Buried electrodes and protection of the semiconductor with a thin passivation layer are used to yield dual‐gate organic transducers. The process technology is scaled up to 150‐mm wafers. The transducers are potentiometric sensors where the detection relies on measuring a shift in the threshold voltage caused by changes in the electrochemical potential at the second gate dielectric. Analytes can only be detected within the Debye screening length. The mechanism is assessed by pH measurements. The threshold voltage shift depends on pH as ΔVth = (Ctop/Cbottom) × 58 mV per pH unit, indicating that the sensitivity can be enhanced with respect to conventional ion‐sensitive field‐effect transistors (ISFETs) by adjusting the ratio of the top and bottom gate capacitances. Remaining challenges and opportunities are discussed.
Gate-bias assisted charge injection in organic field-effect transistors Brondijk, J. J.; Torricelli, F.; Smits, E. C. P.; Blom, P. W. M.; de Leeuw, D. M. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum.
a b s t r a c tThe charge injection barriers in organic field-effect transistors (OFETs) seem to be far less critical as compared to organic light-emitting diodes (OLEDs). Counter intuitively; we show that the origin is image-force lowering of the barrier due to the gate bias at the source contact; although the corresponding gate field is perpendicular to the channel current. In coplanar OFETs; injection barriers up to 1 eV can be surmounted by increasing the gate bias; enabling extraction of bulk transport parameters in this regime. For staggered transistors; however; the injection is gate-assisted only until the gate bias is screened by the accumulation channel opposite to the source contact. The gate-assisted injection is supported by two-dimensional numerical charge transport simulations that reproduce the gate-bias dependence of the contact resistance and the typical S-shaped output curves as observed for OFETs with high injection barriers.
Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The transport of holes in polymer light-emitting diodes ͑PLEDs͒ based on poly͑2-methoxy, 5-͑2Ј ethylhexyloxy͒-p-phenylene vinylene͒ ͑MEH-PPV͒ is investigated as a function of layer thickness. For thicknesses smaller than 100 nm, the current in these thin PLEDs is strongly enhanced as compared to the expected space-charge limited ͑SCL͒ current. Applying the standard SCL model to measurements on a PLED with a thickness of only 40 nm results in an apparent increase of the hole mobility of a factor of 40. We show that this strong increase of the hole transport properties in these thin devices originates from the presence of an Ohmic hole contact. For Fermi-level alignment, holes diffuse from the contact into the MEH-PPV, forming an accumulation layer with a width of a few tens of nanometers. Due to the density dependence of the mobility, the hole transport in this accumulation region is strongly enhanced. For the analysis of thin PLEDs, it is therefore essential that both drift and diffusion of charge carriers are taken into account.
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