Development of solid-state avalanche amorphous selenium for medical imaging

Area of Science:

• Materials Science
• Semiconductor Physics
• Medical Imaging Technology

Background:

• Active matrix flat panel imagers (AMFPI) suffer from limited low-dose performance due to electronic noise from thin film transistor (TFT) arrays.
• High gain avalanche rushing photoconductor (HARP) technology offers signal amplification before readout, mitigating TFT noise.
• Previous HARP structures were designed for vacuum tubes, necessitating adaptation for direct deposition onto TFT arrays.

Purpose of the Study:

• To report preliminary avalanche gain measurements from the first HARP structure developed for direct deposition onto a TFT array.
• To assess the feasibility of integrating HARP technology into AMFPI for improved low-dose imaging.
• To evaluate the performance and uniformity of the novel HARP structure.

Main Methods:

• Fabrication of a p-i-n HARP structure using amorphous selenium (a-Se) on a glass substrate, scalable for large area detectors.
• Measurement of integrated charge via pulsed optical excitation under continuous high voltage bias.
• Evaluation of spatial uniformity by simultaneous sample fabrication and testing across the evaporator.

Main Results:

• Achieved avalanche gain of up to 80, consistent with field dependence observed in previous n-i-p HARP structures.
• Demonstrated spatial uniformity of performance through large area deposition methods.
• Confirmed high reproducibility of results throughout the study.

Conclusions:

• The novel HARP structure shows promising avalanche gain, crucial for practical AMFPI development.
• Direct deposition of HARP onto TFT arrays is a significant step towards quantum noise-limited performance.
• This technology enables AMFPI to achieve single x-ray photon per pixel sensitivity.