Voltage polarity dependent current paths through polycrystalline ZnO varistors

Hofstätter, Michael; Nevosad, Andreas; Teichert, Christian; Supancic, Peter; Dänzer, Robert

doi:10.1016/j.jeurceramsoc.2013.06.017

Cited by 12 publications

(7 citation statements)

References 23 publications

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“…With the grinded surface, just before cutting the active region (i.e., electrodes), lock‐in thermography (Infrared Camera FLIR Titanium, FLIR Systems, Inc., Wilsonville, Oregon, USA) was used to spatially determine the heat generation rate and thus, the current distribution. Based on the depth information given by thermography, grinding steps were repeated until intersection of the relevant grain boundary plane. The cross‐section was then polished with 1 μm diamond suspension and 0.04 μm silicon oxide‐based suspension.…”

Section: Methodsmentioning

confidence: 99%

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Piezotronically Modified Double Schottky Barriers in ZnO Varistors

et al. 2015

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Section: Methodsmentioning

confidence: 99%

“…This was done by performing uniaxial compressive tests on low‐voltage varistors made of only few (<1000) grains. Here, no such averaging of the effects is expected since very few grain boundaries control the electrical characteristics of these devices …”

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confidence: 99%

Piezotronically Modified Double Schottky Barriers in ZnO Varistors

et al. 2015

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“…Nevertheless, the origin of the asymmetric behavior is not known. Asymmetric macroscopic I - V characteristics result from spatially different current paths, which depend on the electric field direction (Hofstätter et al, 2013). These features can be visualized using lock-in IR microscopy.…”

Section: Methodsmentioning

confidence: 99%

“…Investigation of the electrical properties of barriers and their dependence on certain influencing factors are of high interest for the scientific and industrial communities. Owing to the ongoing trend in miniaturization, low-voltage varistors nowadays contain only a few grain boundaries or – in the extreme case – one, single grain boundary that may dominate the macroscopic electrical behavior of the whole component (Hofstätter et al, 2013; Raidl et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Lock-In Infrared Microscopy: A Complementary Investigation Technique for the Analysis of Functional Electroceramic Components

et al. 2015

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Using lock-in infrared microscopy as a tool for current detection on the micrometer scale in AC-driven specimens in combination with iterative grinding procedure allows preparation of current dominating microstructure regions on well-polished surfaces. This technique is applied successfully on varistor components based on specially doped ZnO-based varistor ceramics. This peculiar electroceramic material exhibits exceptional high nonlinear current-voltage (I-V) characteristics, described by a power law according I~V(α), caused by double Schottky barriers at the grain boundaries. As a novelty the thermographic response is used to evaluate local electrical properties, namely the nonlinearity coefficient α, on basis of higher order harmonics with respect to the basic electrical driving AC-frequency. To correlate the observed electrical properties to the microstructure, the polar crystal orientation of the relevant ZnO grains is determined by combining electron backscatter diffraction and orientation-dependent patterns as a result of a chemical etching procedure. These findings support a modified new model for describing the grain boundary controlled current flow in a varistor microstructure including orientation-dependent barrier properties. Hence, the experimentally observed current direction-dependent behavior can be described consistently.

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“…Growing application range of low voltage devices promotes development of multilayer varistors (Lee et al , 2006, 2007; Rubia et al , 2007; Kuo and Tuan, 2008, 2010; Peiteado et al , 2009; Pan et al , 2010; Hirose et al , 2012; Hofstätter et al , 2013; Kulawik et al , 2014; Wan et al , 2010) fabricated in low temperature cofired ceramics (LTCC) technology, destined for protection of such devices against overvoltages. These varistors are manufactured in the analogous manner to that applied for multilayer capacitors by cosintering of several tape cast ceramic foils with screen printed internal electrodes connected in parallel.…”

Section: Introductionmentioning

confidence: 99%

Electrical and microstructural characterization of doped ZnO based multilayer varistors

Kulawik

Szwagierczak

Skwarek

2017

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Purpose The purpose of this study was to develop fabrication procedure of multilayer varistors based on doped ZnO and to investigate their microstructure and electrical properties. Design/methodology/approach Two ceramic compositions based on ZnO doped with Bi2O3, Sb2O3, CoO, MnO, Cr2O3, B2O3, SiO2 and Pr2O3 were used for tape casting of varistor tapes. Multilayer varistors were prepared by stacking of several green sheets with screen printed Pt electrodes, isostatic lamination and firing at 1,050-1,100°C. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) studies were carried out to examine the microstructure and elemental composition of the varistors. Current-voltage characteristics were measured in the temperature range from −20 to 100°C. Findings The desired compact and fine-grained microstructure of multilayer varistors and nonlinear current-voltage characteristics were attained as a result of the applied fabrication procedure. The breakdown voltage of the varistors is 33-35 V and decreases slightly in the temperature range from −20 to 100°C. The nonlinearity coefficient changes from 14 to 23 with rising measurement temperature. Originality/value New improved formulations of varistor ceramic foils based on doped ZnO were developed using tape casting method and applied for fabrication of multilayer varistors with good electrical characteristics. The influence of temperature in the range from −20 to 100°C on the varistor parameters was studied.

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Voltage polarity dependent current paths through polycrystalline ZnO varistors

Cited by 12 publications

References 23 publications

Piezotronically Modified Double Schottky Barriers in ZnO Varistors

Piezotronically Modified Double Schottky Barriers in ZnO Varistors

Nonlinear Lock-In Infrared Microscopy: A Complementary Investigation Technique for the Analysis of Functional Electroceramic Components

Electrical and microstructural characterization of doped ZnO based multilayer varistors

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