Experimental determination of the lateral resolution of surface electric potential measurements by Kelvin probe force microscopy using biased electrodes separated by a nanoscale gap and application to thin-film transistors

Brouillard, Mélanie; Bercu, Nicolas Bogdan; Zschieschang, Ute; Simonetti, Olivier; Mittapalli, Rakesh; Klauk, Hagen; Giraudet, L.

doi:10.1039/d1na00824b

Cited by 4 publications

(1 citation statement)

References 31 publications

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“…[70,72] The feasibility of patterning channel lengths as small as a few tens of nanometers has also been demonstrated, albeit thus far only on rigid silicon substrates. [60][61][62][63]74] The static current-voltage characteristics of organic TFTs with such small channel lengths will possibly suffer from a less well-defined offstate behavior, including a larger off-state drain current and a larger subthreshold swing, unless the gate-dielectric thickness is decreased to about 5 nm. [67,71] These considerations notwithstanding, the fabrication of flexible organic TFTs with channel lengths and gate-to-contact overlaps as small as about 50 nm and transit frequencies in excess of 100 MHz (and potentially approaching 1 GHz) is entirely feasible with the help of electronbeam lithography.…”

Section: Substratementioning

confidence: 99%

High‐Resolution Lithography for High‐Frequency Organic Thin‐Film Transistors

Zschieschang

Klauk

Borchert

2023

Adv Materials Technologies

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Organic thin-film transistors are field-effect transistors comprising a semiconductor in the form of a thin, typically polycrystalline layer of conjugated organic molecules. Since organic transistors can often be fabricated at temperatures no higher than about 100 °C, they are potentially useful for flexible, large-area electronics applications. An important performance parameter of organic transistors is the transit frequency, which is the highest frequency at which the transistors can be operated. The transit frequency of organic transistors is determined in large part by the channel length and the parasitic gate-to-source and gate-to-drain overlap lengths. How small these dimensions can be made depends (at least in the case of transistors fabricated in the lateral device architecture) greatly on the resolution of the lithography method that is utilized for the patterning of the gate electrodes and the source and drain contacts. Patterning methods that have yielded organic transistors with lateral dimensions sufficiently small to provide transit frequencies above 10 MHz include photolithography, laser lithography, stencil lithography, and electron-beam lithography. In this review, these four lithography methods and their roles in the fabrication of high-frequency organic transistors, as well as their prospects for future improvements in the dynamic performance of organic transistors, will be illuminated.

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Section: Substratementioning

confidence: 99%

High‐Resolution Lithography for High‐Frequency Organic Thin‐Film Transistors

Zschieschang

Klauk

Borchert

2023

Adv Materials Technologies

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Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin probe force microscopy

et al. 2023

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The disordered microscopic structure of amorphous semiconductors causes the formation of band tails in the density of states (DOS) that strongly affect charge transport properties. Such band tail properties are crucial for understanding and optimizing thin-film device performance with immense relevance for large area electronics. Among the available techniques to measure the DOS, Kelvin Probe Force Microscopy (KPFM) is exceptional as it enables precise local electronic investigations combined with microscopic imaging. However, a model to interpret KPFM spectroscopy data on amorphous semiconductors of finite thickness is lacking. To address this issue, we provide an analytical solution to the Poisson equation for a metal–insulator–semiconductor junction interacting with the atomic force microscope tip. The solution enables us to fit experimental data for semiconductors with finite thickness and to obtain DOS parameters, such as band tail width, doping density, and flat band potential. To demonstrate our method, we perform KPFM experiments on Indium–Gallium–Zinc Oxide (IGZO) thin-film transistors (IGZO-TFTs). DOS parameters compare well with values obtained with photocurrent spectroscopy. We demonstrate the relevance of the developed method by investigating the impact of ionizing radiation on DOS parameters and TFT performance. Our results provide clear evidence that the observed shift in threshold voltage is caused by static charge in the gate dielectric, leading to a shift in flat band potential. Band-tails and doping density are not affected by the radiation. The developed methodology can be easily translated to different semiconductor materials and paves the way for quantitative microscopic mapping of local DOS parameters in thin-film devices.

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Beyond the blur: Using experimentally determined point spread functions to improve scanning Kelvin probe imaging

Lenton,

Pertl,

Shafeek

et al. 2024

Journal of Applied Physics

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Scanning Kelvin probe microscopy (SKPM) is a powerful technique for investigating the electrostatic properties of material surfaces, enabling the imaging of variations in work function, topology, surface charge density, or combinations thereof. Regardless of the underlying signal source, SKPM results in a voltage image, which is spatially distorted due to the finite size of the probe, long-range electrostatic interactions, mechanical and electrical noise, and the finite response time of the electronics. In order to recover the underlying signal, it is necessary to deconvolve the measurement with an appropriate point spread function (PSF) that accounts the aforementioned distortions, but determining this PSF is difficult. Here, we describe how such PSFs can be determined experimentally and show how they can be used to recover the underlying information of interest. We first consider the physical principles that enable SKPM and discuss how these affect the system PSF. We then show how one can experimentally measure PSFs by looking at well-defined features, and that these compare well to simulated PSFs, provided scans are performed extremely slowly and carefully. Next, we work at realistic scan speeds and show that the idealized PSFs fail to capture temporal distortions in the scan direction. While simulating PSFs for these situations would be quite challenging, we show that measuring PSFs with similar scan conditions works well. Our approach clarifies the basic principles and inherent challenges to SKPM measurements and gives practical methods to improve results.

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Experimental determination of the lateral resolution of surface electric potential measurements by Kelvin probe force microscopy using biased electrodes separated by a nanoscale gap and application to thin-film transistors

Abstract: The lateral resolution of a double-pass Kelvin probe force microscopy system is estimated using 12 nm gap electrodes. The electric fields at the source contact of organic thin film transistors fabricated by stencil or e-beam lithography are compared.

Cited by 4 publications

References 31 publications

High‐Resolution Lithography for High‐Frequency Organic Thin‐Film Transistors

High‐Resolution Lithography for High‐Frequency Organic Thin‐Film Transistors

Accurate determination of band tail properties in amorphous semiconductor thin film with Kelvin probe force microscopy

Beyond the blur: Using experimentally determined point spread functions to improve scanning Kelvin probe imaging

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