Femtosecond laser based high-performance micro-hole drilling on metal with vibration assistance and AgNW/CNT hybrid film patterning

다국어 초록 (Multilingual Abstract)

In this dissertation, development of laser micromachining process for industrial applications and those experimental results are described. First, based on interaction mechanism between femtosecond pulse and material, theoretical background of femtosecond laser micromachining process is introduced. Second, two different researches using femtosecond laser are described in the paper as title of femtosecond laser micro hole drilling integrated with vibration module, patterning technique for silver nanowire (AgNW) / carbon nanotube (CNT) hybrid conductive film.
First, femtosecond laser micromachining integrated with vibration module for micro hole drilling has been studied. Thickness of 30 ㎛ Invar alloy is drilled to investigate on angle control of hole taper by changing parameters including amplitude of vibration module and laser pulse energy. Wavelength of 795 nm, pulse width of 90 fs femtosecond laser system integrated with vibration module, so called the hybrid laser system, is used for the experiment. Displacement of focusing position is generated by moving the objective lens vertically by vibration module. The displacement value is range from 0 to 16 ㎛ by following the amplitude parameter, and the test is conducted without changing parameters except displacement of the focused beam. Comparison between shape of the ablated hole with vibration module and without is reported and discussed about possible mechanisms. Various micro machined holes with different taper angle results are observed, and holes with different taper angle are resulted.
Second, femtosecond laser micromachining for patterning silver nanowire (AgNW) / carbon nanotube (CNT) hybrid conductive film have studied. A femtosecond laser which specifications of 1027nm wavelength and 380fs pulse width is used for the experiment. Ablation test for the AgNW/CNT film is performed at laser fluence values ranging from 9.7 mJ/cm2 to 70.8 mJ/cm2, and the threshold of the film is found at 13.6 mJ/cm2. By increasing laser flunce, diameter of crater is sharply increased until fluence reaches at 65.2 mJ/cm2, and damage to the glass substrate is observed when fluence is over than 67.9 mJ/cm2. Fluence value for line pattering is determined as fluence value of 67.9 mJ/cm2 which is not influenced value to glass substrate. From the measurement result of the patterned line, the irregularly ablated area is easily observed near the completely ablated region. To pattern line without residual at the irradiated area, quasi flat-top beam profile is employed instead of the conventional Gaussian’s. The measurement result of the patterned line shows dramatically decreased uneven area when the quasi flat-top energy distribution is used.

목차 (Table of Contents)

• Abstract······································································ i
• List of Figures······························································ ⅶ
• 1. Introduction ···························································· 1
• 1.1. Femtosecond laser micromachining ···························· 1
• 1.2.
• Overview of interactions between femtosecond pulse and materials ···························································
• 2
• 1.2.1. Absorption ·················································· 2
• 1.2.2. Energy relaxation ·········································· 4
• 1.2.3. Ablation ····················································· 12
• 1.2.4. Femtosecond laser pulse and heat affected zone ······· 18
• 1.2.5. Thin film ablation with femtosecond pulse ············ 19
• 1.3. Organization of dissertation 20
• References 22
• 2.
• Femtosecond laser micro hole drilling integrated with vibration module ······················································
• 29
• 2.1. Introduction························································· 29
• 2.2. Experimental ······················································ 33
• 2.3. Results and discussion ··········································· 34
• 2.4. Conclusions ························································ 37
• References 39
• 3.
• Patterning technique for AgNW/CNT hybrid conductive film ··············································································
• 49
• 3.1 Introduction························································· 49
• 3.2 Experiments ························································ 51
• 3.3 Results and discussion ············································ 52
• 3.4 Conclusions·························································· 56
• References 58
• 4. Conclusions ····························································· 67