Research On Embedded Resistive Materials In Multilayer Ceramic Circuit Substrates And Their Applications

Modern information technology has placed higher demands on electronic devices and entire systems in terms of miniaturization,high reliability and high integration,among which the huge number of passive devices required to realize system functions has seriously hindered the rapid development of circuit substrate integration technology.Multilayer ceramic substrate technology has become a hot spot to be pursued in this field due to the ease of achieving internal embedding of components.In this dissertation,the representative of passive components-resistor was selected,the LaCo_0.4Ni_0.6O₃ and La_0.5Sr_0.5CoO₃ ceramics with excellent electrical conductivity and low cost were used as the conductive phase materials to carry out the research on embedded resistive materials in multilayer ceramic circuit substrates and their applications.By means of solid-phase reaction experiments and first-principles calculations,the resistive and sintering properties of the ceramic materials were optimized,resistive pastes based on the developed materials were formulated,and the feasibility of integration of the developed resistive materials embedded in multilayer ceramic power divider and RC high-pass filter was verified by using matched co-firing means,as follows:1.The resistive and sintering properties of LaCo_0.4Ni_0.6O₃ ceramics were studied by divalent substitution of Zn and Mg ions,respectively.After substitution of a portion of Ni ions by Zn and Mg ions,the average bond lengths of the CoO₆/NiO₆ octahedra grew,the bond population of Co-O and Ni-O increased,the density of states near the Fermi level decreased.Substitution with Zn²⁺resulted in a lowering of the phase formation and densification temperatures and an improvement in the densities of LaCo_0.4Ni_0.6O₃ceramics.Substitution with Mg²⁺led to an increase in the average valence states of Coand Ni ions,but resulted in a small amount of the impurity phases of NiO and La₃Ni₄O₁₀,and the densities and microstructures of LaCo_0.4Ni_0.6O₃ were deteriorated.Both substitutions with Zn²⁺and Mg²⁺caused higher resistivity and negatively increased the temperature coefficient of resistance（TCR）of LaCo_0.4Ni_0.6O₃.At a sintering temperature of 1200℃,the resistivity and TCR of the unsubstituted LaCo_0.4Ni_0.6O₃ were 0.94 mΩ·cm（1064 S/cm）and-313 ppm/℃;the resistivity and TCR of the sample with a Zn content of 0.02 were 1.03 mΩ·cm（971 S/cm）and-873 ppm/℃;the resistivity and TCR of the sample with a Mg content of 0.02 were 1.97 mΩ·cm（508 S/cm）and-756 ppm/℃.2.The resistive and sintering properties of La_0.5Sr_0.5CoO₃ ceramics were modified by Ni,Zn,Cu,and Nb ion substitution,respectively.Specifically,the ionic substitution aggravated the lattice distortion of La_0.5Sr_0.5CoO₃,the chemical bonding properties of CoO₆ octahedra were changed,the charge density distribution became asymmetric.An appropriate amount of substitution could reduce the densification temperature and improve the densification of La_0.5Sr_0.5CoO₃.Firstly,the substitution with Ni ions led to an enhancement in the density of states near the Fermi level,a decrease in the bond population of Co-O,an increase in the conductivity and TCR.At a sintering temperature of 1200℃,the conductivity of the sample with a Ni content of 0.04 was 3155 S/cm（0.317mΩ·cm）,the TCR was 2295 ppm/℃.Secondly,the substitution of Zn ions decreased the sintering activation energy and the crystallite size,increased the bond population of Co-O,weakened the charge transport in the system,and lowered the conductivity and TCR.At a sintering temperature of 1200℃,the conductivity of the sample with a Zn content of 0.05 was 2857 S/cm（0.35 mΩ·cm）,the TCR was 1267 ppm/℃,the change in conductivity before and after thermal aging test was-0.47%.Thirdly,after the substitution with Cu ions,the density of states across the Fermi level reduced,Coions were oxidized to a higher valence state,the crystallinity decreased,the grain boundaries became thicker,the electrical conductivity declined,the TCR went down first and then went up.At a sintering temperature of 1150℃,the conductivity of the sample with a Cu content of 0.06was 2609 S/cm（0.38 mΩ·cm）,the TCR was 1148 ppm/℃,the change in conductivity before and after thermal aging test was-0.72%.Fourthly,after the substitution with Nb ions,the hybridization between p and d orbitals weakened,the conductivity and TCR of the samples were not much affected by the sintering temperature.With the increase of the Nb content,the conductivity of the samples dropped and the TCR varied from positive to negative,and a zero TCR could be achieved within the range of Nb content of 0.05～0.06.At a sintering temperature of 1225℃,the TCR of the samples with a Nb content of 0.06was-168 ppm/℃,and its absolute value was the smallest among samples,and the conductivity was 1670 S/cm（0.6 mΩ·cm）.3.Resistor pastes containing different ratios of Ti O₂ and glass powder were formulated by using La_0.5Sr_0.5Co_0.94Nb_0.06O₃ and La_0.5Sr_0.5Co_0.96Ni_0.04O₃ as the conductive phases,respectively.The surface resistors were tested on alumina substrates and the embedded resistors were tested on dielectric tapes,and the effects of peak sintering temperature and printed dimension on the characteristics of resistor were studied.The sheet resistance of the formulated resistor paste range from tens ofΩ/□to tens of kΩ/□,and the deviation of the sheet resistance was within±31%,showing good resistance performance.Based on the formulated resistor paste,the power divider and RC high-pass filter with simple geometry,high operating frequency,internal buried resistors,and high resistance tolerances were designed and fabricated.The resistor in the power divider was made by La_0.5Sr_0.5Co_0.94Nb_0.06O₃+4wt.%glass powder B resistor paste;the La_0.5Sr_0.5Co_0.96Ni_0.04O₃+5wt.%glass powder A+3wt.%Ti O₂ resistor paste was used for the RC high-pass filter,and the Ferro FX87-103 resistor paste was used for performance comparison.The electrical performance were tested as follows:the return loss of the power divider was better than-15 dB,the insertion loss was better than-1.0 dB,the isolation between the output ports was better than-14.6 dB,the amplitude imbalance was lower than 0.3 dB,and the phase imbalance was lower than 3°;the test results of RC high-pass filters fabricated by the two resistive pasted were similar,with the cutoff frequencies of 1.37 GHz and 1.65 GHz,respectively;the insertion loss and return loss of the filter were slightly higher in the passband.The electrical performance of the power divider and filters deviated from the design values within acceptable limits,which verified the feasibility of embedding the developed resistive materials in multilayer ceramic circuit substrates.This dissertation focused on the research of conductive materials of resistor pastes,the formulation and test of resistor pastes,and the verification in power divider and RC high-pass filter.It meets the requirements of multilayer ceramic circuits on the resistive materials and devices,and provide a new idea for the research and development of low-cost,non-ruthenium resistor pastes and their applications.