Vapor-phase synthesis of sub-15 nm hybrid gate dielectrics for organic thin film transistors
Organic thin film transistors (OTFTs) have been extensively investigated for next-generation electronic devices. However, many of them still suffer from poor device performances, which limits their real-world applications. The use of high-k oxides such as Al2O3 via atomic layer deposition (ALD) can mitigate this issue by increasing the capacitance of the dielectric layer (Ci). However, the abundant –OH functionality at the surface of oxides, and the ionic polarization between the carrier and high-k ionic lattice cause severe hysteresis, drop of mobility, and shift of threshold voltage in OTFTs. Low mechanical flexibility of the layers is also problematic, which hinders the broad use of ALD layers for flexible electronics. To address this issue, we synthesized an ultrathin (<15 nm) and mechanically flexible high-k oxide/non-polar polymer hybrid layer by integrating the ALD and initiated chemical vapor deposition (iCVD) processes into one chamber. The non-polar polymer via iCVD efficiently passivated the polar surface of the Al2O3 layer even with the thickness lower than 4 nm, which was hard to achieve with the conventional solution-based processes. Through the systematic variation of the polymer thickness, it turned out that the hybrid dielectric layer exhibited substantial improvement of overall device performances and long term operation stability against the continuous voltage stress (CVS) for 3000 s. The resulting 15 nm-thick hybrid layer even withstood a tensile strain up to 3.3%, which is far superior to the mechanical flexibility of the Al2O3 layer. Both the hybrid dielectric layer and the new vacuum process are expected to be highly beneficial for realizing high-performance transistors with mechanical flexibility.