Organic-Inorganic Hybrid Approach to Pulse Oximetry Sensors with Reliability and Low Power Consumption

The pulse oximeter (PO) is an essential healthcare sensor that monitors the heart rate and blood oxygen level. With the emergence of wearable form factors, its use is rapidly expanding from applications in clinical environments to fitness, daily activities, and point-of-care applications. However, the relatively high power consumption of commercial POs has been an obstacle to applying them to wearables, which generally have a limited on-board power source. In this work, we propose a hybrid reflection-type (R-type) PO that adopts inorganic light-emitting diodes (LEDs) and a wrap-around organic photodiode (OPD), which are conveniently integrated via lamination. The overall structure is carefully optimized to minimize direct coupling of light from the LEDs to OPDs and to maximize the meaningful signal through an optical simulation. In particular, we provide a method for optical simulation resolving the deepest layer visited by a photon that returns back to a specific point on the skin so that one can better estimate the relative portion of photons that penetrate deeply enough to contribute to the signal in R-type configuration. The resultant hybrid POs, in which red and near-infrared LEDs are alternately turned on, are shown to be operable with the average LED driving power as low as ca. 35 mu W (at 25% duty), demonstrating their immense potential for wearable POs with practical viability.