A Method for Fabricating High Spatial Resolution Scintillator Arrays

Abstract

Scintillators like thallium doped cesium iodide (CsI:Tl) can be fabricated in microcolumnar form using physical vapor deposition (PVD). The microcolumns channel the scintillation light to the photodetector which results in an improved spatial resolution. This has lead to widespread use of microcolumnar CsI:Tl in digital X-ray radiography. We present here a PVD-based method to aggregate microcolumns into structures called macrocolumns to form scintillator arrays suitable for use in nuclear imaging. In this novel approach, patterned substrates with shallow grooves 20 μm wide, 50 μm deep, with pitch ranging 100 - 500 μm were fabricated and adopted. CsI:Tl scintillator was vapor deposited onto these substrates. The optimal deposition parameters resulted in microcolumnar CsI:Tl, which displayed a macrocolumnar structure dictated by the underlying pattern of the substrate. Scanning electron micrographs (SEM) show that the microcolumns within the macrocolumns are highly oriented and perpendicular to the surface of the substrates. Energy resolution approaching that of a single crystal CsI:Tl was achieved. Since the microcolumns are densely packed with minimal gap, they behave as a macrocolumn or a single pixel. Our technique for fabricating scintillator arrays is a cost-effective alternative to mechanical pixelation of scintillators. This technique results in a high fill factor scintillation detector with minimized inter-macrocolumn gap, and high-yield detector arrays without issues related to material loss in mechanical pixelation. Coupling these structured scintillators to silicon photomultipliers (SiPMs) and applying Anger logic, we resolved scintillator pixels that were almost 1/10th the size of the SiPM macro-pixels. Combining this structured CsI:Tl scintillator with SiPMs results in a compact detector that is ideal for X-ray, gamma-ray, and charged particle detection, such as beta and gamma imaging probes and hand held cameras.