Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Low workfunction layer for electron emission
Reexamination Certificate
2000-11-27
2004-11-16
Tran, Minhloan (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Low workfunction layer for electron emission
C257S009000, C313S336000
Reexamination Certificate
active
06818915
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a cold cathode electron source which is sought after for use in applications such as electron-ray excited lasers, elements for a flat type display, and ultra-fast micro vacuum elements. More particularly, the present invention also relates to a semiconductor-applied field emission type electron source which can be integrated and requires a low voltage and a method for producing the same.
BACKGROUND ART
Semiconductor micro-processing technology has made progress so that a micro cold cathode structure can be constructed. This leads to vigorous development of vacuum micro electronics technology. Such a micro cold cathode structure obtained by this technology is thought to achieve a flat-type electron emission characteristic and a high level of current density. In particular, this micro cathode structure is therefore believed to serve as an electron source of a next-generation flat display. Further, the structure has an operating temperature in a range wider than that of a liquid crystal display mode such as a TFT-LCD. For this reason, such a cathode structure is thought to be useful in a display which is carried on vehicles and is required to be resistant to harsh environments.
A reduction in operating voltage, a stable electron emission characteristic, a long life characteristic, and the like are required for these electron sources when used for a flat display. In particular, the stable electron emission characteristic is directly involved in brightness which is basic to the performance of a display, regarded as an important technological target.
To obtain this goal, a method in which a resistor layer is inserted inside the electron source, a method in which a constant-current circuit is incorporated into the electron source and the like have been proposed.
Hereinafter, the configuration of a field emission cold cathode device described in Japanese Laid-Open Publication No. 8-87957 will be described with reference to FIGS.
8
(
a
) and
8
(
b
). This first conventional example adopts a principle such that a constant emitted electron flow amount of a field emission cathode element is obtained using the constant current characteristic of a field effect transistor (FET). FIG.
8
(
a
) is a cross-sectional view of a part of a silicon substrate on which a field emission cathode element and a FET are provided. FIG.
8
(
b
) is a circuit configuration diagram showing an electrical equivalent circuit of the part including the field emission cathode element.
In FIGS.
8
(
a
) and
8
(
b
), reference numeral
810
denotes a field effect transistor (FET);
801
a p-type silicon substrate;
802
a first n-type layer which serves as the source of the FET
810
;
803
a cone-shaped emitter of the field emission cathode element;
804
′ a part of an isolating layer (SiO
2
layer)
804
, the part functioning as a gate isolating layer of the field emission cathode element;
805
a gate layer of the field emission cathode element;
806
a second n-type layer which serves as the drain of the FET
810
;
807
the source electrode of the FET
810
;
808
the gate electrode of the FET
810
;
809
the anode of the field emission cathode element;
811
a source resistor;
812
a gate voltage source (voltage value Vg);
813
an anode voltage source (voltage value Va); and
814
a gate-to-source control voltage source (voltage value Vgs).
As shown in FIG.
8
(
b
), the field emission cathode element has a structure of a triode including the anode (A)
809
, the gate (G)
805
, and the emitter (E)
803
. The drain-source path and source resistor
811
of the FET
810
are connected in series between the emitter (E)
803
and the ground.
In this triode, the anode (A)
809
is connected to the anode voltage source
813
which generates the anode voltage Va. The gate (G)
805
is connected to the gate voltage source
812
which generates a fixed gate voltage Vg. In the FET
810
, the gate
808
is connected to the gate-to-source control voltage source
814
which generates a variable gate-to-source control voltage Vgs.
In the field emission cathode element for use in a field emission cathode device, a predetermined anode voltage Va and a predetermined gate voltage Vg are applied to the anode
809
and the gate
805
, respectively. When a predetermined value of gate-to-source voltage Vgs is then applied to the gate
808
of the FET
810
, emitted electron flow is generated from the emitter
803
without heating the emitter
803
. In this case, the amount of the emitted electron flow by the field emission cathode element is not controlled by the fixed gate voltage Vg applied to the gate
805
, but is controlled by the variable gate-to-source control voltage Vgs applied to the gate
808
of the FET
810
connected to the emitter
803
. In other words, an appropriate gate-to-source control voltage Vgs applied to the gate
808
of the FET
810
allows the FET
810
to operate in a constant current region.
As described above, the amount of the emitted electron flow from the emitter caused by field emission is determined by a characteristic of the FET which is connected in series to the emitter and has a function of supplying electrons which will be emitted. Therefore, optimization of the FET design allows predetermination of the operating conditions and field emission electron flow amount of the FET. In particular, when the field emission is performed in the saturated operating region of the FET, the field emission is free from factors of instability of the emitter itself. As a result, an extremely stable and accurately controlled field emission current amount can be obtained.
Among specifications required for a cold cathode is a high definition which is a very important factor for a display application. In general, in the case of a micro-chip-type cold cathode structure, the emitter emits electrons at a predetermined divergent angle. This is likely to be detrimental. A structure using a focus electrode has been proposed to provide a means for preventing the divergence of an electron path.
FIG. 9
shows a configuration example of an FED using such a structure, as a second conventional example, which is disclosed in Japanese Laid-Open Publication No. 10-74473.
In this FED, a second gate electrode (focus electrode) is formed for each emitter. This gate electrode receives a potential which is negative relative to a first gate electrode (extraction gate electrode) so as to converge electrons emitted from the emitter.
In other words, in
FIG. 9
, reference numeral
91
denotes an insulating layer. An insulating layer
93
is further provided on a gate electrode (extraction electrode)
92
. On the insulating layer
93
a second gate electrode (focus electrode)
94
which has a round opening portion is provided. In this conventional example, the second gate electrode (focus electrode)
94
is provided in such a manner as to surround each emitter
95
. This second gate electrode (focus electrode)
94
is set to a potential lower than the first gate electrode (extraction gate electrode)
92
so that electrons emitted from the emitter are affected by a lens action having a convergence effect. This causes the electron beam paths to converge.
However, the field emission type cathode element of the above-described first conventional example can control the field emission current to be stable for a short time period. In some operating condition, the stability is not secured for a long time period.
Further, whereas the field emission type display device of the second conventional example has a function of converging electron beams, the amount of electrons emitted from the emitter is adversely reduced.
DISCLOSURE OF THE INVENTION
The present invention is provided to solve the above-described problems. Objectives of this invention are as follows: (1) to obtain a field emission type electron source structure which achieves highly reliable operation required for next-generation displays; (2) to obtain a field emission type electron source structure which achieves high density
Matsushita Electric - Industrial Co., Ltd.
Mondt Johannes
RatnerPrestia
Tran Minhloan
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