Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Low workfunction layer for electron emission
Reexamination Certificate
1999-06-17
2001-08-14
Lee, Eddie C. (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Low workfunction layer for electron emission
C313S310000, C313S309000, C313S336000, C313S351000, C438S020000, C445S049000, C445S050000, C445S051000
Reexamination Certificate
active
06274881
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electron emission element having a high electron emission characteristic, a high surface stability and a long life used in, for example, a field emission type display device and an imaging tube; and a method for producing such an electron emission element. The present invention further relates to a field emission type display device configured using the electron emission element and a method for producing the same.
BACKGROUND ART
Liquid crystal display panels are in the widest use today as thin and lightweight display devices. A liquid crystal display panel is a light valve for controlling the voltage applied to a liquid crystal layer by a switching element such as a thin film transistor or an MIM (metal-insulator-metal) element on a pixel-by-pixel basis and thus adjusting the amount of light transmitted through the liquid crystal layer. The liquid crystal display devices are not self-light emission elements which emit light themselves and thus generally have problems of dark images and narrow viewing angles.
As a thin and lightweight self-light emission element solving such problems of the liquid crystal display devices, an electron &mission element has been a target of attention. The electron emission element is not a hot-electron emission type element for heating a cathode to emit electrons as a conventional CRT, but is a cold cathode type element for extracting electrons from the cathode by electric field.
Regarding the conventional electron emission elements, for example, a technology for producing a micrometer-size fine vacuum element utilizing a microscopic processing technology used for producing semiconductor transistors and the like (see, for example, (1) Junji ITO, Oyo Buturi, Vol. 59, No. 2, pp. 164-169, 1990, or (2) Kuniyoshi YOKOO, Journal of the Institute of Electrical Engineers of Japan, Vol. 112, No. 4, 1992) has been developed.
As shown in
FIG. 7
, this electron emission element includes a conductive silicon substrate (cathode substrate)
701
and a silicon layer provided on the silicon substrate
701
and having a conical projection
702
on a surface thereof. The conical projection
702
is formed using microscopic processing technology and acts as an electron emitter section formed of silicon. An anode substrate is provided opposed to the cathode substrate
701
having the electron emitter section. The anode substrate is formed by sequentially depositing a transparent electrode
704
and a phosphor thin film
705
, and optionally a metal thin film, on a transparent glass substrate
703
. The anode substrate is set up so that a surface thereof having the phosphor thin film
705
faces the electron emitter section.
When the cathode substrate and the anode substrate which are included in a light emission element and are opposed to each other are put in a high vacuum and a prescribed voltage is applied between the cathode substrate and the anode substrate, electrons are emitted from the tip of the electron emitter section into the vacuum. The emitted electrons are accelerated by the applied voltage and reach the phosphor thin film
705
. The collision of the electrons with the phosphor thin film
705
causes the phosphor thin film
705
to emit light. The phosohor thin film
703
is allowed to emit light of the three primary colors of red, blue and green or intermediate colors therebetween by changing the materials thereof. The brightness of the light emitted by the phosphor material is controlled by adjusting the voltage a gate electrode
706
.
A display device is formed by arranging a plurality of such light emission elements on a plane.
In the case of the above-described conventional electron emission element, the electron emitter section is formed to be conical so that the field intensity of the tip thereof is increased for emitting electrons under low-voltage operation. Accordingly, the current density at the tip is increased.
In addition, since the electron emitter section is formed of silicon which has a lower conductivity than metal, heat is easily generated at the tip during the operation of the element. Accordingly, the tip of the emitter section is vaporized or melted by heat, which increases the radius of curvature of the tip of the emitter section. As a result the electron emission characteristics are deteriorated.
When the electron emission characteristics are thus deteriorated, the brightness of light emitted from the phosphor is lowered. In order to raise the brightness, the operating voltage needs to be raised to recover the, current following though the emitter section. However, since the electric resistance is large at the tip of the emitter section as described above, the amount of heat generated at this section is further increased. Consequently, the electron emission characteristics are acceleratively deteriorated. As a result, the element is destroyed and the desired electron emission is not realized.
As described above, the conventional electron emission element does not allow the operating current to be increased due to the sharp tip configuration of the emitter section, and therefore provides a low brightness of light and a short life, and is inferior in operating stability and reliability. It in very difficult to put such an element into practical use as a display device.
DISCLOSURE OF THE INVENTION
The present invention for solving the above-described problems has objectives of (1) providing an electron emission element which has a sufficiently large operating current and show& no deterioration of an emitter section, with a long life, and is superior in operating stability and reliability; (2) providing at method for producing such an electron emission element; and (3) providing a field emission type display device utilizing such an electron emission element and a method f or producing the same.
According to one aspect of the present invention, in an electron emission element having an emitter section for emitting electrons, the emitter section includes, on a first conductive electrode, a structure in which at least a first semiconductor layer, a second semiconductor layer, an insulating layer and a second conductive electrode are deposited sequentially, and the first and second semiconductor layers include at least one of carbon, silicon and germanium as a main component, and the first semiconductor layer includes at least one type of atoms among carbon atom, oxygen atoms and nitrogen atoms which is different from the main component, whereby the aforementioned objectives can be achieved.
The first semiconductor layer may be amorphous.
Preferably, the first semiconductor layer has an unpaired electron density of about 1×10
18
cm
−3
or more.
The insulating layer may include at least one of carbon, silicon and germanium as a main component.
In one example, the second semiconductor layer and the insulating layer interpose therebetween a graded area where an element forming the second semiconductor layer and an element forming the insulating layer exist in a mixed state.
Preferably, the graded area has a thickness which is about 0.01 &mgr;m or more and less than the thickness of the insulating layer.
In one example, at least an interface between the second semiconductor layer and the insulating layer has irregularities.
Preferably, the irregularities at the interface has a maximum depth which is about {fraction (1/100)} or more of the thickness of the insulating layer and less than the thickness of the insulating layer.
In one example, an interface between the first conductive electrode and the first semiconductor layer has irregularities.
In one example, the second semiconductor layer includes at is least microcrystals.
The first and second semiconductor layers may include at least hydrogen.
The second semiconductor layer may include therein an amorphous area and a microcrystalline area in a mixed state.
Preferably, the microcrystals included in the second semiconductor layer hag d diameter of about 1 nm to about 500 nm.
A field emission type display device provided in
Akiyama Koji
Kurokawa Hideo
Baumeister Bradley WM.
Lee Eddie C.
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
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