Extending the voltage window in the characterization of electrical transport of large-area molecular junctions

A large bias window is required to discriminate between different transport models in large-area molecular junctions. Under continuous DC bias, the junctions irreversibly break down at fields over 9 MV/cm. We show that, by using pulse measurements, we can reach electrical fields of 35 MV/cm before degradation. The breakdown voltage is shown to depend logarithmically on both duty cycle and pulse width. A tentative interpretation is presented based on electrolysis in the polymeric top electrode. Expanding the bias window using pulse measurements unambiguously shows that the electrical transport exhibits not an exponential but a power-law dependence on bias. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3608154

Memory Solutions for Flexible Thin-Film Logic: up to 8kb, > 105.9kb/s LPROM and SRAM with Integrated Timing Generation Meeting the ISO NFC Standard

© 2019 IEEE. Thin-film transistor (TFT) technologies have long been used predominantly for display fabrication and are attractive for large area, low cost and flexible circuit applications. Thanks to the improving performance of thin-film metal-oxide NFC tags and data processing chips on foil [1], [2], fabs are considering the large-scale production of flexible logic circuits. However, these systems require a memory, but metal-oxide technology lacks reliable, large memory arrays. Today, data storage is limited to ROMs, flipflops and SRAMs. No memory array has been demonstrated with sufficient storage capacity and speed within the typical power and area budget. This paper demonstrates the first large, fast and low-power memory array in flexible metal-oxide technology, comparable to the Si Intel 4000 series in the seventies [3].status: publishe

Binary self-assembled monolayers: Apparent exponential dependence of resistance on average molecular length

We investigate the electrical transport through mixed self-assembled monolayers of alkanemonothiols and alkanedithiols in large-area molecular junctions. To disentangle the role of the molecular length and the interfacial composition, monothiol–monothiol, dithiol–dithiol, and monothiol–dithiol binary combinations are studied. In all cases, we find that the resistance of these mixed SAMs appears to depend exponentially on the average number of carbon atoms, thus resembling monocomponent SAMs, whose resistance is known to depend exponentially on molecular length. However, in monocomponent SAMs this behavior has a single-molecule tunneling origin, which is not directly relevant for mixtures. Furthermore, in certain mixed SAMs the resistance decreases with increasing average layer thickness (the case of monothiol–dithiol systems). We suggest an explanation for the observed dependence of the resistance in the mixed SAMs on their composition within an equivalent circuit model based on a simple assumption concerning their microdomain structure. The simulated dependence is non-exponential but leads to a good agreement between calculated and measured resistances with only two fit parameters.

Probing charge carrier density in a layer of photodoped ZnO nanoparticles by spectroscopic ellipsometry

Changes in the optical constants of a layer of ZnO nanoparticles (5 nm diameter) induced by UV illumination in O2-free atmosphere are determined by using spectroscopic ellipsometry. The onset of optical absorption of ZnO shifts to higher photon energy after illumination. This is interpreted in terms of a Moss-Burstein shift. From the magnitude of the shift, the charge carrier density in the conduction band after UV illumination was determined to be 2 × 1019 cm-3, about one carrier per particle. Kelvin probe measurements give a lower limit for the density of 1018 cm-3. The free carrier density after illumination is high enough to explain the formation of quasi-ohmic contacts between ZnO and the polymeric p-type conductor poly(3,4-ethylenedioxythiophene) (PEDOT)

Short-channel vertical organic field-effect transistors with high on/off ratios

A unique vertical organic field-effect transistor structure in which highly doped silicon nanopillars are utilized as a gate electrode is demonstrated. An additional dielectric layer, partly covering the source, suppresses bulk conduction and lowers the OFF current. Using a semiconducting polymer as active channel material, short-channel (100 nm) transistors with ON/OFF current ratios up to 10 6 are realized. The electronic behavior is explained using space-charge and contact-limited current models and numerical simulations. The current density and switching speed of the devices are in the order of 0.1 A cm −2 and 0.1 MHz, respectively, at biases of only a few volts. These characteristics make the devices very promising for applications where large current densities, high switching speeds, and high ON/OFF ratios are required

High-Throughput Atomic Layer Deposition of P-Type SnO Thin Film Transistors Using Tin(II)bis(tert-amyloxide)

Spatial atomic layer deposition (sALD) of p-type SnO is demonstrated using a novel liquid ALD precursor, tin(II)-bis(tert-amyloxide), Sn(TAA)2, and H2O as the coreactant in a process which shows an increased deposition rate when compared to conventional temporal ALD. Compared to previously reported temporal ALD chemistries for the deposition of SnO, deposition rates of up to 19.5 times higher are obtained using Sn(TAA)2 as a precursor in combination with atmospheric pressure sALD. Growths per cycle of 0.55 and 0.09 Å are measured at deposition temperatures of 100 and 210 °C, respectively. Common-gate thin film transistors (TFTs), fabricated using sALD with Sn(TAA)2 result in linear mobilities of up to 0.4 cm2 V–1 s–1 and on/off-current ratios, IOn/IOff > 102. The combination of enhanced precursor chemistry and improved deposition hardware enables unprecedently high deposition rate ALD of p-type SnO, representing a significant step toward high-throughput p-type TFT fabrication on large area and flexible substrates

A high-resolution thin-film fingerprint sensor using a printed organic photodetector

Organic photodetectors (OPDs) have attracted much attention in recent years, due to their promise in large-area light sensing applications. Here, high-resolution slot-die-coated large-area bulk heterojunction organic photodiode (OPD) arrays are reported. The OPD uses a novel electron transport layer, indium gallium zinc oxide in combination with a molybdenum oxide top-electrode. Together, these effectively reduce dark current densities to very low levels of ≈10−7 mA cm−2 at −2 V. The OPDs show linear behavior in a wide range of light intensities and high detectivity values under reverse bias conditions. When coated on a 508 ppi TFT backplane, a high-quality optical fingerprint scanner capable of imaging in reflection is realized. The optical and electrical properties of the fingerprint sensor are characterized and high-resolution fingerprint images are obtained

Stability of large-area molecular junctions

The stability of molecular junctions is crucial for any application of molecular electronics. Degradation of molecular junctions when exposed to ambient conditions is regularly observed. In this report the stability of large-area molecular junctions under ambient conditions for more than two years is presented. Furthermore, the thermal stability of molecular junctions at elevated temperatures is investigated. A transition temperature at 50 °C was observed for molecular junctions based on self-assembled monolayers of alkanedithiols, above which the resistance decreases exponentially with temperature. This transition temperature limits the process window during fabrication and the temperature window during operation.

Impact of derivatization on electron transmission through dithienylethene-based photoswitches in molecular junctions

<p>We report a combined Non-Equilibrium Green's Function - Density Functional Theory study of molecular junctions made of photochromic diarylethenes between gold electrodes. The impact of derivatization of the molecule on the transmission spectrum is assessed by introducing: (i) substituents on the diarylethene core; and (ii) linker substituents between the gold surface and the diarylethene. We illustrate that substituents on the core shift considerably the HOMO/LUMO level energies in gas phase but do not change the I-V characteristics of the molecular junctions; this behaviour has been rationalized by establishing links between the transmission spectrum and interfacial electronic reorganization upon chemisorption. In contrast, the different linker substituents under study modulate the conductivity of the junction by changing the degree of orbital hybridization with the metallic electrodes and the degree of orbital polarization.</p>