On-chip flexible sensors for human stress monitoring

Abstract

In this thesis, we present a flexible multimodal stress sensor chip where a skin temperature sensor, a skin conductance sensor, and a pulse wave sensor are integrated to improve wearing comfort by minimization skin contact area for human stress monitoring in daily times. The previous stress measurement methods based on physiological data analysis from multiple sensors arouse wearing irritation due to rigid sensors and large contact area between sensors and a skin. We integrate a skin temperature sensor, a skin conductance sensor, and a pulse wave sensor in multi-layered structure on the flexible substrate, thus improving wearing comfort of the stress monitoring device. We designed and fabricated three layered multimodal stress sensor chip using flexible materials. The skin temperature sensor and the skin conductance sensor are located on the top layer to contact with skin. Under the top skin contact layer, insulation layer is located and the pulse wave sensor is in the bottom layer of the device. The pulse wave sensor consists of a piezoelectric membrane and its supporting layer with square window. We used parylene-C as the insulation layer, P(VDF-TrFE) as a piezoelectric membrane, and polyimide as a supporting layer with square window. We measured the performance of each sensor integrated on the flexible multimodal stress sensor chip. The skin temperature sensor has nonlinearity and sensitivity of 0.021% and 0.31Ω/℃, respectively, in the range of human skin temperature change, 30~40℃. The skin conductance sensor shows its nonlinearity and sensitivity as 0.447% and 0.28μV/0.02μS, respectively, in the range of human skin conductance change. The resolution of the sensor was less than 0.02μS which is enough to measure human skin conductance fluctuations. The pulse wave sensor indicates 0.067±0.010s of response time for the artificial cardiac pulse wave which has 800mmHg/s of mean ratio of pressure change by time. The overall flexible multimodal stress sensor ch...