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Photo-polymerization as a tool for engineering the active material in organic field-effect transistors
Umeå University, Faculty of Science and Technology, Physics. (The Organic Photonics & Electronics Group)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The emergence of organic semiconductors is exciting since it promises to open up for straightforward and low-cost fabrication of a wide range of efficient and novel electronic devices. However, in order for this promise to become reality it is critical that new and functional fabrication techniques are developed. This thesis demonstrates the conceptualization, development, realization and implementation of a particularly straightforward and scalable fabrication process: the photo-induced and resist-free imprint patterning technique.Initial experiments revealed that some members of a group of carbon-cage molecular semiconductors – termed fullerenes – can be photochemically modified into dimeric or polymeric structures during exposure to laser light, and, importantly, that the exposed fullerene material retains its good electron-transport property while its solubility in common organic solvents is drastically lowered. With this information at hand, it was possible to design and create well-defined patterns in a solution-deposited fullerene film by exposing selected film areas to laser light and then developing the entire film in a tuned developer solution. An electronically active fullerene pattern emerges at the locations defined by the incident laser beam, and the patterning technique was successfully utilized for the fabrication of arrays of efficient field-effect transistors.In a later stage, the capacity of the photo-induced and resist-free imprint technique was demonstrated to encompass the fabrication of ubiquitous and useful CMOS circuits. These are based on a combination of p-type and n-type transistors, and a blend between a p-type organic semiconductor and an n-type fullerene compound was designed so that the latter dominated. By solution-depositing the blend film on an array of transistor structures, exposing selected transistors to laser light, and then developing the entire transistor array in a developer solution, it was possible to establish a desired combination of (non-exposed) p-type transistors and (exposed) n-type transistors. We finally utilized this combination of transistors for the fabrication of a CMOS circuit in the form of well a-functional organic inverter stage.

Place, publisher, year, edition, pages
Umeå: Print & Media , 2009. , 50 p.
Keyword [en]
Field-effect transistor, photo-polymerization, PCBM, C60, Fullerene
National Category
Physical Sciences
Research subject
Solid State Physics
Identifiers
URN: urn:nbn:se:umu:diva-22127ISBN: 978-91-7264-779-4 (print)OAI: oai:DiVA.org:umu-22127DiVA: diva2:212767
Public defence
2009-05-20, NA430, SE-90187 Umea, Umea, 13:00 (English)
Opponent
Supervisors
Available from: 2009-04-24 Created: 2009-04-23 Last updated: 2009-04-24Bibliographically approved
List of papers
1. C60 Field-Effect Transistors: Effects of Polymerization on electronic Properties and Device Performance.
Open this publication in new window or tab >>C60 Field-Effect Transistors: Effects of Polymerization on electronic Properties and Device Performance.
2007 (English)In: Physical Review B, Vol. 75, no 7, 075203- p.Article in journal (Refereed) Published
Abstract [en]

We have investigated thin-film field-effect transistors (TFTs) with C60 as the active material, and we report the effects of photo-induced polymerization of the C60 film. We find that the effects of a complete polymerization for a typical top-contact C60 TFT is as follows: the electron mobility (μn) at room temperature drops slightly from 0.074 to 0.068 cm2/Vs, the activation energy of μn decreases from 0.10 meV to 0.09 meV, and the threshold voltage for TFT operation decreases markedly by ~15 %. The latter observation suggests that the effective number of electron traps in the C60 film decreases following polymerization. Considering that the polymerization was achieved with a low-energy HeNe laser, it is conceivable that the polymerization approach could be of interest for applications, e.g., organic bulk-heterojunction solar cells, where a stabilized C60 morphology attained with benign means is desired

Identifiers
urn:nbn:se:umu:diva-11904 (URN)
Available from: 2007-12-13 Created: 2007-12-13 Last updated: 2011-01-11Bibliographically approved
2. Photo-induced and resist-free imprint patterning of fullerene materials for use in functional electronics
Open this publication in new window or tab >>Photo-induced and resist-free imprint patterning of fullerene materials for use in functional electronics
2009 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 11, 4006-4011 p.Article in journal (Refereed) Published
Abstract [en]

We report a novel and potentially generic method for the efficient patterning of films of organic semiconductors and demonstrate the merit of the method on the high-solubility fullerene [6,6]-phenyl C61- butyric acid methyl ester (PCBM). The patterning technique is notably straightforward as it requires no photoresist material and encompasses only two steps: (i) exposure of select film areas to visible laser light during which the PCBM mononer is photochemically converted into a dimeric state, and (ii) development via solvent washing after which the nonexposed portions of the PCBM film are selectively removed. Importantly, the method is highly benign in that it leaves the electronic properties of the remaining patterned material intact, which is directly evidenced by the fact that we fabricate fully functional arrays of micrometersized field-effect transistors with patterned PCBM as the active material.

Place, publisher, year, edition, pages
Washington, DC, USA: American Chemical Society, 2009
Keyword
Thin-film transistors, field-effect transistors, plastic solar-cells, C-60 films, soft lithography, MDMO-PPV, devices, spectroscopy, absorption, deposition
National Category
Atom and Molecular Physics and Optics
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-22134 (URN)10.1021/ja807964x (DOI)
Available from: 2009-04-24 Created: 2009-04-24 Last updated: 2012-05-11Bibliographically approved
3. Facile fabrication of organic CMOS circuits via photo-induced imprinting of a single-layer blend
Open this publication in new window or tab >>Facile fabrication of organic CMOS circuits via photo-induced imprinting of a single-layer blend
(English)Article in journal (Other academic) Submitted
Abstract [en]

Organic electronic circuits based on a combination of n- and p-type transistors (so-called CMOS circuits) are attractive, since they promise the realization of a manifold of versatile and low-cost electronic devises. Here, we report a novel photo-induced imprinting method, which allows for a particularly straightforward fabrication of highly functional organic CMOS circuits. A single-layer blend film, comprising a mixture of the n-type semiconductor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and the p-type semicondutor poly-3-hexylthiophene (P3HT) in a 3:1 mass ratio, was deposited from solution onto an array of transistor structures on a substrate. By exposing select film areas to laser light, the PCBM monomers were photo-chemically transformed into a low-solubility and high-mobility dimeric state. Thereafter, the entire film was developed by immersing the substrate into a developer solution, which selectively removed the non-exposed, and monomeric, PCBM. The end result was that the transistors in the exposed areas are n-type, as dimeric PCBM is the majority component, while the transistors in the non-exposed areas are p-type, as P3HT is the sole remaining material. We demonstrate the merit of the method by utilizing the combination of n-type and p-type transistors for the realization of CMOS inverters with a high gain of ~35.

Keyword
organic electronics, field-effect transistor, CMOS, inverter, fullerene, PCBM, P3HT
Identifiers
urn:nbn:se:umu:diva-22135 (URN)
Available from: 2009-04-24 Created: 2009-04-24
4. Facile fabrication of organic CMOS circuits: understanding and optimization of the process
Open this publication in new window or tab >>Facile fabrication of organic CMOS circuits: understanding and optimization of the process
Show others...
(English)Manuscript (Other academic)
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:umu:diva-22136 (URN)
Available from: 2009-04-24 Created: 2009-04-24 Last updated: 2012-02-02Bibliographically approved

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