A Surface Tailoring Method of Ultrathin Polymer Gate Dielectrics for Organic Transistors: Improved Device Performance and the Thermal Stability Thereof

Abstract

wileyonlinelibrary.comand portable devices, the device performance must be substantially improved. To this end, high-performance organic gate dielectric layers with high mechanical stability and large-area processability are urgently requested. [ 1 ] However, OTFTs made of polymer gate dielectrics are suffering from high operating voltage, typically exceeding 20 V, [ 3,4 ] due to the gate dielectrics with the thickness often greater than 100 nm to ensure low gate leakage current. [ 4 ] Thermally crosslinked polymers including poly(4vinylphenol) (PVP), [ 5 ] Cytop, [ 6 ] benzocyclobutene (BCB), [ 7 ] and polyimides (PIs) [ 8 ] have been adopted for gate dielectrics, but only few of them could successfully reduce the operating voltage of OTFTs down to 10 V by reducing the thickness of dielectric layer. Moreover, the high annealing temperature required to induce the crosslinking of polymer gate dielectrics is also problematic, which may cause damage to OTFTs and limit their application to thermally vulnerable substrates.Besides reducing the operating voltage of OTFTs, controlling the interface between dielectric and semiconductor is another critical factor to optimize the performance of OTFTs. [ 9,10 ] Applying selfassembled monolayers (SAMs) [ 10 ] or plasma treatment [ 11 ] had been widely applied to optimize the fi lm morphology of semiconductors on the surface of gate dielectrics. However, most of these SAM treatment procedures require specifi c surface coupling reaction, and had been applied mostly onto inorganic dielectric layers rather than polymer dielectrics, mostly due to the lack of target surface functionalities on most of the polymer dielectrics and/or a reliable, damage-free coupling reaction applicable onto the polymer dielectrics.Recently, we have proposed initiated chemical vapor deposition (iCVD) as a new deposition method to form ultrathin (<10 nm) crosslinked polymer dielectrics with high density. [ 12 ] iCVD is a well-established dry process, which can deposit highly pure polymer thin fi lms in mild process temperature (10-40 °C) and pressure (in the order of 100 mTorr). [ 13 ] Especially, an organosilicon polymer, poly(1,3,5-trivinyl-1,3,5-trimethyl cyclotrisiloxane) (pV3D3), exhibited an extremely low leakage current (less than 10 −9 A cm −2 at 3 MV cm −1 ) even with ultralow thickness (≈6 nm), and chemical/mechanical robustness. Nevertheless, Tailoring the surface of the dielectric layer is of critical importance to form a good interface with the following channel layer for organic thin fi lm transistors (OTFTs). Here, a simple surface treatment method is applied onto an ultrathin (<15 nm) organosilicon-based dielectric layer via the initiated chemical vapor deposition (iCVD) to make it compatible with organic semiconductors without degrading its insulating property. A molecular-thin oxide capping layer is formed on a 15 nm thick poly(1,3,5-trimetyl-1,3,5-trivinyl cyclotrisiloxane) (pV3D3) by a brief oxygen plasma treatment. The capping layer greatly enhances the thermal stability of the diel...

A Low‐Voltage Organic Complementary Inverter with High Operation Stability and Flexibility Using an Ultrathin iCVD Polymer Dielectric and a Hybrid Encapsulation Layer

“…The thermal treatment condition of PTCDI-C13 on pV3D3 was optimized by varying the annealing temperature ( Figure 2 a). Thanks to the excellent thermal stability of pV3D3, [ 18 ] the annealing temperature of PTCDI-C13 on pV3D3 could be increased as high as 300 °C without damaging the insulating performance of the ultrathin pV3D3 layer. The highest mobility was obtained from the PTCDI-C13 TFT with the annealing temperature ranging from 150 to 200 °C.…”

“…Also, note that the TFT characteristics and I G were remained similar for a wide range of pV3D3 thicknesses between ≈8.5 nm and ≈45 nm ( Figure S1 and Table S1 in the Supporting Information for DNTT TFTs and Figure S2 and Table S2 in the Supporting Information for PTCDI-C13 TFTs), thanks to the excellent down-scalability of iCVD process. [ 17,18 ] To develop high-performance OTFTs, it is important to form highly crystalline organic semiconductors to facilitate the charge transport between the source/drain (S/D) electrodes. From the atomic force microscopy (AFM) images and X-ray diffractometer (XRD) spectra, we observed that the asdeposited p-type DNTT semiconductor on the pV3D3 dielectric layer was highly crystalline with large grains ( Figure S3, Supporting Information).…”

“…[ 16 ] The pV3D3 exhibited a high fl exibility and a low leakage current ( J i ) less than 10 −9 A cm −2 up to 5 MV cm −1 with an ultralow thickness down to 10 nm. [ 17,18 ] As well as the dielectric layer for electronic devices, a hybrid encapsulation layer via sequential deposition of iCVD and atomic layer deposition (ALD) was applied directly onto the organic complementary inverter to improve the environmental stability of organic electronic devices. [ 19 ] By adopting these dielectric layers and encapsulation layers together, the newly developed organic complementary inverter in this study exhibited a high gain of 130 V/V at a switching threshold voltage ( V M ) of 1.52 V at a supply voltage of 3 V. It also retained high air stability for more than 3 weeks.…”

Controlled Growth of Ultrathin Film of Organic Semiconductors by Balancing the Competitive Processes in Dip-Coating for Organic Transistors

“…[1][2][3][4][5][6][7][8][9] Generally, the thickness of organic semiconductor layer in organic electronic devices is in the range of several tens of to hundreds of nanometer (nm), which consists of tens of or more molecular layers. [10][11][12][13][14][15][16] On the other hand, ultrathin film (< 15 nm, Figure 1a) of organic semiconductors represents a kind of nano-scale film consisting of monolayer to few molecular layers (Figure 1b). [17][18][19][20][21][22][23] 3 According to the surface morphology, ultrathin film includes continuous and microstructured film (Figure 1a), both of which provide excellent platform for fundamental researches and practical applications.…”

High‐Fidelity, Sub‐5 nm Patterns from High‐χ Block Copolymer Films with Vapor‐Deposited Ultrathin, Cross‐Linked Surface‐Modification Layers

“…For example, polarity‐switching top coats may not be suitable for amphiphilic BCPs with a hydrophilic block, as is the one used in this study, due to the potential diffusion of the solvent and top coat into the hydrophilic block in BCP. Furthermore, achieving thermally stable defect‐free and uniformly thick layers is not a simple task to achieve with spin‐coating, especially for sub‐10 nm thick films …”