We propose a novel method for suppression of quasiparticle poisoning in Al Coulomb blockade
devices. The method is based on creation of a proper energy gap profile along the device. In contrast
to the previously used techniques, the energy gap is controlled by the film thickness. Our transport
measurements confirm that the quasiparticle poisoning is suppressed and clear 2e periodicity is
observed only when the island is made much thinner than the leads. This result is consistent with the
existing model and provides a simple method to suppress quasiparticle poisoning.