Electronic device applications of high‐temperature superconducting cuprates require the production of patterned thin films that are stable and inert in various processing and operating environments; however, the superconducting rare‐earth barium cuprates have been shown to decompose in water and to degrade in superconducting properties in a humid atmosphere. The thermodynamics that forms the driving force for the degradation is reviewed. Protective coatings or removable protective films can realize many applications and facilitate processing of superconducting devices. Diamondlike carbon films as well as amorphous carbon films are investigated as possible protective layers for YBa2Cu3O7-x (YBCO). Amorphous carbon (a‐carbon) films deposited by evaporation are shown to protect superconducting YBCO films from degradation by humidity. The YBCO films with a‐carbon coatings have been shown to have critical current densities four orders of magnitude higher than the uncoated YBCO films after 2 h at a stressing of 100% relative humidity (RH). A similar stressing for 44.5 h has conducting YBCO films but no longer has a measurable critical current density. The a‐carbon coating is an effective passivation layer for short‐term storage (with time ≪2 h and 100% RH and time ≳4 h at 50% RH) at room temperature. The critical current is shown to be a better indicator for the degree of degradation, since the transition temperature remains relatively constant as long as there is enough superconducting YBCO to provide a percolation path for the supercurrent. Degrees of degradation were also assessed by scanning electron microscopy. The versatility of these carbon films lies in that their deposition and removal by plasma oxidation at room temperature are compatible with YBCO films. © 1995 American Institute of Physics.