Preparation and Mechanism of High Energy Density Cyanate Ester Composites with Ultralow Loss Tangent and Higher Permittivity through Building a Multilayered Structure with Conductive, Dielectric, and Insulating Layers

High energy density polymer composites with ultralow loss tangent and higher permittivity for embedded capacitors are urgently required by new generation printed circuit boards. Herein, starting from a conductive layer (C-layer) with negative dielectric permittivity, a dielectric layer (D-layer) with positive dielectric permittivity, and insulating layer (I-layer), six multilayer composites, coded as DCI, CDI, IDCI, DCICD, DCIDC, and CDIDC according to their spatial stacking order, were prepared; among them, the C-layer is a graphite/polyvinylidene fluoride composite, the D-layer is a reduced graphene oxide–(K0.5Na0.5)NbO3/cyanate ester composite, and the I-layer is a boron nitride/cyanate ester composite. The effects of relative position and spatial stacking order of three-, four- and five-layer structures on performances were intensively discussed for the first time. Results show that CDIDC has the highest dielectric permittivity (886, 100 Hz) and biggest dielectric ratio of dielectric permittivity to loss tangent (R = 42275) over multilayered composites based on conductor/polymer reported so far. Besides this, compared to conventional conductor/polymer composite, CDIDC has 72% and 720% higher breakdown strength and energy density, respectively. The mechanism behind outstanding performances reveals that breakdown strength is determined by the position of I-layer, while dielectric permittivity is mainly controlled by the order of C-layer and D-layer when the position of I-layer is fixed.