Tunable Dielectric Material Embedded in LTCC for GHz-Frequency-Range Applications

摘要

Tunable dielectric materials offer an opportunity to realize novel wireless broadband applications such as antenna arrays with electrically controlled propagation delays. This kind of devices with good performance are already realized using discrete components such as diodes or barium strontium titanate (BST) thin films [1-2]. In the first case, however, extra assembling is required whereas with thin films, the production of the component can be expensive in large volumes. One promising method to exploit tunable dielectric materials is to make them compatible to LTCC (Low Temperature Co-fired Ceramics) process, thus enabling inexpensive and flexible manufacturing of functional multilayer ceramic modules (MCMs) for telecommunication industry. Barium strontium titanate with low sintering temperature (～900 ℃) has already been investigated for the LTCC process [3-4]. Additionally, first attempts to integrate it with other LTCC materials have been reported [5]. However, further research to enable a reliable co-firing process is needed since different materials have different shrinkages and thermal expansions easily causing delamination of the layers or warping of the whole module during sintering. In this work, a detailed research of the integration and interaction of the LTCC compatible BST layers with dielectric LTCC layers is presented. For process development, Pressure Assisted Sintering (PAS) is considered to enable flat multilayer multimaterial modules. Additionally, the effects of co-firing on relative permittivity and loss of the BST are reported as well as the temperature dependence of the relative permittivity (20 ℃-400 ℃).