transmission line lowpass filters. A previously reported lowpass filter design for such a system employed a Cu-Al/sub 2/O/sub 3/-Ni-BaTiO/sub 3/-Ni-Al/sub 2/O/sub 3/-Cu lossy uniform width planar transmission line. where the low-permittivity Al/sub 2/O/sub 3/ ceramic wafer merely separates the Cu and Ni conductors. The higher-conductivity Cu conductors served to handle kW-level power frequencies. Above power frequencies, skin-depth restrictions cause current diversion from the Cu line into the inner segment of Ni-BaTiO/sub 3/-Ni that provides subsequent attenuation of milliwatt-level spurious RF interference. Velocity reduction due to the high-permittivity barium titanate (BaTiO/sub 3/) ceramic (/spl epsiv//sub r//spl sim/12,000) enabled compact integrated package size construction (e.g., 10 mm /spl times/1.5 mm /spl times/130 mm). With the aim of increasing the lowpass cutoff response slope, the current paper examines a prototype non-uniform (in width) planar Ni-BaTiO/sub 3/-Ni constituent attenuator segment. For ease of one-dimensional (1-D) ABCD matrix analysis, a four-section Ni-BaTiO/sub 3/-Ni planar attenuator-comprised of four cascaded uniform sections of decreasing step width-was fabricated as a first approximation to an exponential taper. While good agreement was obtained between the predicted and experimental responses of the reverse-connected (narrow-to-wide) attenuator up to about 30 MHz, the discrepancy between the experimental and theoretical forward-connected (wide-to-narrow) frequency responses is attributed here to three-dimensional current constrictions at step interfaces. It is postulated that this can be overcome by the alternate use of a linearly- or an exponentially-tapered line.

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%.