Electrophoretic Deposition on Nonconducting Substrates: A Demonstration of the Application to Microwave Devices

Abstract

Through the use of a sacrificial carbon layer, this work reports a method of performing electrophoretic deposition (EPD) of thick films on fully nonconducting substrates, overcoming the restricting requirement for EPD of a conducting or partially conducting substrate. As a proof of concept, the method was applied to the development of microwave thick films on insulating alumina substrates. The key parameter to be controlled is the thickness of the sacrificial carbon layer; this is expected to be a general result for the application of the processing method. The method allows direct pat terning of the structure and leads to the potential use of EPD in a far wider range of electronic applications (multilayer ceramic capacitors (MLCCs), low temperature cofired ceramics (LTTCs), and biotech devices). Furthermore, in conjunction with work reported elsewhere, the development of specific BaNd2Ti5O14 (BNT) thick film microwave dielectrics opens up a technology platform for a range of high quality factor (Q) devices. More specifically, 100 μm thick BNT layers were achieved with a dielectric constant of 149 and Q of 1161 (10 GHz). These materials can now be integrated with tunable dielectrics or dielectrics on metal substrates to provide a platform for devices in the front end of communication systems and cellular base stations.