the concave portion 20 has a linear groove shape the width of the concave portion 20 is approximately 90 nm which is approximately equal to the width w of the interconnect 4 the length of the concave portion 20 is approximately 400 nm which is approximately equal to the distance d between the first drain 9 and the second source 10 the depth of the concave portion 20 is approximately 25 nm which is approximately equal to each of the depths of the first drain 9 and the second source 10 the concave portion 20 is formed by etching for example by anisotropic etching the upper surface of the silicon substrate 1 to a predetermined depth the distance d 0 between the upper surface of the silicon substrate 1 and the lower surface of the interconnect 4 is approximately 250 nm the distance d 1 between the bottom surface of the concave portion 20 in the upper surface of the silicon substrate 1 and the lower surface of the interconnect 4 is approximately 275 nm subsequently with reference to fig4 and equations descriptions will be provided for an effect of the concave portion 20 fig4 is a view illustrating an equivalent circuit indicating a parasitic element of the case where a transmission signal flows from the first drain 9 to the second source 10 through the interconnect 4 the transmission signal flows from an input terminal 30 to an output terminal 31 both located on the interconnect 4 the interconnect 4 is shown as a first resistance component 33 of.