Origin of the bias stress instability in single-crystal organic field-effect transistors

Lee, B.; Wan, A.; Mastrogiovanni, Daniel; Anthony, John E.; Garfunkel, Eric; Podzorov, Vitaly

doi:10.1103/physrevb.82.085302

Cited by 80 publications

(96 citation statements)

References 15 publications

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“…We found severe carrier trapping for both electron and hole injection, indicative of bias stress: the trapping of injected charges, likely to occur at the semiconductor/dielectric interface. [28][29][30] Bias stress results in many trapped charges sceening the applied electric field, and a subsequent shift in the threshold voltage as a function of time. 24 The manifestation of trapping in the IR measurements, where repeated voltage applications are necessary, is discussed later.…”

Section: Resultsmentioning

confidence: 99%

Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

et al. 2014

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A resurgence in the use of the donor-acceptor (DA) approach in synthesizing conjugated polymers has resulted in a family of high-mobility ambipolar systems with exceptionally narrow energy bandgaps below 1 eV. The ability to transport both electrons and holes is critical for device applications such as organic light-emitting diodes (OLEDs) and transistors (OLETs). Infrared spectroscopy offers direct access to the low-energy excitations associated with injected charge carriers. Here we use a diffraction-limited IR microscope to probe the spectroscopic signatures of electron and hole injection in the conduction channel of an organic field-effect transistor (OFET) based on an ambipolar DA polymer polydiketopyrrolopyrrole-benzobisthiadiazole (PDPPBBT). We observe distinct polaronic absorptions for both electrons and holes, and spatially map the carrier distribution from the source to drain electrodes for both unipolar and ambipolar biasing regimes. For ambipolar device configurations, we observe the spatial evolution of hole-induced to electron-induced polaron absorptions throughout the transport path. Our work provides a platform for combined transport and infrared studies of organic semiconductors on micron length scales relevant to functional devices.

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Section: Resultsmentioning

confidence: 99%

Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

et al. 2014

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“…1. The trend of a decreasing relaxation time with increasing HOMO energy was recently also found by Lee et al 13 A quantitative analysis is presented below.…”

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confidence: 90%

Influence of the semiconductor oxidation potential on the operational stability of organic field-effect transistors

Sharma

Mathijssen

Bobbert

et al. 2011

Applied Physics Letters

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During prolonged application of a gate bias, organic field-effect transistors show a gradual shift of the threshold voltage towards the applied gate bias voltage. The shift follows a stretched-exponential time dependence governed by a relaxation time. Here, we show that a thermodynamic analysis reproduces the observed exponential dependence of the relaxation time on the oxidation potential of the semiconductor. The good fit with the experimental data validates the underlying assumptions. It demonstrates that this operational instability is a straightforward thermodynamically driven process that can only be eliminated by eliminating water from the transistor.

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“…It was observed that the physical and chemical nature of the dielectric/organic interface plays a major role in determining the magnitude this effect 10,11 , but the precise microscopic origin of the phenomenon has remained elusive. Two possible mechanisms have been proposed for p-channel (hole accumulation) devices: one scenario attributes the effect to holes that are transferred from the FET channel to localized states in the gate insulator 11 ; another scenario invokes hole-assisted generation of protons in the presence of water, with the protons subsequently diffusing into the gate dielectric 10 . Both mechanisms lead to the accumulation of 3 positive charge (protons or holes) in the dielectric, which screens the external applied gate voltage, resulting in a reduction of the source-drain current.…”

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confidence: 99%

Very low bias stress in n-type organic single-crystal transistors

Barra¹,

Girolamo²,

Minder³

et al. 2012

Applied Physics Letters

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Bias stress effects in n-channel organic field-effect transistors (OFETs) are investigated using PDIF-CN 2 single-crystal devices with Cytop gate dielectric, both under vacuum and in ambient. We find that the amount of bias stress is very small as compared to all (p-channel) OFETs reported in the literature. Stressing the PDIF-CN 2 devices by applying 80 V to the gate for up to a week results in a decrease of the source drain current of only ~1% under vacuum and ~10% in air. This remarkable stability of the devices leads to characteristic time constants, extracted by fitting the data with a stretched exponential -that are τ ~ 2·10 9 s in air and τ ~ 5·10 9 s in vacuumapproximately two orders of magnitude larger than the best values reported previously for pchannel OFETs. KEYWORDS:Bias stress, Single-crystals, organic n-type transistors. Over the last few years, high-quality n-type transistors based on organic semiconductors have been demonstrated 1 , with performance close to that of the best p-type devices 2 , and capable of operating under ambient conditions. Among these new n-type materials, Perylene Diimide molecules have received great attention, due to both their self-assembling properties and the tunability of the LUMO level, resulting in highly robust charge transport properties 3 . Currently, N,7 and 1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s (PDIF-CN 2 ) is probably the most attractive compound. Thin films can be deposited both by evaporation 4 and from solution 5 leading to high carrier mobility. Single crystal devices 6 exhibit outstanding properties, including the largest electron mobility values 7 reported for n-type organic FETs and band-like electron transport 8 . With these new molecular materials enabling top quality n-type FETs to be realized, it becomes important to explore all aspects of the device electrical characteristics that could limit the device performance.From a practical point of view, an important issue is the degradation of the field-effect transistor performance under prolonged application of a gate voltage (V GS ). This phenomenon, known as bias stress 9 , consists in the continuous decrease of the drain-source current (I DS ) when the transistor is driven in the accumulation regime. The bias stress effect has been widely investigated for p-channel devices. It was observed that the physical and chemical nature of the dielectric/organic interface plays a major role in determining the magnitude this effect 10,11 , but the precise microscopic origin of the phenomenon has remained elusive. Two possible mechanisms have been proposed for p-channel (hole accumulation) devices: one scenario attributes the effect to holes that are transferred from the FET channel to localized states in the gate insulator 11 ; another scenario invokes hole-assisted generation of protons in the presence of water, with the protons subsequently diffusing into the gate dielectric 10 . Both mechanisms lead to the accumulation of 3 positive charge (protons or holes) in the dielectric, which sc...

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Origin of the bias stress instability in single-crystal organic field-effect transistors

Cited by 80 publications

References 15 publications

Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

Electron and hole polaron accumulation in low-bandgap ambipolar donor-acceptor polymer transistors imaged by infrared microscopy

Influence of the semiconductor oxidation potential on the operational stability of organic field-effect transistors

Very low bias stress in n-type organic single-crystal transistors

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