The dependence of the modulation transfer function on the blocking layer thickness in amorphous selenium x-ray...

Area of Science:

• Medical Imaging Physics
• Materials Science
• Semiconductor Device Physics

Background:

• Blocking layers are essential for minimizing leakage current in amorphous selenium (a-Se) x-ray detectors.
• Minimizing leakage current is critical for maintaining signal integrity and reducing noise in medical imaging applications.

Purpose of the Study:

• To experimentally investigate the impact of blocking layer thickness on the presampling modulation transfer function (MTF) and dark current.
• To determine the optimal blocking layer thickness for amorphous selenium x-ray detectors.

Main Methods:

• Fabrication and characterization of prototype single-line CCD-based a-Se x-ray detectors with varying blocking layer thicknesses (1-51 microm).
• Measurement of dark current and presampling MTF as a function of blocking layer thickness.
• Comparison of experimental results with an electrostatic model.

Main Results:

• Dark current increased monotonically with decreasing blocking layer thickness.
• Negligible MTF reduction was observed when blocking layer thickness was significantly smaller than the sampling pitch (25 microm).
• Dramatic MTF decrease near the Nyquist frequency occurred when blocking layer thickness approached or exceeded the sampling pitch.

Conclusions:

• Blocking layer thickness critically influences both dark current and MTF in a-Se detectors.
• Thinner blocking layers reduce dark current but can severely compromise spatial resolution.
• Electrostatic modeling supports the observed MTF degradation due to image charge trapping within the blocking layer.