Improved conductivity of carbonized polyimide by CO₂laser graphitization

Abstract

Direct laser writing (DLW) is a fast and cost-effective technique for printing conductive structures on flexible substrates such as polyimide (PI) by the conversion of insulative PI to conductive carbon.

Physical Sensors Based on Laser-Induced Graphene: A Review

“…As can be seen, a wide range of parameter sets can be used, as long as the threshold energy is reached [99]. In the case of PI, threshold energy of 7.9±0.6 Jcm -2 is needed to form LIG [77], which is in the range of previously reported energy estimations [51,59,99]. Laser parameters also affect the sheet resistance, conductivity, crystallite size, thickness, and wettability of porous graphene.…”

“…Biswas et al have thoroughly investigated the transformation of PI into LIG using a CO2 laser. The carbonization of PI occurred at a threshold power of (0.21 ±0.02) W and a fluence of (3.31 ±0.32) J cm -2 , while graphitization was reported at a power of (0.50 ±0.03) W and a fluence of (7.88±0.47) J cm -2 [77]. The threshold power shows a linear dependence on the laser speed, i.e., a higher speed requires a higher power in order to initiate the graphitization [46] YAG (1064 nm), can be easily integrated into a chamber with environment control and can be equipped with a fast galvoscanning system with a nanosecond pulse, for rapid prototyping and large scale production.…”

“…The former produces amorphous tetrahedral carbon, also known as diamond-like carbon. The latter leads to rapid decomposition of gaseous products, the transformation of the existing sp 3 bonds to sp 2 bonds along with crystallization of the amorphous matrix, and an increase in electrical conductivity [77]. Various laser types, substrate materials, and environmental conditions have been utilized to obtain porous graphene, which are listed in Fig.1a and discussed in more detail in section III-A.…”

“…Typically, the base polymer is heated through a laser, producing LIG and predominantly CO and H2 gases along with hydrocarbon (CxHyNz) species. Considering the most commonly used combination of a CO2 laser and PI, carbonization is reported to commence at 673K, while graphitization occurs upon further heating of the PI to at least 773 K [77]. The gases produced from LIG formation are removed from the system after the course of 1.25 ns [41].…”

“…The amount of laser power can also affect the thickness, line width and crystallinity of LIG (obtained from CO2 laser ablation of PI). The thickness can be tuned in the range from 20 m to 100 µm [42], line width can be in the range of 110m to 240m [86] with crystalline size varying from 20 nm to 40 nm [40,77]. The wettability of the LIG was previously controlled via scanning speed and the frequency of the laser incident radiation [50].…”