Albert J. J. M. van Breemen

Controlled Deposition of Highly Ordered Soluble Acene Thin Films: Effect of Morphology and Crystal Orientation on Transistor Performance

Controlling the morphology of soluble small molecule organic semiconductors is crucial for the application of such materials in electronic devices. Using a simple dip-coating process we systematically vary the film drying speed to produce a range of morphologies, including oriented needle-like crystals. Structural characterization as well as electrical transistor measurements show that intermediate drying velocities produce the most uniformly aligned films.

Multilevel Information Storage in Ferroelectric Polymer Memories

Multibit memory devices based on the ferroelectric copolymer P(VDF-TrFE) (poly-(vinylidenefluoride-trifluoroethylene)) are presented. Multilevel microstructures are fabricated by thermal imprinting of spin-coated ferroelectric polymer film using a rigid Si template. Multibit storage in capacitors and thin-film transistor memory is realized by implementing imprinted ferroelectric polymer films as the insulator and gate dielectric layers, respectively. Copyright

Highly stable carbon nanotube top-gate transistors with tunable threshold voltage

Carbon-nanotube top-gate transistors with fluorinated dielectrics are presented. With PTrFE as the dielectric, the devices have absent or small hysteresis at different sweep rates and excellent bias-stress stability under ambient conditions. Ambipolar single-walled carbon nanotube (SWNT) transistors are observed when P(VDF-TrFE-CTFE) is utilized as a topgate dielectric. Furthermore, continuous tuning of the threshold voltages of both unipolar and ambipolar SWNT thin-film transistors (TFTs) is demonstrated for the first time.

Nanoscale Design of Multifunctional Organic Layers for Low-Power High-Density Memory Devices

We demonstrate the design of a multifunctional organic layer by the rational combination of nanosized regions of two functional polymers. Instead of relying on a spontaneous and random phase separation process or on the tedious synthesis of block copolymers, the method involves the nanomolding of a first component, followed by the filling of the resulting open spaces by a second component. We apply this methodology to fabricate organic nonvolatile memory diodes of high density. These are built by first creating a regular array of ferroelectric nanodots by nanoimprint lithography, followed by the filling of the trenches separating the ferroelectric nanodots with a semiconducting polymer. The modulation of the current in the semiconductor by the polarization state of the ferroelectric material is demonstrated both at the scale of a single semiconductor channel and in a microscopic device measuring about 80,000 channels in parallel, for voltages below ca. 2 V. The fabrication process, which combines synergetically orthogonal functional properties with a fine control over their spatial distribution, is thus demonstrated to be efficient over large areas.

Crossbar arrays of nonvolatile, rewritable polymer ferroelectric diode memories on plastic substrates

In this paper, we demonstrate a scalable and low-cost memory technology using a phase separated blend of a ferroelectric polymer and a semiconducting polymer as data storage medium on thin, flexible polyester foils of only 25μm thickness. By sandwiching this polymer blend film between rows and columns of metal electrode lines where each intersection makes up one memory cell, we obtained 1 kbit cross bar arrays with bit densities of up to 10 kbit/cm2.

X-Ray Detector-on-Plastic With High Sensitivity Using Low Cost, Solution-Processed Organic Photodiodes

We made and characterized an X-ray detector on a 25-μm-thick plastic substrate that is capable of medicalgrade performance. As an indirect conversion flat panel detector, it combined a standard scintillator with an organic photodetector (OPD) layer and oxide thin-film transistor backplane. Using solution-processed organic bulk heterojunction photodiode rather than the usual amorphous silicon, process temperature is reduced to be compatible with plastic film substrates, and a number of costly lithography steps are eliminated, opening the door to lower production costs. With dark currents as low as 1 pA/mm2 and sensitivity of 0.2 A/W the OPD also meets functional requirements: the proof-of-concept detector delivers high-resolution, dynamic images at 10 frames/s, and 200 pixels/in using X-ray doses as low as 3 μGy/frame.

Pulse-modulated multilevel data storage in an organic ferroelectric resistive memory diode

We demonstrate multilevel data storage in organic ferroelectric resistive memory diodes consisting of a phase-separated blend of P(VDF-TrFE) and a semiconducting polymer. The dynamic behaviour of the organic ferroelectric memory diode can be described in terms of the inhomogeneous field mechanism (IFM) model where the ferroelectric components are regarded as an assembly of randomly distributed regions with independent polarisation kinetics governed by a time-dependent local field. This allows us to write and non-destructively read stable multilevel polarisation states in the organic memory diode using controlled programming pulses. The resulting 2-bit data storage per memory element doubles the storage density of the organic ferroelectric resistive memory diode without increasing its technological complexity, thus reducing the cost per bit.

Flexible NAND-Like Organic Ferroelectric Memory Array

We present a memory array of organic ferroelectric field-effect transistors (OFeFETs) on flexible substrates. The OFeFETs are connected serially, similar to the NAND architecture of flash memory, which offers the highest memory density of transistor memories. We demonstrate a reliable addressing scheme in this architecture, without the need for select or access transistors. As proof of principle, a 1 × 4 NAND-like string is fabricated and characterized. Retention up to one month and endurance up to 2500 cycles are shown. Read and write disturb measurements show that the memory array can potentially be scaled up to 8 kbits.

An organic ferroelectric field effect transistor with poly(vinylidene fluoride-co-trifluoroethylene) nanostripes as gate dielectric

We demonstrate the fabrication of an organic Ferroelectric Field Effect Transistor (FeFET) incorporating a ferroelectric gate dielectric made of nanostripes obtained by nanoimprinting poly(vinylidene fluoride-co-trifluoroethylene) over a layer of semiconducting poly(triarylamine). The imprinting process results in a decreased switching voltage for the ferroelectric, by a factor of ca. 1.5, resulting in a decreased operating voltage compared to a reference FeFET with a continuous ferroelectric layer. The transistor consists of a large number of nanostripe-gated transistors placed in parallel, which also offers interesting possibilities for a strong size reduction of organic FeFETs.

Synthesis and properties of ?,?-phenyl-capped bithiophene derivatives

Nine different α,ω-phenyl-endcapped bithiophenes were synthesised, and the effect of the different side chains on the liquid crystalline properties, alignment ability and charge carrier mobility have been studied. An increase in chain length leads to a decrease in the liquid crystalline–isotropic phase (clearing) transition temperature. Remarkably, introduction of an asymmetric carbon centre close to the π-conjugated segment resulted in the loss of the liquid crystalline phase. Alignment on rubbed polyimide was obtained for the liquid crystalline thiophene derivatives lacking heteroatoms in the side chain and for the chiral α,ω-phenyl-endcapped bithiophene. Some bithiophenes showed bipolar charge transport in time-of-flight (TOF) measurements, with mobilities up to 3 × 10−3 cm2 V−1 s−1 in the liquid crystalline state. Field effect transistors revealed mobility for holes up to 1 × 10−3 cm2 V−1 s−1 (crystalline state). From the data set obtained, it can be concluded that the use of linear hydrocarbon chains as solubilising tails in these types of π-conjugated building blocks gives the best overall electronic performance.