Publicação
Development of solution-processed thin-films transistors based on hybrid systems of silicon nanoparticles and carbon nanotubes
| Resumo: | In this work, FET devices were developed using hybrid inks of silicon nanoparticles (SiNPs) and carbon nanotubes (CNTs) in different fractions, with the aim of increasing the conductivity of SiNPs thin films for (opto)electronic applications. The fabrication of the devices included photolithography, thermal evaporation and spray-coating processes, optimised to obtain good adhesion of the photoresist (PR) and definition of the Cr/Au contacts with thicknesses of 5 nm and 50 nm, respectively. Hybrid inks were produced with different fractions of CNTs dispersed in cyrene and, deposited on the FETs by spray-coating at an optimised substrate temperature of 200 ℃, resulting in hybrid films with a thickness of 1.13 ± 0.03 µm. TEM measurements were used to estimate the size distribution of the SiNPs, which was characterised by a log normal distribution with mean diameter dₘₑₐₙ = 36 ± 1 nm and a standard deviation σ = 1.6 ± 0.1. Through SEM, the morphology of the hybrid films obtained revealed an extremely porous and loosely compacted structure with several voids. The coffee ring effect was also observed in the hybrid films, represented by agglomerate structures of SiNPs and CNTs. Additional FTIR measurements revealed the presence of cyrene in the hybrid films, even after deposition of the solutions at 200℃. Electrical characterisation indicated the absence of conduction in the films with 0%, 2.5% and 5% CNTs. For the samples with 10% and 20% CNTs, a linear I-V dependence was observed at low voltages and super-linear at high voltages, indicative of the space charge limited current (SCLC) transport mechanism. The experimental data was fitted according to this model, where the four typical regimes of the transport mechanism were observed. The estimated electrical conductivity values showed an increase between the sample with 10% CNTs (ˉ⁸ Ωˉ¹cmˉ¹) and 20% CNTs (10ˉ⁷ Ωˉ¹cmˉ¹), proving the effect of the CNTs in improving the conductivity of the hybrid films. In comparison, the tetrahydrofuran-dispersed films showed significantly higher conductivity values (σ = 10ˉ⁷ to 10ˉ³ Ωˉ¹cmˉ¹), indicating that this difference between values is strongly associated with differences in the morphology of the hybrid films due to the solvents differences used to prepare hybrid inks. |
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| Autores principais: | Meira, Mónica Sofia Faria |
| Assunto: | Silicon nanoparticles Carbon nanotubes Semiconductor hybrid inks Field-effect transistor Photolithography Charge transport Electrical properties |
| Ano: | 2024 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Aveiro |
| Idioma: | inglês |
| Origem: | RIA - Repositório Institucional da Universidade de Aveiro |
| Resumo: | In this work, FET devices were developed using hybrid inks of silicon nanoparticles (SiNPs) and carbon nanotubes (CNTs) in different fractions, with the aim of increasing the conductivity of SiNPs thin films for (opto)electronic applications. The fabrication of the devices included photolithography, thermal evaporation and spray-coating processes, optimised to obtain good adhesion of the photoresist (PR) and definition of the Cr/Au contacts with thicknesses of 5 nm and 50 nm, respectively. Hybrid inks were produced with different fractions of CNTs dispersed in cyrene and, deposited on the FETs by spray-coating at an optimised substrate temperature of 200 ℃, resulting in hybrid films with a thickness of 1.13 ± 0.03 µm. TEM measurements were used to estimate the size distribution of the SiNPs, which was characterised by a log normal distribution with mean diameter dₘₑₐₙ = 36 ± 1 nm and a standard deviation σ = 1.6 ± 0.1. Through SEM, the morphology of the hybrid films obtained revealed an extremely porous and loosely compacted structure with several voids. The coffee ring effect was also observed in the hybrid films, represented by agglomerate structures of SiNPs and CNTs. Additional FTIR measurements revealed the presence of cyrene in the hybrid films, even after deposition of the solutions at 200℃. Electrical characterisation indicated the absence of conduction in the films with 0%, 2.5% and 5% CNTs. For the samples with 10% and 20% CNTs, a linear I-V dependence was observed at low voltages and super-linear at high voltages, indicative of the space charge limited current (SCLC) transport mechanism. The experimental data was fitted according to this model, where the four typical regimes of the transport mechanism were observed. The estimated electrical conductivity values showed an increase between the sample with 10% CNTs (ˉ⁸ Ωˉ¹cmˉ¹) and 20% CNTs (10ˉ⁷ Ωˉ¹cmˉ¹), proving the effect of the CNTs in improving the conductivity of the hybrid films. In comparison, the tetrahydrofuran-dispersed films showed significantly higher conductivity values (σ = 10ˉ⁷ to 10ˉ³ Ωˉ¹cmˉ¹), indicating that this difference between values is strongly associated with differences in the morphology of the hybrid films due to the solvents differences used to prepare hybrid inks. |
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