Reference / Paper · 1979
A 240-Character Vacuum Fluorescent Display (SID Digest, 1979)
Ise's SID paper on a 240-character dot-matrix fluorescent display, the step beyond calculator digits.
Reference / Paper · 1979
Ise's SID paper on a 240-character dot-matrix fluorescent display, the step beyond calculator digits.
8.3 / 9:50 A.M.: A 240-Character Vacuum Fluorescent Display and its Driving Ability Kazuhiko Kasano, Tokuhide Shimojyo, Mitsuru Masuda and Kentaro K. iyozumi Ise Electronics Corp., Ise, Japan INTRODUCTION A flat panel 240 character Vacuum Fluorescent Display (VFD) has been developed which can display full ASCII character font. A great number of flat panel numerical VFNs which display bright green figures under relatively low driving voltage and power consumption have been used in calculator, clock and ECR markets. (1) As the next step, we developed single line charac- ter VFDs having 20 to 40 characters where anode sub- strates are formed with multi-layer of thick conduct- ive and insulating films. They are used in personal computers, POS terminals, etc. Now, the single line character VFDs have success- fully extended to the multi-line, capable of display- ing 240 characters, in which both thin and thick film technologies have been adopted for the anode sub- . strate. DESIGN Structure of this VFD is illustrated in Fig. 1, where 240 characters are divided into 6 lines of 40 characters, and each character consists of 35 dots (5 x 7) and a cursor. There are 40 grids for time- sharing control of the emission flow from the cathode; a column of 6 characters is covered by one grid. A selection of forty grids enables one to operate the VED with duty factor of approx. 1/40 which leads to a reasonably low voltage to produce high brightness as found in Table 1. In this case, total of 258 lead- outs (36 x 6 = 216 leads for the anode, 40 for the grid and 2 for the cathode) are necessary. The character size is 5(H) x 3.5(W) mm and the dot _ 0.5 mm ‘square. Spacing of lines and columns are equivalent to 3 dots and 2 dots respectively. Display overall is 250(L) x 100(W) x 14.5(T) m, FABRICATION Preparation of Anode It is an important factor to reduce the cross over points in the anode wiring in order to increase yield and reliability of the device through forming a simple insulating layer. The anode substrate is formed with only three layers and there are only two cross over points per dot. A simple three layer structure which consists of the first Al-thin film conductive layer for lead wiring, the glass thick film insulating layer for cross over and the second Al-thin film conductive layer for anode electrode is formed on a glass plate. Approx. 1.5 um thickness Al-film is deposited on all over the surface of a normal soda-lime glass plate by DC magnetron sputtering. Then it is etched to the fine pattern as shown in Fig. 2 using photolitho- graphy, which is served as the first conductive layer. The glass insulating layer having 20 to 30 pm in thickness is screen printed on the processed substrate so as to produce thru-holes only on the dots with the accuracy of the positioning within 75 ym. The second conductive layer is deposited only on the thru-hole points of insulating layer by DC mag- netron sputtering using a metal mask. Dot of the second conductive layer has a size of 0.5 mm square and contacts to the first conductive layer through thru-hole. The cross section of the anode structure thus formed is illustrated in Fig. 3. ‘58 @ SID 79 DIGEST Assembling and Exhausting This process is the same as our previous VED: 1) phosphor is electrophoretically deposited on the anode electrodes, 2) mesh grids are fixed, 3) two filaments coated with cathode materials are stretched over a character line, 4) window glass is sealed with frit, 5) the bulb is exhausted and tipped off at approx. 1 x 10-6 Torr. DRIVING Driving diagram of this VFD is shown in Fig. 4. A microcomputer and an external ROM/RAM have been adopted for this driving circuits. CPU controls the whole driving circuits and I/O data to the host system. : ROM contains the full ASCII character patterns and the control program. RAM memorizes 240 character data which come from the host system. Scanning of column from left to right is controlled by shift registers for the grid. There are shift registers and latches for the anode. A series of 8 bit parallel signals from CPU is shifted 5 times to complete one character pattern. This process should be repeated 6 times to complete 6 characters in a column. And then, these patterns are latched. When grid scanning pulse selects the leftmost colum position, the first latched 6 charac- ters are pushed off to the display, and next 6 char- acters are input to the shift registers during this display timing. The above cycle is repeated 40 times for one display cycle. CONCLUSION A new flat panel 240 character VED having average brightness of 220 £L under standard operating cond- tion (shown in Table 1) has been produced with a combination of thin and thick film technologies, which is proved to be effective for increasing of yield and reliability of this device. Adopt of pP simplified the driving circuits, which opened the way for the wide applications, especially read-out of middle class of the intelligent terminals. Reference: 1) K.Kiyozumi, et al. "Flat Panel Multi-Digit Fluo- rescent Display" SID 76 Int'l Symp. p130 & p131 Table 1 Electrical Characteristics Item Operating Con d. Note Filament Volt. | 8.8 Vac V.ems. Filament Curr. 312 mAac r.ms. Anode Volt. 50 Vp-p du=1/45 ,p.w=100 ps. Anode Curr. 4.5 mAp-p per character Grid Volt. 50 Vp-p du=1/45 ,p.w=100 ps. Grid Curr. 27 mAp-p per colum Cut-off Volt. -12 Vdc against to cathode Brightness 220 £1 average per dot Lead Terminal : A Character : ee a Le Filament Su . renee - aad Filament Tentioner ist Conductive Layer Phosphor Position ‘Fig. 1 Display perspective view Fig. 2 Wiring Pattern of the Anode Dots 2nd Conductive Layer (Anode) Phosphor 20-30 ym 20-30 ym 1 ~tum UN ~ nsulating ’ XS ~ ue % Layer 50] 100 200 100 150.) 50|50.|50] 50 {50. Cross Over Point : ~1.5um " 1st Conductive Layer 500_ym 250 um Glass Substrate Fig. 3 Layer cross section: Detailed illustration of the anode structure 240 CHARACTER VFD LATCH DRIVER 216 Type: DC40066A SHIFT REG. ANODEs- 6Lines | S35dot+Cursor/Line 40. GRIDs 3 CLK ADDRESS BUS AODRESS~ DATA BUS om eux — So SHIFT REG. 6x8 bit WR —_r DATA cpu —y 8 bit Busy <—— Fig. 4 An example of driving block diagram Fig. 5 An engineering model S/D 79 DIGEST ¢ 59