Study On Low Temperature Sintering Properties Of ZnAl₂O₄ Based Microwave Dielectric Ceramics

With the rapid development of the modern wireless communication technology and the consumer of electronics market,and the microwave dielectric ceramics is the cornerstone of wireless communication materials.The development of new electronic materials to meet the requirements of high-frequency and high-speed of the component is a challenge of today’s electronic materials to adapt to high-frequency applications.Low dielectric constant microwave dielectric ceramics are the preferred materials in this field for their excellent dielectric properties.Low temperature co-fired ceramic technology（LTCC）is a remarkable multidisciplinary integrated component technology.It is the first choice for electronic components integration and modularization,also is the realization of highly integrated,high-performance electronic packaging technology.The ZnAl₂O₄ceramic has good microwave dielectric properties,and the raw material is cheap,but because of its sintering temperature is too high,hindering its production applications.In this thesis,the ZnAl₂O₄ ceramics were studied for low temperature sintering applications.The phase composition,crystal structure and microwave dielectric properties of ZnAl2O4ceramics were investigated by ion substitution method and different sintering temperature and sintering time.In this paper,ZnAl_（2-x）(Zn_0.5Si_0.5)_xO₄（x=0.5、1、1.5、2）materials at the B site of ZnAl₂O₄ ceramics were studied by equi-molar Zn and Si substitution.It comes out that when sintered at x=0.5,it was easy to sinter into ceramic,and the sintering temperature zone was wider and had microwave dielectric properties.Therefore,mainly on the ZnAl_（2-x）(Zn_0.5Si_0.5)_x O₄（x=0.5）materials were explored.In this test,five points were sintered from 1350°C to 1550°C.The sintered material was then tested by means of XRD,SEM,and network analyzers and so on.It turns out that the best sintering performance was obtained at 1400°C with the microwave dielectric propertyε_r=7.24,Q×f=23138 GHz andτ_f=-66 ppm/°C.At 1400°C sintering temperature,the effect of sintering heat preservation time on microwave properties was further investigated.From the heat preservation for 2hours to the heat preservation for 10 hours,the best performance was found in the heat preservation for 6 hours.It was also found that the equi-molar amounts of Zn and Si can completely replace Al at the B-site of ZnAl₂O₄ ceramics with increasing holding time.Mixed of ZnO–SiO₂–B₂O₃（ZSB）glass and ZnO-H₃BO₃（ZB）glass cannot reduced the sintering temperature of ZnAl_（2-x）(Zn_0.5Si_0.5)_xO₄（x=0.5）ceramics to 950°C.Therefore,the present invention also makes it possible to obtain a chemical formula of Li_2yy Zn(_1-y)Al_1.5(Zn_0.5Si_0.5)_0.5O₄（y=0.25,0.5,0.75,1）by doping Li ions in the A site to further lower sintering temperature.Sintering tests were performed at 1250°C to 1400°C.At last,the sintering temperature was reduced to 950°C by mixed with glass of Li_2yZn(_1-y)Al_1.5(Zn_0.5Si_0.5)_0.5O₄（y=1）this materials,and the microwave property was also good,which could be used as a LTCC material.In this paper,we have also studied the substitution of Mn for the Al element in the B site,and the dense Zn(Mn_1-xAl_x)₂O₄（0.2≤x≤0.9）solid solutions were synthesized at1250°C for 3 h through solid-state reaction.The densification temperature was much lower than that of the end members.Phase transition from a tetragonal to a cubic structure occurred at x=0.7 with the increase in the x value.As the x value increased from 0.2 to 0.7,theε_r value decreased slightly from 10.28 to 9.54.Theε_r value decreased significantly when the x value exceeded 0.7.This trend inε_r value corresponded to the phase transition of the solid solutions that occurred at x=0.7.The Q×f value increased initially from3144 GHz to 14460 GHz and then decreased after reaching the maximum value at x=0.8.Theτ_f value changed only slightly near the typical value from?60 ppm/°C to?80 ppm/°C.ZB glass and TiO₂ co-doping in the Zn(Mn_0.2Al_0.8)₂O₄ system not only decreased the sintering temperature by 300°C but also effectively controlled theτ_f value to near zero.The（1-y）Zn(Mn_0.2Al_0.8)₂O₄+yTiO₂（y=0.26）ceramics with 5 wt.%ZB glass were sintered well at 950°C for 3 h and exhibited appropriate microwave dielectric properties（ε_r=12.71,Q×f=8126 GHz,andτ_f=1.02 ppm/°C）for LTCC applications at microwave frequency.