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- ItemNovel concept for VCSEL enhanced silicon photonic coherent transceiver(New York, NY : American Inst. of Physics, 2019) Seiler, Pascal M.; Ronniger, Gregor; Troppenz, Ute; Sigmund, Ariane; Moehrle, Martin; Peczek, Anna; Zimmermann, LarsWe present a novel concept for an integrated silicon photonic coherent transceiver using vertical-emitting laser sources at 1550 nm. In a state of the art external modulation configuration, we deploy a VCSEL on the transmit and a HCSEL on the receive side. We demonstrate the feasibility of this approach by externally modulating the VCSEL with QPSK at up to 28 Gbaud. We also perform experiments with the VCSEL-HCSEL configuration in a slave-master optical injection locking setup for future data center interconnects. The results show stable locking conditions and the VCSEL is detuned to perform predominant phase modulation. To the best of our knowledge, this is the first time direct phase modulation of a VCSEL under optical injection locking was demonstrated using two vertically emitting laser sources as master - and slave laser. © 2019 Author(s).
- ItemEnhanced thermal stability of yttrium oxide-based RRAM devices with inhomogeneous Schottky-barrier(Melville, NY : American Inst. of Physics, 2020) Piros, Eszter; Petzold, Stefan; Zintler, Alexander; Kaiser, Nico; Vogel, Tobias; Eilhardt, Robert; Wenger, Christian; Molina-Luna, Leopoldo; Alff, LambertThis work addresses the thermal stability of bipolar resistive switching in yttrium oxide-based resistive random access memory revealed through the temperature dependence of the DC switching behavior. The operation voltages, current levels, and charge transport mechanisms are investigated at 25 °C, 85 °C, and 125 °C, and show overall good temperature immunity. The set and reset voltages, as well as the device resistance in both the high and low resistive states, are found to scale inversely with increasing temperatures. The Schottky-barrier height was observed to increase from approximately 1.02 eV at 25 °C to approximately 1.35 eV at 125 °C, an uncommon behavior explained by interface phenomena. © 2020 Author(s).
- ItemA comprehensive study of charge transport in Au-contacted graphene on Ge/Si(001)(Melville, NY : American Inst. of Physics, 2020) Sinterhauf, Anna; Bode, Simeon; Auge, Manuel; Lukosius, Mindaugas; Lippert, Gunther; Hofsäss, Hans-Christian; Wenderoth, MartinWe investigate the electronic transport properties of Au-contacted graphene on Ge/Si(001). Kelvin probe force microscopy at room temperature with an additionally applied electric transport field is used to gain a comprehensive understanding of macroscopic transport measurements. In particular, we analyze the contact pads including the transition region, perform local transport measurements in pristine graphene/Germanium, and explore the role of the semiconducting Germanium substrate. We connect the results from these local scale measurements with the macroscopic performance of the device. We find that a graphene sheet on a 2 μm Ge film carries approximately 10% of the current flowing through the device. Moreover, we show that an electronic transition region forms directly adjacent to the contact pads. This transition region is characterized by a width of >100 μm and a strongly increased sheet resistance acting as the bottleneck for charge transport. Based on Rutherford backscattering of the contact pads, we suggest that the formation of this transition region is caused by diffusion. © 2020 Author(s).
- ItemTransmitters and receivers in SiGe BiCMOS technology for sensitive gas spectroscopy at 222 - 270 GHz(New York, NY : American Inst. of Physics, 2019) Schmalz, K.; Rothbart, N.; Eissa, M.H.; Borngräber, J.; Kissinger, D.; Hübers, H.-W.This paper presents transmitter and receiver components for a gas spectroscopy system. The components are fabricated in IHP's 0.13 μm SiGe BiCMOS technology. Two fractional-N phase-locked loops are used to generate dedicated frequency ramps for the transmitter and receiver and frequency shift keying for the transmitter. The signal-to-noise ratio (SNR) for the absorption line of gaseous methanol (CH 3 OH) at 247.6 GHz is used as measure for the performance of the system. The implemented mixer-first receiver allows a high performance of the system due to its linearity up to an input power of -10 dBm. Using a transmitter-array with an output power of 7 dBm an SNR of 4660 (integration time of 2 ms for each data point) was obtained for the 247.6 GHz absorption line of CH 3 OH at 5 Pa. We have extended our single frequency-band system for 228 - 252 GHz to a 2-band system to cover the range 222 - 270 GHz by combining corresponding two transmitters and receivers with the frequency bands 222 - 256 GHz and 250 - 270 GHz on single transmitter- and receiver-chips. This 2-band operation allows a parallel spectra acquisition and therefore a high flexibility of data acquisition for the two frequency-bands. The 50 GHz bandwidth allows for highly specific and selective gas sensing. © 2019 Author(s).
- ItemOperando diagnostic detection of interfacial oxygen ‘breathing’ of resistive random access memory by bulk-sensitive hard X-ray photoelectron spectroscopy(London [u.a.] : Taylor & Francis, 2019) Niu, Gang; Calka, Pauline; Huang, Peng; Sharath, Sankaramangalam Ulhas; Petzold, Stefan; Gloskovskii, Andrei; Fröhlich, Karol; Zhao, Yudi; Kan, Jinfeng; Schubert, Markus Andreas; Bärwolf, Florian; Ren, Wei; Ye, Zuo-Guang; Perez, Eduardo; Wenger, Christian; Alff, Lambert; Schroeder, ThomasThe HfO2-based resistive random access memory (RRAM) is one of the most promising candidates for non-volatile memory applications. The detection and examination of the dynamic behavior of oxygen ions/vacancies are crucial to deeply understand the microscopic physical nature of the resistive switching (RS) behavior. By using synchrotron radiation based, non-destructive and bulk-sensitive hard X-ray photoelectron spectroscopy (HAXPES), we demonstrate an operando diagnostic detection of the oxygen ‘breathing’ behavior at the oxide/metal interface, namely, oxygen migration between HfO2 and TiN during different RS periods. The results highlight the significance of oxide/metal interfaces in RRAM, even in filament-type devices. IMPACT STATEMENT: The oxygen ‘breathing’ behavior at the oxide/metal interface of filament-type resistive random access memory devices is operandoly detected using hard X-ray photoelectron spectroscopy as a diagnostic tool. © 2019, © 2019 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
- ItemCorrection: Interface-engineered reliable HfO2-based RRAM for synaptic simulation (Journal of Materials Chemistry C (2019) DOI: 10.1039/c9tc04880d)(London [u.a.] : RSC, 2019) Wang, Qiang; Niu, Gang; Roy, Sourav; Wang, Yankun; Zhang, Yijun; Wu, Heping; Zhai, Shijie; Bai, Wei; Shi, Peng; Song, Sannian; Song, Zhitang; Xie, Ya-Hong; Ye, Zuo-Guang; Wenger, Christian; Meng, Xiangjian; Ren, WeiThere was an error in the author list of this published article. The corresponding authors for this paper are Gang Niu (gangniu@xjtu.edu.cn) and Wei Ren (wren@mail.xjtu.edu.cn). The footnote indicating that Qiang Wang and Gang Niu contributed equally to the work was not intended. The corrected author list and notations are shown here. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers. © The Royal Society of Chemistry 2019.
- ItemDesign and performance analysis of integrated focusing grating couplers for the transverse-magnetic TM00 mode in a photonic BiCMOS technology(London : Biomed Central, 2020) Georgieva, Galina; Voigt, Karsten; Peczek, Anna; Mai, Christian; Zimmermann, LarsFocusing grating couplers for the excitation of the fundamental transverse-magnetic (TM) mode in integrated silicon photonic waveguides are designed and characterized under the boundary conditions of a photonic BiCMOS foundry. Two types of waveguide geometries are considered – a nanowire and a rib waveguide. Wafer-scale experimental results for nanowire TM grating couplers are in excellent agreement with numerical investigations and demonstrate a robust behavior on the wafer. The mean coupling loss and the 3s interval are -3.9 ± 0.3 dB. The on wafer variation is three times lower than for the fundamental transverse-electric (TE) polarization. Similarly, the coupling in rib waveguides is examined as well. The results indicate that the rib waveguides require a modified geometry when designed for TM. In general, the nanowire waveguide type is more suitable for TM coupling, showing a stable and repeatable performance. © 2020, The Author(s).
- ItemProgramming Pulse Width Assessment for Reliable and Low-Energy Endurance Performance in Al:HfO2-Based RRAM Arrays(Basel : MDPI AG, 2020) Pérez, Eduardo; Ossorio, Óscar González; Dueñas, Salvador; Castán, Helena; GarcÃa, Héctor; Wenger, ChristianA crucial step in order to achieve fast and low-energy switching operations in resistive random access memory (RRAM) memories is the reduction of the programming pulse width. In this study, the incremental step pulse with verify algorithm (ISPVA) was implemented by using different pulse widths between 10 μ s and 50 ns and assessed on Al-doped HfO 2 4 kbit RRAM memory arrays. The switching stability was assessed by means of an endurance test of 1k cycles. Both conductive levels and voltages needed for switching showed a remarkable good behavior along 1k reset/set cycles regardless the programming pulse width implemented. Nevertheless, the distributions of voltages as well as the amount of energy required to carry out the switching operations were definitely affected by the value of the pulse width. In addition, the data retention was evaluated after the endurance analysis by annealing the RRAM devices at 150 °C along 100 h. Just an almost negligible increase on the rate of degradation of about 1 μ A at the end of the 100 h of annealing was reported between those samples programmed by employing a pulse width of 10 μ s and those employing 50 ns. Finally, an endurance performance of 200k cycles without any degradation was achieved on 128 RRAM devices by using programming pulses of 100 ns width.
- ItemElectron Population Dynamics in Optically Pumped Asymmetric Coupled Ge/SiGe Quantum Wells: Experiment and Models(Basel : MDPI, 2020) Ciano, Chiara; Virgilio, Michele; Bagolini, Luigi; Baldassarre, Leonetta; Rossetti, Andrea; Pashkin, Alexej; Helm, Manfred; Montanari, Michele; Persichetti, Luca; Di Gaspare, Luciana; Capellini, Giovanni; Paul, Douglas J.; Scalari, Giacomo; Faist, Jèrome; De Seta, Monica; Ortolani, Michelen-type doped Ge quantum wells with SiGe barriers represent a promising heterostructure system for the development of radiation emitters in the terahertz range such as electrically pumped quantum cascade lasers and optically pumped quantum fountain lasers. The nonpolar lattice of Ge and SiGe provides electron-phonon scattering rates that are one order of magnitude lower than polar GaAs. We have developed a self-consistent numerical energy-balance model based on a rate equation approach which includes inelastic and elastic inter-and intra-subband scattering events and takes into account a realistic two-dimensional electron gas distribution in all the subband states of the Ge/SiGe quantum wells by considering subband-dependent electronic temperatures and chemical potentials. This full-subband model is compared here to the standard discrete-energy-level model, in which the material parameters are limited to few input values (scattering rates and radiative cross sections). To provide an experimental case study, we have epitaxially grown samples consisting of two asymmetric coupled quantum wells forming a three-level system, which we optically pump with a free electron laser. The benchmark quantity selected for model testing purposes is the saturation intensity at the 1!3 intersubband transition. The numerical quantum model prediction is in reasonable agreement with the experiments and therefore outperforms the discrete-energy-level analytical model, of which the prediction of the saturation intensity is off by a factor 3. © 2019 by the authors.
- ItemControl of etch pit formation for epitaxial growth of graphene on germanium(Melville, NY : American Inst. of Physics, 2019) Becker, Andreas; Wenger, Christian; Dabrowski, JarekGraphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process. © 2019 Author(s).