KR101322331B1 - A thin film transistor array panel for X-ray detectorand a method for manufacturing the thin film transistor - Google Patents

Abstract

In the present invention, an element having an upper gate structure is applied to a TFT backplane panel for a direct digital X-ray radiography system instead of a conventional lower gate thin film transistor element. This ensures process simplification and device drive stability.

Description

A thin film transistor array panel for X-ray detectors and a method for manufacturing the thin film transistor provided in the substrate {a thin film transistor array panel for X-ray detector and a method for manufacturing the thin film transistor}

The present invention relates to a thin film transistor array substrate, and more particularly, to a thin film transistor array substrate for an X-ray detector.

In the case of Digital X-ray Radiography system, many technologies using Charge Coupled Device (CCD) or Complementary Metal Oxide Semiconductor (CMOS) have been developed.However, in this case, it is easy to manufacture a panel that detects an image signal in the same size as the subject. In this case, an optical lens system is required, in which case distortion of the image may occur and an additional cost is required. Therefore, recently, a digital x-ray radiography system (or flat panel system) using thin-film transistor (TFT) backplane technology has been developed.

In case of flat panel system using thin-film transistor (TFT) backplane technology, which is widely used in existing displays, large area can be manufactured, and thus a system that can measure a subject 1: 1 can be constructed. There is no image distortion. Such a system can reduce manufacturing costs compared to CCD or CMOS, and can be applied by applying a large-area TFT panel technology, which is currently being developed in the display industry, and thus has many advantages.

In the case of the conventional TFT panel technology, the amorphous Si TFT technology currently applied to TFT-LCD is used. All commercially available products have a gate located under the gate insulator and a source and drain electrode located on the semiconductor channel layer. A TFT device having a bottom gate structure is used.

In the case of the lower gate structure, damage to the channel layer occurs during the source and drain etching, and thus, an etch stop layer or an etch back process is used to prevent this.

These processes are additional process operations and, if excluded, can bring benefits to the process.

In addition, since the upper channel layer may be affected when the radiation is exposed, the thickness of the upper radiation sensing material may be increased. Therefore, a new thin film transistor backplane structure is required to prevent damage to the channel layer in this process and to prevent malfunction of the device upon radiation exposure.

Accordingly, an object of the present invention is to provide a thin film transistor array substrate for an X-ray detector capable of preventing damage to a channel layer in a process and preventing malfunction of a device when radiation is exposed.

Another object of the present invention is to provide a method of manufacturing a thin film transistor provided on the substrate.

According to an aspect of the present invention, a thin film transistor array substrate for an X-ray detector includes a plurality of gate lines formed in one direction and some pixel regions intersecting the plurality of gate lines. A thin film transistor having a base substrate having a plurality of data lines formed thereon and an upper gate structure formed in each pixel area; And a photoelectric conversion element formed in each pixel area and connected to the thin film transistor, and generates a charge corresponding to the irradiation amount of the X-ray and charges the capacitor connected to the thin film transistor.

According to another aspect of the present invention, a method of manufacturing a thin film transistor is formed on the base substrate to form a source electrode connected to the photoelectric change element and a drain electrode formed on the same layer as the source electrode and spaced apart at regular intervals. And forming a semiconductor channel layer formed in spaces spaced at the predetermined intervals to cover one end portion of the drain electrode and one end portion of the source electrode facing each other, the source electrode, the drain electrode, and the Forming a dielectric layer covering the semiconductor channel layer; a gate formed over the semiconductor channel layer with the dielectric layer interposed therebetween to shield the X-ray from entering the semiconductor channel layer formed below; Forming an electrode and covering the entire surface of the pixel region to form the gate electrode and the dielectric layer; Includes forming a protective layer.

According to the present invention, an element of an upper gate structure can be applied to a TFT backplane panel for a direct digital X-ray radiography system instead of a conventional lower gate thin film transistor element, thereby providing process simplification and stable device driving.

FIG. 1 is a view schematically illustrating a structure of a TFT backplane panel used in an indirect X-ray imaging system and a structure of a TFT backplane panel used in a direct X-ray imaging system.
2 is a cross-sectional view of a thin film transistor having a bottom gate structure used in a direct digital X-ray radiography system.
3 is a view illustrating a structure of a unit pixel formed on a thin film transistor array substrate for an X-ray detector according to an exemplary embodiment of the present invention.

The present invention improves the shortcomings of the thin-film transistor element of the lower gate structure used for the driving backplane in the existing digital X-ray radiography system, simplifying the process, X-ray (radiation) irradiation A thin film transistor having a top gate structure is applied to protect the device from the device and to improve the stability of the device.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. It will be understood that when an element such as a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the element directly over another element, On the contrary, when a part is "just above" another part means that there is no other part in the middle. It demonstrates in detail so that implementation may be carried out easily. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

FIG. 1 is a view schematically illustrating a structure of a TFT backplane panel used in an indirect X-ray imaging system and a structure of a TFT backplane panel used in a direct X-ray imaging system.

FIG. 1A is a structure of a TFT backplane panel used in the indirect X-ray imaging system according to indirect detection methods, and FIG. 1B is a direct detection method. The structure of the TFT backplane panel used in the direct X-ray imaging system according to the present invention.

The thin film transistor array substrate for a thin-ray detector of the present invention is applied to a TFT backplane panel for a direct digital X-ray radiography system according to direct detection methods as shown in FIG.

The thin film transistor array substrate for a thin-ray detector of the present invention basically consists of a base substrate such as a glass substrate and a plurality of pixels arranged in a matrix form on the base substrate. Each pixel has a structure including one thin film transistor, a photoconductor having one capacitor and an upper and lower electrodes electrically connected to the thin film transistor.

Meanwhile, a thin film transistor formed on a thin film transistor array substrate according to a conventional direct detection method basically has a bottom gate structure.

2 is a cross-sectional view of a thin film transistor having a bottom gate structure used in a direct digital X-ray radiography system.

Referring to FIG. 2, a thin film transistor device having a lower gate structure used in a conventional direct digital X-ray radiography system may be affected by a channel layer during an etching process for patterning a source electrode and a drain electrode. have.

In addition, the channel layer is exposed to incident X-ray (Incident X-ray) from the top, and the channel layer directly meets the passivation (passivation) required for manufacturing the panel.

Therefore, the characteristics of the thin film transistor element may be affected by the material and process conditions of the passivation layer, and when excessive charge is accumulated in the pixel electrode, it may act as a main cause of malfunction of the thin film transistor. Can be.

However, if the thin film transistor is changed into a top gate structure, the channel layer may proceed with the deposition and patterning process after the source and drain electrodes are formed. As a result, unlike the thin film transistor having the lower gate structure, there is no influence by the source electrode and the drain electrode process.

In the thin film transistor having the upper gate structure, the existing gate electrode is disposed on the channel layer, and at the same time, the gate insulating film is also formed on the upper side. Accordingly, since the gate insulating layer moved to the upper portion protects the channel layer, the channel layer is not affected by the passivation layer.

In addition, if the gate electrode moved to the upper part is made of a material capable of shielding the X-lay, the influence of the channel layer from the X-lay incident from the upper part can be prevented, so that the upper photoconductor layer It is possible to afford to select the thickness.

In addition, an unintended operation of the device can be prevented by the voltage difference between the source / drain electrodes and the pixel electrode, thereby enabling more stable panel driving.

Therefore, in the present invention, an element having an upper gate structure is applied to a TFT backplane panel for a direct digital X-ray radiography system instead of a conventional lower gate thin film transistor element.

3 is a cross-sectional view illustrating a cross-sectional structure of a unit pixel formed on a thin film transistor array substrate for an X-ray detector according to an exemplary embodiment of the present invention.

Referring to FIG. 3, a thin film transistor array substrate for an X-ray detector is applied to a digital X-ray imaging system of a direct detection method, and reads out an image signal.

The thin film transistor array substrate includes a base substrate 110 such as a glass substrate in which a plurality of pixel regions arranged in a matrix form is defined, a capacitor 130 and a photoelectric conversion unit 140 provided in each pixel region.

Although not shown in the drawing, a plurality of gate lines formed in one direction and a plurality of data lines crossing the plurality of gate lines are formed on the base substrate 110. The plurality of pixel areas is defined by the plurality of gate lines and the plurality of data lines crossing the plurality of gate lines.

Each pixel region includes a thin film transistor 120 having an upper gate structure and a photoelectric conversion element 140 electrically connected to the thin film transistor 120. In addition, each pixel region is further provided with a capacitor 130 connected to the thin film transistor 120, each pixel region is basically designed to have a 1T-1C (1 Transistor-1 Capacitor) structure.

In detail, the thin film transistor having the upper gate structure is formed in each pixel area defined on the base substrate 110 to be connected to the photoelectric change element 140 and the source electrode 122B. And drain electrodes 122A formed on the same layer and spaced apart at regular intervals. The drain electrode 122A and the source electrode 122B are simultaneously provided through the same process.

The semiconductor channel layer 124A is provided in spaces spaced at regular intervals.

The semiconductor channel layer 124A covers one end of the drain electrode 122A and one end of the source electrode 122B facing each other. In this case, an ohmic contact layer 124B may be provided between the semiconductor channel layer 124A and the drain / source electrodes 122A and 122B.

The ohmic contact layer 124B is a layer for reducing contact resistance between the semiconductor channel layer 124A, the source electrode 122A, and the drain electrode 122B. The ohmic contact layer 124B may be formed of amorphous silicon doped with a high concentration of n-type impurities. have.

A dielectric layer 126 may be provided to cover the drain electrode 122A, the source electrode 122B, and the semiconductor channel layer 124A over the pixel area.

The dielectric layer 126 is a thin film transistor having a lower gate structure in which a gate insulating layer provided under the channel layer is moved above the channel layer. Therefore, it is used as a dielectric for constituting the capacitor 130 connected to the thin film transistor 120 while performing the function of the gate insulating film as in the conventional thin film transistor of the lower gate structure.

A gate electrode 128 is provided on the semiconductor channel layer 124A with the dielectric layer 126 interposed therebetween, and a thin film transistor 120 having an upper gate structure is basically formed.

A passivation layer 139 covering the gate electrode 128 and the dielectric layer 126 is provided over the dielectric layer 126 over the entire pixel area.

The gate electrode 128 is formed on the semiconductor channel layer 124A, and serves to shield the incident X-rays from entering the semiconductor channel layer, so that the semiconductor channel layer 124A is incident from the top. Since the influence from the X-lay can be prevented, the thickness of the upper photoconductor layer described below can be afforded.

In addition, unlike the thin film transistor having the lower gate structure, since the dielectric layer 126 moved upward protects the semiconductor channel layer 124A from the influence of the protective layer, the semiconductor channel layer 124A is a passivation layer. unaffected by layers).

Meanwhile, the capacitor 130 electrically connected to the thin film transistor 120 is formed on the same layer as the source electrode 122B of the thin film transistor 120, and the lower electrode 132 connected to the source electrode 122B and the lower electrode 132. And an upper electrode 136 facing the lower electrode 132 with the dielectric layer 126 interposed therebetween. In this case, the upper electrode 136 of the capacitor 130 may be simultaneously formed by the same process as the gate electrode 128.

The photoelectric conversion element 140 is formed on the protective layer 139.

The photoelectric conversion element 140 includes a pixel electrode 142, a photoconductor layer 144, and a bias electrode 146.

The pixel electrode 142 is formed over the entire pixel region except for the thin film transistor 120. In this case, the pixel electrode 142 is connected to the lower electrode 132 of the capacitor 130 through a via hole Via. Therefore, the thin film transistor 120 having the upper gate structure is connected to the photoelectric conversion element 140 through its source electrode.

The photoconductor layer 144 is provided on the front surface of the passivation electrode 142 and the protective layer 139 exposed by the pixel electrode 142, but is not particularly limited to CdZnTe, HgI _{2 ,} PbI ₂ , and a-. Se and the like.

The bias electrode 146 is disposed on the photoconductor layer 144 over the pixel region with the photoconductor 144 therebetween.

 The material of the source and gate electrodes 122B and 128 of the thin film transistor 120 having the upper gate structure is not particularly limited, but metal materials such as Al, Cr, Mo, and Ti may be used.

The material constituting the semiconductor channel layer 124A is not particularly limited, and amorphous Si and low temperature polycrystalline Si (Low Temperature Poly Silicon, LTPS) may be used.

The material of the dielectric layer 126 is not particularly limited, and oxides such as SiO 2 and Al 2 O 3 and nitrides such as Si 3 N 4 may be used.

The material of the gate electrode 128 provided on the dielectric layer 126 is not particularly limited, but may be a double junction of Pb alloy capable of shielding X-rays or Al, Cr, Mo, Ti, and the like, which are general electrode materials. An electrode can be used.

Looking at the manufacturing process of the upper gate structure thin film transistor composed of the above materials are as follows.

After depositing and patterning a material to be used as the drain and source electrodes 122A and 122B on the base substrate 110, an amorphous Si or low temperature process polycrystalline Si channel layer 124A is deposited and patterned.

After the channel layer 124A process, the dielectric layer 126 is deposited, and then the gate electrode 128 is deposited and patterned to form an upper gate structure, thereby implementing the basic unit thin film transistor device.

 In the case of the capacitor constituting the pixel together with the thin film transistor, the lower electrode 132 may simultaneously deposit and pattern the source and drain electrodes of the thin film transistor 120 unit element, and then form the pixel electrode 142 later. When 1T-1C (1 transistor-1 capacitor) structure is implemented to be electrically connected.

The lower electrode 136 of the capacitor 130 is simultaneously formed when the drain / source electrodes 122A and 122B of the thin film transistor 120 are formed.

After the thin film transistor array process, a photoconductor material is deposited at a process temperature of 60 to 600 degrees through thermal evaporation or RF / DC sputtering, and then the upper electrode is deposited to finish the panel process.

As described above, in the case of the thin film transistor having the lower gate structure, the source and drain electrodes are deposited after the formation of the semiconductor channel layer, and the etching process is performed to form the pattern. Since the channel layer may be damaged, the process of removing the damaged channel layer by using an etch stop layer or a back channel etching process has been performed. However, the thin film transistor having the upper gate structure is not affected by the source and drain patterning process, so no additional process is required.

In addition, in the case of a device having a lower gate structure, a passivation layer is required at the top of a channel when manufacturing a panel. In this case, since the channel layer is directly exposed to such passivastion, materials and processes in which device characteristics are not affected. It is necessary to secure the condition, but the upper gate structure has self-passivation function by the gate insulating film, so the device can be protected by the basic process of the device. And the sensitivity to the process is reduced, it is possible to implement a stable device.

In addition, in the upper gate structure, when an electrode capable of shielding the radiation of the upper gate electrode is used, the influence of radiation to the TFT element can be automatically eliminated even without an additional shielding film.

In addition, when the upper gate electrode is used, a stable operation of the device may be realized by preventing a malfunction of the thin film transistor due to the high voltage of the pixel electrode applied to the upper part during X-ray irradiation.

Claims (6)

A thin film transistor array substrate for an X-ray detector for reading out an image signal in a digital x-ray imaging system,
A base substrate having a plurality of gate lines formed in one direction and a plurality of data lines crossing some of the gate lines and defining some pixel regions;
A thin film transistor formed in each pixel region and having an upper gate structure; And
A photoelectric conversion element formed in each pixel area and connected to the thin film transistor and generating a charge corresponding to a direct dose of the X-ray to charge a capacitor connected to the thin film transistor,
The thin film transistor
A source electrode formed on the base substrate and connected to the photoelectric change element;
A drain electrode formed on the same layer as the source electrode and spaced apart at regular intervals;
A semiconductor channel layer formed in the spaced spaced intervals and covering one end of the drain electrode and one end of the source electrode facing each other;
A dielectric layer covering the source electrode, the drain electrode and the semiconductor channel layer;
A gate electrode formed on the semiconductor channel layer with the dielectric layer interposed therebetween and blocking the X-ray from entering the semiconductor channel layer; And
A protective layer covering the gate electrode and the dielectric layer
Including
Thin film transistor array substrate for X-ray detector.
delete delete The method of claim 1, further comprising a capacitor connected to the thin film transistor,
The capacitor
A lower electrode formed on the same layer as the source electrode and connected to the source electrode;
An upper electrode facing the lower electrode with the dielectric layer interposed therebetween,
The upper electrode of the capacitor,
The thin film transistor array substrate for X-ray detector which is formed at the same time by the same process as the gate electrode.
The method of claim 4, wherein the photoelectric conversion element,
A pixel electrode formed over the passivation layer and formed over the entire pixel region except for the thin film transistor and connected to a lower electrode of the capacitor through a via hole;
A photoconductor covering the passivation layer exposed by the pixel electrode and the pixel electrode; And
A bias electrode formed over the pixel region with the photoconductor therebetween;
Thin film transistor array substrate for X-ray detector comprising a.
delete

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