KR20160083152A - Thin film transistor substrate for display device and method of manufacturing the same - Google Patents

Abstract

The present invention is to improve the compensatory performance of a pixel circuit and to prevent a driving circuit from malfunctioning by differently controlling the threshold voltage of a thin film transistor included in the pixel circuit and the driving circuit of a display device. Accordingly, luminance imbalance and stain generation of the display device can be prevented, and a display quality can be improved. The display device according to an embodiment of the present invention comprises: a pixel including a light emitting display; a pixel circuit which includes a first transistor and drives the light emitting display; and a driving circuit which includes a second transistor and supplies a signal to the pixel circuit. In addition, the threshold voltage of the first transistor is different from that of the second transistor.

Description

TECHNICAL FIELD [0001] The present invention relates to a thin film transistor substrate for a display device and a method of manufacturing the thin film transistor substrate.

TECHNICAL FIELD The present invention relates to a thin film transistor substrate for a display device and a method of manufacturing the same, and more particularly, to a technique for improving unevenness and luminance unevenness.

In recent information society, display has become more important as a visual information delivery medium, and it is necessary to meet requirements such as low power consumption, thinning, light weight, and high image quality in order to take a major position in the future. Currently, flat panel displays (FPDs) are not only capable of satisfying these conditions of display but also have mass productivity. Therefore, various new products are rapidly being produced using the FPDs, and existing cathode ray tubes (CRTs) CRT) as a key part industry. Such flat panel display devices include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an organic light emitting diode display , And OLED).

 The flat panel display device mainly uses an active matrix method in which data signals corresponding to image signals are individually supplied to pixels arranged in a matrix form so that each pixel can display a desired image.

 The active matrix method has a pixel circuit for each pixel to control the image of each pixel. The pixel circuit is composed of a thin film transistor, a capacitor, and the like, receives a signal from the outside, and adjusts the voltage or current supplied to the pixel. In the case of a liquid crystal display device, the voltage applied to the liquid crystal is adjusted to control the amount of light transmitted. In the case of a plasma display panel or an organic light emitting display device, light emitted by adjusting a voltage or current supplied to the light- Adjust the amount.

 The thin film transistor of the pixel circuit serves as a switch or a driver, and the capacitor serves as a storage for storing a data signal of a pixel or a combination of one or more thin film transistors to compensate for deterioration of a pixel.

In a self-luminous element of a current driving type such as a plasma display panel or an organic light emitting display, device characteristics are degraded if the emission time is accumulated. Particularly, since the voltage or current is supplied to the light emitting element through the pixel circuit, the characteristic of the pixel circuit deteriorates greatly and greatly affects the display quality of the light emitting element.

Since the degree of deterioration of the pixel circuit and the light emitting element is different for each pixel, the luminance per pixel becomes nonuniform and unevenness may occur and display quality may be deteriorated. Therefore, it is necessary to compensate the deterioration of the pixel circuit and the light emitting element to have a constant uniform luminance for each pixel.

Disclosed is a thin film transistor substrate for a display device and a method of manufacturing the same that can improve the compensation performance of a pixel circuit and prevent a malfunction of a driving circuit to prevent luminance unevenness and unevenness in each pixel of a display device and improve display quality. do.

A display device according to an embodiment of the present invention includes a pixel including a light emitting element, a pixel circuit including a first transistor and driving the light emitting element, a driving circuit including a second transistor and supplying a signal to the pixel circuit . And a threshold voltage of the first transistor is different from a threshold voltage of the second transistor.

The absolute value of the threshold voltage of the first transistor may be smaller than the absolute value of the threshold voltage of the second transistor.

The threshold voltage of the first transistor may be less than zero and may be greater than the threshold voltage of the second transistor.

Alternatively, the threshold voltage of the first transistor may be greater than zero and less than the threshold voltage of the second transistor.

The first transistor may be a driving transistor connected in series with the light emitting device.

Alternatively, the second transistor may be a buffer transistor that outputs the signal.

According to another aspect of the present invention, there is provided a display device including a first transistor including a first channel layer and a second transistor including a second channel layer, a pixel circuit including the first transistor, A driver circuit, a pixel including the light emitting element and the pixel circuit. And the impurity concentration of the first channel layer is different from the impurity concentration of the second channel layer.

The threshold voltage of the first transistor may be different from the threshold voltage of the second transistor.

Alternatively, the impurity concentration of the first channel layer may be smaller than the impurity concentration of the second channel layer.

The present invention controls a threshold voltage of a thin film transistor included in a pixel circuit of a display device and a thin film transistor included in a driving circuit to improve a compensation performance of a pixel circuit and prevent a malfunction of a driving circuit. As a result, the present invention can prevent unevenness in brightness and stain of the display device and improve display quality.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating the structure of a general organic light emitting display device. FIG.
2 is an equivalent circuit diagram showing the structure of one pixel of a general organic light emitting display device.
3 is a cross-sectional view illustrating a structure of a thin film transistor of a display device according to the present invention.
4 and 5 are sectional views schematically illustrating a method of manufacturing a thin film transistor of a display device according to the present invention.
6 is a graph showing the difference in current value of the organic light emitting diode OLED according to the threshold voltage of the driving transistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Like reference numerals throughout the specification denote substantially identical components. In the following description, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. The names of components used in the following description are selected in consideration of ease of specification, and may be different from actual product names.

1 and 2 show a general organic light emitting display.

An organic light emitting display according to an embodiment of the present invention includes a pixel 40, a gate driving circuit 20, and a data driving circuit 30 arranged in a matrix on a substrate 10. The gate drive circuit 20 supplies an emission signal and a scan signal to the pixel, and the data drive circuit 30 supplies the data voltage to the pixel.

Each pixel includes an organic light emitting element (OLED) and a pixel circuit. The pixel circuit includes one or more thin film transistors (ST, DT, T1, T2) and one or more capacitors (C1, Cs). The pixel circuit receives signals and power from the gate driving circuit 20 and the data driving circuit 30 and drives the organic light emitting diode OLED.

The organic light emitting device OLED is driven by a pixel circuit, and controls the current flowing through the driving transistor DT to adjust the luminance. The driving transistor DT may be connected in series with the organic light emitting diode OLED as shown in FIG. The luminance of the pixel is influenced by the characteristics of the driving transistor DT, so that the deterioration of the driving transistor DT is compensated through the other transistor and the capacitor of the pixel circuit.

In the thin film transistor, when the absolute value of the gate voltage is larger than the threshold voltage, a current starts to flow through the source drain, and the drain current value changes according to the magnitude of the gate voltage. The degradation and compensation of the pixel circuit are greatly affected by the threshold voltage of the driving transistor DT. In particular, as shown in FIG. 6, the threshold voltage of the driving transistor DT affects the compensation performance of the pixel circuit. The horizontal axis represents the threshold voltage of the driving transistor DT, and the vertical axis represents the difference in the current value of the organic light emitting device OLED by pixel. It can be seen that the difference in the current value of the organic light emitting diode OLED decreases as the absolute value of the threshold voltage of the driving transistor DT becomes smaller and approaches 0V. The smaller the difference in the current value of the organic light emitting diode OLED per pixel is, the higher the compensation performance is, and the luminance per pixel can be made uniform.

The gate drive circuit 20 includes a shift register, a buffer unit, and the like, and supplies an emission signal, a scan signal, or the like to the pixel 40 so that the pixels can be sequentially driven. The gate drive circuit 20 may be fabricated as a separate chip and attached to the substrate. The gate drive circuit 20 may be formed of thin film transistors and integrated on a substrate. When the gate drive circuit 20 is integrated on the substrate, the thin film transistor of the gate drive circuit 20 is formed simultaneously with the thin film transistor of the pixel circuit.

The gate driving circuit 20 includes a plurality of thin film transistors and supplies a signal to the pixels according to an externally input signal. A buffer transistor is arranged in the buffer section of the gate drive circuit 20. [ Since the signal of the gate drive circuit 20 is outputted through the buffer transistor and the buffer transistor finally controls the output of the gate drive circuit 20, a thin film transistor having a large channel width can be used as the buffer transistor.

The gate drive circuit 20 mainly uses a value close to 0 V for the OFF voltage of the thin film transistor. Therefore, the smaller the drain current when the gate voltage is OV, the better the OFF characteristic. Particularly, when operating at a high temperature, the threshold voltage shifts and the drain current becomes large, so that a leakage current is generated and the gate drive circuit 20 may malfunction. Accordingly, the absolute value of the threshold voltage of the buffer transistor is large, I am preferable.

When the thin film transistor of the pixel circuit and the thin film transistor of the gate driving circuit 20 are formed on the same substrate at the same time, the threshold voltage and characteristics are similar. However, the smaller the absolute value of the threshold voltage of the driving transistor DT is, the better the compensation performance is, and the larger the absolute value of the threshold voltage of the buffer transistor is, the smaller the leakage current is and the malfunction can be prevented.

The present invention improves the compensation performance of the pixel circuit by preventing the thin film transistor of the pixel circuit and the thin film transistor of the gate drive circuit (20) from being individually adjusted, prevents erroneous operation of the driving circuit, And the display quality can be improved.

The structure of the pixel circuit of the display device and the thin film transistor of the gate drive circuit 20 according to the embodiment of the present invention will be described with reference to FIG. The first transistor 210 may be a driving transistor DT of the pixel circuit and the second transistor 220 may be a buffer transistor of the gate driving circuit 20. [

The substrate 100 may be formed of an insulating substrate such as glass, quartz, or plastic, or may be formed of a metallic substrate such as stainless steel.

A buffer layer 110 is disposed on the substrate 100. The buffer layer 110 may be formed of an inorganic insulating film, an organic insulating film, or the like, and serves to prevent foreign matter, moisture, and the like from penetrating from the outside of the display device.

A semiconductor layer is disposed on the buffer layer 110. The semiconductor layer may include amorphous silicon (a-Si), polycrystalline silicon (Poly-Si), an oxide semiconductor, or an organic semiconductor. This embodiment will be described on the basis of polycrystalline silicon.

The first transistor 210 includes a first channel layer 121 that is a semiconductor layer and a first source / drain layer 123 that is formed on both the first channel layer 121 and the first channel layer 121. The second transistor 120 includes a second channel layer 122 that is a semiconductor layer and a second source / drain layer 124 that is on both the second channel layer 122. The second channel layer 122 is a semiconductor layer. The first and second source / drain layers 123 and 124 are doped with N-type impurities such as phosphorus (P) in the case of NMOS and doped with P-type impurities such as boron (B) Thereby increasing the electrical conductivity and reducing the contact resistance. In the first and second channel layers 121 and 122, P-type impurities such as boron (B) are counterdoped in the case of NMOS and N-type impurities such as phosphorous (P) And the threshold voltage can be adjusted according to the amount of the dose.

The display device according to the exemplary embodiment of the present invention controls the impurity concentration by differentiating the dose amount of impurities between the first channel layer 121 and the second channel layer 122 and the first transistor 210 and the second transistor 220, So that the threshold voltage of the transistor is different. The absolute value of the threshold voltage of the thin film transistor becomes larger as the impurity concentration of the channel layer becomes higher. In the case of NMOS, the threshold voltage generally has a positive value. The higher the impurity concentration, the larger the threshold voltage. In the case of PMOS, the threshold voltage generally has a negative value, and the higher the impurity concentration, the lower the threshold voltage.

The first channel layer 121 does not doped or dopes a dose amount less than the dose amount of the second channel layer 122. The impurity concentration of the second channel layer is made higher than the impurity concentration of the first channel layer and the absolute value of the threshold voltage of the second transistor is made larger than the threshold voltage of the first transistor. Accordingly, the threshold voltage of the first transistor 210 of the pixel circuit and the threshold voltage of the second transistor 220 of the gate driving circuit 20 can be individually adjusted differently.

A gate insulating film 130 is disposed on the semiconductor layer. The gate insulating film 130 is formed of an inorganic insulating film such as SiNx or SiOx or an organic insulating film.

A gate electrode 140 is disposed on the gate insulating film 130. The gate electrode 140 is made of a metal such as Cu, Al, or Mo, a conductive semiconductor material, or an alloy thereof.

An interlayer insulating film 150 is disposed on the gate electrode 140. The interlayer insulating film 150 is formed of an inorganic insulating film such as SiNx or SiOx or an organic insulating film.

Drain electrodes 160 are disposed on the interlayer insulating layer 150 and the first and second source / drain layers 123 and 124 are formed through the contact holes of the gate insulating layer 130 and the interlayer insulating layer 150, And is electrically connected. The source / drain electrodes 160 are made of a metal such as Cu, Al, or Mo, a conductive semiconductor material, or an alloy thereof.

A manufacturing method of a display device according to an embodiment of the present invention will be described with reference to FIGS. 3, 4, and 5. FIG.

A buffer layer 110 is formed on the substrate 100.

A semiconductor layer is formed on the buffer layer 110. The semiconductor layer may be formed of a polycrystalline silicon layer by crystallizing after depositing amorphous silicon.

Impurities are doped in the entire semiconductor layer. In the case of NMOS, P-type impurities such as boron (B) are counterdoped. In the case of PMOS, N-type impurities such as phosphorous (P) are counter doped and the threshold voltage is controlled according to the dose amount .

The first channel layer 121 and the second channel layer 122 are formed by patterning the semiconductor layer.

The step of doping the entire semiconductor layer with impurities may be omitted or may be performed after the step of patterning the semiconductor layer.

As shown in FIG. 4, a first photoresist layer 171 is formed on the first channel layer 121 and doped with impurities. In the case of NMOS, P-type impurities such as boron (B) are counterdoped. In the case of PMOS, N-type impurities such as phosphorous (P) are counter doped and the threshold voltage is controlled according to the dose amount . The first channel layer 121 is prevented from being doped with impurities and the second channel layer 122 is selectively doped with impurities. Therefore, the impurity concentration of the second channel layer 122 becomes higher than the impurity concentration of the first channel layer 121

A gate insulating film is formed on the first channel layer 121 and the second channel layer 122.

The step of selectively doping the impurities may be performed before the step of patterning the semiconductor layer, or may be performed after the step of forming the gate insulating layer 130 as shown in FIG. In this case, the second photoresist layer 172 prevents impurities from being doped into the first channel layer 121, and impurities may be selectively doped to the second channel layer 122 through the gate insulating layer 130 have.

A gate electrode 140 is formed on the gate insulating film 130.

A first source / drain layer 123 and a second source / drain layer 124 are formed by doping impurities. The first and second source / drain layers 123 and 124 are doped with N-type impurities such as phosphorous (P) in the case of NMOS and doped with P-type impurities such as boron (B) Thereby increasing electrical conductivity and reducing contact resistance. The first channel layer 121 and the second channel layer 122 are blocked by the gate electrode 140 and are not doped.

An interlayer insulating film 150 is formed on the gate electrode 140.

A contact hole is formed through the interlayer insulating layer 150 and the gate insulating layer 130 to expose the first and second source / drain layers 123 and 124.

Source / drain electrodes 160 are formed on the interlayer insulating layer 150 to electrically connect the first and second source / drain layers 123 and 124.

The structures and processes described above are in accordance with one embodiment of the present invention and do not limit the scope of the present invention. The present invention can be applied to various display device structures and processes depending on the type of semiconductor and the type of thin film transistor.

While a great many are described in the foregoing description, it should be construed as an example of preferred embodiments rather than limiting the scope of the invention. Therefore, the invention should not be construed as limited to the embodiments described, but should be determined by equivalents to the appended claims and the claims.

121: first channel layer
122: second channel layer
210: a first transistor
220: second transistor

Claims (9)

A pixel including a light emitting element;
A pixel circuit including a first transistor and driving the light emitting element; And
And a driving circuit that includes a second transistor and supplies a signal to the pixel circuit,
Wherein a threshold voltage of the first transistor is different from a threshold voltage of the second transistor.
The method according to claim 1,
Wherein the absolute value of the threshold voltage of the first transistor is less than the absolute value of the threshold voltage of the second transistor.
The method of claim 2,
Wherein a threshold voltage of the first transistor is less than zero and greater than a threshold voltage of the second transistor.
The method of claim 2,
Wherein a threshold voltage of the first transistor is greater than zero and less than a threshold voltage of the second transistor.
The method according to claim 1,
Wherein the first transistor is a driving transistor connected in series with the light emitting element.
The method according to claim 1,
And the second transistor is a buffer transistor for outputting the signal.
A second transistor including a first transistor including a first channel layer and a second channel layer;
A driving circuit including the pixel circuit including the first transistor and the second transistor;
A pixel including a light emitting element and the pixel circuit,
And the impurity concentration of the first channel layer is different from the impurity concentration of the second channel layer.
The method of claim 7,
Wherein a threshold voltage of the first transistor is different from a threshold voltage of the second transistor.
The method of claim 7,
And the impurity concentration of the first channel layer is smaller than the impurity concentration of the second channel layer.

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