2020, Seifert, M.

This paper reports on a significant further improvement of the high temperature stability of RuAl thin films (110 nm) on the piezoelectric Ca3TaGa3Si2O14 (CTGS) and La3Ga5SiO14 (LGS) substrates. RuAl thin films with AlN or SiO2 cover layers and barriers to the substrate (each 20 nm), as well as a combination of both were prepared on thermally oxidized Si substrates, which serve as a reference for fundamental studies, and the piezoelectric CTGS, as well as LGS substrates. In somefilms, additional Al layers were added. To study their high temperature stability, the samples were annealed in air and in high vacuum up to 900 °C, and subsequently their cross-sections, phase formation, film chemistry, and electrical resistivity were analyzed. It was shown that on thermally oxidized Si substrates, all films were stable after annealing in air up to 800 °C and in high vacuum up to 900 °C. The high temperature stability of RuAl thin films on CTGS substrates was improved up to 900 °C in high vacuum by the application of a combined AlN/SiO2 barrier layer and up to 800 °C in air using a SiO2 barrier. On LGS, the films were only stable up to 600 °C in air; however, a single SiO2 barrier layer was sufficient to prevent oxidation during annealing at 900 °C in high vacuum.

2020, Adkison, Kate M., Shang, Shun-Li, Bocklund, Brandon J., Klimm, Detlef, Schlom, Darrell G., Liu, Zi-Kui

We have conducted a comprehensive thermodynamic analysis of the volatility of 128 binary oxides to evaluate their suitability as source materials for oxide molecular-beam epitaxy (MBE). 16 solid or liquid oxides are identified that evaporate nearly congruently from stable oxide sources to gas species: As2O3, B2O3, BaO, MoO3, OsO4, P2O5, PbO, PuO2, Rb2O, Re2O7, Sb2O3, SeO2, SnO, ThO2, Tl2O, and WO3. An additional 24 oxides could provide molecular beams with dominant gas species of CeO, Cs2O, DyO, ErO, Ga2O, GdO, GeO, HfO, HoO, In2O, LaO, LuO, NdO, PmO, PrO, PuO, ScO, SiO, SmO, TbO, Te2O2, U2O6, VO2, and YO2. The present findings are in close accord with available experimental results in the literature. For example, As2O3, B2O3, BaO, MoO3, PbO, Sb2O3, and WO3 are the only oxides in the ideal category that have been used in MBE. The remaining oxides deemed ideal for MBE awaiting experimental verification. We also consider two-phase mixtures as a route to achieve the desired congruent evaporation characteristic of an ideal MBE source. These include (Ga2O3 + Ga) to produce a molecular beam of Ga2O(g), (GeO2 + Ge) to produce GeO(g), (SiO2 + Si) to produce SiO(g), (SnO2 + Sn) to produce SnO(g), etc.; these suboxide sources enable suboxide MBE. Our analysis provides the vapor pressures of the gas species over the condensed phases of 128 binary oxides, which may be either solid or liquid depending on the melting temperature. © 2020 Author(s).

2020, Seifert, M., Lattner, E., Menzel, S.B., Oswald, S., Gemming, T.

Ti-Al thin films with a thickness of 200 nm were prepared either by co-sputtering from elemental Ti and Al targets or as Ti/Al multilayers with 10 and 20 nm individual layer thickness on thermally oxidized Si substrates. Some of the films were covered with a 20-nm-thick SiO2 layer, which was used as an oxidation protection against the ambient atmosphere. The films were annealed at up to 800 °C in high vacuum for 10 h, and the phase formation as well as the film architecture was analyzed by X-ray diffraction, cross section, and transmission electron microscopy, as well as Auger electron and X-ray photoelectron spectroscopy. The results reveal that the co-sputtered films remained amorphous after annealing at 600 °C independent on the presence of the SiO2 cover layer. In contrast to this, the γ-TiAl phase was formed in the multilayer films at this temperature. After annealing at 800 °C, all films were degraded completely despite the presence of the cover layer. In addition, a strong chemical reaction between the Ti and SiO2 of the cover layer and the substrate took place, resulting in the formation of Ti silicide. In the multilayer samples, this reaction already started at 600 °C.

2021, Kissinger, Dietmar, Kahmen, Gerhard, Weigel, Robert

This invited paper reviews the progress of silicon–germanium (SiGe) bipolar-complementary metal–oxide–semiconductor (BiCMOS) technology-based integrated circuits (ICs) during the last two decades. Focus is set on various transceiver (TRX) realizations in the millimeter-wave range from 60 GHz and at terahertz (THz) frequencies above 300 GHz. This article discusses the development of SiGe technologies and ICs with the latter focusing on the commercially most important applications of radar and beyond 5G wireless communications. A variety of examples ranging from 77-GHz automotive radar to THz sensing as well as the beginnings of 60-GHz wireless communication up to THz chipsets for 100-Gb/s data transmission are recapitulated. This article closes with an outlook on emerging fields of research for future advancement of SiGe TRX performance.

2021, Jo, Youngkwan, Mai, Christian, Lischke, Stefan, Zimmermann, Lars, Choi, Woo-Young

Modulation linearity of Si ring modulators (RMs) is investigated through the numerical simulation based on the coupled-mode theory and experimental verification. Numerical values of the key parameters needed for the simulation are experimentally extracted. Simulation and measurement results agree well. With these, the influence of input optical wavelength and power on the Si RM linearity are characterized.

2020, Kissinger, G., Kot, D., Huber, A., Kretschmer, R., Müller, T., Sattler, A.

This paper describes a theoretical investigation of the phase composition of oxide precipitates and the corresponding emission of self-interstitials at the minimum of the free energy and their evolution with increasing number of oxygen atoms in the precipitates. The results can explain the compositional evolution of oxide precipitates and the role of self-interstitials therein. The formation of suboxides at the edges of SiO2 precipitates after reaching a critical size can explain several phenomena like gettering of Cu by segregation to the suboxide region and lifetime reduction by recombination of minority carriers in the suboxide. It provides an alternative explanation, based on minimized free energy, to the theory of strained and unstrained plates. A second emphasis was payed to the evolution of the morphology of oxide precipitates. Based on the comparison with results from scanning transmission electron microscopy the sequence of morphology evolution of oxide precipitates was deduced. It turned out that it is opposite to the sequence assumed until now. © 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.