Electric lamp and discharge devices – Discharge devices having three or more electrodes
Patent
1997-08-25
1998-10-06
Patel, Ashok
Electric lamp and discharge devices
Discharge devices having three or more electrodes
313309, 313336, 313351, 445 24, 445 50, 216 24, 216 25, 438 20, H01J 904, H01J 130
Patent
active
058181539
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to self-aligned gate field emitter devices and to methods of producing the same and has particular, although not exclusive, relevance to such devices as may be employed as switches in electronic circuits.
The concepts of field emission, i.e. the presence of a very thin barrier potential at a surface from which electrons may migrate, are well known. Numerous devices exist which exhibit field emission. One such example is a sharply pointed substrate such as disclosed in "Atomically Sharp Silicon and Metal Field Emitters", IEEE Transactions on Electron Devices, Vol. 38, No. 10, Oct. 1991. This literature describes a method for producing an atomically sharp silicon tip of less than 10.degree.-15.degree. half-angle. It is known that such sharp tips provide the very thin barrier potential necessary for field emission.
However during the fabrication of a device such as described above, great care needs to be taken to ensure that no damage occurs to the field emitter. This problem will be appreciated because such structures are generally microengineered. This term will be understood by those skilled in the art as meaning that fabrication is conducted on scales of around 1.times.10.sup.-6 m.
Furthermore if such a device is fabricated with a gate structure, as will generally be the case when the device is to be employed in electronic circuitry, then accurately positioning the gate with respect to the field emitter is an arduous task when the device is microengineered.
It is thus an object of the present invention to at least alleviate the aforementioned problem.
According to a first aspect of the present invention there is provided a self-aligned gate field emitter device comprising: a substrate carrying a tapered protrusion; the tapered protrusion carrying on electrically insulative layer at least partially covering the protrusion, the electrically insulative material extending along the flanks of the tapered protrusion from the base adjacent the substrate towards the tip of the protrusion remote from the substrate; electrically conductive material formed on the electrically insulative layer and extending further towards the tip of the protrusion than the insulative layer and spaced from the protrusion, the tapered protrusion forming the emitter of the device and the electrically conductive material forming the gate of the device, which gate, in operation of the device, provides control for the level of field emission from the emitter, characterized in that electrically conductive material is partially covered by thermoplastic material substantially around the base of the protrusion for supporting the electrically conductive material.
Because the electrically conductive material overlies the electrically insulative material by some way, then a more rigid device is formed by provision of the thermoplastic material around the electrically conductive material.
Advantageously the electrically insulative material is formed by oxidation of the tapered protrusion. This then obviates the need for a separate coating of insulative material. Alternatively it is possible for the insulative material to be an oxide coating formed on the protrusion. Additionally, the protrusion may be formed from the substrate material itself.
According to a further aspect of the present invention there is provided a method of producing a self-aligned gate field emitter device comprising: providing a substrate of material from which the field emitter is to be produced and forming a tapered protrusion thereon; forming, on the surface of the protrusion, electrically insulative material; coating the electrically insulative material with electrically conductive material; at least partially coating the electrically conductive material with thermoplastic material; planarizing the device such that the thermoplastic material remains around the base of the protrusion substantially remote from the tip thereof to at least partially expose the electrically conductive material; selectively removing at least part of the electrical
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Central Research Laboratories Limited
Patel Ashok
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