Invented by Chenggang Xie, Nalin Kumar, ST DIAMOND TECHNOLOGY Inc, Applied Nanotech Holdings Inc
The ST DIAMOND TECHNOLOGY Inc, Applied Nanotech Holdings Inc invention works as follows
The device is a flat substrate, anode disposed on the substrate and a cathode positioned on the surface. The device consists of a flat substrate with an anode on it and a cathode on the same substrate. The cathode provides an electron emission surface that can emit electrons across a gap, to a large portion of the adjacent surface of anode.
Background for The invention relates to a device that emits a lateral field and explains how it is manufactured.
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The invention is related to field emitters and, more specifically, to lateral luminescent fields emitter devices on flat panel displays.
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There are many ways to emit electrons from a substance by increasing their energy at the surface of the material so that they exceed a certain barrier in energy potential. In order to increase electron energy at the emission surface, charged particles, such as electrons and ions, are used in thermionic, photoemission, or secondary emission. For example, electron emission has been used in cathode-ray tubes found in television sets.
Field emission devices ( “FED’s”) release electrons not by increasing the energy of the electrons, but by lowering the barrier potential at the conductive emission surface. According to quantum mechanics, even though the energy of the electrons in the conductive material is not greater than the potential barrier on the conductor’s surface, a portion of these electrons will tunnel past the barrier and be emitted from the surface. A field of electricity can be used to reduce the potential barrier, increasing the field emission current. These FEDs are used in flat panel displays and electron microscopes. These FED’s have been studied extensively and are widely known. R. J. Noer’s “Electron Field Emmission from Broad Area Electrodes” in Applied Physics A 28 pp. 1-24 (1982).
FEDs have limitations that limit their utility. One limitation is the level of energy that the electrons receive after they have been emitted. A second limitation is the uniformity in emission current. In the discussion that follows, we will explain in more detail how these limitations and others are achieved.
One limitation concerns ionization due to electron energy. After emission, the energy that the electric field imparts electrons can reach a certain level which causes the gases around the electron emission surface ionize. These ionized gasses can damage the emission surface, and prevent further emission. U.S. No. No. To reduce the electrical field required and reduce the amount ionization typical FEDs use low “work function” materials on the emission surface. These are special materials which emit electrons with relatively low energies. R. Gomer. FIELD EMISSION and FIELD IONIZATION. Harvard Univ. Press, pp. Press, pp. 3-4 (1961); also U.S. Pat. No. No.
The electrical field needed for emission can also be reduced by forming the emission surface in a way that the field is concentrated within a small area. U.S. Patent. No. No. No. No. No. No. 5,066,883, S. Yoshioka et al. entitled “Electron-Emitting device with Electron-Emitting region Insulated from Electrodes”. (Thin film with cracks); U.S. No. No. 5,089 742 by D. Kirkpatrick et. al. entitled “Electron Beam source formed with biologically derived tubule materials” (microprotrusions); V. Makhov “Field Emission Cathode Technology & its Application”, Technology Digest IVMC 91 Nagahama, 1991 (edge of the film). This leads to emission at a voltage that is lower than required for a flat reference configuration, thus defining a “field enhancement factor”. H. Busta et al. “Field Emission From Tungsten-Clad Silicon Pyramids”, IEEE Transactions on Electron Devices Vol. 36, No. 11, pg. 2679 (November 1989).
One disadvantage of concentrating the fields in a smaller region is that current emission is limited to a smaller region, resulting in low current and high density electron beams. U.S. Pat. No. No. The typical sharp pointed emitters are also limited by their uniformity. H. Kosmahl “A Wide Bandwidth High Gain Small Size Distributed Amplifier With Field-Emission Triodes for the 10 to300 GHz Frequency range”, IEEE Transactions on Electron Devices Vol. 36, No. 11, pg. 2728 (November 1989). (Explaining that sharp-pointed structures do not produce uniform emission currents, and discussing the relationship between topography). Such beams are therefore not ideal for producing luminescence over a wide area.
The FEDs use a small gap between the emission electrode and accelerator electrode to produce the liberating field. This increases the electrical field without increasing the voltage that drives the field, so less energy is transferred to the electrons following emission. For example, one way to achieve a small separation is by etching a laminated structure that includes a first electrode and a dielectric layer on a flat surface, followed by a second electrode over the dielectric. This allows the bottom electrode to be exposed close to the top electrode. U.S. No. No. 4,307 507 by H. Gray et. al. entitled “Method for Manufacturing a Field Emission Cathode Structure”. No. No. No. No. 4,964,946, H. Gray et. al. entitled “Process for Fabricating Self Aligned Field Emmitter Arrays”. U.S. Pat. No. No. A second way to achieve a small separation is by etching a layer between the electrodes of a substrate in order to produce lateral electron emission. Makhov, “Field Emission Cathode Technology & Its Application”, Technical Digest of IVMC 91 Nagahama, 1991; S. Bandy – “Thin Film Emitter Development”, Technical Digest of IVMC 91 Nagahama, 1991.
There are tradeoffs when lowering the voltage needed to produce electron emissions. Reduced voltage is desired not only to reduce gas ionization but also to increase frequency response because the time needed to bring the field electrode up to the required voltage for emission is reduced. Reduced separation between the field electrode and emission electrode reduces the voltage required. However, as described above, this has the undesirable side effect of increasing the sensitivity of FED emission currents to small variations in separation. FED current density can change up to 10% with a 1% difference in electrode separation. In addition, while it may be desirable to reduce the energy imparted to the emitted electrons to preserve the surface of the emission, it may also be desirable to impart an energy level relatively high to the electrons to allow them to deliver more energy in order to generate more lighting in a display, for example. When field-enhancing shapes are used, higher energy is needed in particular when the total emission is limited by the current density. U.S. Pat. No. No. To increase the operating voltage while limiting ionization damages to emission surfaces, a high vacuum can be used. U.S. Patent. No. No.
To accommodate these tradeoffs, FEDs are typically triode arrangements in which a high-voltage anode is used above a field electrode (i.e. “accelerator”) electro. These devices use a low-voltage field electrode placed in a layer on the same substrate above the electrode for the emission surface. It is possible to precisely control the distance between the field electrodes and emitter ( “cathode”) so that emission takes place uniformly at low voltage. Then, a higher voltage electrode (“anode”) is provided on a second substrate that is aligned over the first. U.S. No. No. 3B showing electron emission 7 towards a third electrode, not shown; U.S. No. No. 4,780.684, H. Kosmahl entitled Microwave Integrated Distributedamplifier with field Emission Triodes”. (conical or triangle shaped emitters with triode structure); H. Kosmahl A Wide-Bandwidth, High-Gain Small Size Distributed Amplifier With Field-Emission Triodes”, IEEE Transactions on Electronic Devices, Vol. 36, No. 11, pg. 2728 (November 1989).
Although the uniformity of the emission current is improved by placing a low-voltage field electrode near the cathode precisely, the spacing between the FED and the anode in triodes is still important. Flat panel displays may have image distortions and uneven brightness due to variations in the anode-cathode distance. The spacers that are used to separate the anode and cathode can allow leakage current, which can increase power consumption, cause distortions in the electrical field and lead to electrode breakdown. Spacers are needed to support the forces between anode-cathode substrates, since there is a vacuum less than 10-6 Torr. The FED triodes used in flat panel displays are difficult to space precisely because the cathode and anode are located on different substrates. U.S. No. No.
The above structures and atmospherics are helpful for flat panel display application, but could be improved. Field enhancing structures like conical tips and film edges can be used to enhance the field. The electron beams are only high density and low current. These beams aren’t ideal for producing luminosity over a wide area. These structures also suffer from limitations in uniformity. The triodes do not work well with flat panel displays, as they need to be precisely aligned in two planes. Also, the spacers can cause problems. “None of these structures provides a large area emission surface that can direct electrons to a luminescent aode, which is desirable for flat panel displays.
The present invention has as its principal objective to provide a way to direct electrons to a large portion of the surface of an anode arranged laterally.
The invention also includes a lateral emitter device, as well as a manufacturing method, that has a uniform field emission and a high field enhancement factor. It requires a low voltage to produce field emission and can be used in a multicolor array lateral luminescent diodes, which are then used for a full color flat panel display with low voltage IC drivers.
The present invention includes a lateral-field emission diode that has a flat substrate of an insulating substance with a layer made of conductive materials covering a portion, an anode placed on the layer and a cathode situated on an insulative material over the conductive layer. The cathode provides an electron emission layer and is so positioned as to allow electrons to be directed laterally from the emission layer to the anode.
Another aspect of the invention is to provide a lateral-field emitter device that includes a flat substrate made from a transparent insulator. The substrate includes a conductive film covering a portion, an anode on top of the conductive film, and a casode on an insulative layer on the conductive sheet. The cathode has at least one side that extends upwards from the substrate, and is facing a corresponding anode side which extends up from the substrate. The corresponding sides of the anode and cathode are spaced uniformly apart, so that the gap is uniform. The cathode emits a stream of electrons along the length the gap when a certain potential is applied to the anode. The electrical field gives the electrons an energy level that is predetermined. Gases in the gap also have an ionization level above the energy of the emitted emitted. Therefore, the electrons that are emitted into the anode don’t ionize them. A vacuum can be used to give the gases a specific density. This density is below a critical density, so the emission surface can be preserved even if a little ionization occurs.
The present invention also includes a method for manufacturing a lateral-field emitter device, which comprises the following steps: (a) preparing a flat substrate; (b) placing a conductive film on it; (c) placing an anode layer on top of the conductive film, (d), positioning an etching mask above the material with the opening so that the material below the opening is exposed, and the material underneath the mask adjacent to the sidewall is exposed, (e), etching beneath the material
This method includes the steps of (a) providing a substantially flat substrate, (b) disposing a conductive layer on the substrate, and (c), disposing an anode material on the conductive layer. This method comprises the steps of: (a) providing an substantially flat substrate; (b) disposing on it a conductive film layer; (c) placing an anode layer on top of that conductive film layer, such that anode beneath the mask remains covered; (d) positioning the mask above the anode layer so as to expose the anode beneath the opening. (e) etching away the anode beneath
In another feature of the invention, the anode or cathode can be arranged in fork-shaped shapes so that they are interlocked to form a rectangular shape. The interleaving shapes can also be arranged in such a way that at least half of the rectangular field emitter formed by the interleaving shapes is luminescent.
