Photon-Quantum-Noise-Limited Pixel Architecture in Amorphous-Silicon Technology for Large-Area Digital Imaging Applications

An X-ray photon-quantum-noise-limited voltage-controlled oscillator (VCO)-based pixel architecture in amorphous-silicon (a-Si) technology is reported for large-area digital medical imaging applications. In this research, the X-ray generated input charge on the input capacitor is converted into an oscillating frequency signal output at the pixel level. The VCO pixel is fabricated in-house using a-Si technology, and experimental results are presented. Readout circuitry is proposed which can be optimized to reduce the fixed pattern noise and fringing effects in an imaging array containing many such VCO pixels. The phase noise and stability performance of the single-pixel VCO are measured and analyzed. This architecture has the lowest input referred noise among all reported a-Si pixel architectures and is the first photon-quantum-noise-limited pixel architecture in a-Si technology. The pixel´s valid input range is measured to be 120 e^- all the way to 5 ×10⁶ e^-. This shows that the pixel has a very high dynamic range. The proposed architecture is particularly promising for large-area photon-quantum-noise-limited digital imaging applications (e.g., protein crystallography) due to its small input referred electronic noise, high sensitivity, and ease of fabrication in large-area a-Si technology.