Design of a flat panel large screen display for high volume manufacture

P. PLESHKO, N. APPERLEY, L.L. ZIMMERMAN, K.A. PEARSON, T.A. SHERK, E.J. St. PIERRE, B. HAIRABEDIAN, F. BRADNEY, R.L.J. FOSTER This paper describes the evolution of the IBM 581 a c plasma panel display. A general overview of plasma technology and the requirement for a large screen display is followed by a description of the 581 hardware architecture. Considerations which must be met for a successful high yield, high volume fabrication process are covered and the manufacturing process itself is outlined. Test results are given which show the plasma panel to operate reliably for over 350 000 hours. Changes which occur to the panel during operation are described. Finally, the presentation and updating of data displayed on the IBM 3290 terminal, which uses the 581 display, are discussed which take account of the special properties of the a c plasma display.

Keywords : display devices (computers); graphic displays; a c plasma panels; large screens; design.

Since IBM introduced its first high volume, alphanumeric is the case for refresh display devices, but is limited only by display product in 1966, the predominant display tech- manufacturability considerations. nology has been the cathode ray tube (CRT). The CRT is still predominant throughout the industry. When flat panel Certain aspects of technology development were necessary matrix display technologies started to be developed many in developing this high information content, matrix- expected this compact type of device to revolutionize the addressed, flat panel display to satisfy manufacturability packaging and appearance of display terminals. So far this and quality requirements. For example, large information has only happened to a limited extent. Although CRTs content matrix displays require long conductor lengths. On continue to predominate, there are now several matrix- our product, the conductor length on the two plates is addressed technologies in use: liquid crystals, light-emitting 360 m per plate. With this large amount of wire length, diodes, vacuum fluorescent displays, ac and dc plasmas and defect densities relating to conductor yield had to be to a lesser degree ac and dc electroluminescent panels. improved. This was done by improving the method of metal deposition and photo-printing of the conductor pattern and Development effort in plasma displays at IBM led in 1974 repair of open and shorted lines. To reduce the interaction to the manufacture of 22, 120,240, 480 and 1024 character of the dielectric reflow process with the metallurgy and to displays for use in the company's products. This level of improve yields, a lower temperature dielectric glass was technology marks a well understood generation from developed together with an accompanying lower tempera- engineering, manufacturing and reliability points of view 1 . ture glass seal material.

This paper describes IBM's more recent ac plasma display To achieve a high quality display, a new spacer technology technology, which was developed from that base to provide was developed which doos not interfere with the operation a large screen, multiple image-format capability. The use of of adjacent cells and has a minimal effect on reducing panel higher information content displays is advantageous for margins. To achieve low failure rates for the panel and applications requiring the scanning of multiple pages of electronics, testing and pre-ageing are employed to reduce reference material and for cross-referencing multiple pages the early life failures and provide a quality control on the or frames of stored information. product.

The ac plasma display technology described is a memory The paragraphs that follow discuss in more detail those technology. Because of this characteristic, the maximum subjects mentioned above. They should give the reader a size or maximum information content of the screen is not general understanding of the design and manufacturing limited by the device's luminance-voltage characteristic as considerations involved in producing this first high-volume- manufactured, flat-panel large-screen display. The authors are at IBM Corporation, Kingston, NY 12401, USA, except N. Apperley and R.L.J. Foster who are at the IBM United LARGE SCREEN DISPLAY OVERVIEW Kingdom Laboratories Ltd, Hursley Park, Winchester, Hants SO21 2JN, UK, and E.J. St. Pierre who is at IBM Corporation, The primary objective in developing a large screen terminal Poughkeepsie, NY 12601, USA. was to provide an interactive display with a large data

DISPLAYS. JANUARY 1984 0141-9382/84/050021-11 $03.00 © 1984 Butterworth & Co (Publishers) Ltd 21 capacity, as well as with functions that fully exploit the area into up to four predefined screen segments. The advantages of displaying a large number of characters. This partition's origin coordinate can be any on the panel. display had to be compatible with the existing family of Each segment is a fully interactive screen, typically with a IBM displays and offer increased functionwithout modifi- character capacity of a 3278 display. These are fully cation to existing application software programs. independent and communicate with different application programs which, with suitable networking, can be running The plasma panel was selected for this display technology. on different hosts. This offers a large viewing area with extremely good defini- tion that is consistent over the entire display surface. The An advanced function has been implemented to divide the design of the package exploited the flatness of the plasma display area into multiple partitions, each appearing as a display panel technology giving a depth of less than 280 mm. mini screen to the operator, but under the control of a This allows more effective use of the operator workspace single application program. In order to allow the application than is possible with CRT technology (Fig. 1). to optimize the layout, each partition can be any rectangular size and can display characters in either of two sizes with The maximum number of characters that can normally be multiple spacing options. The multiple partition function displayed on the plasma panel is 9 920, or 160 columns has been designed so that the operator can keystroke into and 60 rows in a single large page. For example, a report one partition while data is being transmitted between the retrieval application may require that a printer page of host and another partition. This permits more efficient use 132 columns by 60 rows be displayed. The terminal can of the data transmission system. also be customized to display multiple smaller screen sizes.

The ac plasma display can also operate simply as a single The major differences between this terminal and other screen to support applications written for existing terminals. displays supported by the same controller (IBM 3274) are: As the entire display area is then filled by typically only 1 920 characters, the terminal microcode is designed to 1. A large character buffer because of the display capacity; select the larger of the two available character sizes and to 2. More controls than a CRT because plasma panel tech- optimize the spacing for the best human factors considera- nology is non-refreshed. The update of an individual or tions. line of characters involves the selection of the plasma driver for those character positions to erase the current New functions have been designed into the terminal to allow contents. The new character matrices are then displayed the operator to gain efficiency without change to existing by selecting the appropriate panel driver and ionizing the application programs. One is a multiple copy function which plasma at the driver intersections. This is more complex divides the screen into an interactive area, with which than controlling the traditional refresh of a CRT from a programs can communicate, and up to three copy areas, character buffer and character generator, but does permit each containing the same number of characters as an IBM greater flexibility; and 3278 terminal. The copy areas are designed to save and 3. Increased function. display the contents of the interactive area for future reference while the operator continues with the application These differences demanded a new split of function between in the interactive area. the controller and the terminal in order to optimize perfor- mance. It was a requirement that the same controller A multiple interactive screen function divides the display support existing devices with an unchanged interface. For the new displays, the 3274 controls the transmission line discipline to the host and performs a multiplexing function to the terminal.

HARDWARE ARCHITECTURE The opportunities promised by a large, general purpose plasma display panel were attended by problems peculiar to the new size and expanded usage of such a panel. Existing panel data handling techniques were too slow for the twenty-fold increase in pixel count over that of previously available IBM plasma display panels. Neither did the old, alphanumeric-only methods apply well to the new applica- tion line-up. The large, all-points-addressable screen format invited graphics and non-coded image display, the data for which is not organized into characterized spaces. An archi- tecture of the panel-driving logic was developed to yield a user interface allowing adequate performance, and which would be general enough to be incorporated easily into any display product.

Logic architecture Logic architecture defines the functions performed in the subsystem, the interface lines by which these functions are evoked, and the resulting display size and performance. A Fig. 1 The IBM 3290 a c plasma display panel display subsystem is a device which incorporates the basic

22 DISPLAYS. JANUARY 1984 character generator ROM. Additional inputs to the ROM define which line of the character is being written. The out- I Vertical put byte from the character generator is serialized to modu- drivers late one pixel at a time as positioning is synchronously changed. With modification to allow two serialized outputs in place of one, and optionally, to account for the 64-bit chunking, this data source configuration is compatible with loading data to the plasma display driver modules.

Control~ Co~ Erasure of characters or other data from the panel is a function which must be accomplished explicitly, rather than by simply deleting characters from the display buffer, Fig. 2 Hardware sections of the plasma display panel as is the case with a refresh CRT. Although this operation is as data selective as a write, there are many times when the display function, but cannot stand alone. It requires attach- entire width needs to be erased, spanning one to several ment to a data source and controller by way of the logic horizontal lines. Rather than requiring all 960 vertical interface. latches to be loaded with ones, the vertical data loading can be omitted entirely by activating a logic interface line con- The functions to be performed within an ac plasma display current with the erase. This action simulates a 'set high' subsystem are only slightly more complicated than those of condition for the vertical drivers - for the rest of this a refresh CRT display. Picture elements must be addressed, operation only. The actual latch data is unaffected. written, or erased, and then sustained. The functional blocks to accomplish these operations are shown in Fig. 2. The size of the driver modules and the 0.35 mm spacing between lines on the panel result in a staggered inter- This product carries forward the basic concepts evolved for connection. As seen in Fig. 3, all even lines are driven from earlier plasma display panels 2 , which include the use of a one edge of the panel, whereas all odd lines are driven from latched high-voltage driver for every panel line. This was the opposite edge. This physical arrangement of the modules improved through the extension of pixel addressing to makes two serial data lines, one to the even and one to the allow all the on one horizontal line to be written (or odd modules - the most straightforward logic interface erased) at one time. This facilitates the increase in perfor- connection. As mentioned previously, this places upon the mance required by this large display panel. data source the necessity to clock two contiguous bits at a time instead of one. Pixel addressing The data flow portion of the logic is entirely concerned The logic interface lines pertaining to pixel addressing are as with pixel addressing. Means must be provided, via the logic follows: interface, to select and latch one or more horizontal drivers and one or more vertical drivers. The pixels defined by the (4) module select; intersection of the corresponding selected lines on the panel (2) data; are subsequently written or erased. (1) clock for data; (1) axis select; Several techniques exist for addressing plasma display (1) set equivalent of vertical all ones; panels 2-6 . A compromise is often made with performance (1) set all zeroes in vertical drivers. so that several lines share a common driver. As a result, several writes per line of pixels are required, or, in the case of shift panels, random access is sacrificed altogether. Driver-per-line implementation allows this display to offer 960-pixel line updates per write when that is appropriate, but also provides random access to each grouping of 64 pixels when only partial updates are required. A driver module definition which allows this flexibility becomes, therefore, the key architectural element. As it was defined for this product, the majority of the data flow logic is distributed among these modules. The minimum cost equation is strongly influenced by the number of module pins (as it is with other logic applications).

The most cost-effective design today is based on the 40-pin dual-in-line package which allows 32 drivers per module and eight support lines, one of which is a 3 MHz maximum serial input 7 . This practical constraint turns out to be very com- patible with present day techniques for loading data to CRT displays which are inherently serial.

In essence, a common technique for the translation of character codes in a RAM buffer to visual characters on a display is that of presenting each character code to a Fig. 3 Staggered lines on panel

DISPLAYS. JANUARY 1984 23 Control of scan lines. The ability, then, to load and display a partial Logic control is associated with three different areas - or full as an entity is desirable. On the other hand, providing timing to the analogue PFET drive circuits; graphic lines (vectors) must, on raster devices such as plasma accomplishing the correct setting for the sustain voltage at panels, be displayed as sequences of horizontal or vertical power-on time; and generating self-test patterns upon acti- steps or slices of varying lengths. The panel's acceptance of vation of a control line from the logic interface. small amounts "of data, even single points, to be displayed anywhere within the display area is important in the proper An especially cost-effective technique for generating the handling of graphic data. Displaying alphanumerics requires three unique time sequences to the special circuits incorpor- techniques which are intermediate between those of ates the control line data in a ROM. Three sections of the graphics and NCI. ROM are partitioned with each allotted group of 128 18-bit words. Each of the lines to be controlled is assigned one of Image areas may be bulk-erased, and items as small as single the bit positions. Two high order address bits are used to pixel may be selectively erased using the same addressing designate 'write' and 'erase'. As the last word of the sustain and data specification steps that were used to display them. The ability to erase selectively, essential to most applica- partition is read out, a control bit gates a pending write or tions, allows for the movement of graphic and alphanumeric erase to the appropriate bit position of the ROM address cursors, blinking, shape dragging (coupled with an counter. This changes the partition from sustain to the one appropriate xy-input device), alphanumeric backspace and for write or erase, or defaults back to the beginning of correction, independent screen partitioning, and system sustain if nothing is pending. message areas. Because there are relatively high voltages and currents To counteract the effect of image size, the new interface involved in the special circuits, there is the possibility that a allows up to a full scan line of pixels to be written in one logic component failure could cause other circuitry to be step. Thus, each write operation can handle 120 times more overstressed, for instance by attempting to cause a positive data than before. The data loading speed is also much higher and negative sustain polarity at the same time. For this than in earlier plasma panels. The dual data input lines, reason, a level of interlocking logic is placed between the each operating at up to 3 MHz, yield a high transfer rate. ROM outputs and the special circuits. Moreover, the loading of image data into driver registers can partially overlap execution of the write (or erase) command The second control function is that of adjusting the sustain for previously loaded data. This overlap window is 75 #s in voltage and the third is generation of a test pattern in duration - as many as 450 bits, representing 450 pixels, response to a switch operated control line. The purpose of may be loaded in this time. Partial scan lines may be this pattern, generated by a subroutine of the sustain displayed or erased faster than full lines, due to the absence voltage autoadjust program, is to aid in diagnosing which of some or all of the non-overlapped data loading. This is of field replaceable unit is at fault should there be a component particular advantage in vector graphics applications. The failure. Depressing the test switch, and seeing a series of short slices comprising each vector must be written individ- four test patterns repeated successfully as long as the switch ually (unless vectors are pre-converted into raster form in a is depressed gives assurance that the plasma display panel is bit-per-pixel buffer, and that buffer data is written to the operating correctly. panel in scan line mode). These slices are handled at the panel's maximum rate because of their short lengths. The logic interface lines pertaining to control area as follows: Contributing to rapid image erasure are the set all-ones (1) write; control, which effects an all-ones data load without the (1) erase; (1) test; Table 1. Speed of typical operations* (1) reset; (1) oscillator; Operation Time (1) ready. Write full panel 172 ms Technologies (one scan line per write) Implementation of these desired functions involves the Write one row of characters 3.6 ms blending of several logic technologies. Data to panel lines (16 pixels in height) CMOS data retention shift registers, and bipolar DMOS high Write one 9 x 16 character 2.0 ms voltage drivers integrated in a single module. Log/c data path Bipolar LSI for interfacing and de-skewing. Logic control Erase entire panel 6.0 ms PLA for waveform control and test pattern generation; one- Write one full screen vector chip microcontroller for automatic sustain voltage adjust- horizontal 225/~s ment. vertical 6 ms 45 ° 96 ms Function and performance Write 450 × 768 partition 96 ms Because no restrictions are imposed on the type, amount, shape, position or order of arrival of display data, alphanu- *Because execution times of certain operations may vary depending meric, vector graphic and non-coded image (NCI) data are on the nature of the previous operation, and because of internal synchronization requirements and overlap of write and data loading, equally accommodated, even though the methods of Table 1 values, although individually correct, may not appeax to be generation for these data types are disparate. For example, consistent. For this reason, no attempt should be made to derive NCI data is, by its nature, organized by scan lines, or parts any of these values from the others.

24 DISPLAYS. JANUARY 1984 expansion coefficient of 87 x 10 -7 °C-1. This glass was selected because of its excellent flatness. ,,era Float glass substrate\ ~ I I L .Tube The viscosity-temperature relationship of the substrate glass imposes a maximum temperature of about 640°C. The Iif'- 1 dielectric glass layer, which is thermally reflowed over the substrate and metal electrodes, must refiow at less than this maximum temperature. Subsequently, when the device is sealed, and the internal gap space is formed, another low temperature seal glass is used. This seal must be made at a temperature that is low enough to ensure that the MgO /~oat glass substrote secondary emissive layer will maintain its proper electrical function s . The lower bound of the thermal hierarchy is set by the requirement that the device interior Fig. 4 Cross-section through display be baked out under vacuum at about 300°C. The seal glass must be rigid enough at this temperature to withstand the actual load of data, and the ability to select as many as 16 stresses imposed by vacuum baking. scan lines at once. Taken together, these characteristics allow the simultaneous erasure of 16 scan lines, without Each glass then must be carefully designed with reference any data having been loaded. The entire panel can therefore to its viscosity-temperature relationship. At the same time, be erased in 48 steps (48 x 16 = 768 scan lines). Table 1 each glass must be nearly identical in thermal expansion contains examples of the speed of operation of this plasma behaviour to minimize stress. panel for typical actions. A 3 MHz clock rate is assumed. The trend to larger and higher line density displays has spurred the development of materials that can be processed at lower temperatures and which possess wider margins in PLASMA PANEL PROCESS their thermal hierarchy. The driving force for this develop- CONSIDERATIONS ment has been the need for higher yield and more efficient The IBM plasma display is shown schematically in Fig. 4. processes with wider processing latitude. As compared to the earlier generation IBM 3604 plasma display, it has six times the data area and is all-points addressable on a 2.8 x 2.0 lines per millimetre resolution. Thermal-mechanical considerations These enhancements have placed more stringent require- Fabricating the device to the required gap space tolerances ments on both the materials and processes used in the and controlling stresses impose some process considerations. . The former affects process yields, and the latter affects reliability. At first approximation, both are a function of Three primary and interrelated technical considerations that the rate and uniformity of thermal cooling during processing. must be satisfied when constructing such a device are: As the overall size of the device increases, the mechanical thermal hierarchy considerations, thermal-mechanical deformation and stress effects increase in an exponential considerations, and glass-metal interactions. The develop- manner. Consequently, careful control of the thermal ment of a fabrication process that cohesively satisfied all of processes is essential. the competing materials and process requirements proved to be an engineering challenge. Each of these considerations The dielectric reflow process step serves to illustrate this will be discussed further. concern more fully. The substrate has dimensions of approximately 381 x 457 x 6.0 mm thick. In order to Thermal hierarchy achieve the gap spacing of 79/am the reflowed substrate must be flat within 25.4 ~tm. For comparative purposes, Thought must be given to the overall temperature compati- this degree of flatness approaches what can be produced bility of the materials system. This consideration stems on metals by a high quality model shop with conventional from the process strategy which is used. The device structure machining practices. is a composite of glass, metal, and thin-film oxide layers. It is made by a sequence of thermal process steps, At temperatures above the anneal point of the float glass so that each step is conducted at a temperature suitably substrate (540°C), the substrate will deform or relax under lower than previous steps. The sequence of critical process its own weight. Therefore, it must be supported on a rigid steps is reflow, MgO evaporation, seal, and backfill. If the plate, flat within 12.7/lm. Stresses in the substrate produced materials system has been designed with a graduated by thermal gradients can also relax at this temperature. temperature hierarchy, the structure will not degrade at any Upon cooling to a much lower temperature and removing point in the process. Designing the materials system to the thermal gradients, the relaxed stresses will reappear in incorporate this thermal hierarchy feature, while maintain- opposite sign as predicted by classical annealing theory 9 . ing all other required electrical and physical properties, Depending on the magnitude and direction of the stress, required considerable development. the substrate will camber, distort, or be otherwise stressed. A temperature difference as small as 4°C through the thick- The highest permissible process temperature is governed by ness of the plate as it is being cooled through the critical the choice of substrate material. The substrate is a commer- stress relaxation region can produce a substrate camber of cial soda-lime-silica float glass that has an Na2 O content 76/am. This is three times greater than the desired flatness. of 13.9 per cent, a softening point of 722°C, and a thermal It is obvious, therefore, that great care must be exercised to

DISPLAYS. JANUARY 1984 25 cool the substrate uniformly so that the desired flatness is Both types of glass have been used nonetheless in plasma obtained. panel construction.

These problems have been solved by advances in thermal Spacers process control which include an in-line furnace with a Historically, active area spacers in twin substrate a c plasma complex intra-zone power modulation configuration, special displays have been visible in the operating display n and fixturing for thermal load stabilization and gradient control, have caused electrical degradation of the discharge sites atmosphere control, and computer monitoring of process near the spacer elements 12 . Attempts have been made with temperatures. The thermal-mechanical process consideration this plasma display to minimize these effects. has been one of the driving forces behind the development of materials that can be processed at lower temperatures. Figure 4 shows the display construction in which glasses are the primary materials t . Incorporating spacers between the Glass-metal interactions glass plates must not significantly affect the electrical This display contains about 731 m of 71/am wide thin film operation of adjacent discharge sites. Such variables as metal electrode lines. The lines are about 2 #m thick and dielectric thickness, chamber gap, and refractory oxide are a chrome-copper-chrome laminate. The chrome provides characteristics must not be altered in the vicinity of the adhesion to the dielectric and substrate glasses, and the spacers. copper provides conductivity. The lines are formed by vacuum evaporation and photolithographic processes. Each Nickel-iron surface bonded spacers were chosen as satisfying of the nearly 1 700 lines must be operational. requirements of thermal expaasion coefficient, surface oxide properties, stability, ductility and opacity. In the The glass and metal can interact during photo and re flow fabrication process, the nickel-iron spacers are attached to processing to produce defects such as open lines, bubbles, one of the two substrate plates after dielectric reflow. This and loss of adhesion. Substrate cleanliness, metal grain alloy is an inherently stable material which can be cleaned structure and stress, atmosphere, and temperature are by hydrogen firing at 900°C. After hydrogen firing the important variables that must be controlled. nickel-iron alloy is subjected to an oxidation process that makes the surface of the spacer dark and non-reflective. Reaction mechanisms responsible for these defects during This procedure, in conjunction with the geometry of the reflow have been identified. They include: substrate spacer, produces a spacing element which is nearly invisible structural relaxation; substrate alkali diffusion; chromium- in an operating display. Figure 5 shows an individual spacing copper oxidation; contaminant dissolution; glass sintering element and its geometry chosen for high load-bearing kinetics; organics pyrolysis; chemical reduction of heavy capacity and minimum visibility. metal glass fluxes. MANUFACTURE Except for the last two mechanisms, all can be favourably The display glass plates have a Cr-Cu-Cr metal line pattern influenced by reduced temperature processing. The last two covered with a dielectric layer of lead-boron-silica glass. An mechanisms are influenced by the selection of organic MgO thin film layer overlays this xa . The inner cavity is constituents in the thick film glass paste, atmosphere at filled with -argon gas. specific stages of the reflow process, and the glass particle size and milling procedure which is employed. Layers of metallurgy are sputtered onto the substrate. Lines are etched into the metallurgy by a subtractive etch photo- Panel seal lithographic process, and screen-coated with a layer of Constructing plasma display panels it is preferable to fuse dielectric lead glass which is then reflowed. Spacers are the dielectric glass layer (Fig. 4) and then seal device at the attached to the rear plate, and an evaporated thin layer of lowest possible temperature. This reduces undesirable MgO is deposited on both types of plates. A seal rod border material interactions and processing times. Both the is then constructed 14 . This border is melted to form a dielectric glass and the seal material should have thermal expansion coefficients compatible with the other panel components. In addition, the softening point of the seal must lie below that of the dielectric glass by a certain minimum amount. ~'/ / "/ / ~" Shorp Suitable materials are based on lead borosilicate solder glasses with at least 55 weight per cent lead oxide. A wide range of individual property values can be achieved with these glasses, but specific combinations of properties will only occur over limited composition ranges if at all. The "Y ?Z key constraint is the minimum achievable softening point for vitreous glasses with the required expansion level which in turn defines a minimum sealing temperature for the plasma panel ~° .

Seals can be achieved at lower temperatures using devitrify- ing glasses, but here chemical constraints again determine the minimum seal - and hence processing - temperature. Fig. 5 Spacing element

26 DISPLAYS. JANUARY 1984 cavity between the two plates with a tubular connection to it. Unopernted cells f Short-term A new plasma panel manufacturing facility was patterned Ignition after a specially designed pro-production facility *s . There chi?_L_ are two sections of clean room area: the photo line [rant Long-term end, and the main section of the line. Both are on a raised change floor which allows vertical laminar air to flow from filters in the ceiling, through perforated floor tiles, to the return InitialT T air plenum under the raised floor. margin End-of-life margin Ninety per cent coverage with ceiling filters gives a class Unoperated cells 100 or better environment, with 40 linear feet-per-minute Short-term air flow resulting in approximately four air volume changes change per minute. Forty to fifty per cent ceiling filter coverage Extinctionl_ gives class 10 000 or better environment with two air volume voltage t-- changes per minute. Long-term tet~ change In the photolithography process area, class 100 is further guaranteed locally by installing recirculating air showers over the sections of the line where the product is exposed 0 T Operating hours to the environment. The air showers are equipped with static grids to neutralize statically charged particles from Fig. 6 Cell differentiation due to long-term and short-term changes adhering to the product surface. as a function of operating hours

Installation of the plasma panel facility in the Kingston site required disposal facilities for liquids and gas. The liquid power function of operating time and plasma intensity. effluents that contain heavy metals (such as Cr and Cu), use This change occurs in all panels. Its effect is cumulative and a separate drain system to a heavy metal waste processing permanent and constitutes the dominant mode of long-term and disposal plant. Air effluents containing hydrocarbons change. Short-term change is the condition wherein ignition are exhausted through a solvent recovery system which and extinction voltages of unoperated ceils increase as some removes the hydrocarbons. exponential function of operating time, spatial distribution and plasma intensity of neighbouring operated cells. The Automation is used on this manufacturing line in the areas potential for this type of change exists only in very few of loading, plate marking, buffers and accumulators, trans- panels and is believed to be introduced during fabrication. portation carts and conveyors. This change occurs relatively quickly, saturating between 200 and 300 operating hours, is reversible, and constitutes Two computer systems are used. One is for process control the dominant mode of short-term change. and monitoring of equipment parameters such as the pH of the etching solutions. Furnace profiles are monitored and In the normal course of panel operation, some panel cells tied in with a graphic display. Backfill equipment tempera- are operated more frequently than others and therefore ture is monitored and portions of the cycle are controlled incur a greater amount of long-term change. If a panel also at each station. A second computer is tied in with a host has short-term change, the least frequently operated ceils computer and used for product tracking and data collection. experience this change. Both types of change can coexist in Serial readers placed at strategic locations track the product a panel and combine to reduce its margin. If, at any time, plates or panels. In the case of furnaces, readers also trace the margin decreases below a pre-established value known which furnace and fixture was used. as 'end-of-life margin', the panel is then considered to be unsuitable for reliable operation. End-of-life margin is The distinction of this plasma panel manufacturing line lies chosen as the value likely to cause a few picture elements to in adapting a vertical laminar flow clean air system to a large malfunction, leading to possible legibility errors. Figure 6 area. This helps achieve the clean environment described depicts a panel with long-term and short-term changes even with the installation of 25 m furnaces, conveyors and resulting in a time-to-failure of T operating hours. large equipment needed to handle a product of this size. Burn-in strategy for improving reliability RELIABILITY EVALUATION Long-term change is significant during the initial operation An a c plasma display panel has no filaments to burn out or of a panel. Consequently, differentiation is likely to occur to degrade. Its simple, rugged construction allows between operated and unoperated ceils, resulting in a it to operate reliably for a long time. However, as the panel noticeable decrease of margin. To minimize this condition, is broken in with use, predictable changes occur to the a burn-in procedure is used whereby all cells in a panel are 'margin' - the operating range of the sustain voltages of the operated for a few hours at high plasma energies. This is an panel. There are two types of significant change which affect effective way of incurring a large portion of long term change the margin in a panel. These are referred to as long-term in the panel prior to normal operation. When a panel is and short-term changes. operated thereafter, differentiation is much reduced, and panel life (which is the time to reach end-of-life margin) is Long-term change is the condition wherein ignition and significantly extended. Figure 7 shows how panel life extinction voltages of operated cells decrease as some improves with burn-in.

DISPLAYS. JANUARY 1984 27 Ignition voltage aged panels and establish long-term reliability for the panel in the field.

Initial ~/// Long-termT margin change Remainin Figure 8 shows a regression line of long-term change on the i margin cube root of operating hours taken from a typical sample of ////////!/l///i,z////////f panels. The figure also shows the lower bounds of the 98 per Extinction cent and 99.9 per cent confidence intervals for individual voltage Long-term panels 2 . This model predicts that for an average initial change operating margin of 11 V and a defined end-of-life margin of 2.7 V, at least 99.5 per cent of the panels will exceed T 1 Operatingh°urs 350 000 operating hours - equivalent to 132 working years. a ', Normal paneloperation - Ignition Short-term margin changes voltage Incidence of short-term change in panels is considered to be a manufacturing defect against which the product is carefully Margin prior to guarded. Because the tendency of a panel for short-term burn-in change is rare and testing for it is involved, a sampling plan 1 Long-term change for production lots is used to preclude such panels. Extinction I voltage According to the plan, samples from each lot are subjected to 400 hours of pattern ageing, then tested for short-term change on the 0 per cent aged subset of cells. If any are '-T ~ ILong-term change Burn-in found, corrective measures are taken with regard to the lot, period Operating hours manufacturing process, or both. These measures ensure that b Normal panel operation the probability of panels with short-term change escaping Fig. 7 Long-term change for panel: a - with; and b - without burn-in to the field is kept extremely small. Total average reliability for the panel is calculated from projected long-term and short-term margin changes and other possible catastrophic Pattern ageing procedure causes. A simple and inexpensive method was developed for ageing a large number of panels simultaneously. The process PRESENTATION GRAPHICS subjects the panel to three static repetitive patterns which Data that would normally appear in written report form, partition the cells into four interposing subsets. This is such as fractions, or percentages, can often be presented accomplished by busing the terminals of each side of the more effectively as non-alphanumeric renditions on a display panel and connecting them to a sustain driver through four screen. Graphs, pie charts, and histograms are key examples. relays. Energizing the relays in pre-determined combinations In some instances, continuous tone pictures are desirable ignites the four subsets for duty periods of 100, 35, 15 and (Fig. 9). The internal considerations for data to be presented 0 per cent respectively. in graphic form on a display should be compatible with the type of data usually displayed on those devices. Maximum long-term change appears on the 100 per cent aged set with progressively less change appearing on the 35 In graphic displays, the user interacts with a Cartesian plane. per cent and 15 per cent sets. Short-term change, when This requires complex architecture and systems. It is essen- present, appears on the 0 per cent aged set. tial to provide graphic renditions without resorting to the unnecessarily complex design graphics solution. In this way A model for ageing the user is insulated from the complexities of the display Predicting long-term panel reliability requires an ageing architecture, and can concentrate on data he is used to. model for long-term change as a function of operating hours. Such a model was derived from empirical data of In an alphanumeric display, the screen is a montage of long-term change measured on panels which were pattern- 'character boxes' or cells, each of which is a miniature aged for periods between 6 000 and 10 000 hours. A T t/3 12 model was found to fit the data best and to predict long- ....._._._...... Average margin regression line term change fairly accurately over the planned life of the program. I0- 50% With knowledge of expected panel behaviour, initial operat- 8- ing margins and end-of-life margin, it was possible to g I% determine the percentile of panel population expected to 6- reach end-of-life for a given number of operating hours. An E 005% assessment of panel reliability for actual usage, however, ~_ 4- requires establishing the relationship between pattern ageing and ageing in a simulated user environment. Comparisons of 2 [- --~--End-of-life long-term change for the 100 per cent duty operated cells margin with panels exercised with random alphanumeric patterns I [ ~ I _ [ I I [ ~' showed that long-term change produced by alphanumerics O O I I 4 8 16 27 45 64 was about half that produced by 100 per cent duty operated Operating hours (x IO00) cells. This relationship was used to factor data from pattern- Fig. 8 Long-term change as a function of operating hours

28 DISPLAYS. JANUARY 1984 bit slices in such a way that four different ways of compres- sion are tested on the cell. The best of the four compression methods is chosen and presented to the transmission line with a header of up to four bits indicating which of the four compression methods was used. This compressed data, upon arriving at the presentation destination, is expanded back to the usable 18 eight-bit slices and is then ready for USe.

Display mechanism The cell representation is taken from the data stream and placed in random access read/write memory - the same way an alphanumeric character box would be placed. These cell representations can be retrieved at a later time for display. With these possibilities, a datastream can contain cell data to be loaded into the random access memory. The datastream subsequently contains data to be used for retrieval of the data display. Such a set-up makes a very Fig. 9 Forms of data displayed on the IBM 3290 large number of variations in cell data available for presen- tation (Fig. 11). Cartesian plane. Because of the versatility inherent in this cell concept, the user of an alphanumeric display can 1. First, the operator interacts with the display to form the command an almost complete graphic display rendition, character cells necessary for the display. as long as a flexible way can be found to define the cells as 2. Second, the character cells are arranged for transmission micrographs. to the display. This might or might not include cell compression. After the cells are prepared for transmis- In order for micrographs to be compatible with normal sion, the actual transmission of the cell data is effected. display architecture, they are defined as if they were 3. Third, the data is taken from the transmission line and peculiar characters. These micrographs can then be called prepared for load to the program symbol RAMs. This by the display in the same way that alphanumeric characters preparation will include expansion of the data if are. Additional storage for micrographs is required so that necessary. The loading location for each micrograph was normal alphanumeric characters can be used in connection decided in Step 1. with the transiently defined micrographs. Associated hard- 4. Fourth, the datastream with the display description is ware must be supplied for accessing this additional storage. interpreted and the character cells are placed on the display so that the symbol is formed. Microqraph cell structure 3270 EMULATION Each micrograph is 9 x 15 (144) pixels, a size which gives full bit compatibility with the processing hardware byte Attempting to emulate a 3270 type display on a plasma structure. A large screen can contain up to 5120 character display panel poses interesting challenges due to differences boxes. Each micrograph that fits these boxes can have in technology between this type of display and CRT 2144-1 degrees of freedom. For internal handling and displays. The plasma display panel cannot, in all cases, be external transmission of these character configurations, updated as quickly as the data to be presented is changing in many ways have been devised for representing the cell data as 'slices' compatible with normal data. For the 9 x 16 cell, I 2 3 4 5 6 7 8 9 a way of slicing has been defined wherein the leftmost I H I column is divided into vertical slices, while the remainder of 2 H2 the cell is sliced horizontally. This format provides full H3 representation of the cell in 18 eight-bit slices (Fig. 10). 4 vl H4 5 H5 Performance customization H6 Transmission speed is very high for local transmission lines, H7 and the amount of data transmitted does not greatly affect H8 performance. But for transmission over communication H9 lines it is desirable to minimize the amount of data sent. 10 HIO Compression of cells represents a compromise in time con- HII siderations by boosting transmission line speeds but also 12 HI?_ increasing processing time. The net effect is to increase V2 13 total speed and minimize the response time. HI3 14 HI4 Practical examples of cell configurations show that a great 15 HI5 percentage of the pixel positions in the cell structures are 16 HI6 vacant. This discovered redundancy has led to the develop- SS ment of an algorithm that compresses the slices representing a cell so that the cell can usually be represented in less than 144 bit positions. This algorithm is applied to the 18 eight- Fig. 10 Slicing of the 9 × 16 cell

DISPLAYS. JANUARY 1984 29 I 2 3 4 Operator input Code and transmit cell Decode cells to develop cells and place in RAM

I~ • .d

I \ Cell code / ,

--.., Cell decode I Cell XMSN I PS RAM load I 'I r I ', 1 Display description XMSN --.., i f atlon ' i Fig. 1 t Display generation a multiple character keystroking or data stream operation. Whenever a change occurs in the data in the display buffer, In order to overcome this, it is necessary to adopt an the replace row flag is set in the corresponding update list approach that minimizes the amount of data to be updated entry. The plasma display panel update code scans the for a particular operation. On the other hand, a significant update list to find which rows need to be replaced, calcu- amount of time is associated with starting an update opera- lates the appropriate starting coordinates on the plasma tion on the plasma display panel, so an acceptable compro- display panel, and calculates the data start address for any mise has to be reached between this and the amount of data rows that have to be replaced. It then sets up the parameters to be updated in one operation. required by the plasma display terminal adapter and initiates the panel operation. At this point the plasma display panel In addition to the approach adopted for display update it update code is suspended to allow other processing to take was also important to provide some unique approaches for place, while the display adapter is running. This is necessary different forms of cursor and highlighting. On displays that since the time taken to replace a row can be several milli- are continually refreshed at high speed, the hardware seconds, and this time would be wasted if the suspension controls the cursor appearance and the highlighting of data. did not take place, allowing other lower priority processing However, with a plasma display panel this has to be carried to occur. The plasma display panel update code restarts out by a combination of hardware and software. asynchronously when the replace operation is complete.

Since the plasma display panel can also be used with Operations that require large numbers of rows to be different character sizes by varying the font and cell size, it updated at keystroking speeds can pose a problem because is also possible to enhance some of its display characteristics. the time taken to rewrite multiple rows can exceed the time These include multiple screen sizes and the enlargement of available between keystrokes. This is most evident in the portions of the display. areas of scrolling and large field inserts. The approach adopted to cater for these cases was always to update Updating the plasma display panel as a result of certain areas of the panel in preference to others. In the a keystroke or data stream case of insert operations, this means that the rows on the panel in the area of the cursor are updated first and as In order to save time in update operations it is necessary for many other rows as possible are then updated before the the software to eliminate unnecessary updates. This is next keystroke occurs. For scrolling operations the top or achieved by associating each row of data in the display bottom of the panel will be updated first followed by other buffer, from which the displayed data is generated, with an rows in an upward or downward direction depending on the entry in an update list containing flags indicating which direction of the scroll operation. In all cases the display will rows have changed. By restricting updates to a row of data, eventually be completely updated when there is a pause in the time necessary to start the hardware update operation is the keystrokes. acceptable when the amount of data that has changed is small. This start time is fairly insignificant when a large In order to reduce the complexity of the plasma display amount of data has changed. terminal adapter the cursor variations are handled by soft-

30 DISPLAYS. JANUARY 1984 Table 2. Plasma display panel operations to provide character font with the maximum spacing in the panel area various cursor types available. The same process is used by the zoom function, the main difference being that the area used, in this case, Underscore Draw image will always be the full panel. Therefore, if the panel contains Blinking Draw image or none several screens or partitions, and the zoom function is used, the partition containing the cursor will be expanded to Underscore reverse Replace character (normal or occupy as much of the full panel as possible. reverse) Blinking reverse Replace character (normal or CONCLUSION reverse) The challenge presented by a plasma panel of large dimen- sions was to achieve high image display rates, regardless of ware. The old cursor is removed by replacing the row the organization of the incoming data. Central to meeting containing it. The new cursor is created by carrying out this challenge were the driver modules and their surround- additional operations on the row containing it. These ing logic and control which accommodate rapid data operations consist of a combination of'replace', 'write', loading, random access to screen coordinates, and simul- and/or 'erase' operations (Table 2). taneous updates of entire scan lines.

Attribute propagation is performed by the plasma display Important considerations in plasma display panel fabrication terminal adapter for contiguous characters during a 'replace' have been satisfied in this display by the development of or 'write' operation. Row-to-row attribute propagation is reduced temperature processing. This development has carried out by software with hardware assistance from the resulted in an efficient high yield fabrication process. With adapter. Whenever a 'replace' or 'write' operation is carried proper selection of glass constituents, and with suitable out the plasma display terminal adapter returns the field modifier additions, low temperature seal materials and attribute and extended field attribute last encountered dielectric glasses can be obtained for plasma panel display during the operation. This information is saved in the update applications. These have the material properties required list entry for the following row and used by the plasma for plasma display panel design, and are compatible with display panel update code to specify the starting attributes reduced temperature processing. for the following row. The overall result is a reliable a c plasma panel which allows Highlighting rapid display of data in various forms. Flexibility of use and high-volume manufacturability are ensured by advances in Highlighting on the plasma display panel is carried out by software, hardware and processing technology. the combination of hardware within the display adapter and special software. This is partly to reduce the hardware References complexity, and partly because highlights such as blinking require a continuous rewrite in order for the hardware to do 1 Pleshko,P. 'A C plasma display device technology: an overview' Proc Soc Inf Disp 21 2 (1980) the complete function. 2 Kleen,B.G., Lamoureaux, W.R., Pearson, K. The design of a versatile plasma panel subsystem' Proc Soc lnfDisp 20 3 (1979) In order to blink the characters on the plasma display panel 139 it is necessary to replace the characters at appropriate 3 Johnson, W.E., Oster, E.A., Hoehn, HJ. 'Plasma display/memory intervals, and to specify to the display adapter that blinking panel with integral driver circuitry' Soc InfDisp Int Syrup characters should be displayed or not displayed. A similar (1977) 20 approach is required for the blinking cursor. 4 Tucker, P.T., Bitzer, D.L. 'A minimum component per line technique for addressing plasma displays' Soc InfDisp Int Syrup Reverse requires no software involvement but underline and (1977) 22 underscore of characters is carried out by a draw image 5 Czajkowski, R., Coates, W., Fitzhenry, P., Johnson, R.L., Stone, operation following the row replace. The software examines M. 'A microcomputer-driven graphic display system' Soc Inf Disp Int Syrup (1977) 26 the attributes associated with the characters and creates image data for the complete row. 6 Turner, L. 'Implementation of an advanced plasma display terminal' Soc lnf Disp Int Symp (1978) 48 Support of multiple character sizes 7 Copece, R.P. 'Bidfet is key to new driver chips' Electronics (6 July 1978) 40 Since the plasma display panel is effectively an all-points 8 Sherk, T.A., Tummala, R.R. 'Dielectric glass composition' US addressable storage device that can be written selectively, Patent 3 923 530 it is possible to use different character sizes on different 9 Shand, E.B. 'Glass engineering handbook' (McGray-HiU, 1958) parts of the panel. The cell containing the character can also 107 be varied in size giving variations in spacing to improve 10 Cox, S.M. 'Survey of glass materials in microelectronies' legibility. In order to provide multiple character sizes, it is (Ministry of Technology, London, UK, 1968) necessary to provide multiple character font definitions. 11 Dick, G.W., Biazzo, M.R. IEEE Trans Electron Devices ED-23 However, with only a limited number of alternative (1976) 429 character fonts, a great deal of flexibility can be achieved. 12 Sobel, A. IEEE Trans Electron Devices ED-24 (1977) 835 13 Abelfotoh, M.O. 'Influence of surface properties of MgO on the Since the smallest character font used on the plasma electrical characteristics of a c plasma display panels' (Biennial display panel could prove difficult to read under some Display Research Conference, Cherry Hill, NJ, USA, 1978) circumstances (eg when used with minimum spacing), 14 Perry, C.H. 'Seal method for large plasma gas panel displays' IBM every attempt is made to improve the situation whenever Tech Disclosure Bull 22 (1979) 176 possible. To do this a character cell and font size selection 15 Cart, T.W., Cod, E.A. 'Contamination control on active surface process is used which ensures the selection of the biggest of gas display panel' IBM Tech Disclosure Bull 22 (1979) 176

DISPLAYS. JANUARY 1984 31 data proc= ncj

DATA PROCESSING, the international journal for computer managers, and the leading authority on information management issues and computing developments, is publishing an important special issue

What advances have been made in computing in the last 25 years? In its special silver jubilee issue, DATA PROCESSING will review computing developments from punched card readers, magnetic tape, batch processing, through structured programming, online processing, systems design, distributed computing up to personal computing, computer security and networking. Where will computing go in the next 25 years? DATA PROCESSING's anniversary issue will answer this question by looking at:

• f'Lfthgeneration computers • optical discs • functional programming • speech technology • expert systems • supercomputers • knowledge engineering • CAM • cables and satellites • biochips

DATA PROCESSING is published 10 times a year. Subscription price is £70 per annum. Limited numbers of the anniversary issue are available at the single copy price of £8.40. To subscribe to DATA PROCESSING or to order your special issue contact Elena Softley, Editor, Data Processing, Butterworth 'Scientific Limited -- Journals Division, PO Box 63, Westbury House, Bury Street, Guildford, Surrey GU2 5BH, UK. Tel: (0483) 31261. Telex: 859556 SCITECG.

32 DISPLAYS. JANUARY 1984