| With the emergence of the Internet of Things and artificial intelligence,various intelligent devices with human-computer interaction function have gradually become an indispensable element in human life.In the context of the global spread of COVID-19,contact sensing based on traditional electrical equipment has been unable to meet people’s requirements for convenient,effective,health and safety control of electronic devices.Physiological signal monitoring and non-contact sensing through water produced by plant and animal metabolism is an effective alternative.Although a variety of humidity sensors based on different materials and principles have been made and widely used in various areas of people’s life,but with high sensitivity and rapid response and other excellent characteristics of humidity sensor research and development work is still facing great challenges.In this paper,a creative method of preparing wet sensitive film by ion beam sputtering polymer target deposition technology is proposed,and the ion beam sputtering polyimide deposition(PSP)humidity sensor with excellent performance is prepared by taking polyimide as an example.Firstly,the process of ion beam sputtering polyimide wet sensitive film deposition was studied carefully,and the complete process flow and standard process parameters were determined.Then the aging effect and humidity sensing mechanism of PSP moisture sensitive film were discussed and explained by various characterization tests.Then,the sensitivity,response/recovery time,humidity hysteresis and stability of the PSP humidity sensor were tested by using the designed and built dynamic humidity testing system,and the applications of the PSP humidity sensor in respiratory monitoring and contactless sensing were explored.The specific research contents are as follows:(1)Study on the preparation technology of ion beam sputtering polyimide(PSP)wet sensitive film.PSP thin films are prepared by ion beam sputtering polyimide targets and deposited on a glass substrate with a gold fingered electrode to make PSP humidity sensors.The results show that in the threshold voltage range of 500 e V,the larger the sputtering voltage,the larger the humidity response of PSP film;When the sputtering voltage is constant,the PSP film thickness is proportional to the sputtering time,and the response/recovery time of the wet sensitive film increases with the increase of the film thickness.In order to meet the requirements of PSP humidity sensor for high sensitivity and fast response,the sputtering voltage of standard ion beam sputtering polyimide deposition process is 500 e V and the sputtering duration is 10 min(～60 nm/min).(2)Study on aging effect and sensing mechanism of PSP moisture sensitive film.The study found that the prepared PSP moisture sensitive film needs to be aged in a high humidity environment for 24 hours before it has stable humidity response characteristics.By comparing the chemical composition of PSP film before and after aging,we believe that the unaged PSP(NA-PSP)film is composed of various organic gas fragments in the form of free radicals,and there are unsaturated suspended bonds on the long molecular chain.The essence of film aging in humid air is that a large number of suspended bonds gradually tend to saturate during the oxidation process,thus forming hydrophilic fatty chains containing carboxyl and amine groups.In addition,the amorphous porous structure of the film provides a channel for water and gas exchange,which enables water molecules to form multilayer adsorption layers including chemical adsorption and physical adsorption on the PSP film surface,resulting in changes in dielectric constant and capacitance of the film.(3)Study on humidity response characteristics of PSP moisture sensitive film.In this study,a dynamic humidity measurement system was designed and built to test the sensitivity,response/recovery time and humidity hysteresis of PSP moisture sensitive film.The results show that the PSP humidity sensor exhibits ultra-high sensitivity at low frequencies(10 Hz)in the range of 10%-95% RH,with the output signal varying by more than 40,000 times.Even at 1 k Hz operating frequency,the sensitivity is as high as11.9 p F/%RH,which is more than 100 times that of PI film.The PSP film exhibits extremely fast response times with response/recovery times of 2.4 s/1.2 s over the entire test range and is able to respond to small humidity changes at 1% RH within 1s.In addition,the PSP humidity sensor has very little moisture lag,good repeatability and long-term stability.(4)Array integration and application exploration of PSP humidity sensor.With high sensitivity and fast response characteristics,the PSP humidity sensor can not only monitor the different states of human respiration in real time,but also achieve effective contactless sensing.In addition,a 5×5 PSP humidity sensor array was made to detect the shape of wet objects and the moisture status of plant leaves.In conclusion,the ion beam sputtering polymer deposition technique proposed in this study can prepare nanoscale amorphous polymer films.Ion beam sputtering polyimide deposition is an effective method to prepare high performance moisture sensitive polymer films,which has good moisture sensitive characteristics and broad application prospects. |
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