Robert Muller

Influence of the Cu-Te composition and microstructure on the resistive switching of Cu-Te/Al2O3/Si cells

In this letter, we explore the influence of the CuxTe1-x layer composition (0.2   0.7 leads to large reset power, similar to pure-Cu electrodes, x < 0.3 results in volatile forming properties. The intermediate range 0.5 < x < 0.7 shows optimum memory properties, featuring improved control of filament programming using <5 μA as well as state stability at 85 °C. The composition-dependent programming control and filament stability are closely associated with the phases in the CuxTe1−x layer and are explained as related to the chemical affinity between Cu and Te.

A comprehensive model for bipolar electrical switching of CuTCNQ memories

The generally observed bipolar electrical switching of Cu\CuTCNQ\metal memories (metal=Al,Yb,Ti) between two stable resistance states is shown to occur at the CuTCNQ\metal interface and not in the bulk of CuTCNQ. The switching is explained by a model involving electrochemical formation and dissolution of Cu filaments at the interface. In this mechanism, CuTCNQ acts as solid ionic conductor and source for the Cu+ cations. The model also explains earlier reported findings of bipolar switching in CuTCNQ devices, including the apparently contradictory observation that neutral TCNQ appears in the low-resistance state.

Ambipolar injection in a submicron-channel light-emitting tetracene transistor with distinct source and drain contacts

We report on organic light-emitting transistors with a submicron-channel length, gold source, and calcium drain contacts. The respective contact metals allow efficient injection of holes and electrons in the tetracene channel material. Transistor characteristics were measured in parallel with electroluminescence being recorded by a digital camera focused on the transistor channel. In the case of submicron-channel lengths, the transistor source-drain current at higher gate voltages was determined by the source-drain voltage. At larger channel lengths, the source-drain current was limited by the injection of electrons from the calcium contact, as hole ejection to this contact was fully blocked. The hole blocking is explained in terms of a chemical reaction occurring at the Ca/tetracene interface.

CuTCNQ resistive nonvolatile memories with a noble metal bottom electrode

Resistive electrical switching of the organic semiconductor Cu-tetracyanoquinodimethane (CuTCNQ) was investigated between gold bottom and aluminum top contacts. Corresponding Au∕CuTCNQ∕Al crossbar memories achieved several thousand write/erase cycles. The switching process was further studied by current-time measurements, and temperature-dependent measurements of the on state conductivity.

Organic CuTCNQ integrated in complementary metal oxide semiconductor copper back end-of-line for nonvolatile memories

Nanowires of the organometallic semiconductor CuTCNQ were grown from TCNQ vapor in 250nm diameter vias of a Cu back end-of-line process. Corresponding prototypes of cross-point Cu∕CuTCNQ nanowire/Al memories exhibited nonvolatile bistable conductive switching for several ten write-erase cycles with switching currents below 10μA and current densities 1000 times higher than for large-area devices. Scaling of memory elements was also investigated.

Self-aligned surface treatment for thin-film organic transistors

For organic thin-film transistors where source-drain contacts are defined on the gate dielectric prior to the deposition of the semiconductor (“bottom-contact” configuration), the gate dielectric is often treated with a self-assembled molecular monolayer prior to deposition of the organic semiconductor. In this letter, we describe a method to apply an ultrathin solution-processed polymer layer as surface treatment. Our method is compatible with the use of the bottom-contact configuration, despite the fact that the polymeric surface treatment does not stand a photolithographic step. Furthermore, we show that our surface treatment results in superior transistor performance.

Molecular plasmonics: light meets molecules at the nanoscale.

Certain metal nanoparticles exhibit the effect of localized surface plasmon resonance when interacting with light, based on collective oscillations of their conduction electrons. The interaction of this effect with molecules is of great interest for a variety of research disciplines, both in optics and in the life sciences. This paper attempts to describe and structure this emerging field of molecular plasmonics, situated between the molecular world and plasmonic effects in metal nanostructures, and demonstrates the potential of these developments for a variety of applications.

Nonvolatile Cu∕CuTCNQ∕Al memory prepared by current controlled oxidation of a Cu anode in LiTCNQ saturated acetonitrile

In this letter we propose a preparation method of the metal organic charge transfer complex Cu-tetracyanoquinodimethane (CuTCNQ) for use in nonvolatile organic memories. The method, consisting in current controlled oxidation of a Cu electrode in LiTCNQ saturated acetonitrile, is attractive because CuTCNQ growth is limited strictly to anodically polarized Cu metal, and because of material and solvent compatibilities with the requirements of the complementary metal-oxide-semiconductor (CMOS) copper back end-of-line process. Crossbar memories of this CuTCNQ exhibit superior performance compared to corresponding devices prepared by the standard method, which we attribute to a higher compactness of the CuTCNQ layer.

High-performance flexible bottom-gate organic field-effect transistors with gravure printed thin organic dielectric

One of the key advantages of organic field-effect transistors (OFETs) is their ability to form flexible, conformable and lightweight electronic devices, e.g. radio frequency identification (RFID) tags,[1] microprocessors[2] and flexible displays.[3] These require fabrication over large-areas on flexible plastic substrates, the poor dimensional stability of such substrates creating the additional demand of low-temperature processing (<200 °C).[4] While high performance source, drain and gate electrodes and interconnects require metal evaporation under vacuum, ideally the dielectric and organic semiconductor (OSC) should be processed from solution under ambient conditions to reduce fabrication costs. Regarding device architecture, OFETs with a bottom-gate (BG) bottom-contact (BC) geometry (Figure ​1c)1c) have an advantage in that the organic semiconducting layer is deposited last.[5] This affords easy fabrication and patterning of micron-scale OFET channels, electrodes and interconnects by conventional photolithographic methods, whilst avoiding exposure of the active OSC material to UV radiation and aggressive or solubilising chemicals. Furthermore, this architecture is compatible with vacuum sublimation or vapour phase techniques for OSC deposition, allowing access to a wide range of high-performance materials. Such OFETs can form the building blocks of high performance, low-cost electronic circuitry.

Influence of Carbon Alloying on the Thermal Stability and Resistive Switching Behavior of Copper-Telluride Based CBRAM Cells

We report the improved thermal stability of carbon alloyed Cu0.6Te0.4 for resistive memory applications. Copper-tellurium-based memory cells show enhanced switching behavior, but the complex sequence of phase transformations upon annealing is disadvantageous for integration in a device. We show that addition of about 40 at % carbon to the Cu-telluride layer results in an amorphous material up to 360 °C. This material was then integrated in a TiN/Cu0.6Te0.4-C/Al2O3/Si resistive memory cell, and compared to pure Cu0.6Te0.4. Very attractive endurance (up to 1 × 10(3) cycles) and retention properties (up to 1 × 10(4) s at 85 °C) are observed. The enhanced thermal stability and good switching behavior make this material a promising candidate for integration in memory devices.