Electrical properties of epoxy/silver nanocomposites

We investigated the electrical properties of nanocomposites made of epoxy resin filled with 70-nm-sized silver particles. These composites were studied for the fabrication of integrated capacitors in electronics packaging. The dc conductivity was studied as a function of the filler concentration and as a function of temperature. We also studied the ac conductivity and the permittivity in the 10(-1)-10(5) Hz range as a function of the filler concentration. Experimental properties were analyzed using standard percolation theories. The dc conductivity varies as (phi-phi(c))(t), where phi is the filler concentration, phi(c) is the percolation threshold, and t is the dc critical exponent. A very low percolation threshold is obtained (phi(c)=1%) which is believed to be related to a segregated distribution of the fillers in the epoxy matrix. We also measured a very high dc critical exponent (t=5) probably related to the interparticle electrical contact. A universal scaling law is observed for sigma(omega) and epsilon(omega). Above a cutoff frequency (omega(c), which scales with the dc conductivity as omega(c)similar to sigma(dc)(q)) the conductivity and the permittivity follow the universal power laws (sigma similar to omega(u) and epsilon similar to omega(-v)) with critical exponents taking nonstandard values (q=0.83-0.98, u=0.79, and v=0.03). (c) 2006 American Institute of Physics.