Dielectric behavior of bilayer films of P(VDF-CTFE) and low temperature PECVD fabricated Si3N4

We report the investigation of a bilayer approach to reduce the loss, especially the conduction loss at high electric fields, in the poly(vinylidene fluoride - chlorotrifluoroethylene) P(VDF-CTFE) films which exhibit high discharged energy density. There are many challenges for another dielectric layer used in the bilayer to block the conduction loss, including not only low dielectric loss and high resistivity, but also matched dielectric constant to and compatible film fabrication condition with the P(VDF-CTFE) films. We show that Si₃N₄ films, which can be synthesized by the plasma enhanced chemical vapor deposition (PECVD) at 100°C and thus will not cause damage to the P(VDF-CTFE) films, can meet these challenges. Experimental results show that with a proper low temperature PECVD deposition, the Si₃N₄ films display a dielectric constant ~ 7 with a low dielectric loss (<; 0.1%) and low conduction loss at high fields (>; 700 MV/m). Consequently, the bilayer films of Si₃N₄/P(VDF-CTFE) exhibit a high energy density (>; 10 J/cm³ at fields higher than 435 MV/m) with significantly reduced losses.