Stability of deflected-beam metal–insulator–metal tunneling cathodes under high acceleration voltage

Abstract

Metal–insulator–metal (MIM) tunneling cathodes have advantageous features, such as areal electron beams and robustness to surface contamination. Therefore, they are suitable for field-emission displays. This paper reports the long-term stability of MIM tunneling cathodes in display panels operating under a high acceleration voltage (anode voltage). A preliminary life test was carried out using conventional display panels, which consisted of a phosphor-coated anode plate and a cathode plate having matrix-arrayed cathodes. The life test indicated that the pace at which cathodes degrade increases significantly when the acceleration voltage exceeds a few kilovolts. This high-voltage (HV)-induced degradation is presumably attributed to cathodes being bombarded by positive ions originating from residual gases. To suppress HV-induced degradation, the authors propose the concept of a deflected-beam cathode, in which electron beams are deflected so that the recoiling ions fail to hit the cathode. This concept was implemented by introducing deflector electrodes in the cathode plate, thereby forming an electron lens in each pixel. As 6-μm high scan lines were used as the deflector electrodes in this design, the deflected-beam cathodes could be fabricated only by modifying the pattern of the scan lines. The authors also present a simulation-based design procedure using an emitter-landing diagram, which facilitates analysis of the margins for the deflected-beam cathodes. The deflected-beam cathodes thus designed were incorporated into 3.8 cm-diagonal test panels to confirm the validity of the concept. The degree of beam deflection that was observed was in excellent agreement with the results obtained from simulation. A life test extending over a 20 000-h period demonstrated that the HV-induced degradation was suppressed with the deflected-beam MIM cathodes.