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

Abstract

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.

Velocity dispersion in GaN-based surface acoustic wave filters on (0001) sapphire substrates

“…This view is consistent with our finding that the centre frequencies of SAW filters on a conductive GaN layer are almost independent of side-gate bias voltages [10]. More precise studies such as group-delay analyses, however, are required in order to clarify the influence of the electrical properties of GaN layers on SAW transport characteristics.…”

“…The capacitance of Al Schottky contacts on C was found to be 80 ∼ 90 pF/mm 2 . These results indicate [10] that there is formed in C a depletion region with thickness of ∼ 1 µm, below which a conductive neutral region is located. No significant results were obtained for the other two layers, which suggests that their resistivities are markedly high and their residual impurity concentrations are unmeasurably low.…”

“…Recently, (Al)GaN-based surface acoustic wave (SAW) devices have been investigated for the purpose of exploiting both the marked piezoelectric properties and semiconducting characteristics of group-III nitrides [1,5,6,7,8]. Change in filter characteristics due to ultraviolet illumination [9] and that due to DC bias voltages [10] have also been examined.…”

Surface acoustic waves in semi-insulating Fe-doped GaN films grown by hydride vapor phase epitaxy

“…[6][7][8][9][10][11][12][13] In these studies, the thickness and the resistivity of the GaN films were assumed to be key factors to affect the surface acoustic modes and the electromechanical coupling coefficients. 9,10,[14][15][16] The emergence of various acoustic modes is dependent on the ratio between the GaN film thickness and the SAW wavelength. 6,8 The electromechanical coupling coefficient of GaN layers with different thickness and different resistivities were reported in a large range from 0.015% to 4.3%, and it was pointed out that the high resistivity of GaN layer might be preferable for improving the performances of SAW devices.…”

SAW characteristics of GaN layers with surfaces exposed by dry etching

“…GaN-based surface acoustic wave (SAW) devices have also been explored due to the large piezoelectricity of GaN [3]: The properties of GaNbased SAW filters, such as SAW velocity dispersion [4], temperature dependence [5], responce to ultraviolet illumination [6], and side-gate effects [7] have been previously reported.…”