Effect of microstructures on dielectric breakdown strength of sintered reaction‐bonded silicon nitride ceramics

Abstract

Silicon nitride (Si3N4) was prepared from silicon by a sintered reaction‐bonded silicon nitride method using yttria and magnesia as sintering additives. Post‐sintering (PS) of nitrided compacts was carried out at 1850°C under a nitrogen pressure of 1 MPa. Effect of PS time on microstructure and dielectric breakdown strength (DBS) of the prepared Si3N4 ceramics was evaluated. The DBS was measured using specimens with four different thicknesses (0.30, 0.20, 0.10, and 0.05 mm) in order to examine the thickness dependence. The porosity of the sintered Si3N4 decreased by prolonging the PS time, and the full density could be achieved at the PS time of over 6 h. After full densification, rod‐like β‐Si3N4 grains grew up, and their maximum grain size increased from 45.1 to 154.7 μm by prolonging the PS time from 6 to 48 h. The DBS of the thick Si3N4 substrates (0.30 mm) showed little variation from 35.4 to 47.0 kV/mm, regardless of the PS time. On the other hand, that of the thin ones (0.05 mm) dramatically decreased from 99.5 to 9.8 kV/mm with increased the PS time from 6 to 48 h. Because the DBS sharply decreased at the thin substrate sintered for longer time in which some large‐elongated grains might span the substrate thickness‐wise throughout, it was inferred that the interface between β‐Si3N4 grains and grain boundary phase/intergranular glassy films might be a path of the dielectric breakdown.

A Comprehensive Review of Mitigation Strategies to Address Insulation Challenges Within High-Voltage, High-Power-Density (U)WBG Power Module Packages

“…The parameters on which the properties of Si3N4 depend are the sintering temperature and holding time in addition to the size, ratio, and type of sintering additives [38]. When the sintering temperature and holding time are increased, it has the effect of promoting the growth of b-Si3N4 grains.…”

“…Additionally, the crystal lattice's oxygen content is continuously lowered by the dissolving-precipitate process, which in turn enhances the thermal and dielectric properties. However, for thinner thickness, this leads to lower breakdown strength decreasing from 99.5 kV/mm to 9.8 kV/mm only when sintering period was increased from 6 hours to 48 hours [38]. Additionally, impurities interfere with the additive/substrate interface leading to the formation of cracks, and defects and drastically reduce the properties of Si3N4.…”

Dielectric breakdown strength measurement of silicon nitride ceramics by McKewon electrode

“…Matsunaga et al 5) reported that large grains function as defects for dielectric breakdown. Our previous work 6) showed that grains with the lengths larger than the substrate thickness can act as fatal defects. Despite these defects, Si 3 N 4 substrates have relatively high DBS; 4), 5) for example, our another study on DBS of Si 3 N 4 7) showed a very high value of 1.5 kV even with a substrate whose thickness was as small as 15 ¯m.…”

Deformation behaviors and fracture strength of β$\ubeta$‐Si3N4 single crystals

“…For example, because of their excellent mechanical properties and high thermal conductivity, Si 3 N 4 ceramics are nowadays applied to heat‐dissipating substrates of power devices 9,10 . However, their thickness is required to be less than a few 100 µm for improving their heat dissipation ability, whereas the Si 3 N 4 grain size ranges to several 10 µm 11 . In such cases, the single‐crystal grains themselves play a significant role in determining the material properties.…”

“…9,10 However, their thickness is required to be less than a few 100 µm for improving their heat dissipation ability, whereas the Si 3 N 4 grain size ranges to several 10 µm. 11 In such cases, the single-crystal grains themselves play a significant role in determining the material properties. Therefore, it is critically important to correctly evaluate and understand the mechanical behaviors of Si 3 N 4 single crystals for ensuring their structural reliability.…”