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

Many improvements have been made to amorphous silicon (a-Si) flat panel detectors (FPDs) to meet the market needs for different x-ray imaging applications. With the current generation of a-Si FPDs the performance is limited by the a-Si thin film transistors (TFTs). The low electron mobility of a-Si necessitates large TFT’s with large parasitic dataline capacitance, which increases electronic noise and reduces the pixel fill factor (FF). In other words, large TFT’s negatively impact Signal-to-Noise Ratio (SNR). CMOS FPDs were introduced to provide improved low dose imaging performance and faster readout times, but the increase in cost can be prohibitive. IGZO TFTs have an electron mobility that is <10x higher than a-Si, which facilitates a reduction in the size of the TFT while also reducing the pixel discharge time, resulting in an increase to both the detector readout rate and the SNR. Reducing the TFT size is particularly important in achieving adequate low dose performance in dynamic detectors with pixels approaching 100μm. A 31cm x 31cm (100μm) FPD using IGZO TFTs was evaluated at 25 frames/second (fps) in 1x1, 2x2, 3x3, and 4x4 binning. In the 1x1 standard noise configuration, the noise equivalent dose (NED) was 24nGy with a max linear dose (MLD) of 10uGy. The NED was reduced to 6.6nGy in the 2x2, 3.4nGy in the 3x3, and 2.4nGy in the 4x4 mode. The linearity of the IGZO imager was comparable to a-Si imager. The 1x1 MTF was 57.5% at 1 lp/mm and 28.5% at 2lp/mm. The quantum limited DQE in the 1x1 binning mode was 79% at 0 lp/mm and 47% at 1 lp/mm. The 1x1 DQE measured at NED was 71% at 0 lp/mm, 29% at 1 lp/mm. This paper will explore how to optimally employ IGZO and present data from a first IGZO imager, showing that IGZO is an excellent technology for the future of FPDs.