Haixing Meng is a doctoral candidate at the School of Integrated Circuits and Electronics, Beijing Institute of Technology. His research interests focus encompass both indirect and direct X-ray detector.
Ying Li received her Ph.D. degree in condensed matter physics at Zhengzhou University. Then, she worked at the Institute of Semiconductors, Chinese Academy of Sciences as a postdoctoral fellow, under the supervision of Professor Guozhen Shen. She is currently an associate professor of School of Integrated Circuits and Electronics, Beijing Institute of Technology. Her research interests relate to the perovskite-based optoelectronic devices for vision sensing.
Guozhen Shen received his Ph.D. degree (2003) in Chemistry from University of Science and technology of China. He is currently a professor of School of Integrated Circuits and Electronics, Beijing Institute of Technology. His research focused on flexible electronics and printable electronics, including transistors, photodetectors, sensors and flexible energy storage and conversion devices.Flexible X-ray detectors have garnered considerable attention owing to their extensive applications in three-dimensional (3D) image reconstruction, disease diagnosis and non-destructive testing[1−3]. Conventional X-ray detectors typically employ active-matrix backplanes fabricated on rigid glass substrates, which integrate switching transistors and photodetectors[4, 5]. When imaging non-planar objects, traditional planar X-ray detectors are susceptible to image distortion, non-uniformity, data loss, and require extensive post-processing. Consequently, it is critical to develop mechanically flexible X-ray detectors. For traditional semiconductor materials, such as silicon (Si), high-purity germanium (HP-Ge), amorphous selenium (α-Se), and zinc cadmium telluride (CdZnTe), they always impose limitations on the mechanical flexibility of X-ray detectors due to their inherent rigidity[6−9]. To address these challenges, considerable research efforts have been devoted to exploring alternative solutions. Notably, two-dimensional (2D) semiconductors like molybdenum disulfide (MoS2) exhibit superior carrier mobility, enhanced light−matter interactions, and remarkable mechanical flexibility. Most importantly, the van der Waals (vdW) characteristics of 2D materials facilitate heterogeneous device integration, enabling the development of high-performance flexible X-ray detectors[10−15].
In accordance with this line of research, Ahn and Chai et al. reported a flexible active-matrix X-ray detector with a backplane based on 2D MoS2 thin-film transistors (TFTs) and graphene/MoS2 photodetectors, which indicates that these X-ray detectors not only exhibit flexibility but also possess superior electrical and optical properties. This design effectively mitigates geometric mismatch between the object and the image sensor array, thereby preventing image distortion and non-uniformity (Nat. Electronics (2025), https://doi.org/10.1038/s41928-024-01317-7)[16]. A flexible X-ray detector was developed by integrating a large-area active-matrix backplane based on 2D materials with a scintillator film (Fig. 1(a)). The backplane comprises mechanically flexible MoS2 switching transistors and graphene/MoS2 photodetectors, which collect the current generated by the light emitted from the scintillator. To convert X-ray radiation into visible light, a flexible Gd2O2S scintillator film is integrated atop the flexible backplane circuit. Double-layer MoS2 is employed as the channel material for both the TFTs and photodetectors to ensure optimal electrical and optical performance of the detector. The photodetector array is constructed using photoresistors composed of MoS2 channels and optically transparent graphene interdigital electrodes. This design facilitates efficient photon absorption over large areas, ensuring high-contrast images even under low-intensity X-ray conditions. Finally, the flexible X-ray detector is interfaced with an external drive circuit and a current readout circuit for signal acquisition.
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The electrical characteristics of the MoS2 TFTs fabricated on a flexible polyimide substrate exhibit an average mobility of 17.31 cm2∙V−1∙s−1 and a high average Ion/Ioff ratio of approximately 10⁸, thereby fulfilling the stringent electrical requirements for high-performance X-ray detectors. As shown in Fig. 1(b), by incorporating graphene interfinger electrodes with MoS2, the photodetector demonstrates photocurrent enhancements of 150 and 470 times under illumination intensities of 8.5 and 24 μW/cm2, respectively, relative to the dark current. These illumination intensities are comparable to those emitted by scintillators. Visible light mapping images captured using a large-area, high-resolution backplane based on 2D materials exhibit minimal crosstalk, thereby preserving the detailed features of the target image. Subsequently, the flexible backplane composed of 2D materials was laminated with a Gd2O2S scintillator and characterized through X-ray imaging (Figs. 1(b) and 1(c)). The resulting flexible X-ray detector exhibits a sensitivity of 3.49 × 105 μC∙Gy−1∙cm−2 (Fig. 1(d)) and a low detection limit of 63.7 nGy∙s−1 (SNR = 2.5) at dose rates of 100 μGy∙s−1 and 10 keV X-ray spectra. This detection limit is approximately 3600 times lower than the dose required for a standard chest X-ray examination[17]. The high sensitivity and low detection limit ensure clear imaging even at low X-ray doses. Furthermore, the fabricated flexible X-ray detector demonstrates excellent radiation stability under an exposure of 72 mGy and good uniformity (Figs. 1(e) and 1(f)). Notably, for non-planar objects, traditional flat panel detectors produce skewed and distorted images. In contrast, the curvature of the 2D material-based flexible X-ray detector can be adjusted to conform closely to non-planar surfaces, effectively eliminating distortion in X-ray projection imaging and achieving high-quality surface imaging of non-planar objects (Fig. 1(g)). Finally, the acquired data undergo post-processing using a software-aided protocol based on generative adversarial network (GAN)-based software-aided protocol to enhance image quality and resolution[18].
The research highlights of this work include the pioneering design and fabrication of a flexible active-matrix X-ray detector utilizing 2D MoS2 transistors and a graphene/MoS2 photodetector backplane structure. This innovation achieves flexibility while maintaining excellent electrical and optical properties. The flexible backplane successfully covers an area of 3 × 3 cm2 with 3600 pixels. Under low-dose (57 μGy) X-ray irradiation, the detector exhibits a photoelectric responsiveness of 9.37 A∙W−1 and electron mobility of 17.31 cm2∙V−1∙s−1 at the emitted light of 544 nm from a scintillator, demonstrating high sensitivity and superior imaging performance. Importantly, the flexible X-ray detector can conform to the curvature of non-planar objects. Through GAN post-processing technology, inherent device noise is effectively suppressed, enabling high-quality images of non-planar objects even under low X-ray dose conditions. These findings address the issues of image distortion and non-uniformity in traditional rigid X-ray detectors when imaging non-planar objects, providing more accurate and reliable imaging. Notably, high-quality images can be obtained at lower X-ray doses, which is crucial for minimizing radiation risk in medical diagnostics. This research has broad application prospects, not only enhancing the performance of flexible X-ray detectors but also opening new avenues for the development of intelligent imaging equipment, with significant scientific value and wide-ranging applications.
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