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Switching from weakly to strongly limited injection in self-aligned, nano-patterned organic transistors

View Article: PubMed Central - PubMed

ABSTRACT

Organic thin-film transistors for high frequency applications require large transconductances in combination with minimal parasitic capacitances. Techniques aiming at eliminating parasitic capacitances are prone to produce a mismatch between electrodes, in particular gaps between the gate and the interlayer electrodes. While such mismatches are typically undesirable, we demonstrate that, in fact, device structures with a small single-sided interlayer electrode gap directly probe the detrimental contact resistance arising from the presence of an injection barrier. By employing a self-alignment nanoimprint lithography technique, asymmetric coplanar organic transistors with an intentional gap of varying size (< 0.2 μm) between gate and one interlayer electrode are fabricated. An electrode overlap exceeding 1 μm with the other interlayer has been kept. Gaps, be them source or drain-sided, do not preclude transistor operation. The operation of the device with a source-gate gap reveals a current reduction up to two orders of magnitude compared to a source-sided overlap. Drift-diffusion based simulations reveal that this marked reduction is a consequence of a weakened gate-induced field at the contact which strongly inhibits injection.

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(a,b) Electrostatic potential at the semiconductor-dielectric interface, namely the steady-state potential (solid line) and the potential prior starting the injection of charges (dashed line) for (a) an overlap and (b) a gap between source and gate for the operation at VDS = −14 V and VGS = −12 V with an injection barrier of 0.5 eV and a mobility of 1 cm2V−1s−1. (c,d) Average electric field in the steady state (solid arrow) and initial state (dashed line) present in the region extending 100 nm from the position of the source electrode towards the drain. (e) Steady-state hole distribution at the interface for the overlap (black) and gap situation (red). The crosses mark the channel position at which depletion turns into accumulation. (f) Contact voltage VC as a function of the gate bias for a gap (open circles) and an overlap (filled squares) between source and gate for a mobility of μ = 1 cm2V−1s−1 (black symbols) and 10−3 cm2V−1s−1 (grey symbols). As a guide to the eye, the relation VC = /VGS/ is indicated by a dashed line.
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f4: (a,b) Electrostatic potential at the semiconductor-dielectric interface, namely the steady-state potential (solid line) and the potential prior starting the injection of charges (dashed line) for (a) an overlap and (b) a gap between source and gate for the operation at VDS = −14 V and VGS = −12 V with an injection barrier of 0.5 eV and a mobility of 1 cm2V−1s−1. (c,d) Average electric field in the steady state (solid arrow) and initial state (dashed line) present in the region extending 100 nm from the position of the source electrode towards the drain. (e) Steady-state hole distribution at the interface for the overlap (black) and gap situation (red). The crosses mark the channel position at which depletion turns into accumulation. (f) Contact voltage VC as a function of the gate bias for a gap (open circles) and an overlap (filled squares) between source and gate for a mobility of μ = 1 cm2V−1s−1 (black symbols) and 10−3 cm2V−1s−1 (grey symbols). As a guide to the eye, the relation VC = /VGS/ is indicated by a dashed line.

Mentions: To explain the interplay between injection at the contact and charge transport, we first inspect the local potential and hole density distribution for a situation in which the currents differ markedly. Figure 4 compares the potential distribution (solid lines in Fig. 4a,b) and the hole distribution (Fig. 4e) along the dielectric-semiconductor interface at VGS = −12 V. In all plots, the injecting contact, i.e., the source contact, is placed on the left side; the edge of the source contact corresponds to channel position zero.


Switching from weakly to strongly limited injection in self-aligned, nano-patterned organic transistors
(a,b) Electrostatic potential at the semiconductor-dielectric interface, namely the steady-state potential (solid line) and the potential prior starting the injection of charges (dashed line) for (a) an overlap and (b) a gap between source and gate for the operation at VDS = −14 V and VGS = −12 V with an injection barrier of 0.5 eV and a mobility of 1 cm2V−1s−1. (c,d) Average electric field in the steady state (solid arrow) and initial state (dashed line) present in the region extending 100 nm from the position of the source electrode towards the drain. (e) Steady-state hole distribution at the interface for the overlap (black) and gap situation (red). The crosses mark the channel position at which depletion turns into accumulation. (f) Contact voltage VC as a function of the gate bias for a gap (open circles) and an overlap (filled squares) between source and gate for a mobility of μ = 1 cm2V−1s−1 (black symbols) and 10−3 cm2V−1s−1 (grey symbols). As a guide to the eye, the relation VC = /VGS/ is indicated by a dashed line.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5037384&req=5

f4: (a,b) Electrostatic potential at the semiconductor-dielectric interface, namely the steady-state potential (solid line) and the potential prior starting the injection of charges (dashed line) for (a) an overlap and (b) a gap between source and gate for the operation at VDS = −14 V and VGS = −12 V with an injection barrier of 0.5 eV and a mobility of 1 cm2V−1s−1. (c,d) Average electric field in the steady state (solid arrow) and initial state (dashed line) present in the region extending 100 nm from the position of the source electrode towards the drain. (e) Steady-state hole distribution at the interface for the overlap (black) and gap situation (red). The crosses mark the channel position at which depletion turns into accumulation. (f) Contact voltage VC as a function of the gate bias for a gap (open circles) and an overlap (filled squares) between source and gate for a mobility of μ = 1 cm2V−1s−1 (black symbols) and 10−3 cm2V−1s−1 (grey symbols). As a guide to the eye, the relation VC = /VGS/ is indicated by a dashed line.
Mentions: To explain the interplay between injection at the contact and charge transport, we first inspect the local potential and hole density distribution for a situation in which the currents differ markedly. Figure 4 compares the potential distribution (solid lines in Fig. 4a,b) and the hole distribution (Fig. 4e) along the dielectric-semiconductor interface at VGS = −12 V. In all plots, the injecting contact, i.e., the source contact, is placed on the left side; the edge of the source contact corresponds to channel position zero.

View Article: PubMed Central - PubMed

ABSTRACT

Organic thin-film transistors for high frequency applications require large transconductances in combination with minimal parasitic capacitances. Techniques aiming at eliminating parasitic capacitances are prone to produce a mismatch between electrodes, in particular gaps between the gate and the interlayer electrodes. While such mismatches are typically undesirable, we demonstrate that, in fact, device structures with a small single-sided interlayer electrode gap directly probe the detrimental contact resistance arising from the presence of an injection barrier. By employing a self-alignment nanoimprint lithography technique, asymmetric coplanar organic transistors with an intentional gap of varying size (< 0.2 μm) between gate and one interlayer electrode are fabricated. An electrode overlap exceeding 1 μm with the other interlayer has been kept. Gaps, be them source or drain-sided, do not preclude transistor operation. The operation of the device with a source-gate gap reveals a current reduction up to two orders of magnitude compared to a source-sided overlap. Drift-diffusion based simulations reveal that this marked reduction is a consequence of a weakened gate-induced field at the contact which strongly inhibits injection.

No MeSH data available.


Related in: MedlinePlus