Abstract: In a thin film transistor, a gate insulating layer is formed on a gate electrode formed on an insulating substrate. Formed on the gate insulating layer is a semiconductor layer. Formed on the semiconductor layer are a source electrode and a drain electrode. A protective layer covers them, so that the semiconductor layer is blocked from an atmosphere. The semiconductor layer (active layer) is made of, e.g., a semiconductor containing polycrystalline ZnO to which, e.g., a group V element is added. This allows practical use of a semiconductor device which has an active layer made of zinc oxide and which includes an protective layer for blocking the active layer from an atmosphere.

Abstract: In a high voltage or current detector of the type utilizing an insulating tube, polarized light is directed to a photoelectric element mounted on the upper end or contained in the insulating tube so as to modulate the polarized light in accordance with the voltage or current to be measured. The modulated light is directed to a photosensitive element on the lower end of the tube for producing an electric signal which is applied to a meter for displaying the voltage or current.