Electrical Resistance Reduction Induced with CO2 Laser Single Line Scan of Polyimide

Abstract

We conducted a laser parameter study on CO2 laser induced electrical conductivity on a polyimide film. The induced electrical conductivity was found to occur dominantly at the center of the scanning line instead of uniformly across the whole line width. MicroRaman examination revealed that the conductivity was mainly a result of the multi-layers (4–5) of graphene structure induced at the laser irradiation line center. The graphene morphology at the line center appeared as thin wall porous structures together with nano level fiber structures. With sufficient energy dose per unit length and laser power, this surface modification for electrical conductivity was independent of laser pulse frequency but was instead determined by the average laser power. High electrical conductivity could be achieved by a single scan of laser beam at a sufficiently high-power level. To achieve high conductivity, it was not efficient nor effective to utilize a laser at low power but compensating it with a slower scanning speed or having multiple scans. The electrical resistance over a 10 mm scanned length decreased significantly from a few hundred Ohms to 30 Ohms when energy dose per unit length increased from 0.16 J/mm to 1.0 J/mm, i.e., the laser power increased from 5.0 W to 24 W with corresponding power density of 3.44 × 10 W/cm2 to 16.54 W/cm2 respectively at a speed of 12.5 mm/s for a single pass scan. In contrast, power below 5 W at speeds exceeding 22.5 mm/s resulted in a non-conductive open loop.

Laser‐induced Graphene in Facts, Numbers, and Notes in View of Electroanalytical Applications: A Review

“…Micro-Raman scattering characteristics with the ratio I 2D/IG of 0.3-0.5 [23] indicates that graphene has a multilayer structure of 4-5 layers for the electrically conductive layer formed on the polyimide surface. Moreover, they're shown that:…”

“…Raman spectra of: left -graphene oxide (GO) and highly reduced laser-scribed graphene (hr-LSG); right -LIG, polyimide (PI). Adapted with permissions from references [21][22][23]. stacking of graphene sheets along c-axis * The Raman spectrum of crystalline graphite has only one Raman peak at 1580 cm À 1 , which is called the G band.…”

“…The ratio of the intensity of D‐ Raman peak and G‐ Raman peak ( I D /I G ) is often used for the characterization of graphene, for example, to measure the defects present on graphene structure (disorder degree) and the average size of the sp 2 domains [24]. Beside the importance of I D /I G ratio, the I 2D /I G ratio could provide a good indication of high‐quality single‐layer graphene [23].…”

Laser‐Assisted Structuring of Graphene Films with Biocompatible Liquid Crystal Polymer for Skin/Brain‐Interfaced Electrodes

“…As previously reported, it is obviously acceptable that increasing laser power and multiple irradiation are general methods to obtain qualified electrical performance of LIG electrodes with reasonable sheet resistance. [ 36 ] However, there is a trade‐off in this parametric condition to maintain the flexibility and mechanical stability of the LIG‐structured films because the excessive laser power and multiple irradiation generally cause partial damage to the carbon source substrates that substantially affect its mechanical properties. [ 37 ] Therefore, it is important to balance the flexibility and mechanical stability of the electrically high‐performance LIG electrodes by optimizing the physical parameters without the loss of intrinsic properties of the LCP film.…”

Laser-Induced Graphene Stretchable Strain Sensor with Vertical and Parallel Patterns

“…The intensity ratio of D/G indicates an inverse correlation with the degree of graphene crystallinity in the LIG; specifically, a higher D/G implies more numerous defects, lower crystallinity, and thus lower graphitization. Moreover, an intensity ratio of 2D/G > 2 indicates high-quality, single-layer graphene [51]; if 2D/G < 0.6, the produced graphene contains more than four layers. That is, a lower 2D/G ratio indicates a greater number of graphene layers.…”