JPH0854837A - Light emitting device and display panel having it - Google Patents

Abstract

PURPOSE:To provide a light emitting device which is producible at a good yield and has good controllability and a display panel having it. CONSTITUTION:Electrodes 12 for control and a gate insulating film 13 are formed on a glass substrate 11 and a semiconductor layer 14 is formed on it. Data line electrodes 15 are formed on the source side of this semiconductor layer 14 and a light emitting layer 17 and electrodes 18 for light emission, etc., are formed on the drain side. The light emitting device and display panel capable of executing light emission operation with good controllability by selectively controlling the electrodes 12 for control and the electrodes 18 for light emission are realized by adopting such constitution.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting device and a display panel including the same, and more particularly to a technique for driving a light emitting means through a thin film semiconductor layer. The present invention can be used in the field of manufacturing flat displays and the like.

[0002]

2. Description of the Related Art As a conventional display device, a CRT as shown in FIG. 9 is known. As shown in the figure, this CRT electromagnetically or electrostatically deflects an electron beam 2 emitted from an electron gun 1 by a deflection yoke 3 or the like, and a light emitting surface 4
Scanning up. Then, the grid controls the amount of electrons reaching the fluorescent screen to give an image signal. However, such a CRT has a problem that it consumes a large amount of power, and the larger the screen, the longer the depth. On the other hand, as shown in FIG. 10, a large number of needle-shaped electrodes (emitters) 6 are provided upright on the silicon substrate 5 so as to correspond to each pixel, and a strong electric field is placed between the electrodes 6 and a phosphor screen (not shown). Fowler-No
A method of emitting light with an rdheim tunnel current has been proposed. In the figure, 7 is an insulating film and 8 is an extraction electrode (gate electrode). This device is called a Spindt-type cold cathode device, and has the advantages of low current consumption because it does not emit thermoelectrons, and has a flat display.

[0003]

However, the Spindt-type cold cathode device described above is a simple matrix system which is determined by the potential difference between the X electrode (emitter) and the extraction electrode 8 as the Y electrode. When integrated, there is a problem that crosstalk is likely to occur and the contrast is lowered. Further, there is a problem that it is difficult to form the electrode 6 having a needle-like structure with a high yield. Further, there is a manufacturing problem that the space between the phosphor screen and the electrode 6 needs to be evacuated. The problem to be solved by the present invention lies in what kind of means should be taken to obtain a light emitting device which can be manufactured with high yield and has good controllability, and a display panel including the light emitting device.

[0004]

Therefore, the invention according to claim 1 is directed to a semiconductor layer, an input electrode electrically connected to one conductive region sandwiching a channel region of the semiconductor layer, and the semiconductor layer of the semiconductor layer. A light emitting electrode disposed apart from the semiconductor layer on the other conductive region side sandwiching the channel region, and a light emitting layer provided between the light emitting electrode and the other conductive region of the semiconductor layer. The control means is provided so as to face the channel region of the semiconductor layer between the input electrode and the light emitting electrode, and the solution is to solve the problem. The invention according to claim 2 is characterized in that an insulating film is interposed between the semiconductor layer and the light emitting layer. The invention according to claim 3 is characterized in that the light emitting layer is a phosphor film, and the invention according to claim 4 is that the other conductive region, the light emitting electrode, and the light emitting layer sandwiched therebetween are EL.
It is characterized in that it constitutes an (electroluminecence) element. Further, the invention according to claim 5 is characterized in that the control electrode is disposed above and / or below the semiconductor layer. The invention according to claim 6 is
In each pixel portion on the transparent substrate, a semiconductor layer and a selection gate electrode are formed to face each other via an insulating film, and a data line is connected to one conductive region sandwiching the channel region of the semiconductor layer. In addition, a light emitting electrode is provided in the other conductive region sandwiching the channel region of the semiconductor layer via a light emitting layer. Further, the invention according to claim 7 is characterized in that the light emitting layer is a phosphor film,
The invention according to claim 8 is characterized in that the other conductive region, the light emitting electrode, and the light emitting layer sandwiched therebetween form an EL element. Further, the invention according to claim 9 is characterized in that the gate electrode is provided above and / or below the semiconductor layer.

[0005]

According to the present invention, by applying the control voltage to the control electrode, the current inputted from the input electrode side to the one conductive region is made to flow to the other conductive region through the channel region of the semiconductor layer. When the voltage applied between the light emitting electrode and the other conductive region reaches a predetermined voltage, the light emitting layer can emit light. Here, the control electrode acts as the gate of the MOS transistor. When the light emitting layer is a fluorescent film and an insulating film is provided between the light emitting layer and the other conductive region, Fo
The wler-Nordheim tunnel current has the effect of exciting the fluorescent material and causing it to emit light. Further, the light emitting layer interposed between the other conductive region and the light emitting electrode is EL.
In the case of forming a device, when an electric field is applied to the light emitting layer, holes (electrons) are injected and charge recombination occurs,
Has the effect of causing light emission. It is possible to dispose the control electrode above and / or below the semiconductor layer, and in particular, by disposing the control electrode both above and below the semiconductor layer, it becomes possible to make the control system multifunctional and to increase the channel current. It has the effect of substantially increasing the size. In addition, a light emitting device having the above structure is formed on a transparent substrate, a data line is connected to one conductive region of a semiconductor layer, and a light emitting electrode is provided in the other conductive region of the semiconductor layer through the light emitting layer. Device 2
If the pixel is arranged for each pixel arranged in a dimensional matrix, each pixel can be driven reliably, so that a display panel having a large area and an extremely shallow depth can be obtained. As described above, since the light emitting layer and the control electrode can reliably drive the light emitting layer, it is possible to prevent crosstalk from occurring. Therefore, there is an effect of preventing a decrease in contrast. Further, by controlling the voltage of the data line, it has an effect of enabling gradation display of each pixel.

[0006]

The details of a light emitting device according to the present invention and a display panel including the same will be described below with reference to the embodiments shown in the drawings. (Embodiment 1) FIG. 1 is a sectional view of a main part of a display panel in which light emitting devices are arranged in a two-dimensional matrix for each pixel portion on a transparent substrate. In the figure, reference numeral 11 denotes a glass substrate, and a control electrode 12 as a selection gate line, which is made of, for example, a metal film, is formed on the glass substrate 11. Furthermore, a gate insulating film 13 made of, for example, a SiN film 13 is formed thereon by a known film forming technique. A semiconductor layer 14 made of polysilicon or the like is processed on the gate insulating film 13 so as to have a width larger than that of the control electrode 12. Note that the control electrode 12 is set below the center of the semiconductor layer 14 in the width direction so as to be located via the gate insulating film 13. Then, in the semiconductor layer 14, for example, a source region 14A as one conductive region formed by introducing an N-type impurity and a drain region 14B as the other conductive region are formed to form a PMOS transistor. These source region 14A and drain region 14
A region between B and C is a channel region 14C, and in this embodiment, the channel length is set to be slightly shorter than the gate length as shown in FIG.

On the surface of the source region 14A of the semiconductor layer 14, a high concentration (N +) impurity layer 14D for making ohmic contact with a data line electrode, which will be described later, is formed. A data line electrode 15 as an input electrode is formed on the high concentration impurity layer 14D by patterning a conductive film. In this way, the light emitting insulating film 16 having a thin film thickness covers the structure in which the data line electrode 15 is formed on the semiconductor layer 14 and the exposed gate insulating film 13. The light emitting insulating film 16 can be formed of, for example, a SiN film by a CVD method. Further, above the drain region 14B of the semiconductor layer 14, a light emitting layer 17 is formed in a region corresponding to the drain region 14B via the light emitting insulating film 16, and a light emitting electrode 18 is formed on the light emitting layer 17. It is formed of a conductive film. The light emitting layer 17 is made of a phosphor, and the phosphor
The r-Nordheim tunnel current causes the insulating film 16 for light emission.
Light is emitted by flowing through. The gate insulating film 13 on the control electrode 12 side is
The withstand voltage is set high so that leakage does not occur even at a high voltage such as during light emission.

By arranging the light emitting devices in a two-dimensional matrix on the glass substrate 11 as in this embodiment, the following actions and operations are obtained. That is,
In the light emitting device formed in this example, by opening the gate by the control electrode 12, current flows from the data line electrode 15 to the drain region 14B via the source region 14A and the channel region 14C. At this time, when a predetermined voltage is applied to the light emitting electrode 18, a strong electric field is generated between the drain region 14B and the light emitting electrode 18, which causes the Fowler-Nor through the light emitting insulating film 16.
A dheim tunnel current is generated to cause the phosphor of the light emitting layer 17 to emit fluorescence. Therefore, by selectively applying a voltage to the light emitting electrode 18 and the control electrode 12 formed on the glass substrate 11, it is possible to selectively cause a predetermined pixel to emit light. In this embodiment, since the light emitting layer 17 is configured to emit light by turning on / off the MOS transistor, there is no room for adverse effects due to crosstalk as in the conventional case, and a reliable display function is provided.

FIG. 2 is an equivalent circuit of a display panel in which the light emitting devices are arranged in a two-dimensional matrix as described above. As can be seen from this figure, for example, the selection gate line m
Is selected, and the data line n is selected and a voltage is applied to the light emitting gate line l, the light emitting layer of the light emitting device in the portion connected to these lines emits light. FIGS. 3A and 3B are equivalent circuits showing a pixel selected state and a pixel non-selected state. FIG.
In (A), the pixel voltage is selected, and the data voltage Vd reaches below the light emitting electrode 18. Therefore, the Fowler-Nor corresponding to the potential difference between the light emitting electrode applied voltage Vtg and the data voltage Vd.
A dheim tunnel current flows through the light emitting layer 17 to cause fluorescence emission. Further, FIG. 3B shows a pixel non-selected state, in which a voltage is not applied to the control electrode 12 as the selection gate line, and the MOS transistor is in an off state.
Since the potential under the light emitting electrode 18 is substantially the same as that of the light emitting electrode 18, no light is emitted. The Vtg-Vd required for light emission is
Since the absorption energy of a general phosphor is about 16.5 eV, it is considered that the order is 20 V. On the other hand, if such a thin film transistor (TFT) operates as an NMOS, when Vtg = 20V, Vd = 0V and the voltage Vbg = 0V of the control electrode is unselected, Vbg = + 2.
There is a voltage relationship such as selection at 0V.

Although polysilicon is used as the semiconductor layer in this embodiment, an amorphous silicon film may of course be used. By the way, it is known that the characteristics of an amorphous silicon TFT using a SiN film as a gate insulating film change due to charge-up when a high voltage is applied to only one gate for a long time. Therefore,
As shown in the waveform diagram of FIG. 4, if a cycle in which a negative voltage is applied to the control electrode and the light emitting electrode at the time of non-selection is provided to discharge the accumulated charge, stable operation can be expected in the long term. .

When emitting light, the Fowler-Nord is used.
Heim (F-N) tunnel current is generated by the light emitting gate insulating film 1
Since there is a flow in the channel 6, a potential drop occurs in the channel length direction, and the light emitting region in the channel length direction may be local, or the emission intensity may be attenuated in the channel length direction. Therefore,
If the channel width is set larger than the unit area per pixel, the luminance per unit area is improved and the display quality can be improved. Specifically, as shown in FIG. 5, the control electrode 12 formed in the lower layer is set to have an area larger than that of the polysilicon film 14, and the semiconductor layer 14 is formed.
Are formed so as to fit within the plane area of the control electrode 12 and have a meandering shape in order to increase the channel width. With such a configuration, it is possible to improve the luminance per unit area even if the light emitting region is local in the channel length direction or the light emission intensity is attenuated in the channel length direction.

(Embodiment 2) FIG. 6 is a sectional view of the essential portions of Embodiment 2 of a light emitting device according to the present invention and a display panel including the same. In this embodiment, the semiconductor layer 14 as a semiconductor layer is formed in a predetermined shape on the glass substrate 11, and the data line electrode 15 is formed on the source region side of the semiconductor layer 14. The data line electrode 15 is connected so as to make contact with the upper surface and the side surface of the semiconductor layer to reduce the contact resistance. Then, the light emitting insulating film 16 is deposited on such a structure, and the light emitting layer 1 is provided above the drain region of the semiconductor layer 14 via the light emitting insulating film 16.
7 and the light emitting electrode 18 are formed. Further, for example, the SiN film 13 is formed as a gate insulating film, and the SiN film 13 is formed.
The control electrode 12 is formed on the film 13. The structure of this embodiment is a so-called top gate structure in which the control electrode 12 of the first embodiment is arranged on the semiconductor layer, and the operation and operation are almost the same as those of the first embodiment. In this embodiment, there is an advantage that the contact area of the data line electrode 15 can be particularly increased.

(Embodiment 3) FIG. 7 is a cross-sectional view of essential parts showing Embodiment 3 of a light emitting device according to the present invention and a display panel including the same. In this embodiment, a light emitting electrode 18 and a light emitting layer 17 are sequentially laminated on a glass substrate 11, and after patterning these, a light emitting insulating film 16 is conformally formed on the entire surface and flattening insulation is performed thereon. It is formed by providing a film 19. Then, the semiconductor layer 14 is formed on the planarization insulating film 19, and the data line electrode 15 is formed in one region (source side) of the semiconductor layer in the same manner as in the second embodiment. Then, a gate insulating film is formed on the entire surface, and the control electrode 12 is formed on the gate insulating film 13. Also in this embodiment, the action and operation are the same as those in the second embodiment.
Is the same as.

(Embodiment 4) FIG. 8 shows a sectional view of the essential portions of Embodiment 4 of the present invention. As shown in the figure, in this embodiment, the data line electrode 15 formed on the source side of the semiconductor layer 14 is formed so as to extend over both sides and side surfaces of the semiconductor layer 14 to further reduce the contact resistance. It is a thing. Further, the light emitting insulating film 16, the light emitting layer 17, and the light emitting electrode 18 are also formed so as to extend over both sides and side surfaces of the semiconductor layer 14 on the drain side. Further, a so-called double gate structure is formed in which a control electrode 12A is formed above the semiconductor layer 14 and a control electrode 12B is formed below the semiconductor layer 14. In this embodiment, the data line electrode 15
The contact resistance can be reduced, and the light emitting region of the light emitting layer 17 can be widened. Further, since the control electrodes are located above and below, the current flowing through the channel of the MOS transistor can be substantially increased. In addition, according to the present embodiment, the control method of the control electrode can be made multifunctional.

Although the respective embodiments have been described above, the present invention is not limited to these, and various modifications can be made based on the spirit of the present invention. For example, in each of the above embodiments, a fluorescent material is used for the light emitting layer 17, and the fluorescent material is excited by an F-N tunnel current to emit light. However, in the present invention, an EL (electroluminescence) light emitting material is used as the light emitting layer 17. It is also possible to use a light emitting device that emits light by recombining charges by applying an electric field. In this case, the light emitting layer 17 made of an EL material is a charge coupling layer, and the insulating film 16 is a charge (hole or electron) transport layer. A metal film of indium or the like is provided between the transport layer and the semiconductor layer 14 to serve as an electron emission electrode. Also,
The light emitting electrode 18 is formed of ITO or the like to serve as a hole emitting electrode. When an electric field is applied between the light emitting electrode and the electron emitting electrode, holes and electrons emit light and recombine with each other to emit excitation light. The EL material and the fluorescent material can be appropriately selected from various materials. Further, in any of the examples, SiN is used as the gate insulating film of the control electrode 12.
Although a film is used, it is needless to say that another insulating film such as a SiO2 film may be used. Similarly, the light emitting insulating film interposed between the light emitting layer and the semiconductor layer is not limited to the SiN film.

[0016]

As is apparent from the above description, according to the present invention, it is possible to obtain a light emitting device which can be manufactured with a high yield and has good controllability, and a display panel including the same. Further, there is an effect that it is possible to manufacture a large-area flat display having stable light emission characteristics and display characteristics without using liquid crystal, electron beam, or the like.

[0017]

[Brief description of drawings]

FIG. 1 is a sectional view of a main part of a first embodiment of the present invention.

FIG. 2 is an equivalent circuit of a light emitting device formed in a two-dimensional matrix shape provided in the display panel of Example 1.

3A is an equivalent circuit in which the light emitting device of Example 1 is in a pixel selected state, and FIG. 3B is an equivalent circuit in which the light emitting device is in a non-selected state.

FIG. 4 is a diagram showing a timing when the light emitting device shown in FIGS. 3A and 3B is driven.

FIG. 5 is a plan view showing an improved example in which the channel width of the polysilicon film 14 is lengthened in the first embodiment.

FIG. 6 is a cross-sectional view of essential parts showing a second embodiment of the present invention.

FIG. 7 is a cross-sectional view of essential parts showing a third embodiment of the present invention.

FIG. 8 is a sectional view of an essential part showing a fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing the structure of a conventional CRT.

FIG. 10 is a sectional view of a conventional Spindt-type cold cathode device.

[Explanation of symbols]

 11 glass substrate 12 control electrode 13 gate insulating film 14 semiconductor layer 14A source region 14B drain region 15 data line electrode 16 light emitting insulating film 17 light emitting layer 18 light emitting electrode

Claims (9)

[Claims] 1. A semiconductor layer, an input electrode electrically connected to one conductive region sandwiching a channel region of the semiconductor layer, and the semiconductor layer on the other conductive region side of the semiconductor layer sandwiching the channel region. A light emitting electrode disposed apart from the light emitting electrode, a light emitting layer provided between the light emitting electrode and the other conductive region of the semiconductor layer, and the light emitting layer between the input electrode and the light emitting electrode. A light emitting device, comprising: a control electrode arranged to face a channel region of the semiconductor layer. 2. A light emitting device, wherein an insulating film is interposed between the semiconductor layer and the light emitting layer. 3. The light emitting device according to claim 1, wherein the light emitting layer is a phosphor film. 4. The light emitting device according to claim 1, wherein the other conductive region, the light emitting electrode, and the light emitting layer sandwiched therebetween form an EL element. 5. The light emitting device according to claim 1, wherein the control electrode is provided above and / or below the semiconductor layer. 6. A conductive region, in which a semiconductor layer and a gate electrode for selection are formed to face each other with an insulating film in between for each pixel portion on a transparent substrate, and one conductive region sandwiching a channel region of the semiconductor layer. And a data line connected thereto, and a light emitting electrode is provided in the other conductive region sandwiching the channel region of the semiconductor layer via a light emitting layer. 7. The display panel according to claim 6, wherein the light emitting layer is a phosphor film. 8. The display panel according to claim 6, wherein the other conductive region, the light emitting electrode, and the light emitting layer sandwiched therebetween form an EL element. 9. The display panel according to claim 6, wherein the gate electrode is provided above and / or below the semiconductor layer.