Planar Two-dimensional Electron Gas (2DEG) IDT SAW Filter on AlGaN/GaN Heterostructure

Surface acoustic wave (SAW) filters using two-dimensional electron gas (2DEG) as interdigital transducers (IDT) on AlGaN/GaN heterostructure has been demonstrated for the first time using a fluoride-based (CF₄) plasma treatment technique. The CF₄ plasma treatment is used to pattern 2DEG IDT on a planar surface without removing the top AlGaN layer. The RF characteristics of the SAW filters with planar 2DEG IDTs are compared with metal IDT SAW filters. It is shown that the massloading effects and the triple-transit-interference (TTI) are suppressed in the 2DEG IDT SAW devices owing to the removal of the metal IDTs. It is capable of reducing not only the passband ripple, but also the size of devices because 2DEG IDTs can be placed closer. In addition, the detection part of the SAW sensor can be performed on the top of the planar 2DEG IDTs rather than in the SAW propagation path. This novel SAW device can be integrated with high-electron mobility transistors (HEMTs) on AlGaN/GaN heterostructure to deliver a viable approach for single chip GaN wireless sensors.