Temperature Dependence of Surface Acoustic Wave Characteristics of GaN Layers on Sapphire Substrates

Abstract

We measured surface acoustic wave (SAW) characteristics along the [01-10] and [2-1-10] directions of 1.5- and 2-µm-thick GaN layers on (0001) sapphire substrates at ambient temperatures between -50 and 200°C. The extracted thermal coefficient of delay (TCD) for the SAW propagating along the [01-10] direction, which is smaller than that for the SAW propagating along the [2-1-10] direction, decreases when GaN layer thickness, h, multiplied by SAW wave number, k, increases. The TCD for h k = 3.9, which might be close to that in bulk GaN, is as small as 28.3 ppm/deg. These results indicate that GaN is promising for SAW device operation over a wide range of ambient temperatures.

SAW characteristics of GaN layers with surfaces exposed by dry etching

“…RF characteristics of the two filters at room temperature. [5]. Furthermore, the height of the main peak for the sample-A device decreased by 1.5 dB for the ambient temperature increase.…”

“…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.…”

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

“…Measures of the maximum descripancies among the data are also shown. λ = 3.2 µm) [8], possible influence of uncertainty in ambient temperatures, 5 degrees at maximum, on v SAW is likely to be negligibly small. Dashed lines show velocity dispersion curves obtained by calculation using different elastic modulae for GaN [7].…”

“…We simultaneously formed SAW filters with IDT width and separation of 0.8 µm. Details of the filter fabrication process were previously reported [8].…”

“…AlGaN/GaN field-effect transistors have been successfully applied to dual-gate mixers [2] as well as to L-or K-band power amplifiers [3,4]. 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.…”