Study On （Sr,Ca）（Zr,Ti）O₃High-frequency Dielectric Ceramics For Multi-layer Ceramic Capacitors With Copper Inner Electrodes

With the rapid development of mobile communication, electronic components trendtowards small size, high performance and low production cost. As one of the widely usedpassive components, how to lower the production cost of multi-layer chip ceramic capacitors(MLCC) arouses researcher’s interest. It has been known that choosing copper (Cu) to be theinner electrodes of MLCC not only can lower the production cost sharply, but also canenhance the electrical performance of MLCC remarkably due to the electrical resistivity of Cuis much smaller than Pd/Ag alloy. However, the requirement of low temperature sinteringprocess (The melting point of Cu is1083℃) in reducing atmosphere makes most of theexisted dielectric materials no longer applicable. As a result, many new dielectric materialswere studied in the past decade.(Sr,Ca)(Zr,Ti)O3ceramic is a good material for MLCC with NP0-type (Negative-Positive-Zero) temperature characteristic. For (Sr0.55Ca0.45)(Zr0.96Ti0.04)O3(SCZT) ceramicsintered at1300oC, excellent dielectric properties (r=35.5, tan <110-4,C=3.1ppm/℃at1MHz; r≈33, Q×f≈13629GHz, τf≈-6.6ppm/℃at4GHz) and temperature, frequency,electric field stabilities can be achieved. However, if one expects to co-fire with Cu innerelectrodes, its sintering temperature should be lowered and its anti-reduction properties shouldbe modified.In this paper, SCZT powders were synthesized by an oxide solid-state reaction route. Theeffects of sintering temperature and atmosphere on the densities and dielectric properties ofSCZT ceramics with BaO-B2O3-SiO2(30:60:10)(BBS), Li2CO3and MnCO3addition wereinvestigated. The results indicated that the ceramics with1wt%BBS addition can be sintereddensely at1060℃. The sintering temperature of ceramics with1wt%BBS frit and0.5wt%Li2CO3addition can be down to1000℃. For SCZT ceramics sintered simultaneously with1wt%BBS frit,0.5wt%Li2CO3and0.5wt%MnCO3addition at1000℃in reducingatmosphere (96%N2,4%CO) for2h, excellent dielectric properties of r=30.8, tan=2.1410-4,C=4.1ppm/℃at1MHz can be achieved, which allowed for the fabrication of NP0-type MLCC with Cu inner electrodes.In addition, different effects on the sintering temperature of SrZrO3, CaZrO3, SrTiO3andCaTiO3with1wt%BBS frit,0.5wt%Li2CO3,0.5wt%MnCO3addition were alsoinvestigated. For different dielectric materials, the proportion of BBS, Li2CO3and MnCO3should be further adjusted to achieve optimal results.