Design And Implementation Of Seawater Conductivity Meter With Silicon-Based Tetra-Platinum Thin Film Electrode

Seawater salinity is an important parameter for circulation observation,hydrological monitoring,water quality assessment,leapfrogging and other activities.The accurate acquisition of seawater salinity values is important for scientific exploration,resource exploration and military defense.The measurement of seawater conductivity is the key to obtain salinity value.The seawater conductivity meter is divided into fiber optic type,inductive type and electrode type.Electrode type conductivity meter has unique advantages such as high accuracy and small size due to direct contact with seawater and no encapsulated medium.With the development of semiconductor technology,the silicon-based electrode type conductivity meter has become a hot spot for research and application,and continues to develop in the direction of miniaturization and low cost.This project relies on the core key technology project of "Micro-miniaturized temperature,conductivity and depth sensing instrument for unmanned underwater vehicles" at Tan Kah Kee Innovation Laboratory,and has carried out research related to silicon-based four-electrode seawater conductivity meter.Firstly,this project adopts the structural design scheme of symmetrical placement of parallel four-platinum thin-film electrodes,combined with the results of finite element simulation analysis to optimize the design of electrode structure parameters.Secondly,this topic uses silicon nitride deposited thin film to reduce the surface stress of the silicon substrate.The bulk consistent preparation of sensitive units is completed by physical vapor deposition to prepare high-purity platinum metal and annealing to eliminate lattice defects and other semiconductor processes.Meanwhile,a platinum thin-film resistive temperature sensor is spatially co-located on the silicon substrate for in-situ temperature compensation.Finally,a direct reading silicon based four-electrode conductivity measurement prototype was developed after insulation and anti-corrosion encapsulation.The maximum measurement range in laboratory environment is 0～107.41 m S/cm,and the measurement accuracy is ±0.1m S/cm.Tested and identified by the National Marine Standard Metrology Center,the maximum measurement error of the silicon-based four-platinum thin-film electrode type seawater conductivity meter is ±0.073 m S/cm in the range of 0～70m S/cm.In addition,the repeatability,consistency and temperature compensation function of the seawater conductivity tester were also tested and all met the index requirements.The test results show that the seawater conductivity detector designed in this project has the characteristics of high accuracy,large range and miniaturization.The instrument can read the conductivity value of seawater in real time and perform temperature compensation,which is important for the field observation of marine dynamic environmental parameters.