We present a measurement and analysis scheme for determining traceable thermodynamic temperature at cryogenic temperatures using Coulomb blockade thermometry. The uncertainty of the electrical measurement is improved by utilizing two sampling digital voltmeters instead of the traditional lock-in technique. The remaining uncertainty is dominated by that of the numerical analysis of the measurement data. Two analysis methods are demonstrated: numerical fitting of the full conductance curve and measuring the height of the conductance dip. The complete uncertainty analysis shows that using either analysis method the relative combined standard uncertainty (k = 1) in determining the thermodynamic temperature in the temperature range from 20 mK to 200 mK is below 0.5 %. In this temperature range, both analysis methods produced temperature estimates that deviated from 0.39 % to 0.67 % from the reference temperatures provided by a superconducting reference point device calibrated against the Provisional Low Temperature Scale of 2000.

The use of low-temperature platforms with base temperatures below 1 K is rapidly expanding, for fundamental science, sensitive instrumentation and new technologies of potentially significant commercial impact. Precise measurement of the thermodynamic temperature of these low-temperature platforms is crucial for their operation. In this paper, we describe a practical and user-friendly primary current-sensing noise thermometer (CSNT) for reliable and traceable thermometry and the dissemination of the new kelvin in this temperature regime. Design considerations of the thermometer are discussed, including the optimization of a thermometer for the temperature range to be measured, noise sources and thermalization. We show the procedure taken to make the thermometer primary and contributions to the uncertainty budget. With standard laboratory instrumentation, a relative uncertainty of 1.53% is obtainable. Initial comparison measurements between a primary CSNT and a superconducting reference device traceable to the PLTS-2000 (Provisional Low Temperature Scale of 2000) are presented between 66 and 208 mK, showing good agreement within the k=1 calculated uncertainty.

A cantilever-type silicon device for sensing changes in pressure has been designed, fabricated and characterized. The microfabrication process is based on two-sided etching of silicon-on insulator (SOI) wafers. The rectangular cantilevers are 9.5 µm thick, and cover an area of a few square millimeters. The cantilevers are surrounded by thick and tight frames, since on the three free sides there are only narrow, micrometer sized air gaps between the cantilever and the frame. This design and excellent mechanical properties of single crystal silicon enable sensitive detection of time-dependent gas pressure variations, i.e. acoustic waves. The mechanical properties of the cantilever have been characterized by analyzing its dynamic behavior. The resonance frequency and the mechanical vibrational mode patterns have been determined using finite-element method (FEM) simulations and laser interferometry. These results are found to be in good agreement with each other. Initially this mechanical door-like cantilever was designed to be used in ultra-high sensitivity photoacoustic gas sensing, but it can also be applied quite generally in various kinds of sound wave detection schemes.

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In this paper, the influence of the atomic layer deposited alumina (Al 2 O 3) thin films on the dynamics of a high-Q mechanical silicon oscillator was experimentally studied. The resonance frequency and Q value of uncoated oscillators used in this work were about f 0 = 27 kHz and Q = 100 000 at p < 10 −2 mbar and T = 300 K. Deposited alumina film thicknesses varied from 5 to 662 nm. It is demonstrated that the resonance frequency of the mechanical oscillator increases with the film thickness because the added alumina films effectively stiffen the oscillator structure. In addition, it is shown that alumina thin films with thickness up to 100 nm can be deposited on microfabricated mechanical resonant structures without degrading the initially high quality (Q value) of the resonance. The resonance frequency of the silicon oscillator was less sensitive to the changes in ambient temperature with thicker alumina coatings. The reflectivity of silicon at 633 nm was reduced from R Si = 0.35 to R AR = 0.035 by coating the silicon oscillator with an alumina film whose thickness corresponds to the quarter of the optical wavelength serving as a single-layer anti-reflection coating.