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Highly Bendable In-Ga-ZnO Thin Film Transistors by Using a Thermally Stable Organic Dielectric Layer

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ABSTRACT

Flexible In-Ga-ZnO (IGZO) thin film transistor (TFT) on a polyimide substrate is produced by employing a thermally stable SA7 organic material as the multi-functional barrier and dielectric layers. The IGZO channel layer was sputtered at Ar:O2 gas flow rate of 100:1 sccm and the fabricated TFT exhibited excellent transistor performances with a mobility of 15.67 cm2/Vs, a threshold voltage of 6.4 V and an on/off current ratio of 4.5 × 105. Further, high mechanical stability was achieved by the use of organic/inorganic stacking of dielectric and channel layers. Thus, the IGZO transistor endured unprecedented bending strain up to 3.33% at a bending radius of 1.5 mm with no significant degradation in transistor performances along with a superior reliability up to 1000 cycles.

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Related in: MedlinePlus

A schematic of fabrication process for flexible bottom-gated IGZO TFT on a polyimide (PI) substrate, which is peeled off from the PDMS layer.A digital image (top right corner) shows the flexible bottom-gated IGZO TFT under the bending test. The chemical structure of SA7 is shown in a dotted box.
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f1: A schematic of fabrication process for flexible bottom-gated IGZO TFT on a polyimide (PI) substrate, which is peeled off from the PDMS layer.A digital image (top right corner) shows the flexible bottom-gated IGZO TFT under the bending test. The chemical structure of SA7 is shown in a dotted box.

Mentions: Figure 1 demonstrates the schematic of a flexible bottom-gated IGZO TFT fabrication on a 100 μm thick PI substrate, which is explained in detail in the methods section. The digital image of the flexible IGZO TFT under the bending test is shown at the top right corner of Fig. 1. The chemical structure of the commercially available SA7 organic dielectric material is given in dotted box at the bottom of Fig. 1, which is a block co-polymer, consisted of different monomers; glycidyl methacrylate, methacrylic acid, isobornyl acrylate, 2-hydroxyethyl acrylate and styrene. The morphology, i.e., roughness, wrinkles and cracks, of the IGZO semiconducting film plays a critical role in the transistor performance. The sputtered IGZO atoms on the polymer surfaces undergo different kinetic processes including thermal-induced polymer surface modification, surface diffusion of IGZO atoms into the polymer surface, nucleation, island formation and growth30. Those kinetic processes govern stress-induced growth, which results in undesirable wrinkles. In our preliminary studies, we sputtered the IGZO film at an Ar:O2 gas flow of 100:1 sccm on different gate dielectric layers of commonly used PMMA as a reference and SA7 to study the morphology of the IGZO channel layer (SI, S1). The optical image revealed that there were undesirable wrinkles on the IGZO layer when it was deposited on top of the PMMA. However, in the case of SA7, the deposited IGZO film had a smooth surface with no observable wrinkles. Good thermal stability and better adhesion of SA7 to the IGZO layer could be the main reasons for the smooth IGZO surface after subsequent annealing process. Polymers with a good thermal stability can resist against the plasma-induced thermal damages because the thermal-induced surface modification can be occurred during the sputtering.


Highly Bendable In-Ga-ZnO Thin Film Transistors by Using a Thermally Stable Organic Dielectric Layer
A schematic of fabrication process for flexible bottom-gated IGZO TFT on a polyimide (PI) substrate, which is peeled off from the PDMS layer.A digital image (top right corner) shows the flexible bottom-gated IGZO TFT under the bending test. The chemical structure of SA7 is shown in a dotted box.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120347&req=5

f1: A schematic of fabrication process for flexible bottom-gated IGZO TFT on a polyimide (PI) substrate, which is peeled off from the PDMS layer.A digital image (top right corner) shows the flexible bottom-gated IGZO TFT under the bending test. The chemical structure of SA7 is shown in a dotted box.
Mentions: Figure 1 demonstrates the schematic of a flexible bottom-gated IGZO TFT fabrication on a 100 μm thick PI substrate, which is explained in detail in the methods section. The digital image of the flexible IGZO TFT under the bending test is shown at the top right corner of Fig. 1. The chemical structure of the commercially available SA7 organic dielectric material is given in dotted box at the bottom of Fig. 1, which is a block co-polymer, consisted of different monomers; glycidyl methacrylate, methacrylic acid, isobornyl acrylate, 2-hydroxyethyl acrylate and styrene. The morphology, i.e., roughness, wrinkles and cracks, of the IGZO semiconducting film plays a critical role in the transistor performance. The sputtered IGZO atoms on the polymer surfaces undergo different kinetic processes including thermal-induced polymer surface modification, surface diffusion of IGZO atoms into the polymer surface, nucleation, island formation and growth30. Those kinetic processes govern stress-induced growth, which results in undesirable wrinkles. In our preliminary studies, we sputtered the IGZO film at an Ar:O2 gas flow of 100:1 sccm on different gate dielectric layers of commonly used PMMA as a reference and SA7 to study the morphology of the IGZO channel layer (SI, S1). The optical image revealed that there were undesirable wrinkles on the IGZO layer when it was deposited on top of the PMMA. However, in the case of SA7, the deposited IGZO film had a smooth surface with no observable wrinkles. Good thermal stability and better adhesion of SA7 to the IGZO layer could be the main reasons for the smooth IGZO surface after subsequent annealing process. Polymers with a good thermal stability can resist against the plasma-induced thermal damages because the thermal-induced surface modification can be occurred during the sputtering.

View Article: PubMed Central - PubMed

ABSTRACT

Flexible In-Ga-ZnO (IGZO) thin film transistor (TFT) on a polyimide substrate is produced by employing a thermally stable SA7 organic material as the multi-functional barrier and dielectric layers. The IGZO channel layer was sputtered at Ar:O2 gas flow rate of 100:1 sccm and the fabricated TFT exhibited excellent transistor performances with a mobility of 15.67 cm2/Vs, a threshold voltage of 6.4 V and an on/off current ratio of 4.5 × 105. Further, high mechanical stability was achieved by the use of organic/inorganic stacking of dielectric and channel layers. Thus, the IGZO transistor endured unprecedented bending strain up to 3.33% at a bending radius of 1.5 mm with no significant degradation in transistor performances along with a superior reliability up to 1000 cycles.

No MeSH data available.


Related in: MedlinePlus