Abstract: Within a vacuum envelope constituted by a back base plate and a display panel, a thermionic cathode structure and first to third electrode structures are arranged in the mentioned order from the side of the back base plate to the side of the display panel. In the thermionic cathode structure a plurality of coiled heaters are arranged in a planar array such that each coiled heater corresponds in position to each of picture element regions regularly arranged in a fluorescent material layer provided on the inner side of the display panel. The coiled heaters are supported such that their effective thermionic electron emitting portions are held in space such that each of these portions corresponds to each of the picture elements, and their other portions are supported by a plurality of support members. These support members are arranged such that all the coiled heaters are connected in parallel to a heating power supply.

Abstract: A flat display device comprises a vacuum envelope constituted by a back base plate consisting of an elastic metal plate and a display panel and accommodating a thermionic cathode structure and a plurality of electrode structures for controlling the electron beams emitted from the thermionic cathode structure. The thermionic cathode structure is divided into a plurality of sections each including a plurality of coiled thermionic cathode heaters connected in parallel and arranged such that each corresponds to each of picture element regions provided on the back side of the display panel. Voltage supply terminals for supplying power to the parallel coiled heaters in each section are led out through the back base plate via insulating members.