Browse Prior Art Database

Large Area Cold Electron Emitters for Electron Emission

IP.com Disclosure Number: IPCOM000085144D
Original Publication Date: 1976-Feb-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 3 page(s) / 26K

Publishing Venue

IBM

Related People

Chang, IF: AUTHOR [+2]

Abstract

In applications of many display devices and/or imaging devices, there is a need for a cold electron emitter, particularly an area electron emitter. In the past, field emission emitters (cold cathode) have been developed but mainly limited to point source cathodes, such as sharp tungsten wire tips. This is because it requires a high field at the emitting surface for efficient electron emission (for work functions of 4-5 eV, field emission requires 1-5 x 10/7/ V/cm).

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Large Area Cold Electron Emitters for Electron Emission

In applications of many display devices and/or imaging devices, there is a need for a cold electron emitter, particularly an area electron emitter. In the past, field emission emitters (cold cathode) have been developed but mainly limited to point source cathodes, such as sharp tungsten wire tips. This is because it requires a high field at the emitting surface for efficient electron emission (for work functions of 4-5 eV, field emission requires 1-5 x 10/7/ V/cm).

The field at the emitting tip can be described as:

E = Beta V/d

Beta Infinity h/r where V and d are voltage and spacing between anode and emitter, respectively, and h and r are the height and radius of the emitter tip, respectively. It is practical to produce a single point emitter, but it is not trivial to produce a large area electron emitter.

It has been discovered that a tungsten dendritic structure grown on many substrates can be used as an area electron emitter. The dendritic tungsten is a brush-like structure (or velvet-like structure) having arrays of long crystal needles. These sharp needles can be used as electron emitting tips.

Experiments have been carried out to demonstrate whether field emission is indeed possible from a dendritic tungsten material. The figure shows a schematic diagram of an experimental test device which consists of anode 1, insulating spacer ring 2 and dendritic tungsten substrate 3 with dendrites 3A (as cathode). Connecting leads are provided to allow current flow through the dendritic tungsten 3 (self-heating) and to allow radiation heating from a separate heat source 4. Anode 1 comprises tin oxide glass coated with cathodoluminescent p1 phosphor approximately 3 mils thick. Insulating spacer 2 comprises approximately a 5 mil mega structure.

To obtain emission, a voltage is applied between anode 1, and the cathode 3. As t...