The effects of varying the thickness of the TiW barrier layer on the switching characteristics of a ZrO2-based electrochemical metallization memory (ECM) device were investigated. The thickness of the TiW barrier layer may alter the resistive switching characteristics of Cu/TiW/ZrO2/TiN ECM devices. Devices made without a TiW barrier layer exhibit unstable cycle-to-cycle behavior. The switching stability of ZrO2 devices improves after inserting a TiW layer. However, the insertion of TiW beyond critical thickness leads to switching degradation. We suggest that an appropriate TiW barrier layer thickness is necessary for achieving good switching performance.