Addition of Nb 2 O 5 on the electrical properties of buried resistors in low-temperature cofired ceramics
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Nb2O5 was added to buried resistors for low-temperature cofired ceramics, and the electrical properties of the resultant resistors were examined. Remarkable increases in electrical resistivity and attractive decreases in the temperature coefficient of resistance (TCR) were observed by the addition of Nb2O5, which was attributed to the high solubility of Nb2O5 into the PbO–SiO2–Al2O3 matrix glass. With higher dissolved contents of Nb2O5 into the glass, the resistivity of buried resistors increased by approximately six-fold magnitude, while TCR decreased substantially toward zero. It was indicated that the conductance for these buried resistors was limited by tunneling of charge carriers through the thin glass layer penetrating into the ruthenium-oxide agglomerates. A larger separation observed between RuO2 particles due to high solubility of Nb2O5 in the glass increased the charging energy (E) and lump term (Rbo), which in turn gave rise to a higher resistivity and a lower TCR value.
I. INTRODUCTION
Integrating the discrete passive components inside a multilayer, three-dimensional (3D) circuit structure has long been advocated to meet the minimization of size for high-frequency, personal mobile electronic applications. Low-temperature cofired ceramics (LTCC) technology has been utilized and recognized as the most compact way to integrate passive components, which include resistors, capacitors, and inductors. These buried components can be directly integrated with a single firing step in LTCC. However, accompanying challenges have emerged about the physical and chemical incompatibility between different materials during co-firing processes. Examples of what may happen when LTCC and resistors are incompatible have been clearly illustrated. Badly warped co-fired structure, large voids, delamination at LTCC/resistor interfaces, and unstable electrical properties were described elsewhere.1,2 Therefore, achieving the optimal composition of buried resistors with suitable compatibility for LTCC is important. Processing, microstructure, and electrical properties of ruthenium oxide and ruthenate-based resistors were investigated recently.3–5 Special attention was paid to the addition of various oxides and their effects on resistance and temperature coefficient of resistance (TCR).6 However, the detailed effects of the additives in the buried resistors were not explained. In this study, microstructural characterization and electrical properties of buried
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e-mail: [email protected] J. Mater. Res., Vol. 18, No. 5, May 2003
http://journals.cambridge.org
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resistors containing Nb2O5 were examined. Note that Nb2O5 is chosen because it is known to be an effective candidate additive for reducing TCR close to zero.7,8 The distributions of Nb2O5 additives were observed by transmission electron microscopy (TEM) to clarify the mechanism for TCR reduction. It is beneficial to predict electrical properties of buried resistors. Therefore, an understanding of the TCR minimization mechanism is needed before the
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