Growth of organic crystalline thin films with strong second-order nonlinearity for integrated optics

We demonstrate the growth of highly nonlinear crystalline thin films of N-benzyl-2-methyl-4-nitroaniline (BNA) with a controllable crystal orientation. These films are obtained by crystallizing the material in a temperature gradient. Through second-harmonic generation experiments at a fundamental wavelength of 1550 nm, we found a second-order nonlinearity of (153 ± 70) pm/V. This greatly exceeds the value of 54 pm/V for LiNbO3, the benchmark nonlinear crystal. Moreover, the crystalline films are grown on amorphous substrates with processing temperatures not exceeding 115°C, making them suitable for back-end photonic integration on a CMOS chip. We envisage the growth of BNA crystalline films on silicon nitride photonic integrated circuits, where a strong second-order nonlinearity is lacking

Integration of highly crystalline C8-BTBT thin-films into simple logic gates and circuits

Highly crystalline organic thin films possess the charge carrier mobilities needed for high-performance, low-cost flexible electronics. However, only few reports exist that show the integration of these films into short-channel organic circuits. This work describes the integration of highly crystalline layers of the thermally and chemically fragile small molecule C8-BTBT. Thin films of this material are processed by a combination of zone-casting and homoepitaxial vacuum evaporation and display an average charge carrier mobility of 7.5 cm2/V in long channel transistors. The integration of these films into a circuit technology based on a 5 μm channel-length bottom-gate bottom-contact transistor topology results in inverters with gains up to 40 as well as a robust 19-stage ring oscillator. This circuit requires the simultaneous operation of 80 TFTs and displays a stage delay of 40 μs, resulting in an operating frequency of 630 Hz at an operating voltage of 10 V. With the help of circuit modelling, we quantify the relationship between the speed of ring oscillators and the contact resistance of individual transistors. Indeed, the successful integration of highly-crystalline layers with high intrinsic mobility stresses the need for advances in contact engineering

Growth of pentacene thin films by in-line organic vapor phase deposition

We present the extension of the organic vapor phase deposition technique to an in-line geometry, in which the sample travels underneath an elongated showerhead that sprays molecules transported by a stream of carrier gas. Highly uniform pentacene films are grown at web speeds of up to 2.1 m/min, equivalent to an average deposition rate of 105 angstrom/s in a static system. With transistor mobilities of up to 1.5 cm(2)/V s, these pentacene films are of high electrical quality. Importantly, this quality is conserved up to the highest deposition speeds. We discuss the relationships between in-line deposition rate, morphology and crystallinity of the deposited pentacene films and their electrical characteristics. (C) 2009 Elsevier B.V. All rights reserved.status: publishe

Predictive Model for the Meniscus-Guided Coating of High-Quality Organic Single-Crystalline Thin Films

A model that describes solvent evaporation dynamics in meniscus-guided coating techniques is developed. In combination with a single fitting parameter, it is shown that this formula can accurately predict a processing window for various coating conditions. Organic thin-film transistors (OTFTs), fabricated by a zone-casting setup, indeed show best performance at the predicted coating speeds with mobilities reaching 7 cm(2) V(-1) s(-1) .status: publishe

Predicting the optimal process window for the coating of single-crystalline organic films with mobilities exceeding 7 cm2/Vs

Organic thin film transistors (OTFTs) based on single crystalline thin films of organic semiconductors have seen considerable development in the recent years. The most successful method for the fabrication of single crystalline films are solution-based meniscus guided coating techniques such as dip-coating, solution shearing or zone casting. These upscalable methods enable rapid and efficient film formation without additional processing steps. The single-crystalline film quality is strongly dependent on solvent choice, substrate temperature and coating speed. So far, however, process optimization has been conducted by trial and error methods, involving, for example, the variation of coating speeds over several orders of magnitude. Through a systematic study of solvent phase change dynamics in the meniscus region, we develop a theoretical framework that links the optimal coating speed to the solvent choice and the substrate temperature. In this way, we can accurately predict an optimal processing window, enabling fast process optimization. Our approach is verified through systematic OTFT fabrication based on films grown with different semiconductors, solvents and substrate temperatures. The use of best predicted coating speeds delivers state of the art devices. In the case of C8BTBT, OTFTs show well-behaved characteristics with mobilities up to 7 cm2/Vs and onset voltages close to 0 V. Our approach also explains well optimal recipes published in the literature. This route considerably accelerates parameter screening for all meniscus guided coating techniques and unveils the physics of single crystalline film formation.status: publishe

Controlled nucleation and growth of single crystal organic semiconductor films on arbitraty substrates

status: publishe

High-performance single-crystal organic transistors on flex

status: publishe

Functional Pentacene Thin Films Grown by In-Line Organic Vapor Phase Deposition at Web Speeds above 2 m/min

We show in this paper that the organic vapor phase deposition technique can advantageously be extended to an in-line system, where a susceptor moves at a constant speed underneath an elongated showerhead. Highly uniform pentacene films are grown at web speeds of up to 2.1 m/min, equivalent to an average deposition rate of 105 angstrom/s in a static system. These pentacene films are of high electrical quality as proven by transistor mobilities of up to 1.5 cm(2) V-1 s(-1) and five-stage ring oscillators on foil that achieve a frequency of 24 kHz at a supply voltage of 20 V. (C) 2009 The Japan Society of Applied Physic

Influence of Solute Concentration on Meniscus-Guided Coating of Highly Crystalline Organic Thin Films

status: publishe

A growth and morphology study of organic vapor phase deposited perylene diimide thin films for transistor applications

In this work, an in-depth growth study with organic vapor phase deposition of the n-type semiconductor N,N'-ditridecyl-3,4,9,10-perylenetetracarboxylic diimide (PTCDI-C-13) is presented. The organic vapor phase deposition technique allows independent control of more parameters than traditional vapor thermal evaporation, namely, not only deposition flux and substrate temperature but also chamber pressure can be changed. We study the influence of these parameters on the morphology and microstructure of PTCDI-C-13 thin films, and correlate them with electrical properties. Films of PTCDI-C-13 on SiO2 surfaces modified with poly-(alpha-methylstyrene) exhibit. Stranski-Krastanov growth. Upon increasing deposition flux, the resulting surface morphology changes from rough films, characterized by needle growth, to smoother films consisting of small, uniform grains. Notably, increasing the pressure shifts this morphology transition toward lower deposition fluxes. All X-ray reflectivity measurements are indicative of PTCDI-C13 molecules assembling in well-ordered pi-stacks parallel to the substrate. This creates the opportunity to grow PTCDI-C-13 films at conditions maximizing deposition throughput and efficiency, while maintaining the structural and thus electrical quality of the PTCDI-C-13 thin films. Electron mobilities up to 0.1 cm(2)/(Vs) have been demonstrated for a deposition rate of 6.7 angstrom/s, showing that organic vapor phase deposition is a high-throughput deposition technique for perylene diimide n-type organic semiconductors.status: publishe