Low‐Temperature Sintering and Electrical Properties of ZnO–Bi₂O₃–TiO₂–Co₂O₃–MnCO₃‐Based Varistor with Bi₂O₃–B₂O₃ Frit for Multilayer Chip Varistor Applications

Abstract

The effects of a Bi2O3–B2O3 frit (denoted as BiBF) on the densification, phase transformation, microstructure, and nonlinear electrical properties of ZnO–Bi2O3–TiO2–Co2O3–MnCO3 (ZBTCM)‐based varistors have been investigated. The varistor ceramic with the addition of >2 wt% BiBF can be sintered at 900°C and 96.3% of the theoretical density was achieved. SEM revealed that the microstructure of the varistor ceramics with 2 wt% BiBF is uniform, with an average grain size of 13.5 μm. No porosity is observed. The typical ZnO–Bi2O3–TiO2‐based varistor phase compositions were detected for all varistor ceramics but the formation of a secondary phase, Bi4B2O9, became apparent when 4 wt% BiBF was added. The Bi4B2O9 phase crystallized from the Bi2O3–B2O3 frit, acting as a potential barrier at the grain boundary, increases the density of interface states Ns, barrier height Φb, and plays an important role in improving the electrical properties of the varistor ceramics. However, a large amount will be detrimental. Optimum properties were exhibited for the varistor ceramics with 2 wt% BiBF sintered at 900°C, with E1 mA=124.9 V/mm, α=46.2, and JL=0.2 μA/cm2. The reactivity of the varistor ceramic with Ag was also studied. The excellent electrical properties and low sintering temperature, coupled with chemical compatibility with Ag, suggest that Bi2O3–B2O3 frit sintering aids for ZnO–Bi2O3–TiO2–Co2O3–MnCO3 (ZBTCM)‐based varistors have great potential for using the base metal Ag as inner electrodes for low‐voltage MLV fabrication.

Low-temperature sintering of high potential gradient B2O3-doped ZnO varistors

“…Thus, it is urgent to develop the high-voltage ZnO-Bi 2 O 3 -based varistors materials with a low sintering temperature. Wan et al [14,15] reported that adding Bi 2 O 3 -B 2 O 3 frit or Zn-B glass could reduce the sintering temperature of ZnO varistors to 900°C. B 2 O 3 has low melting temperature (450°C) and could form stable glasses in a wide compositional range when substituted for boron in borate based glasses [16][17][18].…”

Nonlinear electrical properties of MnO2-doped TiO2 capacitor varistor ceramics

“…There are several types of practical varistor ceramic systems studied such as ZnO [1], SnO 2 [2], WO 3 [3], SrTiO 3 [4], TiO 2 [5]. ZnO-based varistors with high nonlinear coefficients are the most widely used in electronic circuits and devices [6].…”

Innovative nanocrystal-based technologies for ceramic devices with novel electronic functions

“…The state-of-the-art technology enables to fabricate a multilayer structure with an interelectrode spacing of around 1 m [5], and the commercialization of multilayer ceramic chip capacitors, with the smallest size of 2012 (2.0 mm× 1.25 mm), with extremely large capacitance values of >22 F has recently been realized by Murata Co. Similar fabrication techniques for multilayer tip-type devices have been applied to other electronic ceramics, including thermistors [6], varistors [7], and inductors [8], resulting in a considerable success in the improvement of the performance of their devices. However, since the current powder processing-based ceramic technology has substantial technical limitations that hardly allow creating two-and threedimensional ceramic nanostructures with feature sizes of <100 nm, it is essential to develop innovative nanocrystal-based ceramic technology comparable with the photolithography-based semiconductor (or silicon) technology to open a new horizon in the field of electronic ceramics.…”