Papers by Author: Tomasz Gutt

Abstract: PZT (lead zirconium titanate) is an intermetallic compound exhibiting piezoelectric, ferroelectric, and pyroelectric properties. The perovskite crystallographic structure of the PZT is responsible for the above effects. MEMS structures with piezo layers can be used as sensors, actuators, or converters. The abilities of piezo materials to generate an electric charge as a response to stress and a change of shape as a response to electric field are very attractive in numerous applications. Cantilever structures with a mass attached can accordingly be used as energy harvesters converting energy of environment vibrations. Other applications of cantilevers are small displacement sensors or actuators in micro/nanoscale. Membrane structures can work as ultrasonic transducers. If properly shaped cavity is produced, the structure may be used as a part of ink printer head or as a pressure sensor.For physical description of piezo phenomena, constitutive equations in several forms are used. They work well for bulk piezoelectric, although for thin layers deposited on silicon or similar substrate, piezoelectric coupling coefficients must be redefined because of the interaction of thin piezo layer and thicker substrate.Typical electric characterization of piezo MEMS structures includes CV and IV measurements. QV (charge-voltage) hysteresis loop study is an additional method used for this characterization. Complex electromechanical methods are used for surveying piezoelectric coupling coefficients. These methods employ mechanic actuation and electric response Q measurements or AC electric V (voltage) excitation and measurement of mechanical response v (velocity). In the second case, a very precise tool for velocity evaluation is necessary. Such tool could be for example laser Doppler vibrometer, enabling measurements of picometer resolution in several MHz bandwidth. In many cases resonance features of structures have revealed themselves interesting and became a subject of the study. Some vibrometers make measurement of micro cantilever vibrations excited by Brownian movement of air particles possible.

Abstract: In this article, an influence of nitrogen implantation dosage on SiC MOS structure is analyzed using wide range of nitrogen implantation dose (between ~1013 – 1016). Authors analyzed electrical and material properties of investigated samples using C-V, I-V measurements, Raman spectroscopy, and XPS profiling. It has been shown that surface state trap density is directly connected to implantation damage and thus implantation conditions. Using research results a trap origin at given energy can be concluded.

Abstract: This paper reports on results of interface trap analysis of 3C-SiC MOS capacitors fabricated using four different gate materials and two SiO₂ oxide preparation methods. The results indicate that post-deposition annealing in wet oxygen of PECVD deposited SiO₂ samples increases the near-interface or slow trap densities, compared with wet oxygen thermally oxidized samples. It has also been found that the energy distribution, D_it, of electron states at the oxide/SiC interface of MOS capacitors with different sizes depend on the factor R=P/A, where P stands for the gate perimeter and A for the gate area, which is related to the amount of stress under the edge of the metallic gate.

Abstract: Silicon carbide (SiC) is a wide band gap semiconductor having good thermal conductivity and high break down voltage. Formation of SiO₂ layer in thermal oxidation process completes the set of properties of SiC as a promising material for fabrication of high power and high frequency electronic devices. This picture is perturbed by Near Interface Traps (NIT's) that decrease the surface mobility of charge carriers. The origin of NIT's is still the subject of discussion and there are several candidates for NIT's. One possibility is the formation of carbonic structures during the process of manufacturing of MOS-type structures. The aim of this work was to look for possible carbonic inclusions with Raman spectroscopy. The attention of authors was focused on non-destructive way of application of the experimental technique.

Abstract: A novel method based on the analysis of the C-V hysteresis change with increasing charge release time is proposed. The presence of a band of deep traps was demonstrated using this method in 3C-SiC samples. The same band of deep traps was also observed using photo-electric measurements of barrier height EBS in the same samples.

Abstract: The kinetics of 4H-SiC thermal oxidation by RTP technique and the properties of thin thermal oxide was reported. The thickness of the thermal oxide was determined by spectroscopic ellipsometry and confirmed by electrical measurements. The conductance method was applied to analyse the surface states parameters. The lifetime, density and cross-section of the surface traps were extracted for as-fabricated MOS capacitors and after thermal annealing processes.