JP3486904B2 - Flat screen with individually dipole protected microdots - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a flat screen having microdots individually protected by dipoles. The present invention relates generally to the field of matrix-addressable flat display screens of any size, and all industrial components utilizing such screens, such as televisions, information devices, telecommunications devices, control devices, monitoring devices. It can be applied to various things. Known microdot screens are generally vacuum tubes consisting of two thin glass plates hermetically sealed, the back or cathode plate consisting of a microdot formed field effect emitter matrix grid, and the front or anode plate being transparent. Covered with a conductive film and a luminophore. Each light spot (pixel) is associated with an emitting cathode surface consisting of countless microdots (approximately 10,000 / mm ² ) positioned opposite it. The emission surface is formed by the intersection of the matrix lines (grids) and columns (cathode conductors). Due to the small distance between the dot and the grid (1 μm) and the effect of the dot amplification, a potential difference of at least 100 volts applied between the line and the column results in the emission of electrons and high brightness at the apex of the dot at low voltage of the luminophore Get enough electric field to cause it. The classic structure of the microdot screen cathode is
In particular, consisting of the following, deposited sequentially on a glass or silicon substrate: an insulating layer; a resistive layer of silicon or other material; a "column" consisting of a metal layer which can be placed under or on the resistive layer. conductor ", - insulating layer constituting the insulating grid (Si or SiO _2), - a metal layer constituting the grid. After the above layers are deposited, holes are machined into the insulating grid by known etching techniques, and then microdots are formed therein. The essential purpose of the resistive layer is to limit the current at each emitter to equalize the electron emission, and to limit the maximum current that will flow through the dot in the event of a dot / grid short. The characteristic of the load resulting from the resistor in series with the dot is linear. The voltage drop across this resistor is proportional to the current flowing through it and is considered to be quite large when the current emitted by the dot is large. The voltage to be applied to the dot-resistor protection system increases accordingly, which has a significant effect, especially on screen wear. The device according to the invention proposes to solve this problem. The device not only allows effective control of the current flowing through each microdot, by automatic adjustment of the emission current above the threshold, even when the dots are in direct contact with the grid, but also provides the best uniformity of emission , As well as effective and simple control of the screen brightness. This device consists of a field emission flat screen emission cathode consisting of microdots each individually protected by a series electrical connection with a dipole formed by a depletion type field effect transistor. These dipoles only act on the threshold of protection and the level of emission current, and thus the brightness of the screen, on the polarity of the substrate common to these or some dipoles, and in a global manner (all It is designed so that it can be modified (simultaneously for the dots). BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate one non-limiting embodiment of the present invention, wherein FIG. 1 is a cross-sectional view illustrating the principle of operation of a known microdot screen, and FIG. 2 illustrates the microdot element of FIG. FIG. 3 is a schematic view of a microdot element individually protected by a dipole, FIG. 4 is a cross-sectional view of a microdot emission cathode according to the present invention, and FIG. 5 is a perspective view of a channel of a field effect transistor around the microdot. FIG. The basic principle of a microdot screen is shown in FIG. 1, in which, from bottom to top (actually from back to front), one can see in order: a glass or silicon plate 1, a coating layer 2 A cathode conductor or columnar conductor 3, a resistance layer 4, an insulating layer 5, a line conductor or grid 6, a vacuum space 7, and a front glass layer 8 covering the transparent conductor layer constituting the anode 9 on the inner surface;
Ten. The electron flux 11 emitted under vacuum by the microdots 12 electronically connected to the cathode conductor and adjusted by the potential of the grid 6 is accelerated in the direction of the cathode 9 where the luminophore 10
To excite (functionally triode). Since the distance between the dot and the anode is small, focusing can be obtained by the proximity effect without any photoelectrons. In this type of cathode, each microdot 12 is protected from excess current by being in series with a load resistor (FIG. 2). This resistance is generally constituted by a resistance layer 3 of amorphous silicon (or other material). In the emission cathode according to the present invention, each microdot 12
Is realized by not connecting in series with the load resistor but in series with the dipole 13 whose voltage-current characteristic is nonlinear. This dipole is composed of a field-effect transistor, preferably a depletion-type insulating grid type transistor, and its drain D is a microdot
12 and the source S are connected to the corresponding columnar conductor 3, and the port or "gate" G (or pinch electrode) of each transistor
Is directly connected to the source S or the drain D. This configuration makes it possible to achieve complete protection of the microdot 12 from a short circuit between the dot and the grid 6 by completely blocking the current in the dot. The dipole 13 is preferably a single silicon substrate 4 (bulk or thin film) which may be common to all dipoles
, So that the protection threshold and emission current level can be modified (adjusted for all dots) globally (adjusting the screen brightness)
Fabricated on a single silicon substrate 14 by integrated technology. By way of example, FIG. 4 shows a partial view of a microdot emission cathode protected by a dipole 13 which is formed by diffusion or other (implantation) formation of an N-type doping region 15 in a P-type substrate 14 as a source. , Channel 20
The (depletion transistor) is formed by, for example, N-type ion implantation, and the silica insulating grid layer 16 is obtained by oxidation or adhesion. The pinch electrode 17 is formed by metallization at the same time as the columnar conductor 3. The dots are made in the usual way, but rest on the pinch gate of the transistor.
Preferably, the drain located below the microdots is not overdoped, as is usual in classical MOS structures. The field effect transistors that make up the dipole 13 preferably exhibit a circular geometry, the conductive channels of which are located all around the microdot 12 (FIG. 5). Thus, the operation of the dipole is as follows. An extraction voltage is applied to the electrode 6 (grid). When this voltage is weak (when the dot / source voltage is weak enough to be below the threshold of the depletion transistor)
The dipole in series with 12 is almost equal to the resistance of the injection channel 20, and its value is small enough. When the withdrawal voltage increases and the dot / source voltage is on or above the threshold of the depletion transistor, pinch gate 17 is activated to "pinch" channel 20 and allow the current through the dipole to a certain value, That is, it is primarily reduced to a value (saturation current of the depletion transistor) which is no longer a function of the overall geometry and the voltage of the substrate 14 with respect to the source 15. The dipole voltage loss will no longer be a function of the current flowing through the dot itself, but will be solely a function of the threshold voltage of the depletion transistor. In fact, each dot receives the saturation current of the depletion transistor protecting it. If the transistors have the same geometry, the current flowing through the dots will be the same (regardless of the intrinsic properties of the emission of the dots). This emission cathode is itself formed on silicon by integrated technology. In this case, the columnar conductor 3 and possibly the line conductor (or grid 6) may be constituted by a diffusion layer (embedded or not), but as a modification, the diffusion layer may be doubled by metallization depending on the location (for example, Out of the way or to minimize the coupling capacity). The arrangement of the various components has the purpose of the present invention with a maximum useful effect never obtained by a similar device to date.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 31/12 H01J 31/15 H01J 1/30 H01J 29/04

Claims (1)

(57) Claims 1. In a flat screen including a silicon layer of a first conductivity type, a field effect formed in the silicon layer and connected by a dipole having a non-linear voltage-current characteristic. A plurality of first regions of a second conductivity type coupled to a cathode conductor constituting a source region of the transistor and having a high doping level, and a second region formed in the silicon layer; The region has a central portion forming a drain region and a peripheral portion forming a channel region near the first region, wherein the drain region and the channel region are of a second conductivity type and lower than the first conductive region. A second region having a doping level, the second region being covered with an insulating layer having an opening exposing at least a part of the central portion of the second region, covering the exposed portion of the second region and filling the opening; Conductor layer is provided coupled to the gate electrode, flat screen, characterized in that it comprises a microchip provided on the conductive layer over the opening.