Vapor Phase Self-Assembly of Molecular Gate Dielectrics for Thin Film Transistors

DiBenedetto, Sara A.; Frattarelli, David; Ratner, Mark A.; Facchetti, Antonio; Marks, Tobin J.

doi:10.1021/ja801309g

Cited by 65 publications

(66 citation statements)

References 36 publications

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“…18) was demonstrated. [269] In addition, the structures of the new molecular constituents (1 and 2) are improved over the original molecular component (Stb) of SANDs by (i) their ability to self-assemble via head-to-tail intra-molecular hydrogen-bonds, and (ii) anticipated larger molecular polarizabilities than Stb. Here, the trends in dielectric permittivities are evaluated qualitatively using the Clausius-Mossotti relation e / (3 þ 2aN)/(3 À aN) (where a is the polarizability along the conjugated long axis of the molecule and N is the molecular density in cm…”

Section: à2mentioning

confidence: 99%

Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications

DiBenedetto¹,

Facchetti²,

Ratner³

et al. 2009

Advanced Materials

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575

544

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Principal goals in organic thin‐film transistor (OTFT) gate dielectric research include achieving: (i) low gate leakage currents and good chemical/thermal stability, (ii) minimized interface trap state densities to maximize charge transport efficiency, (iii) compatibility with both p‐ and n‐ channel organic semiconductors, (iv) enhanced capacitance to lower OTFT operating voltages, and (v) efficient fabrication via solution‐phase processing methods. In this Review, we focus on a prominent class of alternative gate dielectric materials: self‐assembled monolayers (SAMs) and multilayers (SAMTs) of organic molecules having good insulating properties and large capacitance values, requisite properties for addressing these challenges. We first describe the formation and properties of SAMs on various surfaces (metals and oxides), followed by a discussion of fundamental factors governing charge transport through SAMs. The last section focuses on the roles that SAMs and SAMTs play in OTFTs, such as surface treatments, gate dielectrics, and finally as the semiconductor layer in ultra‐thin OTFTs.

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Section: à2mentioning

confidence: 99%

Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications

DiBenedetto¹,

Facchetti²,

Ratner³

et al. 2009

Advanced Materials

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575

544

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“…Previous work has shown that materials with large (hyper)polarizabilities generally exhibit significantly higher dielectric responses than other molecular materials. 21,39,40 In this regard, electron-donating and electron-accepting moieties are known to enhance molecular (hyper)polarizabilities when introduced in tandem to conjugated π-systems. 41−44 These molecular materials, commonly referred to as DBA materials ( Figure 1) have inspired significant research in the scientific community for implementation in nonlinear optics, 44−47 charge transfer, 48−50 and charge transport.…”

Section: ■ Introductionmentioning

confidence: 99%

Molecular Donor–Bridge–Acceptor Strategies for High-Capacitance Organic Dielectric Materials

Marks

Ratner

2015

J. Am. Chem. Soc.

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Donor-bridge-acceptor (DBA) systems occupy a rich history in molecular electronics and photonics. A key property of DBA materials is their typically large and tunable (hyper)polarizabilities. While traditionally, classical descriptions such as the Clausius-Mossotti formalism have been used to relate molecular polarizabilities to bulk dielectric response, recent work has shown that these classical equations are inadequate for numerous materials classes. Creating high-dielectric organic materials is critically important for utilizing unconventional semiconductors in electronic circuitry. Employing a plane-wave density functional theory formalism, we investigate the dielectric response of highly polarizable DBA molecule-based thin films. Such films are found to have large dielectric response arising from cooperative effects between donor and acceptor units when mediated by a conjugated bridge. Moreover, the dielectric response can be systematically tuned by altering the building block donor, acceptor, or bridge structures and is found to be nonlinearly dependent on electric field strength. The computed dielectric constants are largely independent of the density functional employed, and qualitative trends are readily evident. Remarkably large computed dielectric constants >15.0 and capacitances >6.0 μF/cm(2) are achieved for squaraine monolayers, significantly higher than in traditional organic dielectrics. Such calculations should provide a guide for designing high-capacitance organic dielectrics that should greatly enhance transistor performance.

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“…[ 21 ] R-SAND was prepared by depositing a ∼ 5 nm thick v-SiO x layer on the as-fabricated SAND via the post-crosslinking of a vapor-deposited HCDS fi lm. [ 28 ] For capacitance and leakage current characterization, ∼ 50 nm Au or ∼ 80 nm a-ZITO TOC top contact electrodes were deposited on the n + -Si/SAND and n + -Si/R-SAND samples by vacuum thermal evaporation at ∼ 2.0 × 10 − 6 Torr or by PLD, respectively, using shadow masks to defi ne 200 μ m × 200 μ m electrodes. For TFTs, ∼ 40 nm a-ZITO TOS fi lms were fi rst deposited, followed by Au or ZITO source/drain electrode deposition through shadow masks to produce 100 μ m × 2000 μ m channels.…”

Section: Methodsmentioning

confidence: 99%

“…[ 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.…”

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confidence: 99%

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

Hennek

Buchholz

et al. 2011

Advanced Materials

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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...

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Vapor Phase Self-Assembly of Molecular Gate Dielectrics for Thin Film Transistors

Cited by 65 publications

References 36 publications

Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications

Molecular Self‐Assembled Monolayers and Multilayers for Organic and Unconventional Inorganic Thin‐Film Transistor Applications

Molecular Donor–Bridge–Acceptor Strategies for High-Capacitance Organic Dielectric Materials

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

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