DISPLAY MODULE

Organic EL display module including a pixel disposed in respective intersections between a plurality of scanning lines and a plurality of data lines, which lines are aligned in a matrix, and a current supply line that supplies electric current to the pixel, wherein the pixel includes an active device selected by the scanning line, a data storage device that stores a data signal that is supplied from the data line by control of the active device, and an organic light emitting device that emits light by the electric current supplied by the current supply line according to the data signal stored in the data storage device, wherein the data storage device provides a lower electrode, an insulating layer and an upper electrode, and wherein the lower electrode has a same layer with a channel layer of the active device and the upper electrode is made of a metal material.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the preferred embodiments of the present invention are described in details with reference to the accompanying drawings. The organic emitting layer of the respective pixels as described below is divided into such types as emitting light with luminance in proportion to the value of the current and with a color (including white) inherent in an organic material in use and incorporating a red, green, blue or other color filter into the organic layer to emit white light so as to display color image.

FIG. 1is a block diagram to show the arrangement of the first embodiment of the display module according to the present invention whileFIG. 2is a circuit view to show the detailed arrangement of one pixel of the module as shown inFIG. 1. In the present embodiment, in the same way as shown inFIG. 10, data lines7, scanning lines8and current supply lines10are provided in the display region2. In the drawings, the scanning lines8are represented with8(n+1),8(n) placed anterior thereto and8(n−1) placed farther anterior thereto while the data lines7are represented with7(m+1),7(m) and7(m−1).

For the sake of conveniences, the scanning line as being scanned (or selected) is regarded as the8(n+1) in the following description. Attention is paid to the Pixel20among the plurality of pixels as selected by the scanning line8(n+1). The first TFT21and the second TFT22that are active devices are a switching transistor and a driver transistor respectively. The gate of the first TFT21is connected to the scanning line8(n+1) and the drain thereof is connected to the data line7(m+1) while the source thereof is connected to the gate of the second TFT22.

The drain of the second TFT22is connected through a current supply line10A to a current supply line10. The source thereof is connected to an anode of an OLED24. One terminal of a capacitor23for a data signal storage device is connected to a point where the source of the first TFT21and the gate of the second TFT22connect while the other terminal thereof is connected to the scanning line8(n) placed anterior to the8(n+1).

In the circuit arrangement of one pixel as shown inFIG. 2, one terminal of the capacitor23that is connected to the point where the source of the first TFT21and the gate of the second TFT22connect is of positive pole while the other terminal thereof as connected to the scanning line8(n) is of negative pole. The OLED24is arranges such that an organic emitting layer, which is not shown in the drawings, interposes between the anode25and the cathode26thereof, the anode25being connected to the source of the second TFT22and the cathode26being connected to an electrode provided on the side of the same and comprising the pixel, which electrode is not shown in the drawings.

In the above arrangement, the driving operation of the respective pixels for display, which pixels are in connection with the prior scanning line8(n), is over wherein the TFTs (the first TFTs) thereof are on off-state condition over most of the one frame (or one field) period. That is, the electric potential of the scanning line8(n) is on a given low voltage state, which state does not fluctuate during most of the one frame (or field) period.

Thus, the capacitor23of the pixel in connection with the scanning line8(n+1) as being scanned stably stores a data signal as written therein from the data line7(m+1), which allows the electric current that conducts into the OLED24through the second TFT22from the current supply line10to correctly correspond to the data signal as stored in the capacitor. This also applies to all the pixels that are in connection with the scanning line8(n+1).

The arrangement hereof allows the voltage of the capacitor23for the data signal storage device to keep intact, so that there is no case where the reference voltage of the capacitor fluctuates owing to the inflow of the electric current into the OLED that occurs in the prior display module as shown inFIG. 10, with the result that there is no fluctuation of the light emitting quantity of the OLED, which allows image to be displayed with high quality. Further, the riddance of the common voltage line of the display module as shown inFIG. 8or9improves the aperture ratio of the pixel and avoids the increase of the number of the production steps thereof, which brings the production cost thereof to reduction.

Then, the arrangement of the display module according to the present invention is more concretely described below.

The data signal (image signal etc.) may be supplied to the data line in analog or time sharing digital quantity, and the system in which the area of the respective pixels is divided may be incorporated. Normally, the pixel circuit is produced by the low temperature polysilicone TFT technique. In this case, it is preferred that the electrodes comprising the capacitor utilize a layer of the channel and gate portions of the transistor. The channel portion thereof is spaced apart from the gate portion thereof by a thin insulating layer, which allows an area for securing the capacitance as required to be rendered narrower.

FIGS. 3 and 4show a plane view of the vicinity of one pixel of the display module according to the present invention. In the drawings, reference numerals7,8(n) and8(n+1), and10indicate a data line, scanning lines, and a current supply line respectively. One pixel is surrounded by the scanning lines8(n) and8(n+1) and the current supply line10, in which the first TFT21, the second TFT22, the capacitor23, the anode25of the OLED as indicated with the dotted line, a contact hole27for connecting the data line7, the scanning lines8(n) and8(n+1) as well as the current supply line10to the respective TFTs and the capacitor23, an aperture28to receive an organic emitting layer therein are included.

The pixel circuit is surrounded by the current supply line10to the OLEDs, which line is disposed vertically with regard to the drawings in the same direction as the data line7to supply image signal and as such, and the gate lines8(n) and8(n+1) as disposed horizontally with regard thereto. The switching transistor for the first TFT21writes the data signal supplied from the data line into the capacitor23of the pixel circuit.

The dual gate system is adopted for the first TFT21in order to abate the decrease of the storage charge of the capacitor23owing to leaking current. The driver transistor for the second TFT22is disposed in folds in order to obtain a comparatively large gate length. The capacitor23is disposed under the wiring system in order to reduce the affect of the pixel upon the aperture28. The other pole (the other terminal) of the capacitor23is electrically connected to the gate line that is scanned anterior to that being scanned.

There are two methods for the connection thereof to the prior gate line according to which electrode (terminal) of the capacitor23is connected thereto.FIG. 3shows the case where the lower electrode thereof is connected thereto whileFIG. 4shows the case where the upper electrode thereof is connected thereto.

Generally, it is required to make either of the electrode thereof conductive for the purpose of forming a capacitor by overlaying two electrodes one over another. The lower electrode thereof is made from the same material as that for the channel portion of the transistor, so that it is basically required to perform doping operation on the whole surface thereof by such method as ion implantation for the purpose of making the whole surface thereof conductive. Such conductive material as metal is normally adopted for the upper electrode thereof.

The ion implantation onto the whole surface of the lower electrode thereof should be performed before the formation of the upper electrode thereof, which is not desirable because it increases the number of production process. The polarity of the electrodes thereof is taken into considerations in the present embodiment in order to dispense with the ion implantation for rendering the whole surface of the lower electrode thereof conductive. It is known that the movement of carrier occurs without performing the ion implantation on the whole surface thereof so as to serve as a capacitor, presuming that where the n-type ion doping is performed is a low-tension side while where p-type ion doping is performed is a high-tension side. Accordingly, the ion implantation is not performed on the whole surface thereof, which is performed after the formation of the upper electrode thereof in this embodiment.

Provided that the first TFT21for the switching transistor is of n-type transistor, the voltage applied to the gate line is on low voltage or off-state condition during most of the frame period and turns into on-state condition only during the writing operation of the data signal. In this case, it is preferable that where the lower electrode thereof is connected to the prior gate line, the n-type ion implantation is performed while the p-type ion implantation is performed where the upper electrode thereof is connected thereto.

In the arrangement as shown inFIG. 3, the other terminal of the capacitor23of the pixel under scanning is connected through a contact hole27as shown therein to the prior gate line8(n).

In the arrangement as shown inFIG. 4, the gate line8(n) extends over to the capacitor portion of the8(n+1) so as to be used as an upper electrode of the same. Thus, the switching transistor is connected to the lower electrode thereof.

FIGS.5(A)-(C) through7(A)-(C) show the formation steps of the respective structural layers of the display module as shown inFIG. 3, the references5(A)-(C) through7(A)-(C) in which drawings indicate the formation of the respective structural layers. The layers as formed by the respective steps are shown with visible outlines.

AtFIG. 5(A), a polysilicone layer30for the channel portion of the transistor and the lower electrode of the capacitor is formed on a glass substrate not shown in the drawing, on which layer laser annealing or heating operation is performed for crystallization. Then, a first insulating layer is formed of p-TEOS and as such on the annealed or heated layer.

AtFIG. 5(B), a conductive layer80for the scanning lines, the gate of the transistor and the upper electrode of the capacitor is formed of titanium Ti or tungsten W and as such. The n-type ion implantation is performed thereon by using the upper electrode thereof as a mask layout.

AtFIG. 5(C), a second insulating layer is formed on the conductive layer80, on the required portions of which layer contact holes270are made by means of the wet etching method and so forth.

AtFIG. 6(A), the drain of the transistor and the current supply line are formed with an aluminum wiring70, the upper and lower sides of which wiring may be sandwiched with titanium Ti or tungsten W and as such.

AtFIG. 6(B), a third insulating layer is formed on the aluminum wiring so as to form a contact hole271for an anode.

AtFIG. 6(C), ITO is coated thereon for an anode of the OLED, on which patterning is performed so as to form an anode25.

AtFIG. 7(A), a passivation film is coated on the anode25, through which file a hole is made so as to provide an aperture28for receiving an organic emitting layer, which aperture corresponds to the emitting region of the module.

AtFIG. 7(B), an organic emitting layer260is coated on the aperture28, which layer is coated on the region of the aperture including the circumferential edge thereof. For color display, an organic emitting layer to emit a given color light is coated on the aperture of the respective pixels.

AtFIG. 7(C), a cathode26to cover the organic emitting layer260is formed so as to obtain a basic panel substrate. Thereafter, this panel substrate is sealed by an appropriate sealing structure so as to be put into a module form. Through the above production steps, the display module embodied in the present invention is obtained.

It should be noted that the present invention is not limited to the OLED display module, but is also applicable to another display module that emits light in the similar manner to the OLED module.

As described above, according to the present invention, the occurrence of line defects resulting from the short-circuit between the electrodes of the capacitor is prevented and the increase of the number of production process is avoided, so that the display module, the aperture ratio of the respective pixels of which module is improved so as to allow image to be displayed with high luminance and quality, is provided.