Addition of TiO 2 on the electrical properties of buried resistors in low-temperature cofired ceramics
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Effects of TiO2 addition on the conduction mechanism of buried resistors in low temperature cofired ceramics were investigated. Remarkable increases in electrical resistivity and attractive decreases in the temperature coefficient of resistance were observed by the addition of TiO2 for all ratios of RuO2/glass investigated. Such significant effects can be attributed to a larger separation observed between RuO2 particles. The results were compared with the calculated data from theoretical model of tunneling barrier, showing that good agreement could be obtained. In addition, while the distance separation was taken into account as a fixed constant, it was found that the resistivity of buried resistor decreased with increasing TiO2 contents in the glass at higher weight ratios of TiO2/glass. This result implies that a substitution takes place due to the Si+4 displacement by Ti+4 in the glass, resulting in a looser network structure and a lower resistivity value.
I. INTRODUCTION
The development trends of wireless communication components, modules, and packaging substrates include high volumetric efficiency, high performance, high level of integration, excellent reliability, and low cost.1,2 To meet the above requirements, low-temperature cofired ceramic (LTCC) technology with integral embedded passives including resistors, capacitors, and inductors has been developed.3,4 Many investigations on buried resistors of these systems have focused on the effects of processing and microstructure on their electrical properties.5–8 Additional studies have been concerned with the effects of various oxides on electrical properties of ruthenium oxide and ruthenate-based resistors because they could reduce the temperature coefficient of resistance (TCR) to near zero.9 However, relatively few fundamental studies have focused on the detailed effects of the oxide additives in buried resistors. In our previous study, we found that the electrical properties of buried resistors were greatly dependent on the microstructure, which correlated closely with Nb2O5 additive contents.10 A larger separation observed between RuO2 particles due to the Nb2O5 particles in the glass matrix, resulted in a higher resistivity and a lower TCR value. In this study, which is an extension of the previous work, a more systematic and detailed investigation was conducted to understand the detailed effects of additives in buried resistors. TiO2 was chosen as an additive because it had a)
e-mail: [email protected] J. Mater. Res., Vol. 18, No. 9, Sep 2003
http://journals.cambridge.org
Downloaded: 15 Mar 2015
been proven that the TCR value of resistors could be reduced to zero,9 and it could also be fully dissolved into the glass. It is then expected that the base composition of glass could be adjusted due to the dissolved behavior of TiO2 additive. Therefore, the effects of TiO2 addition to glass on electrical properties of buried resistors in LTCCs were the major focus of this investigation.
II. EXPERIMENTAL
Resistor pastes were made from the following mate
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