IFF

 ZCH

 ISG

 ZEL

In charge: Prof. R. Waser, IFF, r.waser@fz-juelich.de

Aims and Objectives

The program Solid State Research for Information Technology is devoted to a long-term, highly interdisciplinary basic and applied research in the pre-competitive area well in front of the run-up of the semiconductor industry. The research fields comprise information processing in logic devices, information storage in random access memories (RAM) and mass storage devices, and information transfer on chip and system level as well as by optical and microwave communication. Additionally, specific issues of the sensor technology are investigated.

Significant Results in 2003

Topic 1: Nanoscale Logic Devices and Quantum Electronics

• Strained silicon layers could be prepared on relaxed silicon-germanium within one single growth step by means of the "Jülich Process".
• In cooperation with Infineon and IMEC Leuven it was shown by "Spreading Resistance" measurements that Boron diffusion in silicon nanostructures leads to curved diffusion profiles whereby the diffusion close to surface is retarded.
• Si/Ge nanowires and nanorings with dimensions down to 3 nm could be prepared by self organized growth.
• A novel MOVPE process was developed and patented, in which parasitic deposition is considerably reduced. Deposition reproducibility was thus significantly enhanced which was demonstrated for GaN epitaxy.

Topic 2: Magnetoelectronics and Spintronics

• The research activities encompassed the magnetic and transport properties of selected material systems important for future spintronics applications. Theoretical studies of the model TMR junction Fe/MgO/Fe predicted the ideal system to be a perfect spin filter with a very high TMR effect. Including a monatomic FeO interfacial layer, however, reduces the TMR to the experimentally observed 10% level. The strong antiferromagnetic interlayer coupling originally found for nominally pure Si interlayers has now also been confirmed for Ge-containing spacers, highlighting this phenomenon as a universal feature of epitaxial semiconductor spacers. The Rashba effect in InGaAs/InP quantum wires was found to exhibit a strong variation of the coupling strength with the wire width, opening up tuning possibilities.

Topic 3: Terahertz Electronics

• For LT GaAs photomixing devices an output power of 1 mu W at 850 GHz was achieved. Our AlGaN/GaN HEMT structures on Si and SiC have revealed challenging high-frequency properties. In particular, the phase-noise properties were studied thoroughly. Within our superconductor efforts novel type of Josephson junctions were developed and utilised to extend the frequency range of our Hilbert-spectroscopy up to 4 THz. The investigation of the microwave properties of MgB₂ has revealed challenges for THz applications. Within our efforts towards THz integrated circuits novel schemes for the controlled excitation of defect resonances in electromomagnetic bandgap structures were explored. In addition, our nanoscale varactor structures based on SrTiO₃ films revealed superiour high-frequency properties.
• A process for the fabrication of AlGaAs/GaAs heterostructure Gunn diodes with output power of 100mW at a frequency of 77 GHz was developed. The temperature stability of the diodes could be improved considerably by use of a hot electron emitter layer structure.
• Photomixers based on GaAs deposited at low temperature in MBE (low temperature GaAs) were optimised in their performance such that they can be used in THz-oscillators for radioastronomy (collaboration with the MPI for Radioastronomy, Bonn).

Topic 4: Hysteretic Oxide-Based Memories

• Arrays of SrZrO₃ nanostructures by pulsed laser deposition have been fabricated. The compressive stress originated in the coherent SrZrO₃/SrRuO₃ interface due to the lattice mismatch has been used to grow epitaxial SrZrO₃ in a three-dimensional habit. So-deposited SrZrO₃ is used to fabricate nanoarrays of 1D-dielectric structures from a nanopatterned SrRuO₃ surface.
• In 2003 we made essential progress in understanding the scaling behaviour of ferroelectric materials. We used a self-organisation technique to create ultra-small PbTiO₃ dots on Pt. We have performed a series of key experiments by using an atomic force microscope in the piezo response mode, sampling ferroelectric crystallites of different sizes. We determine the superparaelectric limit to 20 nm. This result is relevant in context with the maximum storage capacitance of ferroelectric random access memories. Based on SrRuO₃/PbZr_0.52Ti_0.48O₃/SrRuO₃ heterostructures we unambiguously observe ferroelectricity down for film thicknesses of 250 nm to 8 nm. For PZT films with thicknesses less than 7 nm resistive switching have been observed. Theoretical explanations are based on the converse piezoelectric effect and its influence on the band structure of PZT and a semiconductor explanation which described the resistive switching with the aid of charge distribution and inner electric fields.
• MOCVD technique has been successfully applied for conformal coverage of Si with the alternative gate oxide HfO_x. Structures of ever-shrinking size are not only fabricated by improved lithographical patterning, but also by molecular or atomic self-assembly.

Topic 5: Molecular - and Bioelectronic-Hybrid Systems

• For the first time, high resolution in situ STM imaging was combined with measurements of local current - distance characteristics. Comparison of the experiments with calculated one-dimensional barrier height profiles provided direct access to local structural and energetic properties of bare and adsorbate-modified electrode/electrolyte interfaces.
• The dynamics of the cell-transistor coupling was investigated on genetically modified cells using field-effect transistors. For the improvement of the signal-to-noise, ratio floating-gate transistors were already developed and their properties for extracellular recording studies could be confirmed. In parallel, by the microcontact-printing method geometrically defined networks were constructed and synaptic transmission was investigated by multiple Patch-clamp technique.