Small‐Dose‐Sensitive X‐Ray Image Pixel with HgI₂ Photoconductor and Amorphous Oxide Thin‐Film Transistor

Abstract

A new X-ray image sensor is demonstrated with an oxide thin-film transistor backplane and HgI2 sensing material. It displays outstanding image quality under a low X-ray exposure and a low electric field. It is promising as a state-of-the-art device to realize highly resolved images at a low X-ray dose for a variety of medical X-ray imaging applications.

Halide perovskites: A dark horse for direct X‐ray imaging

“…95 As for the preparation of thick polycrystalline perovskite, the ultrasonic-assisted mist deposition method is promising for simultaneously achieving the polycrystalline perovskite with a sufficient thickness and with a high crystal quality if the thermal expansion mismatch issue can be well addressed. 102 Besides, the particle-in-binder approach, which has been demonstrated for HgI 2 and PbO based X-ray absorbers, 18,111 might open a new window for the thick polycrystalline perovskite preparation. In addition to the large area and sufficient thickness, a well-developed synthetic protocol should be amenable to various device assembly (with electronics readouts and interfacial interlayers) and manipulation of the key features of perovskites including homogeneity, mobility, carrier lifetime, charge carrier concentration, detect states, and so forth.…”

“…19,22 Moreover, growing high-quality CZT requires a temperature as high as 600 C, which is much higher than the TFT based electronic readout can tolerate (260 C), causing difficulties in device fabrication. 18,23,24 Recently, halide perovskites are emerging as a dark horse with promising photoconductive properties for direct X-ray imaging, including high efficiency for X-ray attenuation and charge transport on top of their solvent processibility. 23,[25][26][27] To date, both single-crystalline and polycrystalline perovskites, engineered by various strategies (eg, tuning chemical composition, reducing material dimension, controlling crystal orientation, etc.…”

“…To this end, alternative materials with high X‐ray absorption capacity, such as mercuric iodide (HgI 2 ), 14 lead iodide (PbI 2 ), 15 lead oxide (PbO), 16 and cadmium zinc telluride (CZT), 17 have been extensively investigated. Although these materials, especially HgI 2 and CZT, show potential for large‐area hard X‐ray imaging, 18,19 challenges still remain in either the crystal growth or device fabrication and operation 20,21 . For example, the growth of large‐area, uniform and high‐quality CZT is still an unsolved issue 19,22 .…”

Direct Thermal Growth of Large Scale Cl-doped CdTe Film for Low Voltage High Resolution X-ray Image Sensor

“…Those visible photons are recieved by an array of amorphous silicon photodiodes located below the scintillator resulting in electron-hole carriers, so that a back panel device (TFT or CMOS) transports the signal charge carriers to external readout integrated circuit (IC). In contrast, the direct type uses photoconductor materials to directly convert X-ray photons to electrical signals 5 – 11 , 13 – 15 , 17 , 19 . Although indirect conversion possibly utilizes the detection capability of high performance photodiode, it shows inherent drawbacks such as complexity of p-i-n photodiode fabrication and spatial resolution limit due to light spreading of scintillator 26 .…”

“…However, any large area APS for direct type detection has rarely been reported yet, because several of difficult issues remain to be resolved: selecting a proper photoconductor material, lowering process costs, forming the photoconductor/CMOS interface without damage, and lowering detector operation voltage. First, in terms of photoconductor materials selection, commercial a-Se, cadmium telluride (CdTe), lead iodide (PbI 2 ), and lead oxide (PbO), and mercury iodide (HgI 2 ) have been mentioned as shown in Supplementary Table S1 9 , 11 , 13 . Commercial a-Se should be as thick as a few hundred μm for somewhat guaranteed stability, requiring at least a few hundred volts for detector operation.…”