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Array testing method using electric bias stress for TFT array

a thin film transistor and array technology, applied in static indicating devices, fault locations by increasing destruction at faults, instruments, etc., can solve problems such as deterioration of tft-lcd image quality during operation, inability to move charges (off current), and unstable amorphous silicon. the effect of stable amorphous silicon

Active Publication Date: 2008-01-31
ORBOTECH LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0017]The defect detection may be applied at the TFT fabrication level to screen defective plates prior to assembly

Problems solved by technology

However, In the case of defective TFTs, the off-current variation with temperature is large enough to deteriorate the TFT-LCD image quality during operation.
Amorphous silicon is not very stable and its properties can be modified when exposed to strong illumination or injection of charge carriers.
The dangling bonds are defects within the amorphous semiconductor layer and contribute to a nonzero density of states within the band gap, thereby resulting in the mobility of charges (off current).
During processing, however, the Si:H bond can be inadvertently broken.
Generation of high energy ions during processing can be due to poor or incorrect process parameters, and may result in a global plate (panel) effect r

Method used

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  • Array testing method using electric bias stress for TFT array
  • Array testing method using electric bias stress for TFT array
  • Array testing method using electric bias stress for TFT array

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Embodiment Construction

[0031]In accordance with the present invention, to detect defects in a TFT panel, an electric bias is applied to the TFT panel for a known time period. The applied electric bias induces charge trapping in the SiNx film and / or state creation in the a-Si:H film, thus giving rise to the TFT threshold voltage shift. The shift in the threshold voltage results in the variation of the TFT IOFF current. The amount of the threshold voltage shift (ΔVT) depends on the applied bias voltage, the duration of the bias, as well as the initial density of state in the films.

[0032]FIG. 7A is an energy band diagram of an MIS device prior to the application of an electric bias. FIG. 7B is an energy band diagram of the MIS device of FIG. 7A after the application of an electric bias causing charges to be trapped in the band gap. FIG. 7C is an energy band diagram of the MIS device of FIG. 7A after the application of an electric bias causing states to be created in the band gap.

[0033]FIG. 8 shows the depend...

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Abstract

A method of detecting thin film transistor (TFT) defects in a TFT-liquid crystal display (LCD) panel, includes, in part, applying a stress bias to the TFTs disposed on the panel; and detecting a change in electrical characteristics of the TFTs. The change in the electrical characteristics of the TFTs may be detected using a voltage imaging optical system or an electron beam. The panel temperature may be varied while the bias stress is being applied. The change in the electrical characteristics is optionally detected across an array of the TFTs.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to testing of thin film transistor (TFT) arrays, and more particularly to testing the functionality and reliability of such arrays.[0002]Thin film transistor liquid crystal displays (TFT-LCD) for, e.g., television applications require brighter backlight for better image quality. FIG. 1 is a cross-sectional view of a TFT-LCD module assembly. The stack includes a polarizer layer 14 and optical film 12, followed by the TFT panel 10 above which liquid crystal layer 16 is formed, and then the backlight 20. Color filter 22 and polarizer 14 are disposed above liquid crystal layer 16. Brighter backlight increases the temperature of TFT-LCD during operation, thus resulting in an increase in the TFT-LCD off current Ioff. For good TFTs, the variation in Ioff as a function of temperature is relatively small, and does not affect the TFT-LCD image quality. However, In the case of defective TFTs, the off-current variation with temperat...

Claims

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Application Information

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IPC IPC(8): G01R31/00
CPCG09G3/006G09G2320/041G09G3/3648G02F1/13
Inventor JUN, MYUNGCHUL
Owner ORBOTECH LTD
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