Capacitance-voltage characteristics of NaNbO3 thin films

By radio-frequency magnetron sputtering of bulk NaNbO3 pellet targets, films of NaNbO3 have been deposited on silicon substrates at different temperatures. Room-temperature deposited films have been annealed at different temperatures. Film samples have been characterized using an x-ray diffraction method. The room-temperature deposited films show a crystalline structure with different orientations, and films deposited at 225 and 270 degreesC show a crystalline structure with a single-face orientation. Films deposited at 300 degreesC and higher temperatures show an amorphous nature. Annealing up to 500 degreesC changes the orientation of the room-temperature deposited films, and annealing at and beyond 600 degreesC results in amorphous films. Capacitance-voltage measurements have been carried out in a metal-insulator-semiconductor configuration by sandwiching a NaNbO3 film between aluminum and silicon. Structural and capacitance-voltage characteristics of the films have been found to be sensitive to sodium and oxygen stoichiometry. Hysteresis in the capacitance-voltage measurements indicates hole injection in the annealed films and electron injection in the films deposited at different temperatures. From the observed characteristics, the capacitance of the accumulation region, capacitance of inversion region, flat-band capacitance, flat-band voltage, amount of hysteresis, density of states, density of interface states, dielectric constant, maximum capacitance of depletion layer, and maximum depletion width have been calculated for the prepared samples. In the crystalline films, with increasing deposition or annealing temperature, the dielectric constant tends to that of the bulk. The charge storage capacity, charge storage density, density of states, and density of interface states for NaNbO3-assisted metal-insulator-semiconductor structure have been found to be quite larger as compared to reported values for other materials, which suggests the superior potential of NaNbO3 films for memory applications. (C) 2003 American Institute of Physics.