Zwitterion-Based Organic High-k Dielectric Materials

Most high-k dielectrics known are based on inorganic materials, where large polarization is due to the slight separation of positive and negative charges in response to an applied field. Organic materials on the other hand, tend to have very low dielectric constants because of the low atomic number of their constituents. However, organic materials offer many advantages including easy of processing and mechanical flexibility. Zwitterionic molecules have charged groups that can be spatially separated by tens of angstroms. However, they are underexplored as dielectric materials. We report the synthesis of a novel zwitterionic molecule which melts below 100 °C. The compound was blended with poly(methyl methacrylate) and its dielectric properties were studied. The frequency-dependent capacitance depends strongly on the amount of zwitterion in the film and on the temperature of the device. At low concentrations of zwitterion and low temperatures, the film shows small capacitance (~3 nF/cm²). Above a specific concentration and temperature, capacitance is greater than 10 μF/cm², consistent with electrostatic double layer formation. In order to achieve this high of a capacitance value, the bulk of the film must be field-free. As such, we suggest that zwitterions exhibit strong electrostatic correlation behaviour. This interpretation is supported by grazing incidence wide angle x-ray experiments which show evidence of zwitterion crystallization only at high concentrations. The demonstrates a non-electrolyte dielectric with a very high capacitance and illustrates the importance of the nanoscale electrostatic environment on the properties of this class of materials.