We report on resistive switching of capacitor-like SrRuO 3 /Ba 0.7 Sr 0.3 TiO 3 / Pt thin films epitaxially grown on SrTiO 3 substrates. We observe a weak but stable hysteresis in the current-voltage curve. By applying short voltage pulses, a high or low resistive state as well as intermediate states can be addressed even at room temperature. We demonstrate a multiple-branch hysteresis curve corresponding to multilevel switching modus revealing different subloops for different write voltages. Furthermore reliability issues such as cycling endurance and data retention are presented. 10 Here, different resistance levels could be addressed by a variation of length and amplitude of the programming voltage pulse. There is still some debate about the physical mechanisms of the resistance change and about the key experimental parameters. Mechanisms under discussion are ͑i͒ trapping/detrapping effects and charge transfer processes via donor and acceptor levels ͑Cr 3+ /Cr 4+ ͒, 10,13 ͑ii͒ a Mott metal-insulator transition, 14 ͑iii͒ formation of local current domains, 12 ͑iv͒ redox processes of extended defects, 15 and ͑v͒ conductivity changes due to a reversal of a local spontaneous polarization. 16 Polarization changes might not be stringently of ferroelectric nature, but might also be due to defect dipoles, e.g., formed by acceptor/oxygen vacancy defect associates. 17 In our present work, we investigate resistive switching of 0.2% chromium-doped Ba 0.7 Sr 0.3 TiO 3 ͑BST͒ capacitorlike thin films of around 40 nm thickness at RT. We investigate in detail multibranch type I͑V͒ curves, which have not been reported for perovskites dielectrics so far. We will present detailed measurements of the multilevel switching and focus on reliability issues such as cycling endurance and data retention.SrRuO 3 ͑SRO͒ bottom electrodes of 100 nm thickness and BST layer of 40 nm thickness are grown in situ epitaxially on single crystalline ͑100͒ oriented SrTiO 3 ͑STO͒ substrates. The films are deposited by pulsed laser ablation while maintaining a substrate temperatur of 700°C and an oxygen base pressure of 0.25 mbar. The epitaxial growth of the bilayers is confirmed by x-ray diffraction measurements ͓Phil-ips PW 3020 ͑Cu K␣͔͒. Pt top electrodes are deposited by sputtering and patterned by optical lithography and a lift-off process to areas of 0.09 mm 2 down to 100 m 2 . The bottom electrode is contacted after removing the BST film from the sample edge by wet chemical etching. A postannealing step in oxygen is performed at 700°C for 5 min. The currentvoltage characteristics are measured with a Keithley 2410 source meter. To protect samples from damages due to high currents a current compliance is used. All samples reveal low initial resistances so that a high voltage treatment prior to quasistatic I͑V͒ characterization or pulse measurements to convert the sample from an insulating state into a low conductive state as described in Ref. 11 for SrTiO 3 single crystals ͑"forming process"͒ is not required here. The stable switching behavior r...

The resistive switching behavior of devices consisting of aluminum top electrode, molecular layer ͑rose bengal͒, and bottom electrode ͑zinc oxide and indium tin oxide͒ is examined. By measuring the current versus voltage dependence of these devices for various frequencies and by systematically varying the composition of the device, we show that the switching is an extrinsic effect that is not primarily dependent on the molecular layer. It is shown that the molecular layer is short circuited by filaments of either zinc oxide or aluminum and that the switching effect is due to a thin layer of aluminum oxide at the zinc oxide/aluminum interface.

GaN-based high electron mobility transistors (HEMT) on Si (111) substrates have large potential for applications in the 5G telecommunication field. However, for this potential to be fully realized, all loss mechanisms need to be minimized. It is known that typical metal-organic chemical vapor deposition (MOCVD) processes used to grow the GaN epitaxial layers can cause considerable parasitic conductivity at the interface of the AlN nucleation layer to the high-resistivity Si substrate, leading to reduced gain and power added efficiency in amplifiers. Reducing this parasitic conductivity is hence of utmost importance to render GaN-on-Si a significant contributor to next-generation 5G power amplifier technology. In this work, we employ secondary ion mass spectroscopy, spreading resistance profiling and insertion loss measurements up to 28 GHz using coplanar waveguides fabricated on the epitaxial layer stacks to study the origin and characterize the parasitic conductivity. While a single heat-up process in an AIXTRON G5+ reactor chamber cleaned using Cl2 does not introduce any extra dopants in the Si substrate, the epitaxial growth of (Al,Ga)N-based HEMT buffer layer stacks leads to the diffusion of Al and, to a lower extent, Ga acceptors into the Si substrate. Optimization of the MOCVD process towards lower growth temperatures leads to a strong reduction of density of diffused acceptors. This reduction goes in line with a significant decrease of the insertion loss from 0.45 dB mm −1 to only 0.20 dB mm −1 at a frequency of 28 GHz.

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