Laser Beam MicroMachining (LBMM) – A review

Influence of laser pulse duration on the electrochemical performance of laser structured LiFePO 4 composite electrodes

Finding ways to scribe indium-tin oxide (ITO) coating plays an important role in the fabrication and assembly of thin film solar cells. Using a femtosecond (fs) laser, we selectively removed the ITO thin films with thickness 120–160 nm on glass substrates. In particular, we studied the effect of laser pulse duration, laser fluence and laser scanning speed on the ablation of ITO. The single pulse ablation thresholds at various pulse durations were determined to ablate ITO thin films. Clean removal of the ITO layer was observed when the laser fluence was above the threshold of 0.30 J/cm

Femtosecond laser ablation of indium tin-oxide narrow grooves for thin film solar cells

This paper presents a review on the modeling of ablation and plasma expansion processes in the pulsed laser deposition of metals. The ablation of a target is the key process that determines the amount of material to be deposited; while, the plasma expansion governs the characteristics of the deposited material. The modeling of ablation process involves a study of two complex phenomena: (i) laser-target interaction and (ii) plasma formation and subsequent shielding of the incoming radiation. The laser-target interaction is a function of pulse duration, which is captured by various models that are described in this paper. The plasma produced as a result of laser–target interaction, further interacts with the incoming radiation, causing the shielding of the target. The shielding process has been modeled by considering the various photon absorption mechanisms operative inside the plasma, namely: inverse Bremsstrahlung, photoionization, and Mie absorption. Concurrently, the plasma expands freely until the ablated material gets deposited on the substrate. Various models describing the plasma expansion process have been presented. The ability of the theoretical models in predicting various ablation and plasma characteristics has also been compared with the relevant experimental data from the literature. The paper concludes with identification of critical issues and recommendations for future modeling endeavors.

Critical assessment of the issues in the modeling of ablation and plasma expansion processes in the pulsed laser deposition of metals

Modeling of femtosecond laser damage threshold on the two-layer metal films

Micromachining thin metal films coated on glass are widely used to repair semiconductor masks and to fabricate optoelectrical and MEMS devices. The interaction of lasers and materials must be understood in order to achieve efficient micromachining. This work investigates the morphology of thin metal films after machining with femtosecond laser ablation using about 1 μm diameter laser beam. The effect of the film thickness on the results is analyzed by comparing experimental images with data obtained using a two-temperature heat transfer model. The experiment was conducted using a high numerical aperture objective lens and a temporal pulse width of 220 fs on 200- and 500-nm-thick chromium films. The resulting surface morphology after machining was due to the thermal incubation effect, low thermal diffusivity of the glass substrate, and thermodynamic flow of the metal induced by volumetric evaporation. A Fraunhofer diffraction pattern was found in the 500-nm-thick film, and a ripple parallel to the direction of the laser light was observed after a few multiple laser shots. These results are useful for applications requiring micro- or nano-sized machining.

Metal thin film ablation with femtosecond pulsed laser

Mechanical metamaterials possess unusual mechanical properties that cannot be found in nature. Auxetic metamaterials have negative Poisson's ratios and tend to expand in a direction perpendicular to the axial extension direction. When the Poisson's ratio of a display circuit board is forced to be −1 by adopting an auxetic metamaterial, a display can be stretchable without image distortion, and this display is called a meta‐display in this study. The critical obstacles to implementing a stretchable display are large stretchability, high deformation uniformity, and low image distortion. The meta‐display overcomes these obstacles by incorporating micro‐LEDs and a kirigami‐based auxetic circuit board. An auxetic meta‐display with a stretchability of 24.5%, Poisson's ratio of −1, and no image distortion under uniaxial stretching is demonstrated. Finally, the roll transfer process enabled the scaling‐up of a 3‐inch meta‐display attachable to surfaces with non‐zero Gaussian curvatures. This conformity to the non‐zero Gaussian curvature helps realize biomedical applications such as wearable display, phototherapy, and skincare.

Auxetic Meta‐Display: Stretchable Display without Image Distortion

Auxetic Meta-Displays In article number 2113299, Bongkyun Jang, Jae-Hyun Kim, and co-workers suggest an auxetic meta-display, which is a new stretchable display with large stretchability, high deformation uniformity, and low image distortion. It is fabricated by transferring micro-LEDs on the circuit board based on auxetic metamaterials with a Poisson's ratio of –1 and exhibits stretching without image distortion and conformal wrapping on non-Gaussian surfaces, enabling a stretchable display and a skin-attachable biomedical device. 

Jaegu Kim

Papers

Metal thin film ablation with femtosecond pulsed laser

Auxetic Meta‐Display: Stretchable Display without Image Distortion

Auxetic Meta‐Display: Stretchable Display without Image Distortion (Adv. Funct. Mater. 22/2022)