Research On Design Methods Of High Sensitivity Microwave Humidity Sensor Based On Micro-nano Fabrication

As one of the most important sensor applications in daily life,humidity sensor has been widely used in weather forecast,agricultural monitoring,food processing,clinical medicine,intelligent home appliances fields.In recent years,the research on humidity sensor is mostly based on low frequency test platforms such as resistors or capacitors with the advantages of low cost and simple preparation and disadvantages of low sensitivity,poor stability,large size and easily affected by the environment.In comparison,RF microwave measurement platform has been further developed in the field of humidity sensing detection due to the characteristics of high stability,perfect compatibility and multi-parameter characterization.This paper takes the design of humidity sensor based on the micro-nano fabrication as starting point,and is committed to solve the problems of low sensitivity,large size and poor stability of current humidity sensors.The design methods and solutions to improve the performance of humidity sensor are analyzed from multi-directional perspectives,which lays a foundation for practical engineering research of humidity sensor.First of all,this paper introduces the synthesis process of humidity sensitive materials starting from the metal oxide materials.The humidity sensitivity is improved by changing the raw material ratio.Rutile Ti O₂ is introduced to solve the hysteresis problem and reduced the hysteresis from 2.45%RH to 0.95%RH.Based on the sensing mechanism of capacitive humidity sensor and microwave humidity sensor,the composite of metal organic framework derivative based magnetic materials modified by carbon dots is designed.The sensitivity of the composite heterojunction structure humidity sensor is significantly improved,which realized the wide sensing range from 5%to 99%RH.Secondly,starting from the metal-insulator-metal capacitive humidity detection unit,the porous structure is designed to improve the contact area of water molecules with sensitive materials and the structure with 20?m hole diameter and 10?m hole distance is settled for the capacitive humidity sensor.The interdigital capacitance microwave circuit is used to calibrate water vapor sensing frequency.The linewidth size,opening design,and symmetrical double ring structure are designed to realize the optimal microwave humdity sensing system which integrates design,optimization,simulation,fabrication and packaging process.The change of microwave transmission and reflection signals are monitored and recorded by Lab VIEW platform.The test results verify the feasibility of humidity detection by using the microwave humidity sensing platform.Then,the humidity sensing layer of capacitive humidity sensor unit is processed by different etching methods to improve the sensing performance.Aiming at the problem of large size and difficult integration of microwave devices based on printed circuit board technology,integrated passive nano-micro fabrication technique is adopted as a breakthrough to design miniaturized microwave humidity sensor based on interdigital capacitor and spiral inductor resonant circuit with size of 0.98×0.8 mm².Compared with the microwave humidity sensor fabricated by traditional printed circuit board technology with sensitivity at k Hz/%RH level,a miniature humidity sensor with sensitivity of 3.4 MHz/%RH is realized in this paper.The yield of the device is increased by inductor etching optimization and capacitor annealing optimization.It solves the problems of unstable device performance and large difference in sensing characteristics of traditional mass production humidity sensors,and further improves the practical application value for mass production of humidity sensors.Finally,the application research of humidity sensor for human body sign monitoring is carried out.Through the preliminary analysis of capacitive humidity sensor for human body sign monitoring,the feasibility of microwave humidity sensor based on integrated passive nano-micro fabrication technique for human breath vapor and skin humidity detection is verified.It solves the miniaturization problem of traditional humidity sensor in the field of intelligent medical health,and achieves biological application of easy integrated multi-functional humidity detection devices.To sum up,aiming at several prominent problems in the humidity sensor applications,a series of modularization research of sensitive material design,device structure design,and fabrication technique optimization is carried out based on the interdisciplinary theoretical analysis,which provides the research foundation and reference value for the practical applications of highly sensitive humidity sensors.