The degradation of Pb(Zr,Ti)O3 [PZT] ferroelectric capacitors with IrO2 top electrode and Pt bottom electrode was evaluated by baking at 200°C in 3% D2/N2 gas at 4.5 Torr up to 20 min. The polarization of the capacitor decreased by more than 60% and the hysteresis loop shifted to positive side when baked for 15 min or more in D2/N2 gas. Auger Electron Spectroscopy indicated that the surface of the IrO2 was reduced to Ir metal during D2 baking. Secondary ion mass-spectroscopy (SIMS) of the PZT capacitor revealed that the degraded PZT contained a D concentration of $5\times 19$ atoms/cm3. The degradation of the capacitor followed a three step mechanism: 1) reduction of the IrO2 top electrode surface to Ir, 2) Deuterium dissociation into to D$+$ ions on the Ir surface and 3) diffusion of D$+$ into the PZT film.