Transitor Damage Characterization by Neutron Displacement Cross Section in Silicon: Experimental

Abstract

The validity of the silicon displacement cross section, D(E), was investigated by simultaneous measurements of neutron spectra phi(E) and of the accumulated damage D = Kphi induced in 2N2222A transistors. The measured values of phi(E) were folded in with D(E) to obtain phi/sub eq/, the l-MeV equivalent fluence for damage to silicon, and the ratios D/phi/sub eq/ = K were obtained for diverse shapes of phi(E) to determine the stability of K to phi(E) variations. The value of K was seen to be constant (within 4 to 5%, 1sigma) within roughly the same standard deviation as the D = Kphi measurements for two modified reactor spectra that varied by as much as 1000% above a few MeV when normalized at the 0.2-MeV threshold of D(E). This helps substantiate the validity of D(E) in characterizing diverse neutron fields for radiation damage of a practical silicon transistor. Earlier studies with large-volume silicon diodes, for monoenergetic neutrons of 0.7 to 14 MeV, tend to corroborate the D(E) validity for transistors over this energy range. These results attest to the shape in terms of gross structure of D(E), which is governed by the accuracy of the ENDF/B-IV neutron cross-section evaluation used and of themore » Robinson functional representation of the Lindhard factor for determining the fraction of recoil-atom and charged particle kinetic energy that is available to cause displacements.« less