DE2445237A1 - PLAYBACK DEVICE WITH A MATRIX OF GLIME CHARGE PLAYBACK ELEMENTS - Google Patents

Description

PHB.32373.

Df. Hßrfcert Rchol «Va / EVH.

Applicant: NV Philips' Gloeüampenfabrlekeu · £ ** H 0 ά 0 I

File No. i PHB-32.373 '

Registration dated Sept. 20, 1974

Playback device with a. Matrix of glow discharge display elements

The invention relates to a display device with a matrix of glow discharge display elements, which by a set of cathodic elements and a set of anode elements is defined in an envelope containing a gas atmosphere, which cathode elements and anode elements are electrically connected in groups to form an addressing system, wherein the surfaces of the elements of each cathode group that are in contact with said gas atmosphere, physically are separated from each other.

When the cathode and anode elements in rows and

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Columns are arranged, the groups of cathode elements can each consist of a column of cathode elements and the Groups of anode elements each consisting of a row of anode elements exist, the addressing system then being a so-called "cross-bar" addressing system. (The expressions "Row" and "Column" are used here purely in a comparative sense 5 in practice the rows from top to bottom and the columns can extend from left to right. In addition, the rows can under extend at an angle different from 90 ° to the columns. Like the columns, they can also be curved).

Such a device can be easier to reproduce Patterns such as charts, digits, or words can be used. There are two modes of controlling such devices:

a cyclic), wherein each discharge cell is excited only during _t ".the period in which the row and the column containing the cell to be addressed, and

b) with memory effect, with each discharge path being ignited during an addressing period and remaining switched on until an "off ¹¹ pulse is supplied.,

Once a discharge is ignited, it is necessary to control the current by means of a limiting resistor to control. In cyclic control, such a resistor is in series with each anode row or each cathode

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column arranged. The resistor is used in succession for all discharges in the row or column, if so the limiting resistors are in the cathode columns, the anode rows must be switched on cyclically will.

If there are η series, a discharge cannot for a time longer than a fraction 1 / n of the total grid period operated (in practice the maximum operating time of any discharge is finite because of its Switch-on time can even be shorter). This operating mode has the disadvantage that, during operation, every discharge at least η times the required mean luminous efficacy must deliver. The grid frequency must also be high enough to avoid a flickering effect on the playback.

With control with memory effect, this problem of the short duty cycle is avoided. Theoretically it is possible that, once a discharge has been set in motion, that is necessary to maintain it Discharge voltage required lower than that · to start voltage required for this discharge. So if the row and column conductors are on a relative Potential difference V are kept, which is greater than the erase voltage Ve for the discharges, but smaller than their ignition voltage is Vs, i.e. Vs> V> Ve, all elements remain switched off until the voltage between the Row tmd column ladders that make up a particular element

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is increased instantaneously to above the ignition voltage. In this case, the element in question ignite and furthermore it remains switched on after the instantly increased voltage is back on its Initial value has decreased. Successive elements can thus be re-energized and remain switched on (Storage effect), unless measures are taken to delete them afterwards. This can be done by that the voltage between the row and column conductors corresponding to a particular element is instantaneous until it is reduced below the erasing voltage.

A major problem arises when attempting to energize a device in this way. The current limiting resistors can then no longer be in series with a whole series of anodes or cathodes, as is the case with the cyclic operating mode described above. A resistor must be permanently arranged in series with each discharge path either in the anode or in the cathode line which leads to this path. This could be achieved relatively easily if either all the individual anodes or, as is the case in the display tube of the Mullard ZM 1251 type, all the individual cathodes had separate external connections, but were in a panel with a "cross-bar ^tt addressing system this is not the case and it is then necessary to arrange the individual resistors within the panel itself.

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In the German patent application P 22 34 "199.7 _: V - \ a way is described in which this can be achieved. Said application describes a design in which the anode electrodes consist of electrically conductive films arranged in rows and columns on the inner surface a transparent window of the device are deposited, the anode films of each row are each electrically connected individually to a common lead of the row via a thin film resistor which is also deposited on said inner surface.

The present invention aims to provide an alternative design in which the internal impedance of the discharge itself is used to regulate the current in such a way that actually the current-voltage characteristic of the known ■ Devices in which a single resistor is placed in series with each path is equivalent.

According to the invention, the desired internal impedance the discharge itself obtained by the fact that in a device of the type mentioned above the surface of the Cathode elements with carbon in finely divided form is provided. The carbon particles preferably have a diameter between 0. OT / um and 10 / um and are preferably microscopic rough. . ·

It has been found that the manufacture of the cathode surfaces with the said atmosphere are in contact, from coal in finely divided form or with

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a microscopically rough surface to a current-voltage characteristic for each discharge path, their Inclination dV / di for "low current densities at the cathode surface is extremely high in a discharge cell in which there is no positive column "

It should be noted that it is known that the positive Inclination dV / di = Rg of such a gas discharge characteristic the cathode surface and the square of the gas pressure is inversely proportional. However, in order to obtain values of Rg which are sufficiently high for the purpose given above, With commonly used cathode materials, the required values of these parameters would be impractical. In particular the low pressure and high current density that would result would lead to faster erosion of the Lead cathode

Because the sputtering speed of coal is significantly slower than that of many other materials, at Application of this material a lower gas pressure and / or a higher current density can be allowed «Nevertheless there are there, a practical lower limit to the pressure caused by the erosion of even these cathodes and also by the possibility it causes the voltage characteristic of the discharge to become unacceptable. The presence of a restrictive lower limit for the value of the gas pressure in turn brings a corresponding restrictive upper limit Limit for the effective surface area of each cathode element

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with itself if the required value (e.g. 400 kn - 2 Mn) for Rg has to be achieved. Empirically it has been found that a suitable value of the pressure for pure neon is hO-60 Torr for cathode element surfaces of about 0.4 now and for anode-cathode distances of "1.3 now. Rg can then be in the range of 700 kh - 1 mn lie.

The charcoal can be in the form of carbon black, colloidal graphite with potassium or sodium silicate, or so-called charcoal * ¹ paper "(sold under the trademark" Papyex "). It can be used as an additive with particles of a semiconductor or insulating material such as silicon carbide or boron carbide , to be available.

The carbon can take the form of a coating or a layer on an electrically conductive, e.g. metal Have substrate. If this is the case, the layer should be maximally compatible with good adhesion Have thickness to extend the life of the device. (Material will inevitably be sputtered during operation and it should be taken into account that immediately after exposure "any part of the substrate the Effect of attaching the charcoal will be lost and Rg will decrease drastically, possibly causing destruction of the device). The carbon coating or layer is therefore preferably on an electrical basis insulating substrate attached, in which case the coating or the layer, the or the surface

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each cathode element of a group forms, preferably electrically with the other coatings or layers of these Group is connected by another conductive material, such as a metal, which is also called insulating Substrate can be attached.

The beneficial effect of attaching the carbon can reduce the secondary emission coefficient for Be attributable to electrons of the cathode surface. Electrons that are emitted from the cathode surface as a result of bombardment with electrons or ions get caught in the undulations of the surface; this is a well-known hypothesis to explain the low Electron-electron secondary emission coefficients of such Surfaces.

The invention is explained in more detail below, for example with reference to the drawing. Show it:

Pig. 1 some current-voltage characteristics of glow discharges,

2 shows a plan view of part of a first glow discharge display tube,

Pig · 3 is a perspective cross-section through part of the in Pig. 2 display tube shown with a Observation window,

FIG. H shows a longitudinal section through part of the display tube shown in FIG. 2 with an observation window, and FIG

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5 shows the separate parts of a second glow discharge display tube.

The curve A of FIG. 1 shows the characteristic of the current i as a function of the voltage V of a conventional glow charge path. As can be seen, initially the current increases slowly with the voltage to _f, but finally a point is reached beyond which the characteristic curve shows a part with a negative slope. This point corresponds to the ignition voltage Vs of the discharge and if this is just exceeded, the current increases rapidly until (in the absence of a current limiting resistor) it reaches a point (not shown) on the slowly rising right part of the curve, that of the applied voltage Vs. is equivalent to. Since the right part of the curve has such a slight inclination, the final current is large and can lead to the destruction ^{T of} the device by an arc discharge.

The curve B, which in a device according to the

Invention obtained corresponds to curve A at low currents, but in the area outside the area of the negative slope it has a much steeper slope than curve A. If the discharge path has the characteristic curve indicated by curve B, if the ignition voltage Vs is just exceeded, the current will only increase to a value i _m which is much lower than the current corresponding to Vs in the right-hand part of curve A. . This lower current does not destroy the device,

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V denotes the minimum operating voltage (extinction voltage) of the discharge once the discharge has been ignited. The operating voltage, which _{corresponds to i m} for curve B, is Ve.

In Fig. 2, a block 1 of electrically insulating material, for example the glass-like material sold under the trade name "Pusite K ^w ", is cast around a set of cathode substrate strips 2 which are guided in a vacuum-tight manner through the side wall of the block 1. The upper surface of each substrate strip 2 is completely covered with a layer 12 of finely divided carbon, which can have a thickness of 50 to 100 / tun, except where the strips 2 are passed through the side wall of the block 1 and where The layers 12 mentioned can be applied by placing colloidal graphite with potassium or sodium silicate in a suitable liquid carrier (eg the colloidal graphite sold under the trade name "Aquadag") under a suitable mask Using compressed air is sprayed onto the substrates.After the spraying, the layers are ^{sintered in a vacuum, for example at 1000 °} C. The upper The surface of the block 1 is provided with a series of cavities 3 which extend down to the coated strips 2. In this way , a physically separate cathode surface is created by the carbon-coated part of each strip 2 on the

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Bottom of each cavity 3 is formed. The cathode substrate strips can be made of an iron-nickel-cobalt alloy that is sold under the trade name "Kovar" is driven.

The upper surface of the block 1 is provided with a set of parallel ribs k- which extend in the longitudinal direction of the block 1 in such a way that they form channels which connect the parallel rows of cavities 3 with one another. The cavities 3 are divided into parallel columns by grooves 5 made in the upper surface of the block. These ribs and grooves can prevent sputtered material of the coated strip on the bottom of a cavity from forming a leakage path between one cavity and the next successive cavity. Further coated cathode substrate strips 6, which are identical to strips 2 ″, are attached to each end of the row will,

Fig. 3 shows in perspective a cross section along the line III-III of Fig. 2. A transparent observation window? latte .9 rests, on top of the ribs k. This window can be made of the type of glass sold under the trade name "Soveril 805.51" and includes a set of parallel anode wires 10 molded into the lower surface thereof. These wires 10

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are arranged in alignment with the cavities 3, so that an anode element is directed towards each cavity, that is to say towards each cathode element. The wires are guided through the side walls of the window 9 in a vacuum-tight manner. They form an ^M cross-bar "addressing system for the series of glow discharge paths obtained together with the cathode substrate strips 2. The window 9 is fused vacuum-tight on all sides to the block 1, as indicated at 11. The anode wires 10 can also be made from under the trade name "Kovar" sold metal alloy.

FIG. H shows a longitudinal section through the part shown in FIG. 1 along the line IV-IV. In FIG. 4 it is shown that the auxiliary cathode substrate strips 6 are practically in the same plane as the substrate strips and each lie in a further channel which extends in the column direction. The channels formed between the ribs k open into these further channels, with all channels being closed on the upper side with the plate 9, FIG. H further shows an anode wire.10.

In a practical embodiment, the openings 3 were arranged in a rectangular matrix of 8 50. Each cavity was 0.75 square and the distance between the surface 12 of a cathode element on the bottom of each cavity and the corresponding anode wire was 1.25 . The depth of a cavity was now 0.75 and the height of the ribs h was 0.6 mm. The center distance

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between the cavities was 1.5 now. The anode wires were pointing took the form of strips that were 0.3 now wide and 0.1 mm thick. The grooves 5 had a depth of 0.25 mm.

After sealing, the inside of the tube was evacuated via an exhaust tube (not shown) and then filled with a gas atmosphere of, for example, pure neon at a pressure of 40 to 60 Torr.

The finished tube was then lathered by applying an operating voltage of 350 V between applied to each cathode and each anode element.

The subsequent application of an operating voltage of at least 280 V across each discharge path had result in visible light from the negative glow region of the glow discharge obtained, the positive column part of the discharge being completely or almost completely was completely suppressed. The current-voltage characteristic of each discharge gap was practically the same as curve B. in Fig. 1, where i was about 100 / uA.

In operation, a constant bias, halfway between Vm and Vs, was established between all of the anode wires 10 and the cathode substrate strip 2 were applied and selected glow discharge paths in the cavities one after the other by simultaneously applying a positive

Pulse to the corresponding anode wire 10 and a negative pulse of the same value to the corresponding Cathode substrate strips 2 addressed, these pulses

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have a sufficient amplitude that the ignition voltage Vs. has just been exceeded in the selected routes. Because of the current-voltage characteristic of each path, a discharge, once addressed, was obtained in it, until the voltage above its occurring voltage to below Vm by the application of pulses of opposite polarity on the corresponding anode wire 10 and the substrate strip 2 concerned. A discharge was made continuously maintained on the cathode substrate strips 6 and it has. It turned out that these continuous discharges caused a sufficient pre-ionization brought about the whole tube in order to ignite the addressed discharge paths in the cavities 3,

Fig. 5 shows an exploded view of a second glow discharge display device with a electrically: insulating cathode substrate plate 13 »an electrically insulating perforated intermediate plate 14, which is e.g. made of alurainium plate that is anodized is, in order to obtain an electrically insulating skin thereon, a spacer plate 151 in which the plate 14 is located, and an electrically insulating transparent observation window plate 16 ·

The openings 18 in the plate 1h are arranged in a rectangular matrix and a rectangle of cathode elements 17 made of finely divided microscopically rough carbon is located on the substrate 13 in alignment with each of these

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Openings. The cathode rectangles in each row are offset against the openings by means of a metal strip 19 is electrically connected to each other. Electrically conductive anode strips 20 are on the underside of the anode plate attached, with a strip 20 in alignment with each of the column openings 18. The strips 19 and 20 form in this way a "cross-bar" addressing system for a number of glow discharge paths, each through a cathode element 17, an opening 18 and the surface element of an anode strip 20 facing these openings 18 is defined. .

The individual parts 17 and 19 can be attached to the substrate by first applying the strip 19 (which can consist of silver) by a screen printing process and then applying the cathode elements 17 using colloidal graphite with potassium or sodium silicate in a suitable liquid carrier over a suitable mask to be sprayed onto the already for the layer 12 in the device according to Fig. 2 to k-described manner, wherein the thickness of each rectangle 17, for example 25 / Uin to 100 / um and each rectangle 17 corresponding to the strips 19

overlapped and in this way with this strip in electrical Connection. The charcoal can also be made into a suitable ink and made by standard thick film techniques can be applied by means of a screen printing process.

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After the rectangles 17 have been attached, the substrate is sintered at, for example, 500 ° C.

The anode strips 20 can also consist of silver and be applied to the window plate 16 by a screen printing process.

The plate lh can have a thickness of 0.6 mm to 1.2 mm, the spacer plate 15 being 25 "to 50 / ura thicker than the plate 14, so that a narrow gap is obtained between the plate lh and the window 16 The openings 18 can have a diameter of 300 μm. The width of the anode strips 20 should preferably not exceed 150 μm, so that these strips do not shield the glow discharge that occurs in the openings 18 below during operation.

After applying the various layers 17i 19 » 20, the outlines of the parts 13, 15 and 16 (which can all be made of glass) are vacuum-tight by means of a soldering glass melted together and the inside is evacuated via an exhaust tube (not shown) and with a Glow discharge atmosphere of e.g. pure neon at 40 to 100 torr. The series of glow discharge paths obtained again had the same voltage-current characteristic the curve B in Fig. 1 on.

The plates 13 and 16 can be slightly larger than the plate i4 and the spacer plate 15 to the electrical To facilitate connection between a Susseren circuit and the strips .19 and 20.

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The spacer plate can also be omitted if there are lugs, e.g. made of insulating material, on the window 16 or the plate 14 can be attached, so that the required small gap is obtained in between.

Although the anode and cathode elements are described in FIGS Embodiments are arranged in rows and columns, it is evident that all forms are more coordinated Tiers can also be used. For example, a polar series can be used, with the interconnected Cathode elements on concentric circles and the interconnected anode elements on radii of these " Circles.

In the two described embodiments the coal of layers 12 or 17 as an additive Particles of a semiconductor or insulating material, such as silicon carbide or = boron carbide, may be present.

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Claims (1)

PHB.32373. - 18 - 28.8.7 **. PAT t Playback device with a matrix of glow discharge display elements, represented by a set of cathode elements and a set of anode elements in an envelope provided with a gas atmosphere is defined, which cathode elements and anode elements are used to form of an addressing system are electrically connected in groups, with the surfaces of the elements each Cathode groups, which are in contact with said gas atmosphere, are physically separated from one another, thereby characterized in that the surface of the cathode elements is provided with 'carbon in finely divided form. 2 «Tube according to claim 1, characterized in that the coal particles have a diameter in the range of 0.01 / µm 10 / µm and are preferably microscopically rough. 3 rash according to claim 1 or 2, characterized in that that the coal particles are mixed with particles of a semiconducting or insulating material k ». Tube according to claim 1, 2 or 3 »characterized in that the« addressing system is a "cross-bar ⁿ addressing system, the cathode and anode elements being arranged in rows and columns and the groups of • cathode elements each consisting of a column or row of cathode elements and the groups of anode elements each consist of a row or column of anode elements. 5098U / 0851 .; · PHB.32373. -19 - 28.8.74. 5. Tube according to one of the preceding claims, characterized in that the coal has the shape of a Has coating or a layer on an electrically conductive substrate, 6. Tube according to claim 5 »characterized in that the substrate of each cathode element of a group Metal strip is that extends in such a way that it is also the substrate of the other cathode elements of these Group forms. 7. Tube according to one of claims 1 to k _t, characterized in that the carbon is attached in the form of a coating or a layer on an electrically insulating substrate. 8. Tube according to claim 7i, characterized in that the coating or the layer, which or which the surface each cathode element of a group forms, electrically is connected to the other coatings or layers of this group by a conductive material which is deposited on the said insulating substrate is attached, 509814/0851 Blank page