Electric lamp and discharge devices – Electrode and shield structures – Cathodes containing and/or coated with electron emissive...
Reexamination Certificate
2002-01-09
2004-10-19
Zarabian, Amir (Department: 2822)
Electric lamp and discharge devices
Electrode and shield structures
Cathodes containing and/or coated with electron emissive...
C313S336000, C438S424000
Reexamination Certificate
active
06806630
ABSTRACT:
BACKGROUND OF THE INVENTION
Another application in emitter devices is described in commonly assigned co-pending U.S. patent application Ser. No. 10/043,376, entitled “PLANAR ELECTRON EMITTER APPARATUS WITH IMPROVED EMISSION AREA AND METHOD OF MANUFACTURE,” the disclosure of which is hereby incorporated herein by reference.
The present invention relates generally to ultra-high density storage devices using field emission electron emitter technology and, more particularly, the present invention relates to an improved field emission emitter that utilizes a Schottky metal-semiconductor barrier to provide solid state emission for use within the storage device.
Memory storage systems have made tremendous advancements over the years from the first use of magnetic tape to magnetic hard drives and now optical drives as well as sophisticated fast memory such as S-RAM and D-RAM. A more recent development has utilized field emission electron emitters within an ultra-high density storage device. The field emission emitters have typically been fabricated in tip-geometry that emit beams of electrons from the sharp points at the end of the tips. Electron beams are utilized to read or write to a storage medium that is located proximate the field emitters. An array of field emitters may match the array of storage areas within the storage medium or a smaller array of field emitters may be moved relative to the storage medium to access the storage locations on the storage medium.
An example of an ultra-high density storage device utilizing field emitter technology is disclosed in U.S. Pat. No. 5,557,596. Each field emitter typically generates an electron beam impinging on a storage area to generate a signal current or voltage. Each storage area can be in one of a few different states, and are most typically in a binary state of either 1 or 0 represented by a high bit or a low bit. The magnitude of the signal current generated by the beam current impinging on the storage area depends on the state of the storage area. Thus, the information stored in the area can be read by measuring the magnitude of the signal current.
The electron beam may also be utilized to write information into the storage area. The power of each electron beam can be increased to change the state of the storage area on which it impinges. By changing the state of the storage area, a bit of information is stored or erased in the storage area, depending upon the beam strength.
The speed and accuracy of information stored, retrieved, and accessed greatly depend upon the efficiency of the field emitters. Further, the manufacturing steps necessary to produce and fabricate field tip emitters is extremely complex. Furthermore, since the storage medium is spaced apart from the field emitters utilized to read or write the information thereof, it is necessary to place those elements within a protective casing under high-vacuum, on the order of 10
−7
Torr or less, in order to protect the delicate surfaces of both the emitter tips and the memory array from environmental effects. High-vacuums are expensive and difficult to achieve.
What is needed in the field emission emitter technology area is a field emission electron emitter that provides a higher efficiency than the prior art, that can be made more consistently at a lower cost than the prior art, and that is more immune to environmental effects as well as the need for high vacuum environments typically required in the prior art.
SUMMARY OF THE INVENTION
According to the present invention, a field emission device, which among other things may be used within an ultra-high density storage system, is disclosed. The emitter device includes an emitter electrode, an extractor electrode, and a solid-state field controlled emitter that utilizes a Schottky metal-semiconductor junction or barrier. The Schottky metal-semiconductor barrier is formed on the emitter electrode and electrically couples with the extractor electrode such that when an electric potential is placed between the emitter electrode and the extractor electrode, a field emission of electrons is generated from an exposed surface of the semiconductor layer. Further, the Schottky metal may be selected from typical conducting layers such as platinum, gold, silver, or a conductive semiconductor layer that is able to provide a high electron pool at the barrier. The semiconductor layer placed on the Schottky metal is typically very weakly conductive of n-type and has a wide band gap in order to create conditions conducive to creating induced negative electron affinity at applied fields necessary to provide electron emission. One type of wide band-gap material can be selected from titanium dioxide or titanium nitride or other comparable materials.
The field emission device further includes a focusing electrode that is electrically coupled to a solid state field controlled emitter and operates in conjunction with the extractor electrode to focus the electron beam emission to a small spot size within the range of 10 to 50 nanometers at the storage medium surface. Dielectric insulating layers are placed between the extractor electrode and the emitter electrode and between the extractor electrode and the focusing electrode. The use of the Schottky metal-semiconductor barrier enhances the ability of flat emitter structures to operate in field emission devices and further optimizes the ability of tip-based emitters in their operation.
A process is further disclosed in accordance with the present invention that is utilized to fabricate the field emission devices as defined above. A first step includes forming an emitter electrode layer upon a substrate surface. Then, a Schottky metal layer is formed on the emitter electrode layer. The emitter electrode layer and the Schottky metal layer may be one and the same. Next, a semiconductive layer is formed over the Schottky metal to form the solid-state field controlled emitter and provide the Schottky metal-semiconductor junction. Next, an extracting electrode layer is formed proximate the conductive semiconductor layer. In an alternative embodiment, a focus electrode layer is formed proximate the extracting electrode layer with necessary dielectric layers placed between the various electrode layers and the semiconductive layer. Alternatively, the semiconductive layer of the Schottky junction is formed after the extracting and focusing structures are created.
One preferred embodiment of the present invention is to utilize the field emission devices within an ultra-high density storage apparatus. Such a storage apparatus comprises a storage medium along with at least one field emission device. The storage medium typically includes a storage area in which one of a plurality of states is placed to represent the information stored in that storage area. The field emission device provides an electron-beam current that is utilized to read and write that information stored in the storage areas. The storage area typically has a large array of storage arrays densely packed and accessed by another array of field emission devices. In that embodiment, the field emission devices may match in array size the array of the storage medium while in other embodiments the field emission devices may be placed in a smaller array and moved relative to the storage area to perform the read and write functions. Alternatively, the storage medium may be moved relative to the electron beam or electron beams steered using electric or magnetic fields, or both.
In operation electrons are injected across the Schottky junction from the metal into the conduction band of the semiconductor and then into vacuum ending up being focused on the medium surface. Typically, the junction has a barrier height ranging from 0.2 eV to 2.0 eV. Under appropriate conditions negative electron affinity is generated in the semiconductor due to injected charge distribution that results in much lower fields required for operation.
REFERENCES:
patent: 3098168 (1963-07-01), Airgain
patent: 3105166 (1963-09-01), Choyke et al.
patent: 3121809 (1964-02-0
Binh Vu Thien
Birecki Henryk
Kuo Huei Pei
Lam Si-ty
Naberhuis Steven L.
Rose Kiesha
Zarabian Amir
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