LIG-OSS: Integrated Laser-Induced-Graphene Sensor and Open-Source Silicon Chip for an Affordable Multifunctional Wearable Sensing System

This paper presents a Multifunctional wearable sensing system that integrates flexible Laser-Induced-Graphene (LIG) based sensors and an Open-Source Analog Front-End (AFE) chip. The LIG sensors are fabricated on polyimide (PI) Flexible Printed Circuit Board (FPCB) through CO2 infrared laser direct-write method. The LIG sensors provide repeatable high-precision temperature sensing, humidity measurement, and strain detection capabilities. The temperature sensing charac- terization shows the resistive LIG sensor has a sensitivity of -0.0493 %/°C, the linear fit R-square factors ≥ 0.9973 across -40 °C to 125 °C. The capacitive humidity sensor achieves a 23.6 times capacitance at 95% relative humidity (RH) compared to the value observed in a dry environment. Our proposed AFE chip contains a hybrid folded-cascode Operational Amplifier (OPAMP) and a Successive Approximation Register Analog- to-Digital Converter (SAR ADC). Designed using open-source analog flow and fabricated in GF180 OpenPDK, the AFE chip serves as a flexible and universal readout platform, adaptable for various sensing applications. A real-time demonstration of finger bending detection is performed to validate the functionality. The multifunctional sensing capability provide by the wearable system is attractive for personal healthcare application. This work underscores the integration of the LIG sensors and the AFE chip, developed using open-source tools which facilitate rapid and affordable prototyping for a multifunctional flexible wearable sensing system.