Markus Andreas Schubert

Individually addressable epitaxial ferroelectric nanocapacitor arrays with near Tb inch −2 density

Ferroelectric materials have emerged in recent years as an alternative to magnetic and dielectric materials for nonvolatile data-storage applications. Lithography is widely used to reduce the size of data-storage elements in ultrahigh-density memory devices. However, ferroelectric materials tend to be oxides with complex structures that are easily damaged by existing lithographic techniques, so an alternative approach is needed to fabricate ultrahigh-density ferroelectric memories. Here we report a high-temperature deposition process that can fabricate arrays of individually addressable metal/ferroelectric/metal nanocapacitors with a density of 176 Gb inch(-2). The use of an ultrathin anodic alumina membrane as a lift-off mask makes it possible to deposit the memory elements at temperatures as high as 650 degrees C, which results in excellent ferroelectric properties.

A 0.13

A 0.13 µm SiGe BiCMOS technology for millimeter wave applications is presented. This technology features high-speed HBTs (f<inf>T</inf>=240 GHz, f<inf>max</inf>=330 GHz, BV<inf>CEO</inf>=1.7 V) along with high-voltage HBTs (f<inf>T</inf>=50 GHz, f<inf>max</inf>=130 GHz, BV<inf>CEO</inf>=3.7 V) integrated in a dual-gate, triple-well RF-CMOS process. Ring oscillator gate delays of 2.9 ps, low-noise amplifiers for 122 GHz, and LC oscillators for frequencies above 200 GHz are demonstrated.

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The bending of a nonconducting piezoelectric ZnO nanowire is simulated by finite element method calculations. The top part is bent by a lateral force, which could be applied by an atomic force microscope tip. The generated electrical potential is ±0.3V. This relatively high signal is, however, difficult to measure due to the low capacitance of the ZnO nanowire (∼4×10−5pF) as compared to the capacitance of most preamplifiers (∼5pF). A further problem arises from the semiconducting properties of experimentally fabricated ZnO nanowires which causes the disappearance of the voltage signal within picoseconds.

SiGe BiCMOS Technology Featuring f

Ferroelectric epitaxial superlattices combining PbZr0.4Ti0.6O3 and PbZr0.6Ti0.4O3 ultrathin films were grown by pulsed laser deposition onto vicinal SrTiO3 (001) substrates. The superlattices were subjected to structural characterization by means of (high-resolution) transmission electron microscopy and x-ray diffraction, to piezoelectric-force microscopy, and to macroscopic ferroelectric measurements. The thickness of the individual PbZrxTi1−xO3 layers was found to play an important role in the overall structure adopted by the superlattices. Superlattices consisting of 22 bilayers of 5nm thin PbZr0.4Ti0.6O3 layers and 3nm thin PbZr0.6Ti0.4O3 layers involve continuous 90° a–c domains, indicating a uniform tetragonal structure.

_{T}

Integration of functional oxides on Si substrates could open a pathway to integrate diverse devices on Si-based technology. Oxygen vacancies (Vo(··)) can strongly affect solid state properties of oxides, including the room temperature ferromagnetism (RTFM) in diluted magnetic oxides. Here, we report a systematical study on the RTFM of oxygen vacancy engineered (by Pr(3+) doping) CeO2 epitaxial thin films on Si substrates. High quality, mixed single crystalline Ce1-xPrxO2-δ (x = 0-1) solid solution films were obtained. The Ce ions in CeO2 with a fluorite structure show a Ce(4+)-dominant valence state in all films. The local crystal structures of the films were analyzed in detail. Pr doping creates both Vo(··) and PrO8-complex defects in CeO2 and their relative concentrations vary with the Pr-doping level. The RTFM properties of the films reveal a strong dependence on the relative Vo(··) concentration. The RTFM in the films initially increases with higher Pr-doping levels due to the increase of the F(+) center (Vo(··) with one occupied electron) concentration and completely disappears when x > 0.2, where the magnetic polaron concentration is considered to decline below the percolation threshold, thus long-range FM order can no longer be established. We thus demonstrate the possibility to directly grow RTFM Pr-doped CeO2 films on Si substrates, which can be an interesting candidate for potential magneto-optic or spintronic device applications.

/f

Selective growth of Ge on nanostructured Si(001) wafers is studied to evaluate the applicability of nanoheteroepitaxy approaches on the Ge–Si system for photonics applications under particular consideration of possible growth mask materials. A gate spacer technology established in advanced silicon microelectronics is used to generate a periodic array of nanoscaled Si pillars. The spacing of these Si pillars is 360 nm; diameter and height are about 100 nm, which is still above the expected geometrical parameters to obtain a compliant behavior of the Si lattice in the pillars. Ge dots are deposited by reduced pressure chemical-vapor deposition on top of the Si pillars. The characterization is done by different x-ray diffraction methods and transmission electron microscopy. It is found that even 30 nm thick Ge dots are fully relaxed and they exhibit a clear network of misfit dislocations. Significantly thicker Ge dots generate additional structural defects, mainly microtwins. A strain partitioning between Si...

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To develop a III/V wide bandgap collector concept for future SiGe heterobipolar transistor performance increase, a heterostructure growth study of GaP on pseudomorphic 4° off-oriented Si0.8Ge0.2/Si(001) substrates was performed. For pseudomorphic GaP/Si0.8Ge0.2/Si(001) heterostructure growth, critical thickness of GaP on Si and maximum thermal budget for GaP deposition were evaluated. A detailed structure and defect characterization study by x-ray diffraction, atomic force microscopy, and transmission electron microscopy is reported on single crystalline 170 nm GaP/20 nm Si0.8Ge0.2/Si(001). Results show that 20 nm Si0.8Ge0.2/Si(001) can be overgrown by 170 nm GaP without affecting the pseudomorphism of the Si0.8Ge0.2/Si(001) layer. The GaP layer grows however partially relaxed, mainly due to defect nucleation at the GaP/Si0.8Ge0.2 interface during initial island coalescence. The achievement of 2D GaP growth conditions on Si0.8Ge0.2/Si(001) systems is thus a crucial step for achieving fully pseudomorphic h...

of 240/330 GHz and Gate Delays Below 3 ps

With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption.

Finite element method calculations of ZnO nanowires for nanogenerators

We report on the structural characterization of Ge clusters selectively grown by chemical vapor deposition on free-standing 50 nm wide Si(001) nanopillars. Synchrotron based x-ray diffraction studies and transmission electron microscopy were performed to experimentally verify the nanoheteroepitaxy theory as a technique to grow high quality Ge on Si(001). Although the structure dimensions are comparable to the theoretical values required for the strain partitioning phenomenon, the compliant character of Si is not unambiguously proven. In consequence, the strain is relieved by nucleation of misfit dislocations at the Ge/Si interface. By gliding out of threading arms, high quality Ge nanostructures are achieved.

Structure and properties of epitaxial ferroelectric PbZr0.4Ti0.6O3∕PbZr0.6Ti0.4O3 superlattices grown on SrTiO3 (001) by pulsed laser deposition

Dislocation networks are one of the most principle sources deteriorating the performances of devices based on lattice-mismatched heteroepitaxial systems. We demonstrate here a technique enabling fully coherent germanium (Ge) islands selectively grown on nanotip-patterned Si(001) substrates. The silicon (Si)-tip-patterned substrate, fabricated by complementary metal oxide semiconductor compatible nanotechnology, features ∼50-nm-wide Si areas emerging from a SiO2 matrix and arranged in an ordered lattice. Molecular beam epitaxy growths result in Ge nanoislands with high selectivity and having homogeneous shape and size. The ∼850 °C growth temperature required for ensuring selective growth has been shown to lead to the formation of Ge islands of high crystalline quality without extensive Si intermixing (with 91 atom % Ge). Nanotip-patterned wafers result in geometric, kinetic-diffusion-barrier intermixing hindrance, confining the major intermixing to the pedestal region of Ge islands, where kinetic diffusion barriers are, however, high. Theoretical calculations suggest that the thin Si/Ge layer at the interface plays, nevertheless, a significant role in realizing our fully coherent Ge nanoislands free from extended defects especially dislocations. Single-layer graphene/Ge/Si-tip Schottky junctions were fabricated, and thanks to the absence of extended defects in Ge islands, they demonstrate high-performance photodetection characteristics with responsivity of ∼45 mA W(-1) and an Ion/Ioff ratio of ∼10(3).