Research On Effect Of Crack Length On The Performance Of Nanocrack-Based Strain Sensor

In recent years,researchers have discovered that nanocracks can be widely fabricated strain sensors.Nanocrack-based strain sensors are usually composed of a conductive layer with nanocracks and a flexible stretchable polymer layer.The performance parameters of nanocrack-based strain sensors include sensitivity,strain range,response time,hysteresis and so on.Recently,nanocrack patterns,such as the length of the crack,play a key role in the performance of the nanocrack-based strain sensor.Therefore,it is necessary to complete the investigation on the effect of the crack length on the performance of the nanocrack-based strain sensor.Therefore,we used a method that can control the generation of nanocracks on the surface of the flexible substrate to manufacture nanocracks with different lengths.First,a chromium film and a gold film were sputtered on the surface of the polydimethylsiloxane(PDMS)substrate successively.Next,a layer of photoresist was spin-coated on the surface of the gold film,and then the photoresist was patterned.There would be some areas of the gold film without photoresist protection after the patterning.Finally,the sample was bent along a steel pipe with a certain radius of curvature,and nanocracks with crack lengths of 50?m,500?m and 5000?m were manufactured on the metal film.It was necessary to determine the bending radius of curvature and the length of the gold film in the process of manufacturing nanocracks.According to the experimental results,The bending radius of curvature is 6 mm and the length of the gold film is 1 mm according to the experimental results.The nanocrack samples manufactured by the above method were fabricated nanocrack-based strain sensors through a wire connection process,and their performances were tested.The nanocrack-based strain sensor with a crack length of 50?m was difficult to collect its resistance signal in the subsequent performance test process due to the too small range.Therefore,the performance tests of the nanocrack-based strain sensors with crack lengths of500?m and 5000?m were carried out.The results showed that the strain ranges of the nanocrack-based strain sensors with crack lengths of 500?m and 5000?m were 0-0.04%and0-0.33%,respectively.And the gauge factor(GF)were 2100 and 3933 at full scale respectively.However,the GF of the former was greater than that of the latter when the strain was 0.04%.The relationship between the crack length and the sensitivity of the nanocrack-based strain sensor was explained based on the overlap model and the tunneling model.The results showed that the relative resistance change(?R/R₀)of the nanocrack-based strain sensor with a crack length of 500?m conformed to the overlap model when the strain range was 0-0.01%.The?R/R₀ conformed to the tunneling model when the strain range was 0.02%-0.04%.The?R/R₀ was jointly determined by the overlap model and the tunneling model when the strain interval was 0.01%-0.02%.For the nanocrack-based strain sensor with a crack length of 5000?m,the?R/R₀ conformed to the overlap model when the strain range was 0-0.1%,and the?R/R₀ conformed to the tunneling model when the strain range was 0.16%-0.33%,and the?R/R₀ was jointly determined by the overlap model and the tunneling model when the strain range was 0.1%-0.16%.When the strain was 0.04%,the?R/R₀ of the nanocrack-based strain sensors with a crack length of 500?m became proportional to the strain,and the?R/R₀ of the nanocrack-based strain sensors with a crack length of 5000?m became an exponential relationship with strain.Therefore,the GF value of the former was greater than that of the latter according to the GF value calculation formula.