Research On Metallic Mesh Transparent Conductive Film Prepared By Random Crackle-template

Electromagnetic interference(EMI) shielding on the optical widows is an important technique in fields such as military defense, aerospace and electronic communication. Metallic mesh transparent conductive film(TCF) has the ability to enhance the EMI shielding effectiveness and keep the widened transmittance spectrum, simultaneously. Unfortunately, most metallic mesh TCFs are based on periodic or sub-periodic elements; the periodic structures naturally generate diffraction patterns that degrade imaging quality for the concentration of high order diffraction energy. Moreover, the high price of traditional micromachining technologies for micro-mesh prevents metallic mesh TCF being widely used in many fields. For the above reasons, a novel metallic mesh TCF which fabricated based on self-forming templates is proposed in this thesis. Theoretical and experimental studies were proceeded deeply based on the TCF, and the main invastigation work and achievements are described as follows:1. The mechanism of the forming processes of crackle template is deeply analyzed. The drying procedure of dispension membrane and the condition for the cracking of the membrane is discussed, firstly. Then a crack propagation model concerning critical membrane stress and membrane thickness is established based on Griffith’s fracture theory. The critical thickness and the influence of membrane thickness on crack formation are calculated based on the model. Results show that the dispersion membrane must arrive at a critical thickness for cracking. The bigger the dispersate particles are, the thicker the critical thickness is. Besides, the crack space grows with the membrane thickness, and thicker membrane will lead to heavier buckling. Relevant results provide powerful theoretical guidance for the preperation of crackle templates and the optimization of fabrication processing.2. By comparing the self-forming crack templates of two different dispersions—the Ti O2 gel and the water-based acrylic emulsion, the later is chosen for fabricating crackle template. Experimental tests show that the emulsion’s critical thickness for cracking is about 900 nm, and more tests were conducted to analyze the influence of emulsion thickness on cracking, finally results showed that the thicknesses located in 2~3μm can result in good crackle templates. Based on the crackle templates, metallic mesh TCF samples are fabricated by Lift-off technique. Further experiments were focus on the optimization of the above processes. Ultimately, a good metallic mesh TCF sample was prepared.3. The performances of the novel metallic mesh TCF sample are evaluated by experiments and tests. The conducting ability, transmissivity, optical diffraction and EMI shielding effectiveness are tested. Experimental results show that, the TCF sample exhibits a low resistance of 2.1Ω/sq, a high transmissivity of 90% at UV/VIS wavelength, and the IR transmisivity of the sample also keeps a high value above 88%; the relative ennergy of the strongest stray light is less than 0.04‰, and the sample achieves an EMI shielding effectiveness of more than 25 d B over 12~18 GHz, which means more than 99.68% electromagnetic ennergy is shielded. Moreover, the shielding effectiveness keeps stable over 12~18 GHz, only with a fluctuation of ±2d B.4. A model for evaluating EMI shielding effectiveness of novel metallic mesh TCF is established based on the existing model of square metallic grids. The newly proposed model is based on structure parameters gotten by statistics and the modificated coefficient. The predicting results show good conformity with testing results, only with a deviation of 2d B. The computational model provides a useful reference for the evaluating of EMI shielding effectiveness on metallic mesh TCF.In conclusion, the novel metallic mesh TCF introduced in this thesis exhibits excellent conductivity, broadband transmission spectrum and high EMI shielding efficiency over broadband microwave. What really got one aflutter is that the TCF showed the uniform distribution of stray light, and the high order diffraction energy only reached 0.04‰, which much smaller than the best performances reported so far. The thesis then comes to the conclusion that the innovative metallic mesh TCF prepared by random crackle-template is promising for high performance EMI shielding optical windows, as well as for curved optical windows.