JP4461552B2 - Self-scanning light emitting device array - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a structure in which a plurality of light-emitting points are provided on one gate island in a light-emitting element array composed of a three-terminal light-emitting thyristor. The present invention relates to an element structure that enables a sum of light outputs when lighted separately.
[0002]
[Prior art]
The present inventors have paid attention to a three-terminal light-emitting thyristor having a pnpn structure as a constituent element of a light-emitting element array, and have already applied for patents (Japanese Patent Laid-Open Nos. 1-238662 and 2-14584) to realize self-scanning of the light-emitting point. No. 2, JP-A-2-92650, and JP-A-2-92651). As a light source for an optical printer, it is easy to mount, the light emitting element pitch can be made fine, and a compact light emitting element array can be produced. Indicated.
[0003]
Further, the present inventors have proposed a self-scanning light-emitting element array having a structure separated from the light-emitting element array by using a transfer element array formed of a light-emitting thyristor having a pnpn structure as a shift register (Japanese Patent Laid-Open No. 2-263668). ).
[0004]
FIG. 1 shows the basic structure of a three-terminal light-emitting thyristor. As an example, a pnpn structure is formed on a p-type substrate. The gate of the three-terminal light-emitting thyristor has a function of controlling the on-voltage, and the on-voltage applied to the cathode is a voltage obtained by adding a voltage drop due to the diffusion potential of the pn junction and a current necessary for turning on to the gate voltage. Further, after turning on, the gate voltage becomes substantially equal to the anode voltage. Therefore, if the anode is grounded, the gate voltage is 0 volts.
[0005]
FIG. 2 is an equivalent circuit diagram of a first basic structure of a self-scanning light-emitting element array using such a three-terminal light-emitting thyristor. Three-terminal light-emitting thyristors T (-1) to T (+2) are used as light-emitting elements, and gate electrodes G _{-1 to} G ₊₂ are provided in the light-emitting thyristors T (-1) to T (+2), respectively. Yes. A power supply voltage V _GA (−5 V) is applied to each gate electrode via a load resistance R _L. Further, each of the gate electrodes G _{−1 to} G ₊₂ is electrically connected through diodes D _{−1 to} D ₊₂ in order to create an electrical interaction. Two transfer clock lines (φ1, φ2) are connected to every other element to the cathode electrode of each single light emitting thyristor. In the figure, φ _S indicates a start pulse.
[0006]
The operation will be described. First, assume that the transfer clock φ1 is at a low level and the light-emitting thyristor T (0) is turned on. At this time, the gate electrode G ₀ is pulled up to near zero volts from the characteristics of the three-terminal light-emitting thyristor. At this time, the gate voltage of each light emitting thyristor is determined from the network of the resistor R _L and the diodes D _{−1 to} D ₊₂ . Then, the gate voltage of the element close to the light emitting thyristor T (0) rises the most, and thereafter the gate voltage decreases as the distance from T (0) increases.
[0007]
However, the effect of lowering the voltage works only in the right direction of the light emitting thyristor T (0) due to the unidirectionality and asymmetry of the diode characteristics. That is, the gate electrode G ₁ is set to a voltage lower than G ₀ by the diode forward rising voltage V _dif , and the gate electrode G ₂ is set to a voltage lower than G ₁ by the diode forward rising voltage V _dif. Is done. On the other hand, no current flows through the gate electrode G- ₁ on the left side of the light-emitting thyristor T (0) because the diode D- ₁ is reverse-biased, and thus has the same potential as the power supply voltage _VGA .
[0008]
The next transfer clock pulse φ2 is applied to the nearest light emitting thyristors T (1), T (-1), and T (3) and T (-3). Among these, the turn-on voltage is the highest. The element having a high T is T (1), and the turn-on voltage of T (1) is the gate voltage + V _dif of the gate electrode G ₁ , which is about twice V _dif . The element with the next highest turn-on voltage is T (3), which is about 4 times V _dif . The turn-on voltages of T (-1) and T (-3) are approximately V _GA + V _dif .
[0009]
From the above, by setting the low-level voltage of the transfer clock pulses between about 2 times the V _dif of approximately 4 times the V _dif, it is possible to turn on only the light-emitting thyristor T (1), the transfer operation It can be carried out.
[0010]
FIG. 3 is an equivalent circuit diagram of the second basic structure of the self-scanning light emitting element array. This self-scanning light emitting element array includes transfer elements (three-terminal light emitting thyristors) T (-1) to T (2) and writing light emitting elements L (-1) to L (2). The configuration of the transfer element portion (transfer portion) shows an example using diode connection. The gate electrodes G _{−1 to} G ₂ of the transfer element are also connected to the gate of the writing light emitting element. A writing signal φ _I is applied to the anode of the writing light emitting element.
[0011]
The operation will be described. Assuming that the transfer element T (0) is in the on state, the voltage of the gate electrode G ₀ is increased from V _GA (-5 volts), becomes substantially zero volts. Accordingly, the voltage of the write signal phi _I is equal to or less than the diffusion potential of the pn junction (about 1 volt), can be the light emitting element L (0) is a light emitting state.
[0012]
In contrast, the gate electrode G _-1 is about 5 volts, the gate electrode G ₁ is about -1 volts. Therefore, the writing voltage of the light emitting element L (-1) is about -6 volts, and the writing voltage of the light emitting element L (1) is about -2 volts. Now, the voltage of the write signal phi _I can write only in the light emitting element L (0) is a range of about -1 to 2 volts. Emitting element L (0) is turned on, i.e., enters the emission state, the voltage of the write signal phi _I lines would be fixed at about -1 volt, the other light emitting element has been selected, an error is prevented that Can do.
[0013]
Emission intensity is decided to the amount of current flowing to the write signal phi _I, it is possible to image writing at any intensity. Further, in order to transfer the light-emitting state to the next element, it dropped to once 0 volts the voltage of the write signal phi _I lines, it is necessary to once turn off the element that is emitting light.
[0014]
[Problems to be solved by the invention]
In order to improve the resolution of the self-scanning light emitting element array, it is necessary to reduce the pitch of the light emitting portions, and the element density on the substrate must be increased. In the case of a self-scanning light emitting element array of a type in which the transfer unit and the light emitting unit are separated, the number of elements in the transfer unit must be increased corresponding to the light emitting unit, and the element density on the substrate increases. This causes problems such as an increase in chip temperature and a decrease in device manufacturing yield.
[0015]
An object of the present invention is to provide a self-scanning light-emitting element array that does not cause the above-mentioned problems by simplifying the element structure.
[0016]
[Means for Solving the Problems]
According to the self-scanning light-emitting element array of the present invention, a large number of three-terminal transfer elements whose threshold voltage or threshold current can be electrically controlled from the outside are arranged one-dimensionally,
Control electrodes for controlling the threshold voltage or threshold current of adjacent transfer elements are connected to each other by electrical means having a unidirectional voltage or current,
A power supply voltage line is connected to each control electrode of the transfer element via each load resistor,
An externally connected n-phase (n is an integer of 2 or more) clock pulse line is connected to one of the remaining two terminals of each one-dimensionally arranged transfer element in order for each n element,
When a certain transfer element is turned on by a clock pulse of a certain phase, the threshold voltage or threshold current of the transfer element in the vicinity of the transfer element is changed through the electrical means,
With a clock pulse of another phase, the transfer element adjacent to the certain transfer element is turned on,
A number of three-terminal light emitting elements whose threshold voltage or threshold current for light emission can be electrically controlled from the outside are arranged one-dimensionally and grouped by m (m is an integer of 2 or more).
Each control electrode of the transfer element is commonly connected to the control electrode of the light emitting element of each group,
One of the remaining two terminals of each of the m light emitting elements in each group is sequentially connected to m lines to which a current for light emission is applied.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 4 is an equivalent circuit diagram of an embodiment of the self-scanning light emitting element array of the present invention. This self-scanning light emitting element array has a structure in which, in the light emitting element array of FIG. 3, the light emitting part is provided with two light emitting elements (three terminal thyristors) with respect to one transfer element (three terminal thyristor) of the transfer part.
[0018]
The light emitting elements of the light emitting section are divided into two groups, and the cathodes of the two light emitting elements of each group are connected to the first write signal line φ _I 1 and the second write signal line φ _I 2. By doing so, the number of write signal lines increases, but the number of light emitting points that can emit light simultaneously becomes two. When such a structure is adopted, two cathode islands are placed on a common gate island without separately taking the gate electrodes of two light emitting section thyristors connected to the same transfer section thyristor. In this case, the element structure becomes simple and the chip can be made small.
[0019]
FIG. 5 shows a structure in which two light emitting points are formed on one gate island. (A) is a top view, (b) is a sectional view along line xx ′. On the p-type layer and the substrate 2, an n-type layer 3, a p-type layer 4, and an n-type layer 5 are stacked to form a gate island and a cathode island. In FIG. 5, 1 is a back electrode, 6 is an insulating film, 11 is a gate wiring, 12 is a cathode wiring of a first light emitting point, 13 is a cathode wiring of a second light emitting point, 21 is a gate electrode, and 22 is a cathode electrode. , 31 indicates a gate island region, and 32 indicates a cathode island region. According to this configuration, two cathode islands are formed on one gate island, and one light-emitting thyristor is formed on each cathode island.
[0020]
In the above embodiment, two light emitting points are formed on one gate island, but two or more light emitting points may be formed. Such a structure simplifies the element structure as described above.
[0021]
In such a self-scanning light emitting element array, when the transfer unit thyristor is turned on, an arbitrary number of light emitting unit thyristors connected to the transfer unit thyristor can be lit at an independent timing.
[0022]
For example, when a 300 dpi color image is to be created using a 1200 dpi binary recording head, the density in the sub-scanning direction is doubled as shown in FIG. (32,000 colors with 32 gradations for each color). This can be realized by two transfer unit thyristors equivalent to 600 dpi and two light emitting unit thyristors connected thereto.
[0023]
In FIG. 6, transfer unit thyristors are denoted by 1 and 2, and light emitting unit thyristors connected thereto are denoted by 1-1, 1-2, and 2-1 and 2-2, respectively. That is, the preceding number indicates the transfer unit number, and the subsequent number indicates the φ _I line number.
[0024]
The gradation can be expressed by how many of these 32 squares are filled (lighted). For simplification, when 2n squares are painted, it is assumed that the squares in the column of φ _I line number 1 and the squares in the column of φ _I line number 2 are independently and randomly painted. At this time, only two light emitting points with the same transfer unit number, that is, two light emitting points on the same gate island, can be lit at exactly the same timing.
[0025]
The problem in this case is that the density becomes a times when adjacent cells with the same transfer unit number are filled simultaneously.
[0026]
The reason will be described below. FIG. 7 shows an example of IL (current sum-light output) characteristics of a light emitting thyristor having two cathode islands on one gate island. This characteristic example shows a comparison between the sum of the light amounts when the two light emitting points are turned on separately and the light amount when the two light emitting points are turned on simultaneously. However, these characteristics are obtained by removing the influence of the light output of heat generation due to power consumption. FIG. 7 further shows a light quantity ratio between simultaneous lighting and separate lighting with a thin dotted line.
[0027]
From the characteristics shown in FIG. 7, it can be seen that when the two light-emitting points are turned on at the same time, the sum of the light outputs is larger than when the light-emitting points emit light separately. For example, when the current sum is 10 mA, simultaneous lighting is 10% brighter. This is due to the following reason. That is, the IL characteristic of one light-emitting thyristor is that the light emission efficiency (light output / current) is low in a small current region, and the light emission efficiency increases as the current increases, resulting in a certain light emission efficiency. This characteristic curve can be regarded as a straight line having a threshold value. When the current is less than the threshold current, the current flows only directly under the electrode, and most of the light emission is blocked by the electrode, so that the light emission efficiency is considered to be low. On the other hand, the current spreads above the threshold value, and light is emitted also in places other than directly under the electrode, so that the light emission efficiency is increased. The IL curve of two simultaneous lighting is close to the curve in the case of separate lighting in a region where the current is small, and approaches when it is regarded as one light emitting point as the current increases. That is, since two light emitting points appear as one light emitting point, the threshold current is only one, and as a whole, the light emission efficiency is increased, and the simultaneous lighting of two lights becomes brighter. Conceivable. In other words, when two light emitting points on one gate island are turned on simultaneously, it can be considered that the two light emitting points interfere with each other.
[0028]
When the light emitting thyristors shown in FIG. 5 are arranged to form a light emitting element array as shown in FIG. 8, when two light emitting points 101 in the same gate island are simultaneously turned on, two light emitting points 100 on another adjacent gate island are simultaneously turned on. When lit, the former combination will be brighter even if the light quantities when lit separately are completely aligned.
[0029]
Now, let the IL characteristic of the single light emitting thyristor be L (i) = f (i). That is, the light output L is assumed to be a function of the current i. When two light emitting points 101 in the same gate island are turned on simultaneously, the light output is
L (i) + L (i) = f (2i)
It becomes. On the other hand, when the two light emitting points 100 of different adjacent gate islands are turned on separately, the light output is
L (i) + L (i) = 2f (i)
It becomes. As described above, f (2i)> 2f (i) is satisfied.
[0030]
Returning to FIG. 6, the probability that both of the two cells of a certain transfer unit number are filled is p ² , and the probability that one of the squares is filled is 2p (1−p). However, p = n / 16. Therefore, the expected value of the concentration of a certain mass is ap ² + 2p (1−p) / 2 = p + (a−1) p ² . Since the original density should be p, (a-1) the linearity of the gradation is distorted by p ^2. Moreover, although it is a somewhat peculiar condition, the thickness slightly inclined as shown in FIG. In the case of a pattern filled with parallel lines of even dots, there is a possibility that unevenness is seen in the sub-scanning direction.
[0031]
FIG. 10 shows the light emission of FIG. 5 in which there is no difference between the sum of the light amounts when the two light emitting points on the same gate island are lighted separately and the light amount when the two light emitting points are lighted simultaneously. An example of an improved thyristor is shown. (A) is a top view, (b) is a yy 'sectional view.
[0032]
In FIG. 10, 1 is a back electrode, 2 is a p-type layer (or p-type substrate), 3 is an n-type layer, 4 is a p-type layer, 5 is an n-type layer, 6 is an insulating film, 11 is a gate wiring, 12 Is the cathode wiring of the first light emitting point, 13 is the cathode wiring of the second light emitting point, 21 is the gate electrode, 22 is the cathode electrode, 31 is the region of the gate island (p-type layer 4), 32 is the cathode island (n The region of the mold layer 5) is shown. The size of the cathode island is 10 μm on one side, and the distance between the cathode islands is also 10 μm.
[0033]
According to this embodiment, the groove 33 is provided in the gate island portion between the two light emitting points. This groove is formed by removing the n-type layer (anode layer) 3 and the p-type layer (gate layer) 4. As can be seen from FIG. 10A, one end of the groove is open at the edge of the gate island. When the width of the groove is W and the length is L, a light emitting element array provided with grooves of each size of W = 5 μm, L = 5, 10, and 20 μm was manufactured. The simultaneous lighting / separate lighting ratio with respect to the current sum of the light emitting element array is shown in FIG. The ratio of separate lighting and simultaneous lighting approaches 1 as the length L of the groove 33 increases. If there is a groove of L = 5 μm or more, the ratio at 20 mA is about 3% at most, which is a sufficient ratio depending on the use of the light emitting element array.
[0034]
Such a groove has an effect of reducing interference between two light emitting points provided on one gate island.
[0035]
FIG. 12 shows a plan view of another embodiment of the light-emitting element array of the present invention. In the embodiment of FIG. 10, the structure is such that two light emitting points (cathode islands) are provided on one gate island. However, in this embodiment, the transfer section described in the circuit of FIG. 3 is also formed on the same gate island. belongs to. In FIG. 12, 11 is a gate wiring, 12 is a cathode wiring of a first light emitting point, 13 is a cathode wiring of a second light emitting point, 14 is a transfer portion cathode wiring, 15 is a transfer portion coupling diode wiring, and 21 is a gate electrode. , 22 indicate cathode electrodes.
[0036]
Also in this embodiment, the groove 33 is provided in the gate island portion between the cathode islands of the light emitting portion. The shape of the groove is the same as in the embodiment of FIG. The same effect as in the example of FIG. 10 was obtained.
[0037]
FIG. 13 shows still another embodiment of the light emitting element array of the present invention. (A) is a top view, (b) is a yy 'sectional view. In the embodiment of FIG. 10, the gate island is removed from the gate layer 4 to the anode layer 3. However, by removing only a part of the gate layer 4 and providing the groove 34, interference between two light emitting points can be prevented. It is possible to reduce. In the drawing, the depth of the groove 34 is indicated by D. In this case, by removing half the thickness of the gate layer 4, the ratio of separate lighting and simultaneous lighting was 1.03, and the effect was recognized.
[0038]
In each of the embodiments described above, the case where the substrate is p-type has been described. When the substrate is an n-type layer, the lowermost layer is the cathode layer and the uppermost layer is the anode layer.
[0039]
【The invention's effect】
According to the present invention, in a self-scanning light emitting element array of a type in which a transfer part and a light emitting part are separated using a three-terminal light emitting thyristor having a pnpn structure, a structure in which a plurality of light emitting thyristors are provided on one gate island is provided. Therefore, it is not necessary to increase the number of elements in the transfer section corresponding to the light emitting section, and an increase in element density on the substrate can be prevented, so that the element structure can be simplified.
[0040]
Furthermore, according to the present invention, the groove provided in the gate island portion serves to weaken the interference between the adjacent cathode islands or anode islands, so that the influence between the two adjacent light emitting points can be reduced as much as possible. The difference in light output between lighting and simultaneous lighting can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a basic structure of a three-terminal light-emitting thyristor.
FIG. 2 is an equivalent circuit diagram of a first basic structure of a self-scanning light-emitting element array.
FIG. 3 is an equivalent circuit diagram of a second basic structure of the self-scanning light-emitting element array.
FIG. 4 is a diagram showing an example of a self-scanning light emitting element array according to the present invention.
5 is a diagram showing a structure of two light emitting points formed on one gate island of the light emitting unit of FIG. 4;
FIG. 6 is a diagram for explaining the formation of a color image by a printer head.
FIG. 7 is a diagram illustrating an example of IL characteristics of a light-emitting thyristor in which two light-emitting points are formed on one gate island.
8 is a diagram showing a light-emitting element array using the light-emitting thyristor of FIG.
FIG. 9 is a diagram for explaining the occurrence of unevenness in the sub-scanning direction by the printer head.
FIG. 10 is a diagram showing an embodiment of a light emitting element array according to the present invention.
11 is a diagram showing a ratio of light output of simultaneous lighting / separate lighting in the light emitting element array of FIG.
FIG. 12 is a view showing another embodiment of the light-emitting element array of the present invention.
FIG. 13 is a view showing still another embodiment of the light-emitting element array of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Back electrode 2 1st p-type layer and board | substrate 3 1st n-type layer 4 2nd p-type layer 5 2nd n-type layer 6 Insulating film 11 Gate wiring 12 Cathode wiring 13 of 1st light emission point 13th Cathode wiring 14 of light emitting point 2 Shift portion cathode wiring 15 Shift portion coupling diode wiring 21 Gate electrode 22 Cathode electrode 31 Gate island region 32 Cathode island region 33, 34 Groove 100 Two adjacent light emitting points on different gate islands 101 Two adjacent luminous points on the same gate island

Claims (2)

A number of three-terminal transfer elements whose threshold voltage or threshold current can be electrically controlled from the outside are arranged one-dimensionally,
Control electrodes for controlling the threshold voltage or threshold current of adjacent transfer elements are connected to each other by electrical means having a unidirectional voltage or current, and a power supply voltage line is connected to each control electrode of the transfer element. Connect through each load resistor,
An externally connected n-phase (n is an integer of 2 or more) clock pulse line is connected to one of the remaining two terminals of each one-dimensionally arranged transfer element in order for each n element,
When a certain transfer element is turned on by a clock pulse of a certain phase, the threshold voltage or threshold current of the transfer element in the vicinity of the transfer element is changed through the electrical means,
With a clock pulse of another phase, the transfer element adjacent to the certain transfer element is turned on,
A number of three-terminal light emitting elements whose threshold voltage or threshold current for light emission can be electrically controlled from the outside are arranged one-dimensionally and grouped by m (m is an integer of 2 or more).
Each control electrode of the transfer element is commonly connected to the control electrode of the light emitting element of each group,
One of the remaining two terminals of the m light emitting elements of each group is connected in sequence to m lines to which current for light emission is applied,
The three-terminal transfer element and the three-terminal light-emitting element are each composed of a three-terminal light-emitting thyristor having a pnpn structure, and the m three-terminal light-emitting elements are provided on one gate island,
In the gate layer of the gate island portion between the cathode island or the anode island constituting the m number of three-terminal light emitting elements provided on the one gate island, a groove having one end opened at the edge of the gate island portion is provided, the groove may have a thickness smaller than the depth of the cathode islands or anode Island adjacent shorter than the length length of one side and the gate layer, the cathode islands or anode adjacent portion where the groove is provided between the islands A self-scanning light-emitting element array having a width smaller than the above distance .   2. The self-scanning light emitting device according to claim 1, wherein the m three-terminal light emitting elements and the transfer element connected to the m three-terminal light emitting elements are provided on one gate island. Element array.

Images