TOKYO -- Pioneer Electric Corp. has developed an electron-emission device that could open the way for a flat-panel display with a conversion efficiency 150 times higher than that of a CRT. The device also may find use as an electron source for a high-speed vacuum microelectronics device.

The High Efficiency Electro-Emission Device (Heed) features a metal-insulator-silicon (MIS) diode structure. In a demonstration by the company, Pioneer engineers applied 90 V on the device and 5 kV to accelerate electrons.

Using the regular phosphor normally used for CRTs, the Heed emitted a dazzling light with a brightness of 80,000 candela per square meter. No other cold cathode devices, such as field-emission devices (FEDs), achieve such brightness.

The structure of the device includes a platinum anode, a 400-nm-thick silicon oxide layer as an insulator, a 5,000-nm silicon layer, and aluminum cathode piled up on a substrate. Electrons begin to emit from the platinum anode when about 60 V are applied between the platinum anode and aluminum cathode. When 90 V are applied, emission current reaches 1.8 mA /cm2. ''The device showed the conversion efficiency from energy to electron at 30 percent, which is about 150 times higher compared with CRT's 0.2 percent,'' said Kiyohide Ogasawara, general manager at Pioneer's R&D laboratory.

Previous MIS diode cold cathode devices needed an insulator layer that was very thin--only several nanometers thick--to contain just about 10 atoms, generate a tunnel effect and emit electrons. ''To form such a thin layer uniformly is difficult, and it is subject to have defects that cause short circuit,'' said Ogasawara. ''The Heed device has a 400-nm-thick insulator, which is easier to form and is more reliable.''

In theory, 12 nm is the maximum thickness of an SiO2 insulator layer that can emit electrons by tunnel effect, he said. The electron emission from the Heed device uses something called the Negishi effect, named after Pioneer engineer Nobuyasu Negishi. Pioneer researchers will continue studying the Heed to learn its characteristics, life, reliability and production technology.

The device's relatively high driving voltage can be lowered if necessary, said Ogasawara. ''If we make the insulator layer thinner, for example, the voltage can be lowered,'' he said. Cold cathode devices such as FEDs are promising for flat-panel displays, and so are the Heeds. Pioneer intends to develop the device into a form of passive-matrix display.

At the same time, Pioneer researchers intend to propose the device as a electron source for vacuum microelectronics devices, the company said. Pioneer's technology achieves high brightness using conventional CRT phosphors.

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