Petr Vasina

Noise and transport characterisation of tantalum capacitors

Abstract A low frequency noise and charge carrier transport mechanisms were investigated on tantalum capacitors made by various producers. The model of Ta–Ta2O5–MnO2 MIS structure was used to give physical interpretation of I–V characteristics in normal and reverse modes. The noise in time and frequency domain was examined and noise sources were identified. We evaluated correlation between leakage current and noise spectral density and discussed corresponding quality and reliability indicators.

1/f noise in metallic thin films

Studies of 1/fa noise in vast ensembles of thin film resistors are described. The distribution of the exponent a in the spectral density power law is found to be normal, the mean value being near unity and depending on the sample preparation technology. The scattering range of the values of a is typical of the resistor manufacturers. The noise voltage spectral density distribution is shown to depend on the frequency, being close to normal. The number of fluctuators is shown to be much less than the number of free electrons in the specimen.

Failure modes of tantalum capacitors made by different technologies

Abstract Tantalum capacitor failure modes have been discussed both for the standard manganese dioxide cathode and the new conductive polymer (CP) type. For standard tantalum in the normal operation mode, an electrical breakdown can be stimulated by an increase of the electrical conductance in channel by an electrical pulse or voltage level. This leads to capacitor destruction followed by thermal breakdown. In the reverse mode, we have reported that thermal breakdown is initiated by an increase of the electrical conductance by Joule heating at a relatively low voltage level. Consequently, a feedback cycle consisting of temperature–conductivity–current–Joule heat–temperature, ending with electrical breakdown was created. Both of these breakdown modes possess a stochastic behavior and can be hardly localized in advance. CP capacitors have shown a slightly different current conductivity mechanism compared to standard tantalum capacitors. The breakdown of CP dielectrics is similar to avalanche and field emission breaks. It is an electromechanical collapse due to the attractive forces between electrodes, electrochemical deterioration, dendrite formation, and so on. However, some self-healing of the cathode film has been reported. This can be attributed to film evaporation, carbonizing or reoxidation. Not all of the breakdowns of CP capacitors can lead to self-healing or an open circuit state. Short circuits can also occur.

Generation of 1/f spectrum by relaxation process in thin film resistors

Relaxation processes with various time constants generate a 1/f spectrum when they are driven by a single random time series. Such simple processes may be the origin of the noise generated in some kinds of thin film resistors.

2 × 2 SIW rectangular ring slot antenna array for 60 GHz band

In this paper, a novel low profile 2 × 2 SIW rectangular ring slot antenna array for 60 GHz band is proposed. It radiates linearly polarized wave with maximum radiation in the perpendicular direction to the antenna plane. Experimental results prove that the proposed antenna achieves the impedance bandwidth of 5.7 % for the reflection coefficient less than -10 dB and the gain of 13 dBi.

RTS noise in integrated circuits

The objective of this paper is twofold. First, the model theory of the RTS noise developed by Sikulova1 is applied to an analysis of the RTS noise in bipolar Schottky IC’s. This theory makes it possible to evaluate quantities characteristic of the processes of carrier capture, emission, and recombination. Second, a new non‐invasive method of potential spectroscopy of IC’s is presented, which makes exclusive use of the IC external pins. An attempt is made to localize the sources of the observed RTS noise. Experiment results are in a good agreement with the mentioned theoretical model.

Textile linear polarization reconfigurable ring slot antenna for 5.8 GHz band

In this paper, a textile linear polarization reconfigurable antenna for 5.8 GHz band is proposed. It radiates linearly polarized wave which can be controlled in the range of angles ± 30° with respect to the longitudinal axis of the antenna with maximum radiation in the perpendicular direction to the antenna plane. Measured results prove that the proposed antenna achieves at least impedance bandwidth of 11.2 % (angle 0°) for the reflection coefficient less than -10 dB and according simulation achieved the simulated gain between 6.5–7.5 dBi in the perpendicular direction to the antenna plane.

Polarization reconfigurable SIW circular ring-slot antenna

In this paper a linearly polarization reconfigurable substrate integrated waveguide (SIW) circular ring slot antenna for 5.8 GHz ISM band is proposed. The antenna consists of two dielectric layers: a feeding layer and a radiator layer. In the feeding layer, an SIW operating in the fundamental mode TE10 is accommodated. The radiator layer, which is fed by the SIW, contains etched circular ring-slot. The proposed antenna has a broadside radiation pattern and radiates linearly polarized wave which can be controlled in the range of the angles ± 45° with respect to the longitudinal axis of the antenna.

Polarization and fluctuation characteristics of tantalum solid electrolyte capacitors

A new method of tantalum capacitor testing and reliability prediction is presented based on the analysis of polarization mechanisms and noise characteristics. Polarization mechanisms of the Ta 2 O 5 dielectric layer include electron polarization, fast ion polarization and ion relaxation polarization. Impurities usually add a fourth polarization type, migration polarization, which is effective in the mHz-kHz frequency region.