Reinforced Self‐Assembled Nanodielectrics for High‐Performance Transparent Thin Film Transistors

Abstract

Transparent thin fi lm transistors (TFTs) have stimulated great scientifi c and technological interest due to potential applications in "invisible" electronics, such as transparent touch panels and see-through displays. [1][2][3][4][5][6] Since the fi rst demonstration of transparent TFTs using a crystalline ZnO semiconductor, [ 7 ] extensive efforts have sought to enhance performance by increasing the fi eld-effect mobility ( μ FE ) and/or lowering the operating voltage. [8][9][10][11][12] Principal foci have included the semiconductor and gate dielectric, two essential TFT materials. Among the diverse transparent semiconductors, amorphous transparent oxide semiconductors (a-TOSs) offer distinctive attractions vis-à-vis organics and crystalline TOSs, including good mobility, excellent environmental stability, low-temperature processability, optical transparency, smooth surfaces, and compositional uniformity. [ 4 , 13-15 ] For example, amorphous Zn-In-Sn-O (a-ZITO) fi lms afford moderate TFT performance at operating voltages ≥ 10 V when paired with a SiO 2 gate dielectric. [16][17][18][19][20] An effective approach to enhancing TFT performance is to introduce a self-assembled nanodielectric (SAND; Figure 1 a ) composed of a saturated hydrocarbon layer, a π -polarizable stilbazolium layer, and a chlorosiloxane-derived SiO x "capping" layer. These gate dielectrics can be deposited near room temperature by straightforward wet chemistry, and have large capacitances, low leakage, high breakdown fi elds, and suppress trapped charge between the dielectric and semiconductor for many classes of organic and inorganic semiconductors. [21][22][23] Nevertheless, while SANDs exhibit good chemical and thermal stability, [24][25][26] recent work suggests that direct exposure to high-energy ions and plasmas present in pulsed laser deposition (PLD) semiconductor growth processes, seriously degrades SAND dielectric properties and TFT performance. [ 27 ] It would therefore be highly desirable to devise approaches to enhancing SAND robustness. We report here that a simple vapor-derived hexachlorodisiloxane (HCDS, Cl 3 SiOSiCl 3 ) coating ("v-SiO x ") greatly enhances SAND durability with respect to PLD laser plumes. This "reinforced" SAND (R-SAND) enables the growth of high-quality, optically transparent a-ZITO TOS channels and TFTs operating at voltages of ≤1.0 V with mobilities as high as 140 cm 2 /V · s.After SAND fi lms were fabricated via solution processing, [ 21 ] a ∼ 5 nm thick v-SiO x layer was grown by HCDS vapor deposition, followed by ambient exposure for crosslinking. [ 28 ] Figure 1b shows capacitance vs. frequency (at 2.0 V) data for SAND, R-SAND, and v-SiO x fi lms measured as n + -Si/dielectric/Au devices. Compared to SAND, which exhibits a high capacitance ( C i ) of ∼ 220 nF/cm 2 at 2.0 V/10 KHz, C i for R-SAND is ∼ 180 nF/cm 2 measured under the same conditions. The slightly smaller R-SAND C i is not unexpected considering the series-connected nature of the top v-SiO x layer, which by itself exhibits C i ∼ 750 n...

Source/drain electrodes contact effect on the stability of bottom-contact pentacene field-effect transistors

“…[1][2][3][4][5] In the last few decades, many promising organic materials with high charge mobilities have been developed. [6][7][8] Unfortunately, in spite of the high bulk mobility of many organic materials, the corresponding OFETs often exhibited relatively low performance when utilizing these organic materials to fabricate bottomcontact (BC) devices. 9 However, the commercialization of OFETs is still highly desirable for the BC configuration, as they not only significantly improve the sensitivity of OFET-based sensors, but they also dramatically reduce device cost.…”

Polymer-Based Gate Dielectrics for Organic Field-Effect Transistors

“…Efforts have been made to reduce the thickness of the dielectric layer. To overcome the drawbacks accompanied by decreased film thickness, such as decreased film uniformity and pinholes that lead to substantial leakage current, the use of SAMs , and SANDs , were reported. However, the full coverage of an ultrathin self-assembled layer requires additional processing controls and depends strongly on the outside environment and surface corrugation.…”

“…A smooth film morphology without pinholes or defects is preferable to suppress the leakage current and increase mobility. The improved performance is demonstrated for many dielectric self-assembled monolayers or multilayers (SAMs) and self-assembled nanodielectrics (SANDs) because of their well-ordered structures. ,,− Polymer-based nanocomposites have larger surface roughness compared to polymer materials due to the presence of nanoparticles (NPs). This is one problem that sets back the application of nanocomposites for their application in FETs.…”

Molecular Motions in Functional Self-Assembled Nanostructures

“…Ever since the pioneering studies in 1993 [124,125], organic-inorganic mono- and multilayer films gained significant attention for their tunable thicknesses, processing ease and insulating properties leading to their integration in organic transistors [6,7,44,126,127]. Especially, recently developed self-assembled nanodielectrics (SANDs) were found to exhibit promising properties for a variety of opto-electronic applications, including thin-film transistors (TFTs) (Figure 6) [7,126–128]. This new class of gate dielectrics consisting in the stacking of ordered active molecular assemblies onto solid surfaces allows optimizing device performance by their robust insulating properties.…”