Research ArticleMATERIALS SCIENCE

Passive radiofrequency x-ray dosimeter tag based on flexible radiation-sensitive oxide field-effect transistor

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Science Advances  29 Jun 2018:
Vol. 4, no. 6, eaat1825
DOI: 10.1126/sciadv.aat1825
  • Fig. 1 Oxide thin-film transistors as direct detectors for x-ray radiation.

    (A) Scheme showing the transistor structure and the generation of trapped positive charge in the dielectric as a consequence of x-ray absorption. Negative carriers accumulating in the channel counterbalance the trapped positive charge. (B) Photograph showing a flexible matrix of IGZO-based transistors fabricated on a PEN foil. The inset shows a micrograph of a single transistor pixel. (C) Variation in oxide transistor drain current as a function of time, before, during (yellow background, 35-keV Mo tube, 300-mGy total dose), and after a 10-s x-ray exposure at varying gate voltages. (D) Transistor transfer curves acquired before and after exposure to 300-mGy radiation dose. Semic, semiconductor.

  • Fig. 2 Dynamics of ionization charge formation and recombination.

    (A) Threshold voltage shift of oxide transistor due to 1-s x-ray exposures of varying dose; inset shows the threshold voltage shift scales linearly with total exposure dose. (B) Threshold voltage as a function of time after x-ray exposure: Recombination processes lead to the annealing of trapped charges in the dielectric on a slow time scale. (C) Normalized threshold voltage shift for different exposure doses: The threshold recovers its initial value following a universal stretched exponential.

  • Fig. 3 Dependence of oxide-TFT detector on dielectric thickness.

    (A) Scaling of capacitance with dielectric thickness. The inset shows the multilayer structure of the dielectric. (B) Threshold voltage shift as a function of total dose for oxide transistors with different dielectric layers. (C) X-ray sensitivity, defined as the threshold voltage shift per dose, as a function of dielectric thickness. The line represents a quadratic fit according to the model described in the text.

  • Fig. 4 Programmable passive RFID radiation sensor based on ROXFET.

    (A) Electrical circuit diagram showing how the radiation-sensitive oxide TFT is connected to the commercial passive RFID sensor and how the programming voltage VC is applied. (B) Picture of flexible RFID x-ray sensor tag. (C) TFT channel impedance Z as a function of VC. The RFID switches its status in a narrow interval close to the turn-on voltage of the transistor. (D) Channel impedance Z as a function of time for different RFID programming voltages VC. At time = 0, the sensor was exposed to x-ray (30 mGy/s) for the indicated amount of time, leading to an order-of-magnitude decrease in Z and switching the RFID status. The inset shows the obtained threshold dose necessary to switch RFID status as a function of VC.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/4/6/eaat1825/DC1

    Supplementary Information

    fig. S1. Fast transistor operation and switching: Gate capacitance CG as a function of gate voltage VGS for different frequencies.

    fig. S2. Fast transfer characteristic acquisition.

    fig. S3. Calculated attenuation length spectra for silicon oxide, tantalum oxide, and the multilayer dielectric based on National Institute of Standards and Technology database.

    fig. S4. Accelerated recovery of ROXFET due to application of positive gate voltage.

    table S1. Properties of a set of IGZO transistors with W = 320 μm and L = 20 μm and varying multilayer dielectric thickness.

  • Supplementary Materials

    This PDF file includes:

    • Supplementary Information
    • fig. S1. Fast transistor operation and switching: Gate capacitance CG as a function of gate voltage VGS for different frequencies.
    • fig. S2. Fast transfer characteristic acquisition.
    • fig. S3. Calculated attenuation length spectra for silicon oxide, tantalum oxide, and the multilayer dielectric based on National Institute of Standards and Technology database.
    • fig. S4. Accelerated recovery of ROXFET due to application of positive gate voltage.
    • table S1. Properties of a set of IGZO transistors with W = 320 μm and L = 20 μm and varying multilayer dielectric thickness.

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