Analysis of a new indium gallium zinc oxide (IGZO) detector

Freestone, Steven; Weisfield, Richard L.; Tognina, Carlo; Job, Isaias D.; Colbeth, Richard E.

doi:10.1117/12.2549469

Cited by 13 publications

(15 citation statements)

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“…For example, a previous study 11 involving a CMOS FPD (Xineos-3030HR, Teledyne DALSA, Eindhoven, NL) operated at matched pixel size (0.1 mm) exhibited ∼390 e − rms electronic noise (∼1.8× lower than IGZO). In terms of lag, the 10 th -frame lag at 5 fps was 1.0% for the a-Si:H FPD, ∼1.4× larger than for IGZO.As discussed in Freestone et al, 20 this relatively modest reduction is not surprising, because the dominant component of lag is trapped charge in the photodiode, which is the same for both FPDs. The high electron mobility and smaller footprint of IGZO TFTs enables improved pixel fill factor (at equivalent pixel pitch) compared to conventional a-Si:H TFTs.…”

Section: Discussionmentioning

confidence: 61%

“…The 2D imaging performance of the IGZO FPD is consistent with anticipated improvements associated with superior material characteristics of the IGZO pixel switching element. 20 As shown in Table 1 and Figure 2a, the high electron mobility of IGZO results in low levels of electronic noise and detector lag. The electronic noise of the IGZO FPD was ∼700-900 e − rms for 1×1 readout (0.1 mm pixels) and ∼1200 e − rms for 2×2 binning (0.2 mm pixels).…”

Section: Discussionmentioning

confidence: 95%

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Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

et al. 2022

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Background Indirect detection flat‐panel detectors (FPDs) consisting of hydrogenated amorphous silicon (a‐Si:H) thin‐film transistors (TFTs) are a prevalent technology for digital x‐ray imaging. However, their performance is challenged in applications requiring low exposure levels, high spatial resolution, and high frame rate. Emerging FPD designs using metal oxide TFTs may offer potential performance improvements compared to FPDs based on a‐Si:H TFTs. Purpose This work investigates the imaging performance of a new indium gallium zinc oxide (IGZO) TFT‐based detector in 2D fluoroscopy and 3D cone‐beam CT (CBCT). Methods The new FPD consists of a sensor array combining IGZO TFTs with a‐Si:H photodiodes and a 0.7‐mm thick CsI:Tl scintillator. The FPD was implemented on an x‐ray imaging bench with system geometry emulating intraoperative CBCT. A conventional FPD with a‐Si:H TFTs and a 0.6‐mm thick CsI:Tl scintillator was similarly implemented as a basis of comparison. 2D imaging performance was characterized in terms of electronic noise, sensitivity, linearity, lag, spatial resolution (modulation transfer function, MTF), image noise (noise‐power spectrum, NPS), and detective quantum efficiency (DQE) with entrance air kerma (EAK) ranging from 0.3 to 1.2 μGy. 3D imaging performance was evaluated in terms of the 3D MTF and noise‐equivalent quanta (NEQ), soft‐tissue contrast‐to‐noise ratio (CNR), and image quality evident in anthropomorphic phantoms for a range of anatomical sites and dose, with weighted air kerma, Kw${K_w}$, ranging from 0.8 to 4.9 mGy. Results The 2D imaging performance of the IGZO‐based FPD exhibited up to ∼1.7× lower electronic noise than the a‐Si:H FPD at matched pixel pitch. Furthermore, the IGZO FPD exhibited ∼27% increase in mid‐frequency DQE (1 mm−1) at matched pixel size and dose (EAK ≈ 1.0 μGy) and ∼11% increase after adjusting for differences in scintillator thickness. 2D spatial resolution was limited by the scintillator for each FPD. The IGZO‐based FPD demonstrated improved 3D NEQ at all spatial frequencies in both head (≥25% increase for all dose levels) and body (≥10% increase for Kw${K_w}$ ≤2 mGy) imaging scenarios. These characteristics translated to improved low‐contrast visualization in anthropomorphic phantoms, demonstrating ≥10% improvement in CNR and extension of the low‐dose range for which the detector is input‐quantum limited. Conclusion The IGZO‐based FPD demonstrated improvements in electronic noise, image lag, and NEQ that translated to measurable improvements in 2D and 3D imaging performance compared to a conventional FPD based on a‐Si:H TFTs. The improvements are most beneficial for 2D or 3D imaging scenarios involving low‐dose and/or high‐frame rate.

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Section: Discussionmentioning

confidence: 61%

Section: Discussionmentioning

confidence: 95%

Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

et al. 2022

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“…The scintillator and sensor are the core part and determine the main performance of the FPD. Amorphous silicon (a-Si), CMOS, IGZO [10], and flexible FPD are all indirect conversion detectors. In contrast, direct conversion FPDs do not require scintillators.…”

Section: Introductionmentioning

confidence: 99%

A Novel Sub-Pixel-Shift-Based High-Resolution X-ray Flat Panel Detector

Liu

Kim

2022

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In this paper, we describe a novel sub-pixel shift (SPS)-based X-ray flat panel detector (FPD), which can achieve high resolution while maintaining a high SNR (signal-to-noise ratio). In the proposed architecture, an XY precision shift stage is applied to complete the sub-pixel shift process. In addition, image acquisition and high-resolution image composition are integrated in the FPD hardware. According to the relevant standards for detector image quality evaluation, we tested and evaluated some image quality indicators. The results show that the proposed FPD with SPS outperforms the original FPD without SPS technology. More specifically, the measured pixel size of the proposed FPD was reduced from 162 to 140 μm for 2 × 2 sub-pixel shift mode, and 132 μm for 4 × 4 sub-pixel shift mode, that is, the basic spatial detector resolution was improved by 13.6% for the simplest 2 × 2 sub-pixel shift mode, and by 18.5% for 4 × 4 sub-pixel shift mode. With this method, a lower-price FPD is elevated both in resolution and to meet imaging quality requirements.

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“…Examples of such semiconductors are indium gallium zinc oxide (IGZO) and low-temperature, laser-recrystallized polycrystalline silicon (poly-Si)both of which were previously developed for fabrication of monolithic, large area displays. In a demonstration of this strategy, a prototype AMFPI array incorporating IGZO (which has an electron mobility approximately an order of magnitude higher than that of a-Si:H) exhibited reduced electronic additive noise, as low as~700 e. 8 Concerning the alternative strategy of enhancing the signal, two general approaches are being investigated. One approach focuses on the substitution of present AMFPI x-ray converters with alternatives that offer significantly (i.e., order of magnitude) higher imaging signal per x-ray interactionsuch as provided by CsI:Tl coupled with a-Se operated under conditions of avalanche multiplication, or by various forms of polycrystalline HgI 2 .…”

Section: Introductionmentioning

confidence: 99%

“…Examples of such semiconductors are indium gallium zinc oxide (IGZO) and low‐temperature, laser‐recrystallized polycrystalline silicon (poly‐Si) — both of which were previously developed for fabrication of monolithic, large area displays. In a demonstration of this strategy, a prototype AMFPI array incorporating IGZO (which has an electron mobility approximately an order of magnitude higher than that of a‐Si:H) exhibited reduced electronic additive noise, as low as ~700 e 8 …”

Section: Introductionmentioning

confidence: 99%

Empirical noise performance of prototype active pixel arrays employing polycrystalline silicon thin‐film transistors

et al. 2020

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In the spirit of overcoming the signal-to-noise limitations of active matrix, flat-panel imagers (AMFPIs) which employ array circuits based on a-Si:H thin-film transistors (TFTs), an empirical investigation of the noise properties of prototype active pixel arrays based on polycrystalline silicon (poly-Si) TFTs is reported. Like a-Si:H, poly-Si supports fabrication of large area, monolithic x-ray imaging arrays and offers good radiation damage resistance, while providing electron and hole mobility orders of magnitude higher. Compared to pixel circuits typically consisting of a single addressing switch in an AMFPI array, the pixel circuit of an active pixel array includes an amplifier that magnifies the imaging signal prior to readout by external acquisition electronics. Also, while readout erases signal stored in the pixels for AMFPI arrays, active pixel arrays allow multiple nondestructive readout, which can be used to reduce noise. The prototype arrays investigated in this paper were developed to explore the effect of variation in amplifier design on noise. Methods: A pair of prototype arrays incorporating single-stage and two-stage poly-Si pixel amplifiers were examined. The arrays incorporate various amplifier designs in which dimensions of some of the three (or four) poly-Si TFTs per pixel circuit for the single-stage array, and some of the five poly-Si TFTs for the two-stage array, were varied. The arrays were operated using a recently developed electronic data acquisition system that allows variation of operational conditions such as voltages and timing of control signals. The arrays were operated in the absence of radiation in various correlated multiple sampling modes, with and without the injection of charge directly into the pixel circuits for measurements of in-pixel gain and pixel noise. Pixel noise, referred back to the input of the pixel amplifier, was compared to predictions generated by a sophisticated circuit simulation model. Results: Across the various pixel circuit designs, the median in-pixel gain for the single-stage and two-stage arrays was measured to be 99.3 and 925, respectively. These gain levels were sufficient to reduce the contribution of external noise, defined as the electronic additive noise in the absence of noise contributions from circuitry in the pixel and referred back to the input of the pixel amplifier, to less than 340 e. As a result, median pixel noise results as low as~695 e and 866 e, acquired using eight samples, were observed from the best-performing single-stage and two-stage designs, respectively. While the magnitude of pixel noise predicted by simulation was lower than the measured results, there was generally good agreement between simulation and measurement for the functional dependence of noise on operating voltages, timing, and sampling mode. Conclusions: The single-stage and two-stage arrays examined in this study demonstrated pixel noise well below that typically demonstrated by AMFPIs. Through proper design, it should be possible to maintain the noise levels...

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Analysis of a new indium gallium zinc oxide (IGZO) detector

Cited by 13 publications

References 0 publications

Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

Technical assessment of 2D and 3D imaging performance of an IGZO‐based flat‐panel X‐ray detector

A Novel Sub-Pixel-Shift-Based High-Resolution X-ray Flat Panel Detector

Empirical noise performance of prototype active pixel arrays employing polycrystalline silicon thin‐film transistors

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