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首页> 外文期刊>Medical Physics >Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors.
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Active pixel imagers incorporating pixel-level amplifiers based on polycrystalline-silicon thin-film transistors.

机译：有源像素成像器结合了基于多晶硅薄膜晶体管的像素级放大器。

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摘要

Active matrix, flat-panel imagers (AMFPIs) employing a 2D matrix of a-Si addressing TFTs have become ubiquitous in many x-ray imaging applications due to their numerous advantages. However, under conditions of low exposures and/or high spatial resolution, their signal-to-noise performance is constrained by the modest system gain relative to the electronic additive noise. In this article, a strategy for overcoming this limitation through the incorporation of in-pixel amplification circuits, referred to as active pixel (AP) architectures, using polycrystalline-silicon (poly-Si) TFTs is reported. Compared to a-Si, poly-Si offers substantially higher mobilities, enabling higher TFT currents and the possibility of sophisticated AP designs based on both n- and p-channel TFTs. Three prototype indirect detection arrays employing poly-Si TFTs and a continuous a-Si photodiode structure were characterized. The prototypes consist of an array (PSI-1) that employs a pixel architecture with a single TFT, as well as two arrays (PSI-2 and PSI-3) that employ AP architectures based on three and five TFTs, respectively. While PSI-1 serves as a reference with a design similar to that of conventional AMFPI arrays, PSI-2 and PSI-3 incorporate additional in-pixel amplification circuitry. Compared to PSI-1, results of x-ray sensitivity demonstrate signal gains of approximately 10.7 and 20.9 for PSI-2 and PSI-3, respectively. These values are in reasonable agreement with design expectations, demonstrating that poly-Si AP circuits can be tailored to provide a desired level of signal gain. PSI-2 exhibits the same high levels of charge trapping as those observed for PSI-1 and other conventional arrays employing a continuous photodiode structure. For PSI-3, charge trapping was found to be significantly lower and largely independent of the bias voltage applied across the photodiode. MTF results indicate that the use of a continuous photodiode structure in PSI-1, PSI-2, and PSI-3 results in optical fill factors that are close to unity. In addition, the greater complexity of PSI-2 and PSI-3 pixel circuits, compared to that of PSI-1, has no observable effect on spatial resolution. Both PSI-2 and PSI-3 exhibit high levels of additive noise, resulting in no net improvement in the signal-to-noise performance of these early prototypes compared to conventional AMFPIs. However, faster readout rates, coupled with implementation of multiple sampling protocols allowed by the nondestructive nature of pixel readout, resulted in a significantly lower noise level of approximately 560 e (rms) for PSI-3.
机译：采用a-Si寻址TFT的2D矩阵的有源矩阵平板成像器（AMFPI）由于其众多优势而在许多X射线成像应用中变得无处不在。然而，在低曝光和/或高空间分辨率的条件下，其信噪性能受到相对于电子加性噪声的适度系统增益的限制。在本文中，报告了一种通过使用多晶硅（poly-Si）TFT引入像素内放大电路（称为有源像素（AP）体系结构）来克服此限制的策略。与a-Si相比，多晶硅具有更高的迁移率，可实现更高的TFT电流，并有可能基于n沟道和p沟道TFT进行复杂的AP设计。表征了采用多晶硅TFT和连续a-Si光电二极管结构的三个原型间接检测阵列。原型包括采用像素结构和单个TFT的阵列（PSI-1），以及分别采用基于三个和五个TFT的AP体系结构的两个阵列（PSI-2和PSI-3）。虽然PSI-1的参考设计类似于常规AMFPI阵列，但PSI-2和PSI-3并入了额外的像素内放大电路。与PSI-1相比，X射线敏感性结果表明PSI-2和PSI-3的信号增益分别约为10.7和20.9。这些值与设计期望在合理的范围内，表明可以调整多晶硅AP电路以提供所需的信号增益水平。 PSI-2表现出与PSI-1和其他采用连续光电二极管结构的常规阵列相同的高水平的电荷俘获。对于PSI-3，发现电荷陷获明显降低，并且在很大程度上与施加在光电二极管两端的偏置电压无关。 MTF结果表明，在PSI-1，PSI-2和PSI-3中使用连续的光电二极管结构会导致光学填充因子接近于1。此外，与PSI-1相比，PSI-2和PSI-3像素电路的复杂性更高，对空间分辨率没有明显影响。 PSI-2和PSI-3都表现出高水平的加性噪声​​，与传统的AMFPI相比，这些早期原型的信噪比性能没有丝毫改善。但是，更快的读出速率，加上像素读出的非破坏性所允许的多种采样协议的实施，导致PSI-3的噪声水平明显降低，约为560 e（rms）。

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