The Reserch And Application Of Low Permittivity And Low Loss LTCC Ceramic Based On CaWO₄

Currently, mobile communication devices, and microwave systems are moving towards miniaturization, high-frequency, high-speed, integrated, low loss of direction. Therefore, for application reasons, the LTCC material with low permittivity and appropriate microwave dielectric properties enables fabrication of devices for high speed applications.In consideration of the defect of low melting point glass, we used two low melting point oxides to lower the sintering temperature of CaWO4. They were BCB and Li2WO4. It was also found that some pits existed in the surface of Ca WO4 grains, which might be due to the volatilization of BCB. For the ceramics sintered at 875℃, with the increase of x, the Q×f values first increased and then decreased. At x=1.2, the Ca WO4+xwt.%BCB(0.6≤ x ≤ 1.4) ceramics sintered at 875℃/2h presented good microwave dielectric properties: εr =9.547, Q×f =6.07×104 GHz and τf =-41 ppm/℃. With the increase of Li2WO4, the optimal sintering temperature gradually decreased. At x=0.1, the(1-x)Ca WO4-x Li2WO4(0≤ x ≤0.14) ceramics sintered at 900℃/2h presented excellent microwave dielectric properties: εr =9.002, Q×f =11.76×104 GHz and τf =-55 ppm/℃. The ceramic was a chemically compatible with silver, which makes it a very promising candidate for LTCC application. The results showed two low-melting oxides can reduce the sintering temperature of Ca WO4, and achieved good dielectric properties. The mechanism of that BCB and Li2WO4 reduced the sintering temperature of Ca WO4 was same, which was mainly attributed to that the appropriate liquid phase of BCB and Li2WO4 promoted the sintering of Ca WO4.Although the CaWO4-Li2WO4 presented excellent microwave dielectric properties, its TCF value was a large negative. In order to overcome this problem, we used TiO2 and CaTiO3 to adjust its TCF value to near zero. We knew that the adding of TiO2 in Ca WO4-Li2WO4 ceramic deteriorated the Q×f value from our results. On the other hand, the dense ceramic could be obtained as the adding of CaTiO3 in CaWO4-Li2WO4 ceramic. At y=5, the CLW+y %wt CaTiO3(3≤ y ≤7) ceramics sintered at 900℃/2h presented microwave dielectric properties: εr =10.31, Q×f =5.63×104 GHz, τf =1.2 ppm/℃.We used the CLW+5%wt CaTiO3 ceramic to make a GPS microstrip antenna. It could be seen from the simulation results that our low loss ceramic was better for the high gain antenna. Also, the test results of the GPS antenna were up to the design standard except the center frequency. The deviation of center frequency could be attributed to the imprecision of the process control.