No abstract

This paper presents the small-signal and noise characterisation of different technologies based on CVD and SiC graphene field effect transistors. The noise model, built on noise figure measurements under 50Ω using the F50 method, was verified by additional source-pull measurements, with a special care to the GFET stability. The four noise parameters were then extracted using the validated F50 model up to 18 GHz and correlations between noise and small-signal parameters were shown for two different configurations: top-gated and back-gated GFETs.

Miniaturized, microfabricated microelectromechanical systems (MEMS)-based wafer probes are used here to evaluate different contact pad metallization at low tip forces (<mN) and low skate on the on-wafer pads. The target application is low force RF probes for on-wafer measurements which cause minimal damage to both probes and pads. Low force enables the use of softer, more conductive metallisation. We have studied four different thin film contact pad metals based on their thin film electrical resistivity and micro-hardness: gold, nickel, molybdenum, and chromium. The contact pads sizes were micrometre (1.9×1.9 µm2) and sub-micrometre (0.6×0.6 µm2). The contact resistance of Au-Au, Ni-Au, Mo-Au, and Cr-Au was measured as a function of tip deflection. The tip force (loading) of the contacts was evaluated from the deflection of the cantilever. It was observed that an overtravel of 300 nm resulting in a contact force of ~400 µN was sufficient to achieve a contact resistance <1 Ω for a sub-micrometre gold contact pad. Our results are compared with an analytical model of contact resistance in loaded metal-metal contacts—a reasonable fit was found. A larger contact resistance was observed for the other metals—but their hardness may be advantageous when probing other materials. Using a combination of a rigid silicon cantilever (>1000 Nm-1) and small contact pads enabled us to show that it is the length of the pad (in contact with the surface) which determines the contact resistivity rather than the total contact pad area.

Near-field scanning microwave microscopy (NSMM) has to face several issues for the establishment of traceable and quantitative data. In particular, at the nanoscale, the wavelength of operation in the microwave regime appears disproportionate compared to the size of the nano-object under investigation. Incidentally, the microwave characterization results in poor electrical sensitivity as the volume of the wave/material interaction is limited to a fraction of the wavelength. In addition, the definition of nanoscale microwave impedance standards requires accurate knowledge of the material and dimensional properties at such scale. In this effort, a quantitative error analysis performed on micrometric metal oxide semiconductor (MOS) structures is proposed. In particular, atomic force microscopy (AFM) image together with the magnitude and phase-shift images of the complex microwave reflection coefficient using a Keysight TM 's LS5600 AFM interfaced directly with a vector network analyzer, without electrical matching strategy, are performed around 9.5GHz. From a detailed analysis of the raw data, completed with a FEMbased electromagnetic modeling, quantitative capacitances extraction and system limitations are exemplary shown.

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