Using thin-film technology with its characteristic low masses and high aspect ratios a new range of possibilities is made available for the use of dynamic thermal measuring principles. Based on this, a micromachined sensor was developed for the measurement of transient thermal signal responses leading to the thermal characterization of fluids at low sample volumes. The achieved resolution allowed the measurement of thermal parameters of the investigated fluids, i.e., thermal conductivity and specific heat, inside microfluidic systems at a high sensitivity, enabling the detection of inter-fluid boundaries, e.g., as found in micromixers and -reactors, making the sensor a useful tool for micro fluidic system characterization. This is achieved via the measurement of the frequency dependent thermal signal response.

Dynamic thermal sensor - principles in MEMS for fluid characterization

A kinetic inductance thermometer is applied to x-ray calorimetry, and its operation over a wide range of fre-quencies and geometries is discussed. Three amplifier configurations are described, one using a superconducting quantum int.erference device (SQUID) amplifier, another incorporating an FET amplifier in an amplitude modulated system, and the third, using a tunnel diode frequency modulated oscillator circuit. The predicted performance of each configuration is presented. 1. INTRODUCTIONWe are interested in fabricating bmad band x-ray detectors operating between 0.1 and 10 keY with thehighest achievable energy resolution. In principle, x-ray microcalorimeters operating at cryogenic temperaturesshould be able to cover this energy band with a 1 eV resolution.1'2 To date, 12 eV has been achieved using resis-tive sensors thermally connected to an x-ray absorbing material.3 In these devices, the resistive Johnson noise ofthe sensor is always present and is a limitation to the overall performance. To further improve the resolution of thedevice, the Johnson noise must be reduced. If the Johnson and amplifier noise can be reduced, the temperaturefluctuation noise will dominate the noise spectrum over a much larger range in frequencies. Experiments arecurrently being carried out with calorimeters using dielectric sensors.4 In principle, dielectric calorimeters are freeof Johnson noise, and produce signal strengths far above the remaining amplifier noise. Another way to circumventJohnson noise is through the use of superconducting materials. Below the critical temperature, only the residualresistance from superconducting surfaces need to be considered, and they prove to be negligible.5 As suggested byMcDonald,6 the temperature dependence of the kinetic inductance in a superconducting thin film can be utilized as

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Application of kinetic inductance thermometers to x-ray calorimetry

We are developing a dielectric microcalorimeter for X-ray spectroscopy. We will present the results of our measurement of the dielectric permittivity, the spontaneous polarization, and the pyroelectric coefficient of the mixed-crystal quantum ferroelectric KTa(1-x)Nb(x)O3 with a doping of x = 0.012, as a function of temperature and bias voltage across the device. The effects of surface layers on the permittivity and the pyroelectric coefficient are discussed. We also show the signal results from infrared LED and alpha-particle radiation.

Feasibility of KTa1-xNbxO3 as a dielectric or pyroelectric microcalorimeter

We are developing a cryogenic dielectric microcalorimeter for X‐ray spectroscopy This type of detector takes advantage of the temperature dependence of the dielectric permittivity in ferroelectric and pyroelectric materials It should have many advantages over traditional resistive devices, for example, minimal self heating and the reduction of Johnson noise Several properties of dielectrics are important to their operation as a microcalorimeter Here we present the measurements of the dielectric permittivity, ϵ = (δD/δE)T/ ϵ0 and the spontaneous polarization, Ps , for the mixed‐crystal quantum ferroelectric KTa1−xNbxO3 (KTN) with a doping of x = 0012, as a function of temperature and electric field across the device Prototype dielectric microcalorimeters have been developed and operated between 42 K and 13 K We also show the signal response from infrared LED radiation and a spectrum from an α‐particle source

A Dielectric Microcalorimeter for Photon Counting X-ray Spectroscopy

The initial development work on a dielectric microcalorimeter is presented. It focuses on the dielectric properties of the ferroelectric material KTa(1-x)Nb(x)O3 (KTN). Measurements of the temperature dependent dielectric constant are given together with the first alpha particle detection results from a prototype composite microcalorimeter operating at 1.3 K. A nonthermal mechanism for detecting 6 MeV alpha particles in a monolithic KTN sample is also reported.

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Test results of a prototype dielectric microcalorimeter

Photon counting x‐ray spectroscopy using microcalorimeters combines the high resolution power of a Bragg crystal with the broad bandwidth capability and high efficiency of charge sensitive detectors. To date, the developers of microcalorimeters take advantage of the strong temperature dependence of resistance in doped semiconductor crystals for converting the calorimeter temperature changes into useful voltage signals. Resistive sensors limit the ultimate sensitivity of microcalorimeters because they dissipate heat and add Johnson noise to the electronic conversion circuit. Potentially, these detrimental properties can be eliminated by exploiting the temperature dependence of the dielectric constant in ferroelectric materials. A mixed crystal quantum ferroelectric shows great promise for a dielectric thermal sensor. We present results from our most recent measurements which include the first detection of individual 6 MeV alpha particles with a dielectric calorimeter operating at 1.2 K.

A new thermal sensor for x‐ray microcalorimetry

We report on the current status of our work on x-ray microcalorimeters for use as high resolution x-ray spectrometers. To
maximize the x-ray collecting area and the signal to noise ratio, the total heat capacity of the device must be minimized. This
is best achieved if the calorimeter is divided into two components, a thermal sensor and an x-ray absorber. The thermal sensor
is a neutron transmutation doped (NTD) germanium resistor made as small as possible to minimize the heat capacity of the
calorimeter. The thermistor can be attached to a thin x-ray absorber with large area and low heat capacity fabricated from
superconducting materials such as niobium. We discuss results from our most recent studies of such superconducting
absorbers and present the x-ray spectra obtained with these composite microcalorimeters at a temperature of 0. 1 K. An energy
resolution of 19 eV FWHM has been measured.

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Timothy E. Pfafman

Papers

Test results of a prototype dielectric microcalorimeter

A new thermal sensor for x‐ray microcalorimetry

X-ray microcalorimeters with germanium-resistance thermometers