MEMS Passive Wireless Humidity Sensors Based On Microporous PTFE

Humidity is important not only for meteorological monitoring,but also for agricultural planting,industrial control and medical fields.In recent years,with the rise of concepts such as wearable electronic devices,electronic skin and flexible display,more and more researchers have paid attention to flexible humidity sensors.Commonly,the substrate materials of flexible humidity sensors include polyimide(PI),polyimide Ethylene phthalate(PET),polydimethylsiloxane(PDMS)and so on.Compared with these materials,the hydrophobic microporous polytetrafluoroethylene(PTFE)has the advantages of stable chemical properties,good thermal stability and excellent mechanical properties.Moreover,hydrophobic characteristic and microporous structures make it breathable.So it has the potential to be an excellent substrate of flexible humidity sensors.In addition,humidity sensors face a variety of complex application environments,while wired humidity sensors can not be used in harsh environments,sealed spaces rotation conditions and so on.In these cases,passive wireless humidity sensors should be applied.In this paper,an LC passive wireless humidity sensor based on hydrophobic PTFE microporous material is designed and fabricated.The main work is as follows:(1)Based on a hydrophobic PTFE microporous substrate,a humidity sensitive capacitor with GO as the sensitive material is proposed.The structure and fabrication processes are developed.Both static and dynamic performances of the humidity sensitive capacitor are tested.The results show a sensitivity of 20.68 f F/%RH and a maximum hysteresis of 2.51%RH over the range of30%RH～90%RH.The response time and recovery time are 10 s and 3 s,respectively.Also,the breathable property of the substrate is verified.(2)In order to reduce the dielectric loss of GO at high humidity,a polyvinylidene fluoride/polytetrafluoroethylene(PVDF/PTFE)isolation layer with network structure is fabricated between the interdigitated electrode and GO sensitive layer by an electrospinning process.Effects of solution dosage,PTFE concentration and electrospinning speed on the performance of humidity sensitive capacitors are studied.(3)Based on the humidity sensitive capacitor,an LC passive wireless humidity sensor fabricated on the hydrophobic PTFE microporous substrate is designed and manufactured.The static and dynamic characteristics of the sensor are tested.The results show that,in the range of30%RH～75%RH,the sensitivity of the sensor is 11.689 k Hz/%RH and the maximum hysteresis is3.25%RH.The response time and recovery time are 4 s and 2 s,respectively.But the resonant frequency of the sensor is indistinguishable at 90%RH.With electrospun isolation layer,the quality factor of the sensor is improved,especially at high humidity,which increases the humidity detection range of the sensor.