Bi_2O_3-MoO_3 Binary System: An Alternative Ultralow Sintering Temperature Microwave Dielectric

摘要

Preparation, phase composition, microwave dielectric properties, and chemical compatibility with silver and aluminum electrodes were investigated on a series of single-phase compounds in the Bi_2O_3-MoO_3 binary system. All materials have ultralow sintering temperatures <820℃. Eight different xBi_2O_3-(1-x) MoO_3 compounds between 0.2 ≤ x ≤ 0.875 were fabricated and the associated microwave dielectric properties were studied. The β-Bi_2Mo_2O_9 single phase has a positive temperature coefficient of resonant frequency (TCF) about +31 ppm/℃, with a permittivity ε_r = 38 and Q_r = 12500 GHz at 300 K and at a frequency of 6.3 GHz. The α-Bi_2Mo_3O_(12) and γ-Bi_2MoO_6 compounds both have negative temperature coefficient valuesrnof TCF～-215 and～-114 ppm/℃, with permittivities ofrnε_r= 19 and 31, Q_f=21 800 and 16700 GHz at 300 K measured at resonant frequencies of 7.6 and 6.4 GHz, respectively. Through sintering the Bi_2O_3-2.2MoO_3 at 620℃ for 2 h, a composite dielectric containing both α and β phase can be obtained with a near-zero temperature coefficient of frequency TCF = -13 ppm/℃ and a relative dielectric constant ε_r = 35, and a large Q_f～12000 GHz is also observed. Owing to the frequent difficulty of thermochemical interactions between low sintering temperature materials and the electrode materials during the cofiring, preliminary investigations are made to determine any major interactions with possible candidate electrode metals, Ag and Al. From the above results, the low sintering temperature, good microwave dielectric properties, chemical compatibility with Al metal electrode, nontoxicity and price advantage of the Bi_2O_3-MoO_3 binary system, all indicate the potential for a new material system with ultralow temperature cofiring for multilayer devices application.