脈衝X射線輻射下低溫多晶矽薄膜電晶體時間響應之研究

Study on the Time Response for the Low Temperature Poly-Silicon Thin-Film Transistors under Pulsed X-ray Irradiation Stress

陳維琳(Wei-Lin Chen)

指導教授 ： 戴亞翔

國立交通大學/電機學院/光電工程系所/碩士(2020年)

摘要

近年來數位X射線感測系統漸漸被廣泛使用於生活中，為了增加感測電路的增益以便有效降低輻射劑量並確保輻射安全，許多研究提出使用電子遷移率較高的低溫多晶矽（LTPS）薄膜電晶體（TFT）取代非晶矽薄膜電晶體。作為X射線感測系統的一部分，TFT長時間暴露於X射線輻射下，其穩定性是重要的議題，因此在這份研究中我們將探討LTPS TFT在穩定正偏壓以及脈衝X射線輻射下的特性。我們建立了一個實時測量系統，以觀察在X射線照射的當下薄膜電晶體的變化。
我們將量測在相同的X射線輻射劑量但不同脈波頻率下汲極電流的改變對於時間的響應現象，此種響應行為可以被分為受X射線輻射時的「激發行為」以及受輻射後的「回復行為」。這兩種響應行為可以被配適公式以及配適參數適當的分析。並且我們發現TFT暴露於脈衝X射線輻射下的脈衝時間長短會影響汲極電流的變化趨勢。此外，我們利用提出的擬合公式和擬合參數的結果來預測各種組合下的漏極電流變化。證明了在相同X射線輻射劑量下，無論受輻射時間長短如何變化，依舊可以利用本論文中的公式以及參數進行很好的預測，即使應用在快速脈衝輻射上亦是如此。這份研究實質上顯示了元件在多個X射線輻射下的時間響應，將有助於預測X射線感測系統中元件的使用壽命，可以在未來開發X射線應用產品上作為參考使用。

關鍵字

X射線 ； 低溫多晶矽 ； 薄膜電晶體 ； 時間響應

並列摘要

Digital X-ray sensing systems have gradually been widely used in people's lives in recent years. In order to improve the gain for large signal and reduce the X-ray radiation dose for radiation safety, many studies have proposed to replace amorphous silicon (a-Si) thin film transistors (TFTs) with low-temperature polycrystalline-silicon (LTPS) TFTs which have higher carrier mobility. As a part of the X-ray sensing system, the TFTs are exposed to X-ray radiation for a long time. Its stability is an important issue. Therefore, we investigate the characteristic of LTPS TFTs under stable positive bias and pulsed X-ray irradiation in this study. A real-time measurement system is used to observe how electrical properties are actually changing under the irradiation of X-rays.
The drain current change with respect to time is measured under the same X-ray radiation dose but different pulse frequencies. This response behavior can be categorized into "the excited behavior" when the TFTs are exposed to X-ray and "the recovering behavior" after exposure to radiation. These two response behaviors can be well analyzed by the fitting formulas and parameters. It is found that the time that the TFTs are exposed to pulsed X-ray irradiation can affect the drain current, and the change in drain current under various circumstance can be fairly forecasted by the proposed formulas and fitting parameters. It is proved that under the X-ray radiation dose, no matter how long the exposure time is, the formulas and parameters proposed in this paper can still make a good prediction, even if it is applied to fast pulse radiation. This work substantially shows the time response of the TFTs under multiple pulsed X-ray irradiation which will help to forecast the service life of the component in the X-ray sensing system and can be used as a reference to development of X-ray application products in the future.

並列關鍵字

X-ray ； Low Temperature Poly-Silicon ； Thin-Film Transistors ； Time Response

參考文獻

References

1. Knüpfer, W., E. Hell, and D. Mattern, Novel X-ray detectors for medical imaging. Nuclear Physics B-Proceedings Supplements, 1999. 78(1-3): p. 610-615.

2. Kasap, S.O. and J. Rowlands, Direct-conversion flat-panel X-ray image detectors. IEE Proceedings-Circuits, Devices Systems, 2002. 149(2): p. 85-96.

3. Partridge, M., B.-M. Hesse, and L. Müller, A performance comparison of direct-and indirect-detection flat-panel imagers. Nuclear Instruments Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors Associated Equipment, 2002. 484(1-3): p. 351-363.

4. Tai, Y.-H., et al., A source-follower type analog buffer using poly-Si TFTs with large design windows. IEEE electron device letters, 2005. 26(11): p. 811-813.