Investigation and tuning of graphene electrodes for solution-processable metal oxide thin-film transistors in the area of low-cost electronics - CMOT

The CMOT project aims to tailor and develop solution based metal oxide thin-film transistors (MOTFTs) with graphene electrodes for the field of flexible, low-cost electronics. For this purpose, work-function engineering of both graphene and reduced graphene oxide electrodes was carried out. Additionally, the reduction of processing temperatures is of vital interest for flexible substrates. Thus, a laser-based technology for reduction of graphene oxide, conversion of the solution based metal oxide precursor and patterning of graphene electrodes and metal oxide semiconductor was developed.

Within the CMOT project the following results were achieved:

• Work function engineering of graphene electrodes in the range of 3.9 eV ≤ Φ ≤ 5.6 eV
• Waterless transfer process of monolayer graphene on the metal oxide film
• Laser induced graphene oxide reduction and patterning for application as electrode (R_sh ≈ 1 kΩ/sq)
• Development of UV-laser source with ps pulse length tailored for metal oxide conversion
• MOTFTs with laser converted metal oxide (μ_eff= 0.9 cm²V^-1s^-1)
• Selective laser structuring of graphene and graphene oxide
• Flexible beam shaping with spatial light modulator (SLM) for sequential edge deletion of MOTFTs with ultrashort pulse lasers
• Enhanced reliability of the MOTFTs by implementation of an yttrium oxide passivation layer
• MOTFTs with graphene electrodes (μ_eff= 2 cm²V^-1s^-1) exceed the performance of MOTFTs with conventional Ti/Au electrodes (μ_eff = 1 cm²V^-1s^-1)

The interim results of the project are both of scientific and industrial interest. Several conference contributions as oral [1, 2] and poster presentation [3, 4] have been given. Also one paper for peer review has been submitted [5]. The results concerning the technology of flexible beam shaping for thin film structuring, which was set up and evaluated by LPKF, show it can be deployed for several areas of laser material processing. The possibility to adapt the beam shape almost arbitrarily to the application is beneficial for the productivity and flexibility of the laser process. LPKF sees potential for application in PCB processing (e.g. drilling of plated through contacts), glass processing and plastic welding and wants to evaluate and exploit this technology further. 3D-nano expects to benefit from the results of experimental research on the novel type of nanomaterials that is lacking today in the marketplace. It will therefore form the basis of a potentially substantial business opportunity for the company like 3D-nano.

[1] Kasischke, M., et al. “Selective Femtosecond Laser Ablation of Graphene for Its Micro-Patterning.” ICALEO Congress Proceedings 2016 - 35th International Congress on Applications of Lasers & Electro-Optics, San Diego, CA, USA; 10/2016

[2] Kasischke, M., et al. “Graphene oxide reduction induced by femtosecond laser irradiation.” Nanostructured Thin Films X. Vol. 10356. International Society for Optics and Photonics, 2017.

[3] Subasi, E., et al. “Solution-processed bottom-contact metal-oxide thin-film transistors with transparent graphene electrodes.” Graphene Week 2017, Athens, Greece

[4] Kasischke, M., et al. “Femtosecond lasers as micro-machining tool for graphene structuring and graphene oxide reduction.” Graphene Week 2017, Athens, Greece

[5] Kasischke, Maren, et al. "Simultaneous nanopatterning and reduction of graphene oxide by femtosecond laser pulses." Applied Surface Science 445 (2018): 197-203.

Project Details