CMOS Direct Time Interval Measurement of Long-Lived Luminescence Lifetimes

We describe a Complementary Metal-Oxide Semiconductor (CMOS) Direct Time Interval Measurement (DTIM) Integrated Circuit (IC) to detect the decay (fall) time of the luminescence emission when analyte-sensitive luminophores are excited with an optical pulse. The CMOS DTIM IC includes 14x14 phototransistor array, transimpedance amplifier, regulated gain amplifier, fall time detector, and time-to-digital convertor. We examined the DTIM system to measure the emission lifetime of oxygen-sensitive luminophores tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) ([Ru(dpp)(3)](2+)) encapsulated in sol-gel derived xerogel thin-films. The DTIM system fabricated using TSMC 0.35 mu m process functions to detect lifetimes from 4 mu s to 14.4 mu s but can be tuned to detect longer lifetimes. The system provides 8-bit digital output proportional to lifetimes and consumes 4.5mW of power with 3.3V DC supply. The CMOS system provides a useful platform for the development of reliable, robust, and miniaturized optical chemical sensors.