The Fabrication and Characterization of Direct Conversion Flat Panel X-ray Imager with TlBr Film

Authors

Moh Hamdan, Kenji Shimazoe, Hiroyuki Takahashi, Mitsuhiro Nogami, Keitaro Hitomi, Shinya Asakura, Takanori Tsunashima, Takashi Nakamura

Abstract

The novel direct conversion flat panel detectors (FPDs) utilizing thallium bromide (TlBr) films are developed and characterized in this study. Thin TlBr films, deposited using an evaporation technique, achieved thicknesses of 10 μm and 50 μm. A pixel sensor array, with a pixel size of 235 × 235 μm² and a sensitive area of 29.61 × 39.48 mm², was developed using low-temperature polysilicon thin-film transistor (LTPS TFT) technology as the initial study to explore performance characteristics of developed imaging system. The TlBr film was characterized based on the current-voltage (I-V) profile, showing a resistivity of 2.78 × 10¹⁰ Ω·cm. The LTPS TFT showed a leakage current of about 10^-13 A, while the noise of TlBr FPD system was around 10⁴ e^- rms, primarily limited by the readout system. The detector system was characterized using radiation from an X-ray tube with a voltage in the range of 30 kV - 100 kV and a current of 2 mA, involving an X-ray test chart as the object with the processing time of 18.15 - 18.30 ms per frame. Based on the contrast and contrast-to-noise ratio (CNR) values, the 10 μm and 50 μm TlBr FPD clearly captured the image in operation between 30 kV and 100 kV. The 50 μm TlBr FPD demonstrated improved sensitivity, showing pixel values with 10 times higher intensity and enhanced line pair detail at 30 kV X-ray operation. The 10 μm TlBr achieved spatial resolution of 267 μm full width at half maximum (FWHM), while the 50 μm TlBr achieved 250 μm FWHM. In the X-ray imaging demonstration, the shape and structure of anchovy was clearly distinguished. The TlBr film FPD presents promising potential for a room temperature X-ray imager.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment: https://doi.org/10.1016/j.nima.2024.169372