Andrzej Kolek

noise in polymer thick-film resistors

noise properties of carbon black/polyesterimide and (carbon )/polyesterimide thick-film resistors are studied. In resistive inks either high-structure carbon black or medium-structure carbon black was used. The influence of the content p of carbon black and graphite in resistive inks and curing temperature on sheet resistance and noise intensity C is considered. It is shown that a higher curing temperature causes a decrease in the resistors volume and influences and C indirectly, via changes of the parameter p. It is then found that an increase in p leads to a simultaneous decrease of sheet resistance and noise intensity C. The relation is found in this case for all measured resistors. The values of noise exponent are estimated and a comparison with the noise properties of conventional cermet thick-film resistors is made. It is shown that the noise intensities of carbon black/polyesterimide resistors are comparable to those of cermet resistors.

Modeling of Mid-Infrared Quantum Cascade Laser by Means of Nonequilibrium Green's Functions

Nonequilibrium Greens function (NEGF) calculations of mid-infrared quantum cascade laser (QCL) that preserve real-space basis have been performed. The approach developed in this paper relies on two improvements introduced to nonequilibrium Greens functions/Poisson computational scheme. First, the boundaries of single laser stage were carefully designed as to maintain its periodicity with the whole quantum cascade structure. Second, the NEGF/Poisson solver was equipped with several controlling features that enable the restoration of convergence of the method for quite complex structures with many resonances and boundary conditions for Poisson equation set inside the structure. With this simulation tool, calculations for an anticrossed diagonal design of mid-infrared QCL have been performed. Results agree with experimental data (threshold current of ~4.2 kA/cm2 at material gain of ~70/cm) and the current understanding of carrier transport in such devices.

Nonthermal carrier distributions in the subbands of 2-phonon resonance mid-infrared quantum cascade laser

Nonequilibrium Green’s functions model of mid-infrared quantum cascade laser that utilizes double-phonon resonance scheme is analyzed. Good agreement with experimental data is found. For quantities not accessible experimentally, it is shown that electronic distributions in lower active region subbands are nonthermal and have local maximum at higher in-plane energy. In upper subband, carrier distribution is thermal-like. Upper state lifetime is strongly reduced from optical phonon value by interface roughness and alloy scatterings. Net gain originates from population inversion at subbands bottom which is not suppressed by high-k absorption because of nonparabolicity which shifts absorption peak to lower frequencies.

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 characteristics of resistors buried in low-temperature co-fired ceramics

The comparison of noise properties of conventional thick film resistors prepared on alumina substrates and resistors embedded in low-temperature co-fired ceramics (LTCCs) is presented. Both types of resistors were prepared from commercially available resistive inks. Noise measurements of LTCC resistors below 1 kHz show Gaussian 1/f noise. This is concluded from the calculations of the second spectra as well as from studying the volume dependence of noise intensity. It has occurred that noise index of LTCC resistors on average is not worse than that of conventional resistors. A detailed study of co-fired surface resistors and co-fired buried resistors show that burying a resistor within LTCC substrate usually leads to (significant) enhancement of resistance but not of noise intensity. We interpret this behaviour as another argument in favour of tunnelling as the dominant conduction mechanism in LTCC resistors.

Investigation of a near mid-gap trap energy level in mid-wavelength infrared InAs/GaSb type-II superlattices

In this report, we present results of an experimental investigation of a near mid-gap trap energy level in InAs10 ML/GaSb10 ML type-II superlattices. Using thermal analysis of dark current, Fourier transform photoluminescence and low-frequency noise spectroscopy, we have examined several wafers and diodes with similar period design and the same macroscopic construction. All characterization techniques gave nearly the same value of about 140 meV independent of substrate type. Additionally, photoluminescence spectra show that the transition related to the trap centre is temperature independent. The presented methodology for thermal analysis of dark current characteristics should be useful to easily estimate the position of deep energy levels in superlattice photodiodes.

High performance GaAs/AlGaAs quantum cascade lasers: optimization of electrical and thermal properties

In this paper we present the development of mid-infrared GaAs/AlGaAs QCLs technology and discuss basic characteristics of lasers fabricated at the Institute of Electron Technology. We also show that reliable simulation methods which can deal with the complicated physical phenomena involved in the quantum cascade lasers operation are necessary to predict the behaviour of new structures and optimize their performance. The developed lasers show the record pulse powers of 6 W at 77 K and up to 50 mW at 300 K. This has been achieved by careful optimization of the epitaxial process and by applying a high reflectivity metallic coating to the back facet of the laser. The devices have been successfully used in prototype ammonia detection system working in ppb range.

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)

Synchrotron infrared transmission spectroscopy of a quantum cascade laser correlated to gain models

We measure the broadband optical gain and absorption spectra between 0.1 and 0.7 eV in a two-phonon resonance design quantum cascade laser, with the infrared beam of a synchrotron light source, and correlate them to established simulation models, based on the density matrix formalism, and on the non-equilibrium Greens function theory. We show that accounting for the distribution of carriers in momentum space improves the description of the high-energy absorption from the excited states located close to the active wells and results in an accurate prediction of the gain.