Characterization of a CMOS SPAD sensor designed for fluorescence lifetime spectroscopy

The characterization of a 10×10-SPAD detector module fabricated in a 0.35μm High Voltage CMOS technology is presented. The detector is designed to find application in Fluorescence Lifetime spectroscopy and is capable of performing lifetime measurement by using the time-gated technique. The characterization explores the dark count distribution, the detector dynamic range and the gating performances. More than 70% of single SPADs have a dark count rate lower than 1 kHz at the excess bias voltage of 1.8V and do not exceed 2 kHz at the bias voltage of 4.8V. Exploiting the intrinsic features of the detector a direct measurement of the optical cross talk between neighboring SPAD in the matrix was performed. The cross talk was found to be in the range from 2% to 3% for lateral neighbors and between 0.3% and 0.5% for diagonal neighbors. A dynamic range exceeding 120 dB was observed with a maximum count rate before saturation of 500 MHz. Time gating resolution was found to be less than 1 ns. A fluorescent lifetime measurement of ZnS-ZnSe quantum-dot reference slides was performed and the non-uniformity of the calculated lifetime value was lower than 1% across the matrix. The application of the detector in the construction of a lifetime acquisition system is analyzed estimating the detector data throughput. External resources needed to build the acquisition system are estimated and the FPGA-based acquisition system used during characterizations is described.