An apparatus in one example comprises an insulating piezoelectric layer, a base electrode along a first side of the insulating piezoelectric layer, and at least one gradient electrode along a second side of the insulating piezoelectric layer. The at least one gradient electrode is configured to provide a voltage gradient across an aperture of a surface acoustic wave (SAW) filter. The base electrode and the at least one gradient electrode are configured to provide a voltage bias across the insulating piezoelectric layer. The voltage bias comprises a gradient based on the voltage gradient across the aperture of the SAW filter. The base electrode and the at least one gradient electrode are configured to control at least one frequency characteristic of the SAW filter based on the voltage bias across the insulating piezoelectric layer.