Computer-aided design and analysis of circuits and semiconductor – Nanotechnology related integrated circuit design
Reexamination Certificate
2001-05-04
2002-12-17
Siek, Vuthe (Department: 2825)
Computer-aided design and analysis of circuits and semiconductor
Nanotechnology related integrated circuit design
C716S030000, C716S030000, C257S088000, C257S079000, C257S080000, C257S091000, C257S093000, C257S099000, C438S401000, C438S022000
Reexamination Certificate
active
06496973
ABSTRACT:
TECHNICAL FIELD
The present invention relates to generally a self-scanning light-emitting device, particularly to a method of designing a mask pattern used in forming metal lines for a self-scanning light-emitting device.
BACKGROUND ART
A light-emitting device in which a plurality of light-emitting elements are arrayed on the same substrate is utilized as a light source of a printer, in combination with a driver circuit. The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a pnpn-structure as an element of the light-emitting device, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 2-92650, and 2-92651.) These publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such self-scanning light-emitting device has a simple and compact structure for a light source of a printer, and has smaller arranging pitch of thyristors.
The inventors have further provided a self-scanning light-emitting device having such structure that an array of light-emitting thyristors having transfer function is separated from an array of light-emitting thyristors having writable function (see Japanese Patent Publication No. 2-263668.)
Referring to
FIG. 1
, there is shown an equivalent circuit diagram of a fundamental structure of this self-scanning light-emitting device. According to this structure, the device comprises transfer elements T
1
, T
2
, T3, . . . and writable light-emitting elements L
1
, L
2
, L
3
, . . . , these elements consisting of three-terminal light-emitting thyristors. The structure of the portion of an array of transfer elements includes diode D
1
, D
2
, D
3
, . . . as means for electrically connecting the gate electrodes of the neighboring transfer elements to each other. V
GK
is a power supply (normally 5 volts), and is connected to all of the gate electrodes G
1
, G
2
, G
3
, . . . of the transfer elements via a load resistor R
L
, respectively. Respective gate electrodes G
1
, G
2
, G3, . . . are correspondingly connected to the gate electrodes of the writable light-emitting elements L
1
, L
2
, L
3
, . . . A start pulse &phgr;
s
is applied to the gate electrode of the transfer element T
1
, transfer clock pulses &phgr;
1
and &phgr;
2
are alternately applied to all of the anode electrodes of the transfer elements, and a write signal &phgr;
I
is applied to all of the anode electrodes of the light-emitting elements.
The operation of this self-scanning light-emitting device will now be described briefly. Assume that as the transfer clock &phgr;
1
is driven to H (high) level, the transfer element T
2
is turned on. At this time, the voltage of the gate electrode G
2
is dropped to a level near zero volts from 5 volts. The effect of this voltage drop is transferred to the gate electrode G
3
via the diode D
2
to cause the voltage of the gate electrode G
3
to set about 1 volt which is a forward rise voltage (equal to the diffusion potential) of the diode D
2
. On the other hand, the diode D
1
is reverse-biased so that the potential is not conducted to the gate G
1
, then the potential of the gate electrode G
1
remains at 5 volts. The turn on voltage of the light-emitting thyristor is approximated to a gate electrode potential+a diffusion potential of PN junction (about 1 volt.) Therefore, if a high level of a next transfer clock pulse &phgr;
2
is set to the voltage larger than about 2 volts (which is required to turn-on the transfer element T
3
) and smaller than about 4 volts (which is required to turn on the transfer element T
5
), then only the transfer element T
3
is turned on and other transfer elements remain off-state, respectively. As a result of which, on-state is transferred from T
2
to T
3
. In this manner, on-state of transfer elements are sequentially transferred by means of two-phase clock pulses.
The start pulse &phgr;
s
works for starting the transfer operation described above. When the start pulse &phgr;
s
is driven to a low level (about 0 volt) and the transfer clock pulse 02 is driven to a high level (about 2-4 volts) at the same time, the transfer element T
1
is turned on. Just after that, the start pulse &phgr;
s
is returned to a high level. Assuming that the transfer element T
2
is in the on-state, the voltage of the gate electrode G
2
is lowered to almost zero volt. Consequently, if the voltage of the write signal &phgr;
I
is higher than the diffusion potential (about 1 volt) of the PN junction, the light-emitting element L
2
may be turned into an on-state (a light-emitting state).
On the other hand, the voltage of the gate electrode G
1
is about 5 volts, and the voltage of the gate electrode G
3
is about 1 volt. Consequently, the write voltage of the light-emitting element L
1
is about 6 volts, and the write voltage of the light-emitting element L
3
is about 2 volts. It follows from this that the voltage of the write signal &phgr;
I
which can write into only the light-emitting element L
2
is in a range of about 1-2 volts. When the light-emitting element L
2
is turned on, that is, in the light-emitting state, the amount of light thereof is determined by the amount of current of the write signal &phgr;
I
. Accordingly, the light-emitting elements may emit light at any desired amount of light. In order to transfer on-state to the next element, it is necessary to first turn off the element in on-state by temporarily dropping the voltage of the write signal &phgr;
I
down to zero volts.
According to the circuit shown in
FIG. 1
, the cathodes of the light-emitting thyristors are connected to the ground, but it is apparent for those who skilled in the art that the anodes may be connected to the ground by opposing the polarity of the circuit.
In the self-scanning light-emitting device in which a transfer part and a light-emitting part are separated, the structure of the thyristor of the transfer part are substantially the same as that of the thyristor of the light-emitting part. Therefore, the thyristor used as the transfer element in the transfer part emits the light in its on-state. At this time, a large current as in the thyristor of the light-emitting part is unnecessary to be applied to the thyristor of the transfer part to drive it, i.e. a small fraction of current to be applied to the thyristor of the light-emitting part is applied. Therefore, the light output of the thyristor of the transfer part is smaller than that of the thyristor of the light-emitting part. As the timing of light emission in the thyristors of the transfer part is different from that in the thyristors of the light-emitting part, the light emission of the thyristors of the transfer part becomes a noise for the light emission of the light-emitting part when the self-scanning light-emitting device is used as a light print head. In order to suppress the noise, a light-shielding is required for the transfer part. The thyristors of the transfer part essentially have the structure for preventing the light from emitting outward. That is, the light is shielded by a metal (Al) line for applying a clock pulse. In this case, in order to make light shielding effective, it is required that the Al line is formed so as to be overlapped with the gate electrodes. The Al line is formed by depositing Al film and patterning it using a mask pattern in an etching process.
The thickness of the Al film is selected so thick as about 1 &mgr;m in order that the Al line is not discontinued at the steps on the surface of the elements. When such thicker Al line is patterned, the resulting size of patterned Al line varies widely, because the side etching to the Al line proceeds. Taking account of this variation of the size of resulting Al line and a mask pattern misalignment, it is required that a mask pattern size is designed in such a manner that the gap is not caused between the Al line and the gate electrode.
On the other hand, in the thyristors of the light-emitting part, the electrode for ap
Kusuda Yukihisa
Ohno Seiji
Ohtsuka Shunsuke
Dimyan Magid Y
Nippon Sheet Glass Co. Ltd.
RatnerPrestia
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