An Integrated Microelectromechanical Conductivity--Temperature--Depth Sensor With Small Size, High Resolution, and High Accuracy

Abstract

Salinity, temperature and depth (CTD) are fundamental environmental parameters in oceanography, which play a critical role in marine scientific research, ecological conservation, and resource exploration. CTD sensors fabricated using micro-electro-mechanical system (MEMS) technology offer significant advantages, including small size, low power consumption, cost-effectiveness, and high performance, making them a prominent research focus over the past decade. In this study, we developed a miniaturized integrated CTD MEMS sensor chip by combining three sensing elements: a piezoresistive pressure sensor, a four-electrode conductivity sensor, and a platinum resistance temperature sensor, utilizing a standardized MEMS fabrication process. The chip has a size of $2\times 2\times 0.9$ mm³. Our best chip shows conductivity (for salinity) resolution of $\sim ~0.0005$ mS/cm, temperature resolution of $\sim ~0.0027~^{\circ }$ C and pressure resolution (for depth) of $\sim $ 0.67 kPa (6.7 cm water depth). An AI (artificial intelligent) algorithm is also employed to enhance the performance of the CTD sensor. After optimization, the accuracies of the sensors decreased from 0.02°C to 0.004°C (temperature sensor), from 0.02 MPa to 0.002 MPa (pressure sensor), from 0.08 mS/cm to 0.02 mS/cm (conductivity sensor), respectively. Chips with moderate or lower performance (due to the natural distribution induced by process deviation) thus got enhance with comparable performance with the best chips. The current report indicates that the MEMS CTD sensor, embedded with the AI algorithm, might be a viable route towards future marine applications.[2026-0026]