X7R dielectrics for high energy density capacitors

This paper summarizes the results of a project dedicated towards the development of dielectrics for high energy density discharge capacitors. The primary goal was to produce capacitors with the following specifications: 1) the capacitors must fit within a space which is 1 x 1 x 0.020 "; 2) have at least 0.10 mu F over a temperature range -55 similar to 125 degrees C, at 1000 V; 3) are able to withstand voltage surges to 2000 V without failure; and 4) fast charge/discharge cycle (200 ms to 1000 V, then hold at the voltage for 2 min and discharge through a 150 m Omega resistor with a peak current 2000 A in 200 ns). Key factors to this project were the magnitude of the dielectric constant (K) at high field levels, and the breakdown strength (BDS). Studies on a commercially available X7R composition yielded a dielectric with a K = 920, and an average BDS = 250 kV/cm. Processing studies showed the dielectric could be lapped down to a thickness of 4 mils. Thermal annealing was necessary to retain the mechanical and electrical integrity. These boundary conditions forced the development of a multilayer capacitor instead of the originally conceived single layer capacitor.