According to the invention, there is provided seed and plants of the hybrid corn variety designated CH399948. Paths for high-frequency signals are cut off, and high-frequency signals can be prevented from leaking although there are parasitic capacitances due to the protecting elements being connected. The present invention is further directed to a method for forming a device of increasing operation voltage over an existing device of same functionality by adding a few steps in the early manufacturing process of the existing device therefore without drastically affecting the device performance. The overhang hangs over the airway and has an air window formed in the overhang and communicating with the airway.