Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure
Reexamination Certificate
2000-02-18
2001-12-04
Le, Hoanganh (Department: 2821)
Electric lamp and discharge devices: systems
Cathode ray tube circuits
Combined cathode ray tube and circuit element structure
C315S003500, C315S005390, C315S169100, C313S309000, C313S351000
Reexamination Certificate
active
06326729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cathode emitting electron, and more particularly relates to a field emission cathode emitting an electron beam which is modulated in accordance with a high frequency within the millimeter wave or microwave region. The present invention also relates to an electromagnetic wave generating apparatus comprising such a field emission cathode.
2. Explanation of the Related Art
Heretofore, electron beam devices, semiconductor devices and lasers have been used as a means for generating an electromagnetic wave.
As the electron beam device, there has been known a microwave electron tube such as magnetron and klystron. In this microwave electron tube, microwave energy is obtained by an interaction between an electron beam and a electric field of the microwave. Such microwave electron tube has been generally used for generating a relatively high power output and has a relatively high efficiency. However, when a wavelength of the electromagnetic wave to be generated becomes shorter, circuit structures composing the device are liable to be very small, the modulation of the electron beam might be very difficult, and a size of the device might become extremely large.
In the semiconductor device, an electromagnetic wave is generated by the modulation of electron travelling within the semiconductor material. However, since the. travelling velocity of electron within the semiconductor material is low, any useful electromagnetic wave generating apparatus of the order lower than millimeter wave region has not been developed.
Lasers generally generate light wave, but an infrared laser has been developed. As a far infrared laser, there has been developed a gas laser excited with light. Therefore, the apparatus is liable to be large in size and complicated in structure.
As explained above, any useful apparatus for generating a high power electromagnetic wave within the millimeter wave or microwave region with a high efficiency has not been developed.
SUMMARY OF THE INVENTION
The present invention has for its object to provide a novel and useful field emission cathode which can generate efficiently a high power electron beam modulated at any desired frequency within the millimeter wave or microwave region, while the structure of the field emission cathode can be simple and small.
Another object of the present invention is to provide an apparatus for generating efficiently a high power electromagnetic wave within the millimeter wave or microwave region by a cooperation of the electron beam emitted by the above mentioned field emission cathode, while the apparatus is small in size, simple in structure.
According to a first aspect of the present invention, a field emission cathode comprises:
a collector region made of an N type semiconductor material;
at least one cathode tip formed in a surface of said collector region;
an insulating layer provided on the surface of said collector region and including at least one opening which surrounds said at least one cathode tip;
a gate electrode provided on said insulating layer and including at least one opening which surrounds said at least one cathode tip;
a base region made of a P type semiconductor material and being provided such that a pn junction is formed between said collector region and said base region; and
at least one emitter region made of an N type semiconductor material and being provided such that a pn junction is formed between said base region and said at least one emitter region;
wherein by connecting a high frequency supply source across the emitter region and the base region and by connecting a DC supply source across the gate electrode and the emitter region, an electron beam modulated in accordance with a high frequency of said high frequency supply source is emitted from said cathode tip.
In the field emission cathode according to the first aspect of the present invention, said collector region, base region and emitter region may be formed by a semiconductor substrate such as silicon (Si), germanium (Ge), gallium arsenide (GaAs) and indium phosphide (InP). In the field emission cathode according to the first aspect of the invention, the cathode tip is formed on one surface of the semi-conductor substrate and the base and emitter regions are formed in the other surface of the semiconductor substrate. Therefore, the cathode tip structure can be precisely and easily formed and at the same time the base and emitter regions can be also formed precisely and easily.
In a preferable embodiment of the field emission cathode according to the first aspect of the invention, a plurality of arrays each including a plurality of linearly aligned cathode tips are formed in one surface of said semiconductor substrate, and a corresponding plurality of arrays each including a plurality of linearly aligned emitter regions are formed in the other surface of the semiconductor substrate. In this embodiment, emitter electrode and base electrode may be advantageously formed in an interdigital manner. Further, it is preferable to form the cathode tip to have a sharp front end. Then, an efficiency of the generation of the electron beam can be improved due to a concentration of the electric field at the sharp front end of the cathode tip.
According to a second aspect of the invention, a field emission cathode comprises:
an emitter region made of an N type semiconductor material having the Gunn effect;
at least one cathode tip formed in a surface of said emitter region;
an insulating layer including at least one opening which surrounds said at least one cathode tip;
a gate electrode provided on said insulating layer and including at least one opening which surrounds said at least one cathode tip; and
an emitter electrode electrically connected to said emitter region;
wherein a high electric field domain is produced periodically with a high frequency within said emitter region by applying a DC supply voltage across the gate electrode and the emitter electrode, and an electron beam modulated in accordance with said high frequency is emitted from said cathode tip.
As is well known, the Gunn effect pertains to high-frequency oscillation of electrical current flowing through n-type bulk semiconductors such a gallium arsenide (GaAs), indium phosphide (InP) and Cadmium Tellurium (CdTe). It was discovered by J. B. Gunn in 1963 (J. B. Gunn, Solid State Communications, Vol. 1, p. 88 (1963)). The effect is used in solid state devices, e.g., Gunn diodes, to produce short radio waves called microwaves. The Encyclopaedia Britannica defines the Gunn effect as follows:
“In material displaying the Gunn effect electrons can exist in two states of mobility, or ease of movement. Electrons in the state of higher mobility move through the solid more easily than electrons than electrons in the lower mobility state. When no electrical voltage is applied to the material, most of its electrons are in the high mobility state. When an electrical voltage is applied, all its electrons begin to move just as in ordinary conductors. This motion constitutes an electrical current, and in most solids greater voltages cause increased movement of all the electrons and hence greater current flow. In Gunn-effect materials, however, a sufficiently strong electrical voltage may force some of the electrons into the state of lower mobility, causing them to move more slowly and decreasing the electrical conductivity of the material. In electronic circuits incorporating the Gunn diode, this unusual relationship between voltage and current (motion) results in the generation of high-frequency alternating current from a direct-current source.” Definition of Gunn effect, (Feb. 13, 2001) <http:// www.britannic.com>
In the field emission cathode according to the above mentioned second aspect of the invention, the emitter region including the cathode tip may be made of N type compound semiconductor material having the Gunn effect such as GaAs and InP.
In the field emission cathode according to the first aspect of the present i
Mimura Hidenori
Yokoo Kuniyoshi
Le Hoang-anh
Stevens Davis Miller & Mosher LLP
Tohoku University
Vo Tuyet T.
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