Effects of amount of yttria on dielectric breakdown strength of sintered reaction‐bonded silicon nitride

Abstract We prepared sintered reaction‐bonded silicon nitride (Si ₃ N ₄ ) ceramics using various amounts of yttria (Y ₂ O ₃ ) and a fixed amount of magnesia as sintering additives and evaluated their effects on the microstructure and dielectric breakdown strength (DBS). The DBS tests were conducted at substrate thicknesses of approximately .3, .2, .1, and .05 mm for each sample. All the prepared samples exhibited a high relative density (> 98%) and were composed of grains of almost identical sizes and shapes. The DBS decreased as the amount of added Y ₂ O ₃ increased, with the degree of decrease being more pronounced for the thinner substrates. In the case of substrates with the largest Y ₂ O ₃ amount (5 mol%), the DBS decreased to the level observed for the thinnest substrate of .05 mm. The presence of yttrium ions around the grains increased the electrical conductivity of the glassy phase, resulting in a decreased DBS. Therefore, a smaller amount of Y ₂ O ₃ led to a higher DBS. The observed decrease in the DBS (.05 mm) was attributed to the connection between the top and bottom surfaces of the substrate through a highly conductive path.