Incremental printing of symbolic information – Light or beam marking apparatus or processes – Scan of light
Reexamination Certificate
1995-09-21
2001-10-02
Yockey, David F. (Department: 2861)
Incremental printing of symbolic information
Light or beam marking apparatus or processes
Scan of light
C347S238000, C257S088000
Reexamination Certificate
active
06297842
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an array of light-emitting elements and an optical head assembly, more particularly to an array and assembly employing organic electroluminescent (EL) elements.
One well-known application of light-emitting arrays is in the optical heads of electrophotographic printers. Linear arrays of light-emitting diodes (LEDs) have long been applied in this way, for example. The optical head assembly of a typical LED printer comprises a printed circuit board on which are mounted a plurality of LED array devices and their driver integrated circuits (ICs). The diodes in the arrays form an image by illuminating a photosensitive drum.
This LED printing technology is limited in resolution, however, because the LED array devices and their driver ICs are interconnected by wire bonding. A separate bonding wire is required for each LED. Mutual contact between different bonding wires must naturally be avoided, so the LEDs cannot be spaced too closely together. Even if driver ICs are provided on both sides of the LED arrays, so that the bonding wires can be placed alternately on one side and the other, high dot resolution (higher than six hundred dots per inch, for example) appears to be unachievable.
Resolution is not the only problem in the use of LED arrays. Assembly of the optical head is time-consuming and difficult, because even at the comparatively moderate resolution of three hundred dots per inch, printing on standard letter-size (or A4 size) paper requires a row of over two thousand dots, so there are over two thousand bonding wires to be individually attached. Moreover, since each LED array typically provides only sixty-four LEDs, there are some forty LED array devices and a similar number of driver ICs to be individually die-bonded to the printed-circuit board, in precise positional relationships to one another.
Reliability is a further problem: with over two thousand closely-spaced bonding wires, it is difficult to ensure that no pair of adjacent bonding wires will make mutual contact. Cost is also a problem. Fabrication of the LED arrays is expensive, because a compound semiconductor such as gallium arsenide (GaAs) is employed, and the small size of compound semiconductor wafers permits comparatively few arrays to be fabricated per wafer, driving up the cost per array.
Use of arrays of zinc-sulfide (ZnS) light-emitting elements has also been proposed. Zinc sulfide is an electroluminescent material that can be deposited directly onto the surface of a driver IC, eliminating the need for separate array and driver devices. A ZnS light-emitting element, however, is not as easily driven as a LED. The necessary drive voltage is measured in tens of volts and may exceed one hundred volts, so special drive circuitry capable of withstanding high voltages must be provided. Furthermore, an alternating-current power supply must generally be employed, instead of the direct-current supplies normally used with integrated circuits.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to increase the dot resolution of an array of light-emitting elements.
A further object of the invention is to simplify the driving of an array of light-emitting elements.
Another object is to reduce the cost of manufacturing an array of light-emitting elements.
Still another object is to simplify the manufacture of an optical head assembly.
Yet another object is to reduce the cost of an optical head assembly.
Still another object is to improve the reliability of an optical head assembly.
The invented light-emitting array comprises a semiconductor substrate having a surface on which a plurality of output terminals are formed. Organic electroluminescent elements are created over these output terminals, in electrical contact with the output terminals. The electroluminescent elements are driven by an integrated circuit formed in the semiconductor substrate, which supplies direct current at a certain voltage to each of the output terminals, and switches this current on and off at each output terminal individually.
The invented optical head assembly has at least one of the invented light-emitting arrays mounted on a printed circuit board.
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Abiko Ichimatsu
Jiang Yichao
Koizumi Masumi
Nomoto Tsutomu
Frank Robert J.
Oki Data Corporation
Sartori Michael A.
Venable
Yockey David F.
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