Krzysztof Mleczko

Evaluation of conductive-to-resistive layers interaction in thick-film resistors

Low-frequency noise spectroscopy is used to examine the interactions between resistive and conductive films that take place during thick-film resistor (TFR) fabrication. Two noise parameters are introduced to quantitatively describe the strength of these interactions. They refer to intensity and repeatability of the noise generated in the resistor interfaces. Extensive experimental studies performed on ruthenium dioxide and bismuth ruthenate TFRs terminated with gold, platinum–gold, palladium–silver and platinum– silver contacts from various manufacturers allow to establish criteria of pastes compatibility and to evaluate compatible systems of pastes for standard ‘‘on-alumina” and low-temperature co-fired ceramic (LTCC) resistors. It is found that gold contacts form low-size-effect, stable, low-noise interfaces both with ruthenium dioxide and bismuth ruthenate TFRs. Silver-containing terminations can be used with bismuth ruthenate but not with ruthenium dioxide resistors. Manufacturer optimized system of pastes for LTCC technology works best when used to produce high-resistive, co-fired devices.

Noise resolution of RuO2-based resistance thermometers

Low-frequency noise was measured for RuO2-based thick film resistors at liquid helium temperatures down to 0.36 K. The 1∕f-type spectrum and squared voltage dependence of power spectral density observed at low voltages attribute the noise as coming from equilibrium resistance fluctuations. Measurements carried out at different temperatures show that the magnitude of noise intensity (index) increases significantly as temperature goes down. Due to this fact, the resolution of RuO2 thermometers increases above the instrument resolution. The quantity which describes a sensor resolution is defined and calculated for RuO2 thick film sensor. Some remarks on measurement strategy and sensor optimization are supplied.

Noise and switching phenomena in thick-film resistors

Low frequency noise spectroscopy is employed to examine fluctuating phenomena that take place in the material of resistive films and in the film/termination interface of a thick-film resistor. It has been found that the excess low frequency noise apart from the 1/f component contains contributions from thermally activated noise sources with energies in the range 0.015–0.6 eV. These sources are nonuniformly distributed over the whole resistor volume, most probably in the glassy matrix or conductive grain boundaries. All noise sources are subjected to the switching phenomenon which abruptly changes the densities of local currents that describe the coupling of the resistance to noise processes produced in the fluctuators. Redistribution of currents results in switching between different sets of active noise sources that build up the noise spectrum. Extensive experimental studies that consider the influence of various parameters of fabrication process, sample geometry, substrate and operation exposures suggest that the most likely origin of the switching phenomenon is the relaxation of mechanical stress which in thick-film resistors appears due to the mismatch of the thermal expansion coefficients of the materials contained in resistive films, conductive terminations and the substrate. (Some figures in this article are in colour only in the electronic version)

Noise properties of Pb/Cd-free thick film resistors

Low-frequency noise spectroscopy has been used to examine noise properties of Pb/Cd-free RuO2- and CaRuO3-based thick films screen printed on alumina substrates. Experiments were performed in the temperature range 77–300 K and the frequency range 0.5–5000 Hz with multiterminal devices. The measured noise has been recognized as resistance noise that consists of background 1/f noise and components generated by several thermally activated noise sources (TANSs) of different activation energies. The total noise has been composed of the contributions generated in the resistive layer and in the resistive/conductive layers interface. These noise sources are non-uniformly distributed in the resistor volume. Noise intensity of new-resistive layers has been described by the noise parameter Cbulk. Pb/Cd-free layers turned out to be noisier than their Pb-containing counterparts; however, the removal of Pb and Cd from resistive composition is hardly responsible for the increase in the noise. In the case of RuO2 layers noise increases most likely due to larger grain size of RuO2 powder used to prepare resistive pastes. Information on the quality of the resistive-to-conductive layers interface occurred to be stored in the values of noise parameter Cint. Pb/Cd-free RuO2-based resistive pastes form well-behaved interfaces with various Ag-based conductive pastes. In contrast, CaRuO3-based paste forms bad contacts with AgPd terminations because the density of TANSs increases in the interface area.

1/f noise versus magnetic field in RuO/sub 2/ based thick film resistors

Low frequency noise has been measured in RuO/sub 2/+ glass thick film resistors in subkelvin temperatures and in magnetic fields. Samples were fabricated from laboratory-made pastes, which did not contain any modifiers (only RuO/sub 2/ and glass of known volume fractions). Measurements performed with ac technique show that below 4 K relative noise intensity increases significantly and becomes a factor limiting the resolution of RuO/sub 2/ temperature sensors. Magnetic field does not influence this resolution.

Implementation of RuO2-glass based thick film resistors in cryogenic thermometry

In the work we analyse the results of investigations of RuO2-glass based compounds, with regard to their implementation in low temperature thermometry. Based on measurements made down to 0.3 K we have shown that the sensitivity, S = dR/dT, of our sensors is comparable to the sensitivity of commercial sensors. The influence of the magnetic field on the investigated sensors in the range up to 10 T was checked. The magnetoresistance MR = (R0 − RB)/R0 of our v = 10% sample is approximately five times smaller than for the Rox RX-202A Lake Shore sensor (B = 7 T, T = 0.47 K). We present results of investigations of the stability during thermal cycling: resistance changes during cycling lead to differences in temperature indication after a period of time.

Noise sources in polymer thick-film resistors

Purpose – The paper aims to get the knowledge about electrical properties, including noise, of modern polymer thick-film resistors (TFRs) in a wide range of temperature values, i.e. from 77 K up to room temperature. The sample resistors have been made of different combinations of resistive compositions, either ED7100 or MINICO (M2013, M2010), and conducting pastes (for contacts) Cu- or Au-based, deposited on FR-4 laminate. Design/methodology/approach – The paper opted for an experimental study using either current noise index measurement in room temperature for large batch of samples or noise spectra measurement in temperature range 77-300 K for selected samples. Obtained noise maps, i.e. plots of power spectral density of voltage fluctuations vs frequency and temperature, have been used for evaluation of noise describing parameters like material noise intensity C and figure of merit K, for TFRs made of different combinations of resistive/conductive materials. Comparison of the parameters gives the inform...

Magnetoresistance of RuO/sub 2/-glass films

RuO/sub 2/-glass based materials gain the application in construction of modern temperature sensors in cryogenics. This is due to their high temperature sensitivity, remaining virtually insensitive to magnetic field. The paper addresses the question about electrical charge transport mechanism in these materials which is still open: there are many experimental studies which draw to different and sometimes contradicting conclusions. Resistance of laboratory made thick films consisting of RuO/sub 2/ and glass mixture of precisely controlling ratio have been studied in temperature range form 0.3 K to 300 K and magnetoresistance in magnetic field up to 10 T or temperatures below 4.2 K. It has been observed that at the lowest temperatures (T <) magnetoresistance changes sign from negative to positive when magnetic field increases. At higher, temperatures only positive magnetoresistance has been revealed. Data analysis involving possible conduction mechanisms (weak localization, hopping) has been performed. Conclusions are helpful in understanding physics of electron transport in RuO/sub 2/ based thick film resistors and might be useful in optimization and designing modern temperature sensors made of inhomogeneous materials.