Development Of Integrated Temperature And Conductivity Sensor Chip

With the rapid development of modern information technology and the arrival of the 5G era,the Internet of Things(IoT)-Internet of Everything(IoE)is an indispensable part of Industry 4.0.As the "eyes" and "skins" of the IoT,the development of sensors is towards miniaturization and multifunctional with the development of MEMS technology.Thin film sensors based on micromachining processes are considered to be the best candidate because of their small size,fast response,high precision,and easy to be integrated.At present,most sensors in China are mainly single-function sensors.If multiple parameters are tested,sensors with different functions need to be assembled separately and then integrated through peripheral circuits.This will greatly increase the area of the sensor.Therefore,research on integrated multi-function sensors is urgently needed.According to the above background,an integrated temperature and capacitance coupled contactless conductivity detection(C4D)sensor chip was proposed,which has the characteristics of small volume,simple process and stable performance,and can monitor temperature and conductivity simultaneously.At the same time,the temperature measured by the temperature sensor can be used to compensate the conductivity measurement.Temperature sensor and conductivity sensor were fabricated and tested respectively and then multi-function sensors were integrated and tested.In order to improve the performance of platinum resistance,the effects of different substrate materials,different annealing temperatures and different annealing times on electrical properties of electrical resistance were investigated.The results have shown that the platinum resistors have good linearity and repeatability on both silicon substrates and alumina substrates.Platinum resistance on different substrates is affected differently by annealing.The platinum resistance on the silicon substrate was greatly affected by the annealing time,and the TCR reached 3107 ppm/°C after annealing at 800 °C for four hours.The platinum resistance on the alumina substrate is greatly affected by the annealing temperature,and the resistance value increases more after annealing from 500 °C to 700 °C,and increases most at 600 °C,and the TCR reaches 2975 ppm/°C at 800 °C.It has been found that the diffusion to Pt film and oxidation of titanium after 500 °C may be the main cause of TCR changes.In the sensor test after packaging,the TCR of the sample annealed at 800 °C for 2 hours reached 3235 ppm/°C.In the development of C4 D sensor,a four-electrode structure was designed and barium strontium titanate(BST)thin film was used as a protective layer.The dual ion beam sputtering power and the factors causing the change in the dielectric constant of BST were explored.Experiments show that the four-electrode(100 Hz~10 kHz)conductivity sensor with BST protection layer has a wider measurement bandwidth than the two electrodes,and the bandwidth is reduced compared with the unprotected layer(20 Hz~10 kHz),but they have similar cell constants.This shows that the introduction of BST has no significant effect on the performance of the original four electrodes.During the integrated sensor test,the conductivity sensor can clearly sense the change of conductivity with temperature.The temperature compensation coefficient is calculated to be about 2%,which is closed to the standard KCl temperature coefficient.At the same time,the BST passivation layer also improves the performance of platinum resistance temperature sensor and has more stable electrical performance.