X-ray imaging with scintillator-sensitized hybrid organic photodetectors

Journal name:
Nature Photonics
Volume:
9,
Pages:
843–848
Year published:
DOI:
doi:10.1038/nphoton.2015.216
Received
Accepted
Published online
Corrected online

Abstract

Medical X-ray imaging requires cost-effective and high-resolution flat-panel detectors for the energy range between 20 and 120 keV. Solution-processed photodetectors provide the opportunity to fabricate detectors with a large active area at low cost. Here, we present a disruptive approach that improves the resolution of such detectors by incorporating terbium-doped gadolinium oxysulfide scintillator particles into an organic photodetector matrix. The X-ray induced light emission from the scintillators is absorbed within hundreds of nanometres, which is negligible compared with the pixel size. Hence, optical crosstalk, a limiting factor in the resolution of scintillator-based X-ray detectors, is minimized. The concept is validated with a 256 × 256 pixel detector with a resolution of 4.75 lp mm−1 at a MTF = 0.2, significantly better than previous stacked scintillator-based flat-panel detectors. We achieved a resolution that proves the feasibility of solution-based detectors in medical applications. Time-resolved electrical characterization showed enhanced charge carrier mobility with increased scintillator filling, which is explained by morphological changes.

At a glance

Figures

  1. Hybrid organic X-ray image sensor.
    Figure 1: Hybrid organic X-ray image sensor.

    a, Schematic of the image sensor with an a-Si:H backplane and a hybrid frontplane. b, Photograph of a fully processed imager and micrograph of an individual pixel with one TFT (98µm pitch). c, 70kV X-ray image (magnified to region of interest) of a resolution test target. d, MTF of HPD-imagers with different layer thickness (d) and two conventional indirect X-ray converters. The theoretical limit is determined by the pixel size. e, 70kV X-ray images of integrated circuit devices (photograph on the right) realized with an HPD image sensor (left) and a conventional stacked device (centre).

  2. Influence of scintillator fraction on layer morphology.
    Figure 2: Influence of scintillator fraction on layer morphology.

    ac, SEM cross-sections (FIB cuts with 52° tilt angle), red boxes and insets highlight voids inside the devices. df, 3D surface profilometry of samples. Scanning resolution is 1µm in both axis.

  3. Optoelectronical properties of HPDs.
    Figure 3: Optoelectronical properties of HPDs.

    a, Dark current–voltage characteristics with different GOS:Tb volume fractions and an active area of 1cm². b, X-ray sensitivity irradiated with a spectrum of 70kV bremsstrahlung and dose rate of 1mGyair s−1 at different external bias. c, Pulse response of the 57vol%-HPD biased from 0 to −10V (0 to −1V µm−1); dose rate: 1.5mGyair s−1, 100ms pulse duration. d, Corresponding rise (black) and fall (red) time dependent on the applied bias.

  4. Mobility and morphology characteristics.
    Figure 4: Mobility and morphology characteristics.

    a, X-CELIV properties with different GOS:Tb volume fraction. The inset represents a typical X-CELIV peak. The error bars are based on the uncertainties in the average layer thickness davg and reading the time of the current maximum tmax. b, GIWAXS Debye–Scherrer rings and out-of-plane line profiles, incident angle ai= 0.24°, = 15° while the x-axis represents qxy, the 57% (1:1:16) HPD as deposited and annealed. Intensity has been normalized, while the x-axis represents the absolute value of the scattering vector q.

Change history

Corrected online 13 November 2015
In the version of this Article originally published online, the following affiliation for the author Oier Bikondoa had not been included: Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK. This has now been added and the subsequent affiliation renumbered in all versions of the Article.

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Author information

Affiliations

  1. Siemens Healthcare GmbH, Technology Center, 91058 Erlangen, Germany

    • Patric Büchele,
    • Sandro F. Tedde,
    • Rene Fischer,
    • Markus Biele,
    • Wilhelm Metzger &
    • Oliver Schmidt
  2. Light Technology Institute and Institute of Microstructure Technology, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany

    • Patric Büchele &
    • Uli Lemmer
  3. Institute of Materials for Electronics and Energy Technology (i-MEET), Friedrich-Alexander-University Erlangen-Nuremberg, Martensstrasse 7, 91058 Erlangen, Germany

    • Moses Richter,
    • Gebhard J. Matt,
    • Rene Fischer,
    • Markus Biele &
    • Christoph J. Brabec
  4. INM – Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbruecken, Germany

    • Genesis N. Ankah &
    • Tobias Kraus
  5. Masdar Institute of Science and Technology, Abu Dhabi 54224, UAE

    • Samuele Lilliu
  6. XMaS, The UK-CRG Beamline, ESRF-The European Synchrotron, CS40220, Grenoble Cedex 9, 38043, France

    • Oier Bikondoa
  7. Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK

    • Oier Bikondoa
  8. School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff CF24 3AA, UK

    • J. Emyr Macdonald

Contributions

P.B. carried out device fabrication and characterization, and analysis of the results. M.R. executed X-CELIV experiments. G.N.A. executed FIB-cutting and SEM experiments. S.F.T. executed X-ray imaging and XRD measurements, as well as X-ray device analysis. R.F. executed X-ray imaging and arranged X-ray setup. M.B. executed and helped with analysis of pulse measurements. W.M. executed GOS:Tb characterization. G.J.M. conducted and helped with the X-CELIV measurement. S.L. directed, executed and analysed XRD experiments. O.B. set up the synchrotron beamline. J.E.M. submitted the proposal for XRD experiments and helped with the XRD analysis. C.J.B. directed and helped with X-CELIV analysis. T.K. directed and helped with FIB/SEM analysis. U.L. helped with optoelectronical characterization and analysis of X-ray response measurements. O.S. directed device fabrication, and helped with device analysis.

Competing financial interests

The authors declare no competing financial interests.

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