Per Eklund, Single-step synthesis process of Ti3SiC2 ohmic contacts on 4H-SiC by sputter-deposition of Ti, 2015, Scripta Materialia, (99), 53-56. http://dx

Water’s salinity plays an important role in the environment. It can be determined by measuring conductivity, temperature, and depth (CTD). The corresponding sensor systems are commonly large and cumbersome. Here, a 7.5 × 3.5 mm chip, containing microstructured CTD sensor elements, has been developed. On this, 1.5 mm2 gold finger electrodes are used to measure the impedance, and thereby the conductivity of water, in the MHz frequency range. Operation at these frequencies resulted in higher sensitivities than those at sub-MHz frequencies. Up to 14 kΩ per parts per thousand salt concentration was obtained repeatedly for freshwater concentrations. This was three orders of magnitude higher than that obtained for concentrations in and above the brackish range. A platinum electrode is used to determine a set ambient temperature with an accuracy of 0.005°C. Membranes with Nichrome strain gauges responded to a pressure change of 1 bar with a change in resistance of up to 0.21 Ω. A linear fit to data over 7 bars gave a sensitivity of 0.1185 Ω/bar with an R2 of 0.9964. This indicates that the described device can be used in size-limited applications, like miniaturized submersibles, or as a bio-logger on marine animals.

Extreme temperature measurements of Ni/Ti/Al contacts to p-type SiC (Na= 1∙1018cm-3), with a specific contact resistivity ρc= 6.75∙10-4Ωcm2at 25 °C, showed a five time increase of the specific contact resistivity at -40 °C (ρc= 3.16∙10-3Ωcm2), and a reduction by almost a factor 10 at 500 °C (ρc= 7.49∙10-5Ωcm2). The same response of ρcto temperature was seen for contacts on lower doped epitaxial layer. Also N-type nickel contacts improved with higher operational temperature but with a considerably smaller variation over the same temperature interval. No degradation of the performance was seen to either the Ni/Ti/Al or the Ni contacts due to the high temperature measurements.

Abstract. Ohmic CoSi 2 contacts to n-type 4H-SiC showing low contact resistance have been made by sputter depositing sequential layers of Si and Co on 4H-SiC substrates followed by a two-step rapid thermal anneal at 600 °C and 950 °C. The contacts formed have been characterized at temperatures ranging from -40 °C to 500 °C with a specific contact resistance of 3.8•10 -5 Ωcm 2 at 25 °C and a minimum of 6.0•10 -6 Ωcm 2 at 500 °C.

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