This PDF file contains the front matter associated with SPIE Proceedings Volume 8478 including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
In this paper, we present the results of achieving stable organic thin film transistors (OTFTs) under bias stress conditions.
We discuss the various factors that have been found to influence the operational stability of the OTFT. This has enabled
Plastic Logic to achieve a reliable active matrix backplane on low cost flexible substrates which is a key enabler for
electronic paper displays.
To enable the integration of organic transistors into flexible displays we have developed passive materials for a robust, layer-to-layer compatible device stack to be manufactured using a variety of industrially applicable coating and printing processes. The solution processable materials for the OSC protection and the passivation material are designed for good interlayer adhesion and OTFT stability. The 365 nm UV-curable protection layers for the OSC are compatible with fabrication processes commonly used in the display industry, e.g., sputtering of metals. Fabrication of ink-jet printed devices is demonstrated with usage of a passive material suitable for further pixel integration. The bias stress and ambient stability was shown for the integrated stacks of transistors with the carrier mobility greater than that of amorphous silicon. We further demonstrate the development of formulations, suitable for high throughput roll-to-roll processing of soluble small molecule semiconductors allowing a high degree of structural order in the final solid film. Transistor mobility <2 cm2/V·s is achieved with a range of viscosity values compatible with flexographic printing. Fine pattern of OSC is demonstrated with flexographic printing by adjusting the viscosity of the formulation. Uniform layers are achieved with coating and printing techniques and uniformity values are sufficient for display application.
We have fabricated high-mobility ambipolar polymer transistors and have integrated multiple transistors to demonstrate
their implementation into CMOS-like logic circuitry. The performance of a selenophene-based polymer semiconductor
PSeDPPBT is initially screened using standard long-channel field-effect transistors. The polymer exhibits high and
balanced hole and electron mobilities of ∼ 0.5 cm2/Vs and ∼ 1.0 cm2/Vs, respectively. Next, exploiting the beneficial
electronic properties of PSeDPPBT, we have fabricated ambipolar inverters, ring oscillators and logic NOR gates.
Ambipolar inverters are shown to exhibit voltage inversion with proper noise margins and no voltage loss over multiple
stages. The potential speed of ambipolar logic is demonstrated by the realization of ambipolar ring oscillators with
unprecedented performance. The feasibility to perform logic operations is demonstrated by the fabrication of ambipolar
NOR gates. The combined results, (i) no loss in voltage over multiple inverters, (ii) the unprecedented speed, and (iii) the
accomplishment of a functionally complete logic operation, demonstrate the feasibility of ambipolar logic as a reliable
substitute for complementary-based logic in order to realize cost-efficient electronics.
We have successfully developed a method for directly forming organic single-crystal thin films at designated locations on a substrate by solution-phase growth. An original micropattern, in which small rectangular regions were connected to a large rectangular region, was designed. The small regions and the large region were used as nucleation control regions (NCRs) and a growth control region (GCR), respectively. The key to success was to vary local supersaturation of a solution droplet by making a large difference in solvent evaporation between a NCR and a GCR. We found that the NCR played a very important role in forming a single nucleus and in investigating the possibility of control of the crystal orientation. By using the developed micropattern and controlling the solvent vapor pressure during growth, we fabricated single-crystal arrays of a stable organic semiconductor, 3,9-bis(4-ethylphenyl)-peri-xanthenoxanthene (C2Ph-PXX).
A terminal charge and capacitance model is developed for transient behavior simulation of electrolyte-gated organic field effect transistors (EGOFETs). Based on the Ward-Dutton partition scheme, the charge and capacitance model is derived from our drain current model reported previously. The transient drain current is expressed as the sum of the initial drain current and the charging current, which is written as the product of the partial differential of the terminal charges with respect to the terminal voltages and the differential of the terminal voltages upon time. The validity for this model is verified by experimental measurements.
We report on the material properties and device characteristics of field-effect transistors (FETs) consisting of hybrid mono-layer graphene/organic semiconductor active layers. By capping with selected organic and polymeric layers, transformation of the electronic characteristics of mono-layer graphene FETs was observed. The off-state current is reduced while the on-state current and field-effect mobility are either unaffected or increased after depositing π−conjugated organic semiconductors. Significantly, capping mono-layer graphene FETs with fluoropolymer improved the on-off current ratio from 5 to 10 as well as increased the field-effect mobility by factor of two compared to plain graphene FETs. Removal of π−conjugated organic semiconductors or fluoropolymer from graphene FETs results in a return to the original electronic properties of mono-layer graphene FETs. This suggests that weak reversible electronic interactions between graphene and π−conjugated organic semiconductors/fluoropolymer favorably tune the material and electrical characteristics of mono-layer graphene.
Within this work we present the synthesis and applications of a novel material designed for n-type self-assembled monolayer field-effect transistors (SAMFETs). Our novel perylene bisimide based molecule was obtained in six steps and is functionalized with a phosphonic acid linker which enables a covalent fixation on aluminum oxide dielectrics. The organic field-effect transistors (OFETs) were fabricated by submerging predefined transistor substrates in a dilute solution of the molecule under ambient conditions. Investigations showed a thickness of about 3 nm for the organic layer which is coincides to the molecular length. The transistors showed bulk-like electron mobilities up to 10-3 cm2/Vs. Due to the absence of bulk current high on/off-ratios were achieved. An increase of the electron mobility with the channel length and XPS investigations point to a complete coverage of the dielectric with a dense monolayer. In addition, a p-type SAMFET based on a thiophene derivative and our new n-type SAMFET were combined to the first CMOS bias inverter based solely on SAMFETs.