Abstract: A semiconductor structure is provided. The semiconductor structure includes a substrate, a channel layer, a barrier layer, a compound semiconductor layer, a gate electrode, and a stack of dielectric layers. The channel layer is disposed on the substrate. The barrier layer is disposed on the channel layer. The compound semiconductor layer is disposed on the barrier layer. The gate electrode is disposed on the compound semiconductor layer. The stack of dielectric layers is disposed on the gate electrode. The stack of dielectric layers includes layers having different etching rates.

Abstract: A universal socket includes a barrel seat, a resilient member and a rotating component. The barrel seat has an inner wall surface having four receiving surface portions, and four linking surface portions each connected between two adjacent ones of the receiving surface portions and having two flat surface segments. The rotating portion is retained in the barrel seat, and has four corner surfaces corresponding in position to the receiving surface portions, respectively, and four contacting surfaces each connected between two adjacent ones of the corner surfaces and biased by the resilient member to abut against one of the flat surface segments.

Abstract: A universal socket includes a barrel seat, a resilient member and a rotating component. The barrel seat has an inner wall surface having four receiving surface portions, and four linking surface portions each connected between two adjacent ones of the receiving surface portions and having two flat surface segments. The rotating portion is retained in the barrel seat, and has four corner surfaces corresponding in position to the receiving surface portions, respectively, and four contacting surfaces each connected between two adjacent ones of the corner surfaces and biased by the resilient member to abut against one of the flat surface segments.