Patent Application
20060151777
Ballistic electron emitters may be employed in a variety of applications. For example, ballistic electron emitters may be used in lithography applications, display applications, and in storage devices.
A ballistic electron emitter may include an emitter that is embedded in a dielectric material and may further include a metal film formed on the surface of the dielectric material. An electric field may be applied across the emitter and the metal film to cause the emitter to emit electrons. The emitted electrons may accelerate through the dielectric material to the metal film under the influence of the applied electric field. The accelerated electrons may pass through the metal film and emerge as ballistic electrons.
The metal film in a prior ballistic electron emitter may be a single layer of a precious metal, e.g. gold or platinum. Unfortunately, a single metal film may not adequately adhere to a dielectric material. For example, a gold film may not maintain adequate adhesion to an oxide structure. In addition, a single precious metal film may have a relatively high resistivity and/or a relatively high work function. Unfortunately, a relatively high resistivity and/or a relatively high work function may cause a leakage current in a metal film and thereby reduce the efficiency of ballistic electrons emission from the metal film.
An electron emitter is disclosed that includes a metal film having a set of layers that are selected and arranged to adhere the metal film to a remainder of a structure of the electron emitter while avoiding electron loss in the metal film. A multiple layer metal film according to the present techniques enables a balance among adhesion properties, metal diffusion, and oxide properties that might otherwise hinder the performance of an electron emitter.
Other features and advantages of the present invention will be apparent from the detailed description that follows.
The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:
The metal film 12 includes a set of layers of materials that are selected and arranged to adhere the metal film 12 to the intervening structure 14. The layers of materials in the metal film 12 may also be selected and arranged to avoid oxidation and to avoid diffusion among the metal layers in the metal film 12.
The metal film 12 has a total thickness that is selected to avoid electron loss in the metal film 12. For example, the thickness of the metal film 12 may be selected to avoid electron loss caused by scattering as the accelerated electrons from the emitter structure 16 move through the metal film 12. In one embodiment, the metal film 12 has a total thickness less than 10 nanometers.
The intervening layer 14 may be a dielectric material. Examples dielectric materials include silicon dioxide and aluminum oxide. Alternatively, the intervening layer 14 may be a semiconductor material.
In one embodiment, the top layer 20 is gold because gold does not readily oxidize. Other materials that may be selected for the top layer 20 because they do not readily oxidize include silver, platinum, iridium, rhodium, and palladium.
The material for the bottom layer 22 may be selected because it adheres well to the intervening structure 14 and does not react with the material of the top layer 20. In one embodiment, the bottom layer 22 is molybdenum because molybdenum adheres well to a dielectric material or a semiconductor material that may be used in the intervening structure 14 and because molybdenum is immisible with the gold material of the top layer 20. For example, molybdenum does not form inter-metallic compounds with gold.
Other materials that may be selected for the bottom layer 22 because they adhere well to silicon and oxides of silicon and because they do not form inter-metallic compounds with the materials that may be used in the top layer 20 include cobalt, nickel, rhenium, and rhodium. Chromium may be used for silver and gold top layer 20 metals as may molybdenum and tungsten. Chromium, molybdenum, and tungsten may be problematic with other top layer 20 metals due to inter-metallic compound formation that would enhance scattering and hence electron loss.
The total thickness of the top and bottom layers 20 and 22 is selected to minimize the loss of the accelerated electrons that move through the top and bottom layers 20 and 22. In one embodiment, the top and bottom layers 20 and 22 have a total thickness less than 10 nanometers.
The top layer 20 and the bottom layer 22 and diffusion barrier 24 have a total thickness that is selected to minimize electron loss caused by scattering as the accelerated electrons from the emitter structure 16 move through. In one embodiment, top layer 20 and the bottom layer 22 and the diffusion barrier 24 have a total thickness of less than 10 nanometers.
The layers of the metal film 12 may be deposited by sputtering. For example, the kinetic energy of material deposition provided by sputtering may increase the adhesion of the metal film 12 to the intervening layer 14. Alternatively, the layers of the metal film 12 may be deposited using evaporation or chemical vapor deposition or other such means.
The foregoing detailed description of the present invention is provided for the purposes of illustration and is not intended to be exhaustive or to limit the invention to the precise embodiment disclosed. Accordingly, the scope of the present invention is defined by the appended claims.
