Fabrication of Reflectance Pulse Oximeter with Ring-Shaped Photodiode

This paper reports fabrication and evaluation of reflectance type pulse oximeter with ring-shaped photodiode. The pulse oximeter can measure a blood oxygen saturation (SpO₂). SpO₂ is used as an index of respiratory diseases. Therefore measurements of SpO₂ prevent apnea syndrome and asthma. We have developed a system for measuring SpO₂ in daily life. A small and stably measurable sensor is required for the system. Because of realization of the sensor, LEDs are located in the center of a ring-shaped photodiode. This structure collects lights from all directions for reducing noises of body motion. In a previous study, a pulse wave sensor using the ring-shaped photodiode was fabricated, and could measure the pulse wave. In this paper, the improved sensor to measure SpO₂ is shown. Photodiodes is evaluated on current-voltage characteristics.