  The main proposal of this paper is to analyze the size of the Cooper pairs
composed by unbalanced mass fermions from different electronic bands along the
BCS-BEC crossover and study the binding energy of the pairs. We are considering
an interaction between fermions with different masses leading to an inter-band
pairing. In addiction to the attractive interaction we have an hybridization
term to couple both bands, which in general acts unfavorable for the pairing
between the electrons. We get first order phase transitions as the
hybridization break the Cooper pairs for the the $s$-wave symmetry of the gap
amplitude. The results show the dependence of the Cooper-pair size as a
function of the hybridization for $T=0$. We also propose the structure of the
binding energy of the inter-band system as a function of the two-bands
quasi-particle energies.
