Nanoimprint lithography for organic electronics (original) (raw)
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Residue-free room temperature UV-nanoimprinting of submicron organic thin film transistors
Organic Electronics: physics, materials, applications, 2009
In this study we report on an innovative nanoimprint process for the fabrication of entirely patterned submicron OTFTs in a bottom-gate configuration. The method is based on UV-Nanoimprint Lithography (UV-NIL) combined with a novel imprint resist whose outstanding chemical and physical properties are responsible for the excellent results in structure transfer. In combination with a pretreated stamp the UV-curable resist enables residuefree imprinting thus making etching obsolete. A subsequent lift-off can be done with water. The UV-NIL process implies no extra temperature budget, is time saving due to short curing times, eco-friendly due to a water-based lift-off, simple because it is etch-free and completely r2r compatible. It works perfectly even if ultra-thin organic and hybrid films are used as gate dielectrics. On this basis entirely patterned functional submicron OTFTs with pentacene as the semiconductor are fabricated showing clear saturation, low switch-on voltage ($3 V) and a sufficiently high on-off ratio (10 3).
Photolithographic patterning of organic electronic materials
Organic electronics, 2006
The past two decades were characterized by tremendous progress in the performance of organic electronic devices such as light emitting diodes, thin film transistors, and photovoltaic cells [1], [2] and [3]. The progress has been so remarkable, that the term organic electronics is ...
Microelectronic Engineering, 2013
Solution processed poly(3-hexylthiophene) organic field effect transistors with channel lengths down to 750 nm were fabricated by nanoimprint assisted inkjet printing. The nanoimprint lithography was used to define sub-micron channels into a resist because of its high resolution. A silver-containing ink was inkjet-printed onto a pre-patterned resist layer to form a metallic film, which acts as source and drain electrodes after lift-off. This process replaces the expensive vacuum evaporation of gold electrodes. The transistor short channel effect was suppressed successfully by constant field downscaling. However, samples with inkjet-printed silver electrodes have limited current density. They also have lower effective charge mobility due to higher charge injection barrier, as well as the rough metal surface. Gold nanoparticles were added into the silver ink to modify its work function and therefore reduce the contact resistance between electrodes and polymer. This emphasizes the importance of the metal-semiconductor contact especially for short channel organic transistors.
Towards All-Organic Field-Effect Transistors by Additive Soft Lithography
Small, 2009
Unconventional nanofabrication is attractive for organic electronics because of its potential impact in manufacturing low-cost electronics starting from soluble precursors that can be processed and patterned via a sustainable technology. So far, the major endeavor aimed at the development of organicbased devices has been through the design of new materials, [2] novel synthetic procedures and purification methods, [3] optimized conditions for thin film growth, [4] and original methods for nanofabrication. In particular, a strong effort was devoted to the technological control of organic semiconductors in transistors. [2] Yet, only a limited number of studies have focused on new approaches for low cost fabrication of electrodes and their integration with the organic materials. Successful examples of unconventional electrode manufacturing include stencil printing of Au nanoparticles, inkjet printing, Ag electroless plating followed by microcontact patterning, lamination, microtransfer printing of Ag nanoparticles, metal transfer printing, and soft lithography. Although inkjet printing is probably the most straightforward example of an additive process where both the electrodes and the active layers can be realized on the same platform, the fabrication of the electrodes and the active layers often relies on different processes, specifications, and platforms. Precisely, standard microfabrication approaches consisting of photolithography and/or electron-beam lithography followed by vacuum metallization are generally used for the source and drain definition, while wet methods (spin-coating, layer-by-layer deposition, etc.) are employed for the deposition of the active layer. Clearly, there is a gap in material processing as these major device components are manufactured on different footings and often with severe compatibility limitations. It is therefore important to bridge this technological gap. Towards this direction, our contribution concerns the development of additive manufacturing processes on large areas, which are suitable for patterning both inorganic and organic materials at the micro-and nanoscale. Our methodology also lowers the processing costs by simplifying the fabrication steps. We report here on a simple and versatile way to fabricate micro-and nanoengineered organic field-effect transistors (OFETs) from solution processable materials by additive lithographic techniques. Remarkably, the electrical characteristics reveal that our soft-engineered OFETs perform better than their counterparts produced with standard microfabrication approaches. [14] The OFETs were built in a bottom-gate, bottom-contact architecture. Heavily-doped Si wafers were used both as substrates and gate terminals. The gate dielectrics consisted of thermally grown SiO 2 layers. As shown in , the electrodes were fabricated by micromolding-in-capillaries (MIMIC) [15] and, for comparison purposes, by drop-casting combined with photolithography. Similarly, the active layers were integrated by drop-casting and by lithographically controlled wetting (LCW), which ensures easy transfer of micro-and nanometric motifs from stamps to solution processable materials.
Microelectronic Engineering, 2012
P-type poly (3-hexylthiophene) (P3HT) organic field effect transistors (OFETs) with channel length down to 500 nm were fabricated. The gold source and drain electrodes were patterned using UV-based nanoimprint lithography and a lift-off process. To reduce mold costs, an opaque silicon nanoimprint-mold was used instead of expensive quartz molds for UV-nanoimprint. This new technique, called non-transparent UV-nanoimprint lithography, can be applied due to the impact of indirectly propagating light. Finally, the electrical performance of OFETs was tested. However, the OFETs with short channels show inhibited saturation ability and a weak gate control. The reasons for this short channel effect were discussed.
Patterning organic–inorganic thin-film transistors using microcontact printed templates
Applied Physics Letters, 2001
We report the simple, low-cost, and parallel fabrication of patterned organic-inorganic thin-film transistors ͑TFTs͒ by microcontact printing a molecular template on the substrate surface prior to film deposition. We printed molecules with hydrophobic tail groups on the gate oxide surfaces of TFTs to chemically, differentiate the substrate surface and confine the self-assembly of thin films, deposited from solutions flooded across the entire surface, to the transistor channels. TFTs are fabricated with good device characteristics and no current leakage. This process is more general to the patterning of other solution-deposited thin-film materials.
Organic thin-film transistors fabricated by microcontact printing
Applied Physics Letters, 2004
We have fabricated organic thin-film transistors (OTFTs) using a microcontact printing technique (μCP) that employs thin polydimethylsiloxane stamps on a rigid silicon substrate in order to reduce macroscopic distortions. Systematic variation of the printing pressure, printing time, and concentration of eicosanethiol, the “molecular ink” in the μCP process, permits the fabrication of devices with smaller channel lengths (Leff) than nominally defined by the stamp. Interdigitated Ti/Au electrode structures with Leff down to 100 nm could be fabricated which, after additional surface treatment and vacuum deposition of αα′-dihexylquaterthiophene, yield OTFTs with excellent characteristics.
Self-aligned flexible organic thin-film transistors with gates patterned by nano-imprint lithography
Organic Electronics, 2015
Many applications that rely on organic electronic circuits still suffer from the limited switching speed of their basic elements -the organic thin film transistor (OTFT). For a given set of materials the OTFT speed scales inversely with the square of the channel length, the parasitic gate overlap capacitance, and the contact resistance. For maximising speed we pattern transistor channels with lengths from 10 lm down to the sub-micrometre regime by industrially scalable UV-nanoimprint lithography. The reduction of the overlap capacitance is achieved by minimising the source-drain to gate overlap lengths to values as low as 0.2 lm by self-aligned electrode definition using substrate reverse side exposure. Pentacene based organic thin film transistors with an exceptionally low line edge roughness <20 nm of the channels, a mobility of 0.1 cm 2 /Vs, and an on-off ratio of 10 4 , are fabricated on 4 00 Â 4 00 flexible substrates in a carrier-free process scheme. The stability and spatial distribution of the transistor channel lengths are assessed in detail with standard deviations of L ranging from 185 to 28 nm. Such high-performing self-aligned organic thin film transistors enabled a ring-oscillator circuit with an average stage delay below 4 ls at an operation voltage of 7.5 V.
Patterning Poly(3-Hexylthiophene) in the Sub-50-nm Region by Nanoimprint Lithography
IEEE Transactions on Nanotechnology, 2011
We use thermal and room temperature nanoimprint lithography (NIL) for directly patterning the photoactive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT) in the sub-50-nm region. Different types of molds were used to directly imprint the desired structures into P3HT thin films. Good pattern transfer is achieved independent of the presence of other underlying polymer layers or the type of substrate incorporated. Further, we discuss the future application of this technology to the fabrication of ordered heterojuction organic photovoltaic devices and demonstrate that the NIL process involved does not damage the polymer or alter its chemical or electrical properties.
Organic transistors realized by an environmental friendly microcontact printing approach
Organic Electronics, 2010
A patterning method was developed that allows for combining the advantages of a low cost microcontact printing process on rigid and flexible substrates with the advantages of conventional semiconductor processing. The patterning approach combines printing of selfassembled monolayers with selective dewetting while being compatible with conventional semiconductor processes. Alkyl thiol self-assembled monolayers were printed on gold and silver films on rigid and flexible substrates. The printed regions turn hydrophobic while the bare regions remain hydrophilic. The hydrophilic regions of the surface were selectively wetted by a polymer like poly-methyl methacrylate. The selectively patterned poly-methyl methacrylate is used as etch resist while the bare regions of the gold film were patterned by a potassium iodide/iodine solution. The potassium iodide/iodine etchant is compatible with conventional semiconductor processing in contrast to the commonly used ferri/ferrocyanide etching solutions. The method allows for patterning of gold and silver films with submicron dimension on flexible and rigid substrates. Organic thin-film transistors were realized with drain and source fabricated by the proposed approach. The performance of the organic transistor is comparable to devices fabricated by photolithography.