Abstract
The article presents the very first materials to the ultralow temperature cofired ceramic (ULTCC) technology with the sintering temperature of 400 °C. The dielectric composites are based on a rutile and anatase with commercial GO17 sealing glass. In addition to the bulk samples, the tape casting procedure is also introduced to show its feasibility to cofiring with commercial Ag electrodes at 400 °C. The structural, microstructural, thermal, and microwave dielectric properties in the green and sintered samples were investigated. The optimum amount of glass to fabricate substrates was found to be 30 vol %. The ULTCC substrates with the anatase TiO2A-30GO17 and rutile TiO2R-30GO17 that were sintered at 400 °C showed a relative permittivity of 9.9 and 15 and a dielectric loss of 0.006 and 0.003, respectively, at the measurement frequency of 9.9 GHz. The temperature dependences of the relative permittivity were +70 and −400 ppm/°C, respectively. Moreover, the coefficients of the thermal expansion of the substrates were 7.4 and 8.3 ppm/°C in the measured temperature range of 50–300 °C. A preliminary test to study the feasibility of the anatase TiO2A-30GO17 for a dual band antenna was performed due its relatively stable temperature behavior.
Highlights
The era of multilayer capacitor technology has led to the utilization of multilayer ceramic processes in high temperature cofired ceramics (HTCC), low temperature cofired ceramics (LTCC), and, very recently, in ultralow temperature cofired ceramics (ULTCC).[1−11] This change has been due to the continuous and rapid growth in the electronic and telecommunication fields, with corresponding demands for new ways to use ceramics to enable miniaturization, high packing density, and reduced cost for devices
The rutile TiO2 phase has an εr of 100 and a tan δ of 6 × 10−5 in the microwave frequency range together with an exceptionally high-temperature coefficient of resonant frequency of ∼ 450 ppm/°C when sintered at 1500 °C.18,19. It is utilized as a τf tuning dielectric dopant for the negative τf ceramic materials in LTCC and the high-temperature dielectric materials used for telecommunication applications
The sintering temperature in both cases is 400 °C, the TiO2A-30GO17 substrate could be modified by relatively small additions of the TiO2R phase with a negligible effect on the measured permittivity and loss values of εr of 9.9 and 0.003 at 5.1 GHz, these being at the same level as those achieved for the commercial Dupont 951 LTCC substrate sintered at 850 °C
Summary
The era of multilayer capacitor technology has led to the utilization of multilayer ceramic processes in high temperature cofired ceramics (HTCC), low temperature cofired ceramics (LTCC), and, very recently, in ultralow temperature cofired ceramics (ULTCC).[1−11] This change has been due to the continuous and rapid growth in the electronic and telecommunication fields, with corresponding demands for new ways to use ceramics to enable miniaturization, high packing density, and reduced cost for devices. The rutile TiO2 phase has an εr of 100 and a tan δ of 6 × 10−5 in the microwave frequency range together with an exceptionally high-temperature coefficient of resonant frequency (τf) of ∼ 450 ppm/°C when sintered at 1500 °C.18,19. Most commonly, it is utilized as a τf tuning dielectric dopant for the negative τf ceramic materials in LTCC and the high-temperature dielectric materials used for telecommunication applications. In this work, we introduce a procedure to fabricate rutile and anatase TiO2-based ULTCC substrates by the liquid phase sintering method with good densification and microwave performance even at an ultralow sintering temperature. The names of the research compositions indicate the amount of GO17 (20, 30, 40 vol %) and rutile (R) and anatase (A) phase TiO2, for example, TiO2A30GO17 and TiO2R-20GO17
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