Deterioration in the piezoelectric property of ScAlN thin films by negative ion bombardment increased in low-pressure sputtering deposition

ScAlN films are known to have piezoelectric properties much larger than AlN films and can be deposited using a RF magnetron sputtering method. In general, sputtering deposition at low gas pressure improves the film quality, because increasing mean free path of sputtered particles results in reducing their thermalization and scattering. However, negative ion bombardment to the substrate increase at low pressure. We have previously shown that carbon and oxygen impurities in the Sc ingots cause negative ion bombardment, which degrades the piezoelectric properties of ScAlN films. In this study, we have demonstrated that the piezoelectric properties of ScAlN films are deteriorated by the negative ion bombardment increased in low-pressure sputtering deposition.