High performance ZnO varistors prepared from nanocrystalline precursors for miniaturised electronic devices

Abstract

An industrially viable solution-based processing route using minimal amounts of solvent has been used to prepare bulk quantity nanopowders (average particle size 15 AE 3 nm) for the fabrication of ZnO varistors. The xerogels, calcined powders and sintered materials were fully characterised. The preparation of varistors from nanopowders has been optimised by studying the effect of temperature on grain growth, densification and breakdown voltage. The varistors are prepared by sintering at 1050 C for 2 hours, a temperature that is significantly lower than that used in the current industrial process. Highly dense varistor discs prepared from the sintered material produce devices, with a breakdown voltage 85% higher than that of commercial varistors, making them suitable for use in miniaturised electronic circuitry. Improved performance of these materials has been attributed to the small grain size and better dispersion of additives on ZnO grains.

Antibacterial properties of F-doped ZnO visible light photocatalyst

“…Zinc oxide (ZnO), a wide band gap semiconductor (3.37 eV), has a vast range of applications which include but are not limited to photocatalysts [8], varistors [9,10], pharmaceutical products [11], and lasers [12]. As a photocatalyst, in the presence of UV radiation, ZnO facilitates production of reactive oxygen species (ROS) on its surface [13].…”

Advances in the synthesis of ZnO nanomaterials for varistor devices

“…a is regarded as the most signicant parameter for the varistor action. 2,3 It can be determined either from the reciprocal slope of the log V-log I curve (Fig. 2) Another critical application parameter for ZnO varistors is the threshold or breakdown voltage (V c ), which marks the transition from linear to nonlinear mode.…”

“…To make a non-linear material, various metal oxides have to be incorporated into the ZnO. 1,3,5,6 These oxides are added to control one or more of the properties such as the electrical characteristics (breakdown voltage, non-linearity and leakage current), grain growth or sintering temperature. This can be readily observed by XRD (Fig.…”

“…[1][2][3][4][5][6][7][8][9][10] A sudden variation in the electrical condition of circuits arising from lightning strikes, electro-static discharge, etc. would cause a transient voltage to be generated from the energy stored due to the circuit capacitance and conductance, 2 so that a key varistor attribute of transient overvoltage protection requires the impulse energy to be dissipated at a voltage low enough to guarantee the survival of the electrical components.…”

Synthesis and Sintering of ZnO Nanopowders

“…It was determined that the grain growth process followed a standard phenomenological kinetic grain growth, controlled by the diffusion of zinc ions within the structure [15]. For applications as a varistor, the ZnO microstructure needs to exhibit the finest microstructure, in order to present a higher number of active grains and grain boundaries [16]. Some strategies, such as low-temperature sintering (below 950 • C) [17], or two-step sintering [18] were investigated in more recent years.…”