Adam Witold Stadler

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.

Numerical simulations of low-frequency noise in RuO2-glass films

The paper deals with low-frequency noise in RuO2-glass thick resistive films at low temperatures. Careful measurements performed with ac technique reveal that below liquid helium temperature and in the low frequency limit excess noise of the films is a pure resistance noise for low bias voltage, but at larger voltages depends sublinearly on voltage square. The model is proposed which shows that the observed noise suppression is due to inhomogeneous heating of devices under test. In this model conduction is via hopping and the noise is due to fluctuation of activation energies of the inter-site conductances. Numerical simulations show that there is an interesting scaling of noise that can be used to identify the local (microscopic) mechanism of heat transfer from electron to phonon systems.

Chosen electrical, noise and stability characteristics of passive components embedded in printed circuit boards

This paper presents systematic studies of electrical, noise and long-term stability parameters of resistors (thin-film or polymer thick-film) and capacitors embedded in Printed Circuit Boards (PCBs). The temperature dependence of resistance or capacitance were determined in a wide temperature range (from -180°C to 130°C) and analyzed as a function of geometry of passives and cladding process. The in-situ accelerated ageing process (basic properties of passives measured directly at ageing conditions) was carried out to perform long-term behavior analysis. Low frequency noise measurements were made in room temperature using noise spectra measurements in dc bridge configuration. The R(T) characteristics are linear with almost constant, negative value of differential TCR (of about -60 ppm/K for 100 Ω/sq Ni-P resistors). Both groups of investigated resistors revealed similar range of relative resistance changes after ageing processes but the results showed the quite different behavior of both groups versus time. It means that the dynamics of ageing changes was different. Only positive resistance changes were observed for Ni-P resistors, whereas the shape of characteristics for polymer ones were much more complex, exhibited increase as well as decrease in resistance under environmental exposure. 1/f noise generated by resistance fluctuations was found as the main noise component but the significant difference of noise level was observed for both groups of investigated resistors. The C(T) characteristics are nonlinear with larger capacitance changes at higher temperature. Capacitors exposed to elevated temperature exhibited capacitance and dissipation factor decrease. The relative changes were from the range from -12% to -2% for capacitance and up to -60% for dissipation factor. The value of relative drift of parameters was dependent strongly on dielectric composition and size. Moreover the results revealed nonlinear characteristics in temperature domain as well.

Thermally activated noise sources in thick film resistors of RuO/sub 2/ and glass

A study on low-frequency noise sources in thick film resistors made of resistive pastes based on ruthenium dioxide and glass has been presented. The paper focuses on the excess noise spectrum dependence on temperature in the range 77 K < T < 300 K. A special technique has been invented to measure noise spectra as a function of temperature. Experimental data have been then analyzed to extract characteristic values of activation energy and time constant describing features of the measured spectra. It has been proved that the noise in RuO2+glass thick film resistors is caused by two-states systems with thermally activated kinetics. The distribution of activation energies that govern transition in two-state systems has been determined. The maximum of the distribution energy of ~0.2 eV has been found. The final conclusion is that the mechanism coupling fluctuations of two state systems to the resistance depends on temperature weaker than exponentially

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...