Tunable threshold voltage and flatband voltage in pentacene field effect transistors

Wang, Annie; Kymissis, Ioannis; Bulović, Vladimir; Akinwande, Akintunde I.

doi:10.1063/1.2349299

Cited by 84 publications

(47 citation statements)

References 11 publications

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“…The results are consistent with other reports, and a plausible explanation is that UV treatment creates excess negatively charged sites on the pentacene/PMMA interface. 6,7 Accordingly, the S.S. was enlarged and the V th positively shifted. However, the linear field-effect mobility ͑ FET ͒ was not affected by UV treatment and was about 0.1 cm 2 /V s for both devices.…”

Section: Resultsmentioning

confidence: 97%

High Photoresponsivity of Pentacene-Based Organic Thin-Film Transistors with UV-Treated PMMA Dielectrics

Zan

Yen

2008

Electrochem. Solid-State Lett.

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A simple UV-treatment process for poly͑methyl methacrylate͒ ͑PMMA͒ dielectric is proposed to enhance photoresponsivity of pentacene-based organic thin-film transistors. The UV treatment creates excess negatively charged sites on the PMMA dielectric, which makes the device exhibit a large photoinduced current and prolongs persistent conductance recovery. In order to describe time-dependent photoinduced current, double-time constant equations are proposed. Based on time-constant fittings, slow-varied responses are found to be influenced by the UV treatment. The rapid-varied response is independent of gate bias and UV treatment. A plausible model for spatial carrier distribution is discussed and proposed to describe this observed phenomenon. © 2008 The Electrochemical Society. ͓DOI: 10.1149/1.2936224͔ All rights reserved. Organic thin-film transistors ͑OTFTs͒ have received intense attention due to their low cost, light weight, and low-temperature processing compatible with flexible substrates. The integration of OTFTs with other organic devices such as organic light emitting devices and organic solar cells also opens up the field of flexible optoelectronics.1,2 In this field, OTFTs not only act as field-effect transistors, but their application in phototransistors is also important for light detection and photoswitching. However, only a small number of researchers have published works on organic phototransistors. Researchers have observed reversible photocurrent and lightinduced threshold voltage shift.3-5 Pentacene-based OTFTs with Ta 2 O 5 gate dielectrics were also proposed to obtain high photoresponsivity. 4 In this paper, an approach to enhance photoresponsivity of pentacene-based OTFTs is proposed. By using poly͑methyl methacrylate͒ ͑PMMA͒ as the dielectric and applying UVlight treatment, photoresponsivity of OTFTs can be significantly enhanced. By analyzing the response lifetime, the underlying mechanism is investigated carefully. The proposed approach is simple and compatible with the development of all-organic electronics. ExperimentalFirst, the Ni/Pd bilayer was deposited on a glass substrate as a gate electrode. The PMMA was dissolved with a 95 wt % in anisole and was spun onto the gate electrodes. The following was the curing process. The glass substrate was heated with PMMA dielectric on a hot plate at 90°C for 30 min at atmosphere. The solvent was removed and the PMMA was solidified to serve as a gate dielectric. The thickness of the PMMA dielectric was about 360-370 nm. Then, some samples were exposed to UV light ͑Jelight Company, GLS-144 UV Lamp͒, with a wavelength of 175-285 nm and irradiation of 0.043 mW/cm 2 for 90 s. Both the UV-treated PMMA and the untreated ͑standard͒ PMMA dielectrics were transferred into a vacuum chamber for the deposition of 100 nm thick pentacene film and 100 nm thick gold ͑Au͒ electrodes. The device channel width ͑W͒ and length ͑L͒ were 1000 and 100 m, respectively. The illumination system was a combination of a probing bench ͑Cascade microtech, RHM-06͒ and a halogen lamp...

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Section: Resultsmentioning

confidence: 97%

High Photoresponsivity of Pentacene-Based Organic Thin-Film Transistors with UV-Treated PMMA Dielectrics

Zan

Yen

2008

Electrochem. Solid-State Lett.

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“…28 The oxygen plasma treatment instead of UV-ozone assisted reactions may further roughen the surface in comparison. Since parylene is known to degrade under UV irradiation, the plasma approach may be more gentle, since the UV degradation weakens the dielectric properties of parylene.…”

Section: Discussionmentioning

confidence: 99%

Towards flexible organic thin film transistors (OTFTs) for biosensing

Werkmeister

Nickel

2013

J. Mater. Chem. B

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We have studied parylene-N and parylene-C for their use as substrates and gate dielectrics in OTFTs. Parylene-N films with a thickness of 300 nm show the required dielectric properties, as verified by breakthrough-voltage measurements. The surface roughness measured for 300 nm thick parylene-N films is 4-5 nm. However, initial growth of parylene depends on the subjacent surface. This results in different thicknesses on Au electrodes and substrate materials for thin films. Capping of micro-

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“…2 and 3͔ displayed a significant gate hysteresis before and after passivation between forward ͑V GF ͒ and backward ͑V GB ͒ sweeps of the gate voltage. This phenomenon is often observed in CNT based transistors, and it is attributed to charge injection from nanotube at large gate voltages, 14 water molecules, 5 trapped charges at parylene-SWNT interface, 15 other trapped charges from solution processed CNTs 16 ͑e.g., surfactant, ionic molecules, etc.͒ and contamination originating during the fabrication of the device. 16 Prior to the deposition of the source and drain electrodes, the parylene-C surface was roughened in an oxygen plasma to improve the adhesion of chromium/ gold electrodes.…”

Section: Applied Physics Letters 97 153120 ͑2010͒mentioning

confidence: 99%

“…This oxygen plasma treatment breaks the bonds on the parylene surface and induces fixed and mobile charges at the parylene-SWNT interface which can create hysteresis in the CNT FETs. 15 Furthermore, DEP assembly was conducted using nanotubes suspended in deionized water, and both assembly and the I-V study were conducted in atmospheric conditions which all contribute to the observed hysteresis before encapsulation.…”

Section: Applied Physics Letters 97 153120 ͑2010͒mentioning

confidence: 99%

Parylene-C passivated carbon nanotube flexible transistors

Selvarasah

Busnaina

et al. 2010

Applied Physics Letters

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Carbon nanotubes are extremely sensitive to the molecular species in the environment and hence require a proper passivation technique to isolate them against environmental variations for the realization of reliable nanoelectronic devices. In this paper, we demonstrate a parylene-C passivation approach for CNT thin film transistors fabricated on a flexible substrate. The CNT transistors are encapsulated with 1 and 3 m thick parylene-C coatings, and the transistor characteristics are investigated before and after passivation. Our findings indicate that thin parylene-C films can be utilized as passivation layers for CNT transistors and this versatile technique can be readily applied for the encapsulation of CNT devices such as field effect transistors, p-n diodes, and logic circuits fabricated on flexible substrates. © 2010 American Institute of Physics. ͓doi:10.1063/1.3499758͔Single-walled carbon nanotubes ͑SWNTs͒ with their unique physical, electrical, and mechanical properties are being considered as a potential replacement for existing semiconducting materials in flexible electronics. Their mobility can exceed 10 5 cm 2 / V s −1 , and they have large current carrying ͑10 9 A / cm 2 ͒ capability, higher ON/OFF ratios ͑Ͼ10 5 ͒ and extreme mechanical flexibility. 1 SWNT based field effect transistors ͑FETs͒ exhibit p-type behavior in the ambient environment, and they can be converted to n-type by doping e.g., polymer functionalization. 2 Carbon nanotube ͑CNT͒ flexible devices such as high frequency FETs, p-n diodes, and logic circuits have already been reported. 3 Their large surface area to volume ratios and extreme sensitivity to the molecular species in the environment ͑e.g., oxygen, moisture, etc.͒ can significantly affect the electrical properties of CNT transistors. [4][5][6] To isolate SWNT based flexible transistors from environmental factors, thin and flexible passivation layers need to be investigated prior to deployment of these devices in real world applications.Several groups have already explored passivation of CNT based devices with thin polymeric films yet had limited success. For example, Dai et al. 5 have reported a 1.7 m polymer ͓polymethyl-methacrylate ͑PMMA͔͒ coating for passivating CNT based transistors. When the PMMA encapsulated devices were exposed to a humid ambient, the electrical characteristics of the transistors changed due to permeation of water molecules through PMMA. Similarly, Zhang et al. 7 used SU-8/PMMA ͑2 m / 200 nm͒ to passivate their CNT FETs. After exposing their devices to an NO 2 environment for 1 h, they have noted that the gas molecules diffused through the SU-8/PMMA layer and caused variations in the transistor behavior. In addition to polymeric encapsulants, Kaminishi et al. and Kim et al. 8 ͑15 nm deposited using atomic layer deposition ͑ALD͒ at 300°C͒ layers as passivation layers for CNT FETs. The drawback with both Si 3 N 4 and ALD based deposition methods is that both materials are either deposited at or require annealing steps at elevated temperatures which lim...

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Tunable threshold voltage and flatband voltage in pentacene field effect transistors

Cited by 84 publications

References 11 publications

High Photoresponsivity of Pentacene-Based Organic Thin-Film Transistors with UV-Treated PMMA Dielectrics

High Photoresponsivity of Pentacene-Based Organic Thin-Film Transistors with UV-Treated PMMA Dielectrics

Towards flexible organic thin film transistors (OTFTs) for biosensing

Parylene-C passivated carbon nanotube flexible transistors

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