Side-gate effects on transfer characteristics in GaN-based transversal filters

We examine the transfer characteristics of transversal filters with side gates fabricated on unintentionally doped GaN layers grown on (0001) sapphire substrates. By positively biasing the side gates, the transfer characteristics of the filters are efficiently improved, which means that GaN-based transversal filters with side gates are potentially applicable for filtering and modulating rf signals. We further examine the capacitance in an interdigital transducer, which decreases when the side-gate bias voltage increases. This indicates that the variation in the transfer characteristics is likely to be attributable to a change in the depletion-layer thickness in the GaN layers.