A Correction Method Based On Nanocomposite Coating For High-quality Real-time Infrared Imaging

IR thermal imaging has many advantages,such as high spatial resolution,high temperature resolution,non-contact,real-time,portable and so on.Therefore,it becomes an important way to realize the temperature measurement of micro devices.However,if the target surface is heterogeneous,due to the nonuniformity of emissivity,large measurement errors will accur.It is the biggest bottleneck affecting the application of IR thermal imaging.Therefore,it is necessary to correct the IR measurement error caused by emissivity.To overcome the above-described difficulty,in this paper,an ultrathin nanocomposite coating is introduced to achieve the homogeneity of the target surface,enabling high-precision and high-resolution real-time IR thermal imaging.The contents of this paper are as follows.1.Preparation and characterization of the nanocomposite coating.Nano radiation Black Carbon（BC）and Polyimide were selected as the raw materials,and by ultrasonic,high-energy ball milling,vacuum treatment,spin technology and curing,the ultrathin nanocomposite coating was fabricated.Finally,different characterization methods were used to evaluate the key properties of the coating.Experimental results show that the emissivity of the nanocomposite coating is affected by BC content.The higher the content of BC,and the higher the emissivity of the nanocomposite coating.However,the high content will lead to the agglomeration of BC.Only when the content is less than 6 wt.%can the BC be distributed compactly and uniformly in polyimide,without agglomeration.When the BC content is 6wt.%,the thermal conductivity of the nanocomposite coating is 0.35w/（m?K）,and its electrical conductivity is 1.684×10^-1 s/m.Combined with the measured results and heat conduction model,it can be derivated that the temperature gradient in the vertical direction of the coating is relatively small.So,the BC content was preliminarily confirmed as 6wt.%.2.Technology of temperature calibration based on Pt resistance temperature sensor.To evaluate the improvement of IR temperature measurement accuracy after coating modification,a temperature calibration device was designed and fabricated based on MEMS technology.It uses large area film resistance heater and high thermal conductivity Si substrate to form a large range of approximate isothermal body,further forming a series of small range of isothermal area.In isothermal region,it is integrated with Pt sensor and test strip made of different materials.In this paper,the measured value by Pt sensor is used as the benchmark of actual temperature measurement,and compared with the results of IR temperature measurement to evaluate the IR temperature measurement accuracy.Results show that actual temperature distribution of isothermal zone meets the design requirements,and the measurement results of Pt sensor are stable and reproducible.3.The correction effect of the ultrathin nanocomposite coating and its influencing factors.To evaluate the effect of the ultrathin nanocomposite coating and optimize its thickness and BC content,IR temperature measurement tests were carried out under the conditions of no coating and different coating.Results show that when the test device surface is uncoated with the nanocomposite coating,the temperature difference between IR measured temperature for different material is about 60K,and the deviation between IR measured temperature and the actual temperature ranges from 60K to100K.When the test device surface is coated with the optimal nanocomposite coating,the deviation between IR measured temperature and the actual temperature,as well as the temperature difference between IR measured temperature for different material,decreases to 1K.The optimal nanocomposite coating is with thickness of 2μm and has 6wt.%BC.Also,combined with the above-described results,this paper discusses and analyzes other factors that influencing IR thermal imaging accuracy,and establishes corresponding formula.3.Application of ultrathin nanocomposite coating correction method in thermal MEMS devices.In this paper,micro-hotplates with single temperature zone and multiple temperature zones are designed and fabricated.Experimental results show that under the action of the nanocomposite coating can the IR thermal imaging correctly capture the heat source,and correctly reflect the actual temperature distribution.The thinnest wire width can be identified is7μm.