  Quarkonium correlation functions at finite temperature were studied in a
region of the quark mass for charmonia to bottomonia in quenched lattice QCD
with $O(a)$-improved Wilson quarks. Our simulations were performed on large
isotropic lattices at temperatures in the range from about 0.80$T_c$ to
1.61$T_c$. We investigated quarkonium behavior in terms of temperature
dependence as well as quark mass dependence of the quarkonium correlation
functions and related quantities at both vanishing and finite momenta.
