Polycrystalline Mercuric Iodide Films on CMOS Readout Arrays

Area of Science:

• Materials Science
• Medical Imaging
• Semiconductor Devices

Background:

• High-resolution x-ray imaging is crucial for medical diagnostics.
• Existing technologies face limitations in resolution, speed, and radiation dose.
• Advancements in detector materials and readout electronics are needed.

Purpose of the Study:

• To develop novel high-resolution x-ray imaging devices.
• To utilize polycrystalline mercuric iodide (HgI2) films directly grown onto CMOS readout chips.
• To evaluate the performance characteristics of these new HgI2-coated CMOS devices.

Main Methods:

• Polycrystalline mercuric iodide (HgI2) films were grown directly onto CMOS readout chips via a thermal vapor transport process.
• Prototype 400x400 pixel HgI2-coated CMOS devices with 30 μm x 30 μm pixels were fabricated and tested.
• Performance metrics including sensitivity, dark current, and image response to a slit aperture were measured.
• X-ray computed tomography (CT) imaging was performed to assess spatial resolution and dose efficiency.

Main Results:

• The HgI2-coated CMOS devices demonstrated a sensitivity of 6.2 μC/Rcm² and a low dark current of approximately 2.7 nA/cm².
• A planar image response of 80 μm FWHM to a 50 μm slit aperture was achieved.
• X-ray CT images showed a point spread function adequate for 50 μm spatial resolution at reduced radiation doses compared to phosphor-based systems.
• The use of CMOS technology enabled small 30 μm pixels and fast readout speeds (8 fps for a 3200x3200 array).

Conclusions:

• Direct growth of HgI2 films on CMOS readout chips yields high-performance x-ray imaging detectors.
• These devices offer significant potential for improved spatial resolution and dose reduction in medical CT imaging.
• The integration with CMOS technology provides scalability, speed, and design flexibility for future x-ray imaging systems.