A single chip PPG sensor with enhanced IR sensitivity for low power and small size

Abstract

A single chip Photoplethysmography(PPG) sensor was developed for continuous measurements of heart rate from a mobile device. In order to utilize it in various mobile applications, it was necessary to achieve low power and small size of PPG sensors. For low power and small chip size of the PPG sensor, a photodiode(PD) for sensing signals and an analog front end(AFE) for signal amplification and ADC should be implemented in a single chip. The single chip PPG sensor which is implemented on a standard CMOS process with low operating voltage could be more suitable for mobile devices. In order to operate at a low voltage, reduction of Si thickness is required, and for this, high quantum efficiency(QE) of 43% at 940nm were obtained at 3um thickness by back side trench(BST) pattern and ARL optimization. In addition, to improve the performance of the PPG sensor, the leakage current of <0.1nA and capacitance of <200pF were measured by 20um pixel array. As a result, the low-power, small size single-chip PPG sensor showed similar performance to conventional high-voltage and large PPG sensor.