A 64 × 64 SPAD Array For Quantum Ghost Imaging with Integrated TDCs and Event-Driven Readout in a 40 nm CMOS Technology

The exploitation of quantum phenomena has become a pioneering frontier allowing imaging in scenarios where direct illumination is challenging or impractical. Quantum Ghost Imaging (QGI), among various techniques, stands out as a robust and promising approach. While in traditional imaging light interacts directly with the scene, QGI makes use of two separate quantum-correlated beams, one illuminating the object and later being detected by a non-spatially resolved sensor, the other one being straight detected by a pixelated sensor. The scene is then reconstructed by comparing the time tags associated to the detected photons. This work focuses on the design of the spatially solved imager, a 64 × 64 pixel Single-Photon Avalanche Diode (SPAD) sensor. It is implemented with a 3D-stack approach employing the STMicroelectronics C40 technology node for the bottom tier containing the processing electronics, a dedicated imaging technology for the top die embedding the SPAD array, and a microlens array for enhancing the collection efficiency. The integrated 12-bit Time-to-Digital Converters (TDCs) resolution is 200 ps and their stability to process-voltage-temperature (PVT) variations is guaranteed by a shared on-chip wide-tuning range Phase-Locked-Loop (PLL). The event-driven jump readout approach maximizes the acquisition duty-cycle allowing the chip to operate at up to 1.2 Mframe/s.