Piotr Firek

Application of a composite plasmonic substrate for the suppression of an electromagnetic mode leakage in InGaN laser diodes

We demonstrate an InGaN laser diode, in which the waveguiding quality of the device is improved by the introduction of highly doped (plasmonic) layer constituting an upper part of the GaN substrate. Thanks to this, we were able to suppress the electromagnetic mode leakage into the substrate without generating additional strain in the structure, in contrast to the typical design relying on thick AlGaN claddings. The plasmonic substrate is built as a stack of gallium nitride layers of various electron concentrations deposited by a combination of hydride epitaxy and high-pressure solution method. The mentioned improvements led to the reduction of the threshold current density of our devices down to 2 kA/cm2 and to the optimization of the near and far field pattern.

Silver micropowders as SiC die attach material for high temperature applications

This work is devoted attaching technology between SiC structures and DBC substrates for creating SiC devices able to work at temperature up to 350°C. Our current work was concentrated on finding so called “pressure sintering” procedure in air using Ag micro particles. A special test samples with a size corresponding to the dimension of the SiC structures were assembled to DBC substrates with different surface finishing by Ag micro powder sintering. In the first series of experiments DBC substrates with Cu electroplated by Ni (3÷5 μm) and Au (above 1 μm) were used. It was found that by modifying application procedure of Ag micro powder onto DBC substrate with Cu/Ni/Au metallization, it is possible to obtain good adhesion between attached samples. The sintering is performed in air at temperature of 400°C for 40 min and pressure of 10 MPa. In the second series of experiments the SiC structures with Ni/Au metallization were assembled to DBC substrate with Cu/Ni/Au metallization. The adhesion higher than 10 MPa was obtained for such prepared samples.

Stack of Nano-Films on Optical Fiber End Face for Label-Free Bio-Recognition

This paper presents a study on sensing capabilities of stacks of nano-films deposited on a single-mode optical fibers end face for application in label-free bio-recognition. The stack consist of five nano-films of periodically interchanging materials characterized by different refractive indices (n at λ = 1550 nm), aluminum AlxOy (n ~ 1.58 RIU) and titanium TiOx (n ~ 2.42 RIU) oxides layers. The stack was deposited with the reactive magnetron sputtering technique. It has been found that the structures show sensitivity to refractive index of surrounding liquid (74.4 nm/RIU and 44.3 dBm/RIU) and negligible sensitivity to variations of temperature. Moreover, we show that these structures when functionalized can be used for selective detection of biological layer formation on their surface. In this study, a biotin-avidin complex was used to show a label-free bio-recognition capability of the approach. Avidin concentration of 1 mg/ml induced shift of the resonance wavelength and change in reflected power by 3 nm and 0.8 dBm, respectively, when BSA, which is nonspecific to biotin, resulted in a negligible change in spectral response. The approach seems to be very interesting, especially when such advantages as batch device fabrication, sensor robustness, and fully automatized stack deposition process are taken into account.

MISFET structures with barium titanate as a dielectric layer for application in memory cells

This work shows investigations of La 2 O 3 containing BaTiO 3 thin films deposited on Si substrates by Radio Frequency Plasma Sputtering (RF PS) of sintered BaTiO 3 + La 2 O 3 (2 wt.%) target. Round, aluminum (Al) electrodes were evaporated on top of the deposited layers. Thus, metal-insulator-semiconductor (MIS) structures were created with barium titanate thin films playing the role of an insulator. The MIS structures enabled a subsequent electrical characterization of the studied film by means of current-voltage (I―V) and capacitance-voltage (C-V) measurements. Several electronic parameters, i.e., e ri , p, V FB , ΔV H were extracted from the obtained characteristics. Moreover, the paper describes technology process of MISFETs fabrication and possibility of their application as memory cells. The influence of voltage stress on transfer and output I-V characteristics of the transistors are presented and discussed.

Properties of AlN thin films deposited by means of magnetron sputtering for ISFET applications

Abstract This work presents the investigations of AlN thin films deposited on Si substrates by means of magnetron sputtering. Nine different sputtering processes were performed. Based on obtained results, the tenth process was prepared and performed (for future ISFET structures manufacturing). Round aluminum (Al) electrodes were evaporated on the top of deposited layers. The MIS capacitor structures enabled a subsequent electrical characterization of the AlN films by means of current-voltage (I-V) and capacitance-voltage (C-V) measurements. Based on these results, the main parameters of investigated layers were obtained. Moreover, the paper describes the technology of fabrication and electrical characterization of ISFET transistors and possibility of their application as ion sensors.

Sensing properties of periodic stack of nano-films deposited with various vapor-based techniques on optical fiber end-face

This work presents a study on sensing capabilities of stacks of nano-films deposited on a single-mode optical fiber end-faces. The stacks consist of periodically interchanging thin-film layers of materials characterized by different refractive indices (RI). The number of layers is relatively small to encourage light-analyte interactions. Two different deposition techniques are considered, i.e., radio frequency plasma enhanced chemical vapor deposition (RF PECVD) and physical vapor deposition by reactive magnetron sputtering (RMS). The former technique allows to deposit stacks consisting of silicon nitride nano-films, and the latter is well suited for aluminum and titanium oxides alternating layers. The structures are tested for external RI and temperature measurements.

Comparison of Al2O3 nano-overlays deposited with magnetron sputtering and atomic layer deposition on optical fibers for sensing purposes

In this work we compare effects of thin (<300 nm) aluminum oxide (Al2O3) deposition using advanced physical (Magnetron Sputtering - MS) and chemical (Atomic Layer Deposition – ALD) vapor deposition methods on optical fibers. We investigate an influence of the process parameters on optical properties of the nano-films deposited with MS. In order to investigate the properties of the films directly on the fibers, we induced long-period fiber grating (LPG) in the fiber prior the deposition. Thanks to LPG sensitivity to thickness and optical properties of the overlays deposited on the fiber, we are able to monitor Al2O3 nano-overlay properties. Moreover, we investigate an influence of the overlays deposited with both the methods on LPG-based refractive index (RI) sensing. We show and discuss tuning of the RI sensitivity by proper selection of both thickness and optical properties of the Al2O3 nano-overlays.

ISFET structures with chemically modified membrane for bovine serum albumin detection

Purpose The purpose of this paper is to present possibility of fast and certain identification of bovine serum albumin (BSA) by means of ion-sensitive field effect transistor (ISFET) structures. Because BSA can cause allergic reactions in humans, it is one of reasons for development of sensitive sensors to detect residual BSA. BSA is commonly used in biochemistry and molecular biology in laboratory experiments. Therefore, to better understand the mechanism of signal transduction in simulated biological environment and to elucidate the role of adsorption of biomolecules in the generation of a signal at the interface with biological systems, the measurements of ISFET current response in the presence of BSA as a reference protein molecule were performed. Design/methodology/approach To fabricate transistors, silicon technology was used. The ISFET structures were coupled to specially designed double-side printed circuit board holder. After modification of the field effect transistor (FET) device with 3-aminopropyltriethoxysilane (APTES), a sensor with high sensitivity toward reference biomolecules was obtained. The current–voltage (I-V) characteristics of structures with and without gate modification were measured. Keithley SMU 236/237/238 measurement set was used. Deionized water solution and 0.05 per cent BSA were used. Findings In this research, a method of preparation of a biosensor based on a FET was developed. Sensitivity of APTES-modified FET device toward BSA as a biomolecule was investigated. I-V relationships of FET devices (with and without modification), being the effect of the interactions with the solution containing 0.05 per cent BSA, were measured and compared to the measurements performed for solutions without BSA. Originality value Compared to SiO2-containing ISFETs without modification or other different dielectrics, the application of APTES as the part of the membrane induced significant increase in their sensitivity to BSA.

Measuring thermal conductivity of thin films by Scanning Thermal Microscopy combined with thermal spreading resistance analysis

While measuring the thermal properties of a thin film, one of the most often encountered problems is the influence of the substrate thermal properties on measured signal and the need for its separation. In this work an approach for determining the thermal conductivity κ of a thin layer is presented. It bases on Scanning Thermal Microscopy (SThM) measurement combined with thermal spreading resistance analysis for a system consisting of a single layer on a substrate. Presented approach allows to take into account the influence of the substrate thermal properties on SThM signal and to estimate the true value of a thin film κ. It is based on analytical solution of the problem being a function of dimensionless parameters and requires numerical solution of relatively simple integral equation. As the analysis utilizes a solution in dimensionless parameters it can be used for any substrate-layer system. As an example, the method was applied for determination of the thermal conductivities of 4 different thin layers of thicknesses from 12 to 100nm. The impact of model parameters on the uncertainty of the estimated final κ value was analyzed.

Reactive impulse plasma ablation deposited barium titanate thin films on silicon

Thin (100 nm) nanocrystalline dielectric films of lanthanum doped barium titanate were produced on Si substrates by means of reactive impulse plasma ablation deposition (IPD) from BaTiO3 + La2O3 (2 wt.%) target. Scanning electron microcopy and atomic force microscopy showed that the obtained layers were dense ceramics of uniform thickness with average roughness Ra = 2.045 nm and the average grain size of the order of 15 nm. Measurements of current-voltage (IV) characteristics of metal-insulator-semiconductor (MIS) structures, produced by evaporation of metal (Al) electrodes on top of barium titanate films, allowed to determine that the leakage current density and critical electric field intensity (EBR) of investigated layers ranged from 10-12 to 10-6 A cm-2 and from 0.2 to 0.5 MV cm-1, respectively. Capacitance-voltage (C-V) measurements of the same structures were performed in accumulation state showing that the dielectric constant value (εri) of films is of the order of 20.