Science

A quantum-based synthesizer for generation of AC voltages of arbitrary waveforms (Josephson Arbitrary Waveform Synthesizer, JAWS) is based on SNS Josephson junctions due to their high critical current density of about 100 kA/cm². SNS junctions allow the integration of a large number of sub-µm junctions in short compact series arrays (lumped arrays), which have a typical length of about 1.5 mm allowing an operation at 10 GHz. In spite of the geometric limitations, these lumped arrays are a simple solution for a broad-band operation for the JAWS. The goal of the ongoing development is to further increase the output voltage of the synthesized AC waveforms.
The integration density of these pulse-driven arrays was significantly increased by arranging the Josephson junctions within a meandered lumped array (cf. Fig. 1). The whole meander forms the inner conductor of a co-planar waveguide, which is dimensioned to an impedance of 50 Ohm. Up to...

A chirp filter is a linear device that is designed to give a surface-acoustic-wave (SAW) signal delay which varies substantially with frequency. It is also called dispersive delay line (DDL). Such devices are often used in pulse-compression radar systems, and for real time Fourier transformations. A prototype chirp filter with a time-bandwidth product of 4000 (T = 10µs; B = 400MHz) has been developed based on black YZ-cut Lithium Niobate (YZ-LiNbO₃). This type is called Reflective Array Compressor (RAC), and the schematic structure is shown in Figure 1.
LiNbO3 is strongly piezoelectric and therefore especially suitable for the design of large bandwidth SAW filters. An inter digital transducer (IDT) is used to transform a microwave signal into a surface acoustic wave propagating along the substrate surface. Vice versa, due to the duality of the piezoelectricity, the surface acoustic wave can also be detected by an IDT and be transformed...

In the `Electron Counting Capacitance Standard´ experiment a capacitor is charged by a well-known number of electrons, and the voltage developing is measured using a Josephson voltage standard. Eventually the `Electrical Quantum Triangle´ can be realized by tracing the capacitor's capacitance to the von-Klitzing constant, which tests the consistency of the three fundamental electrical quantum effects (quantum-Hall, Josephson and the single-electron tunnelling effect). The realization of the Electrical Quantum Triangle with an uncertainty of a few parts in 107 is considered an important milestone on the way to a new system of units, being entirely based on fundamental constants. PTB, as one of few metrology institutes world-wide, pursues the setup of this experiment for some time past (Fig. 1).
In the last year the operation of a five-junction single-electron tunneling (SET) pump, fabricated at PTB, was tested for the first time. Here, a...

In einem durch die VW-Stiftung geförderten Vorhaben sollen die Herstellung, die physikalischen und chemischen Eigenschaften und mögliche Anwendungen von frei aufgehängten, monolagigen "Nanoblättern" untersucht werden. Die drei beteiligten Partner sind Arbeitsgruppen der Universität Bielefeld, der Universität Heidelberg und der PTB. Die Nanoblätter bilden ultradünne Membranen mit der Dicke eines einzelnen Moleküls (1-2 nm). Sie basieren auf vernetzten, selbstorganisierenden Monoschichten, die sich von ihrem Substrat ablösen lassen und als freistehendes Nanomaterial stabil sind. Wir wollen mechanische Eigenschaften wie Moduli, Zugfestigkeiten und Resonanzfrequenzen untersuchen. Auch die elektrischen Eigenschaften wie Leitfähig- keit und Kapazität, und chemische Eigenschaften wie Oberflächenfunktionalisierung und Gasadsorption sollen charakterisiert werden. Mögliche Anwendungen dieser Nanoblätter könnten ultradünne, elektronentransparente...

Mit dem Eintritt Bulgariens in die EU ergab sich die Notwendigkeit, die korrekte Rück- führung der dortigen nationalen Normale für Wechselspannung durch einen interna- tionalen Vergleich sicherzustellen. In einem bilateralen Vergleich zwischen dem BIM in Bulgarien und der PTB wurden 3 Volt Wechselspannungen bei Frequenzen von 55 Hz, 1 kHz, 20 kHz und 100 kHz gemessen. Die Messwerte zeigen eine sehr gute Überein- stimmung (degree of equivalence) von besser als 8 µV/V. Es wurde eine Verbindung zu dem Key Comparison CCEM-K6.a hergestellt, an dem die PTB früher teilge- nommen hatte. Der bilaterale Vergleich wurde als EUROMET.EM-K6.a in die Daten- bank des BIPM aufgenommen.

The novel method is based on a single airline one-port measurement which is performed with the pre-calibrated vector network analyzer. By applying a sophisticated numerical analyzing scheme to the measured broadband data set, the complexvalued residual system error parameter of the analyzer can be extracted over the entire frequency range. From the error terms, a second-order calibration of the analyzer can be performed. The method enables an easy performance check of mechanical calibration kits as well as of electronic calibration units. In collaboration with PTB WG 8.42 und in cooperation with Rohde & Schwarz, the method is currently extended to 2-port measurements. A corresponding publication has been awarded at the 69. ARFTG conference 2008 for best paper.

The Josephson junctions with Al2O3-double barriers (SINIS junctions) used at PTB for programmable voltage standards can be damaged during the rather complex fabrication process. The reason why some critical currents strongly deviate from the average value is not known. A technological alternative are SNS junctions with only one normal conductor as effective tunnel barrier. They may reduce the problem of process-induced damages to a minimum and would, moreover, simplify the fabrication process. However, due to the low resistivity of the normal conductors used up to now, programmable voltage standards on the basis of SNS junctions could only be driven at frequencies up to 20 GHz. A new technology recently developed at NIST has the potential to overcome the frequency limit set by the IcRn-product (Ic: critical current, Rn: normal resistance of the junction). This technology is using a co-sputtered high-resistive NbxSi1-x alloy embedded...