Jakub Grochowski

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.

Transparent Amorphous Ru–Si–O Schottky Contacts to In–Ga–Zn–O

Transparent amorphous oxide semiconductors (TAOSs), such as In-Ga-Zn-O (a-IGZO), are the subject of intensive experimental and theoretical research aimed at applications in transparent electronics. With the development of novel device applications came an increased demand for the understanding and control of a-IGZO Schottky contact properties. Rectifying contacts are suitable for the development of Schottky diodes and metal-semiconductor field-effect transistors (MESFETs) for fast and low power consumption integrated circuits and active-matrix displays. We propose fabrication of Schottky barrier to a-IGZO based on transparent conductive oxide (TCO), namely Ru-Si-O. We have found that atomic composition and microstructure of this TCO are effective in preventing interfacial reactions in the contact region which allows to avoid pre-treatment of the semiconductor surface. Ru-Si-O Schottky contacts to a-IGZO have been fabricated by means of reactive sputter-deposition. We provide comprehensive results on effects of Ru-Si-O chemical composition on properties of rectifying contacts to a-IGZO. Depending on oxygen content in Ru-Si-O sputtering atmosphere, for a specific process window (from 10% to 20% of O2 in sputtering atmosphere), highly rectifying transparent Schottky barriers are obtained without additional a-IGZO surface treatment.

Tuning properties of long-period gratings by atomic layer deposited zinc oxide nano-coating

This work presents an application of thin zinc oxide (ZnO) films obtained using atomic layer deposition (ALD) for effective tuning of spectral response and the refractive-index (RI) sensitivity of long-period gratings (LPGs). The technique allows for an efficient and well controlled deposition at monolayer level of excellent quality nano-films as required for optical sensors. The effect of ZnO deposition on spectral properties of the LPGs is discussed. We correlated the increase in ZnO thickness with the shift of the LPG resonance wavelength and proved that similar films are deposited on fibers and silicon reference samples in the same process run. The thin overlay effectively changes the distribution of the cladding modes and thus also tunes the device’s RI sensitivity. The tuning can be simply realized by varying number of cycles, which is proportional to thickness of the high-refractive-index (n<1.9 in infrared spectral range) ZnO film. The advantage of this approach is precision in determining the film thickness resulting in RI sensitivity of the LPGs.

Enhancement of Ru–Si–O/In–Ga–Zn–O MESFET Performance by Reducing Depletion Region Trap Density

In this letter, we investigated the effect of magnetron cathode current (I_c) during reactive sputtering of In-Ga-Zn-O (a-IGZO) channel layer on properties of metal-semiconductor field-effect transistors with Ru-Si-O Schottky gate electrode. One can observe that as I_c increased from 90 to 150 mA channel mobility (μ_ch) and subthreshold swing (S) improved from μch = 7.5 cm²/V·s and S = 580 V/dec to μch = 8.8 cm²/V ·s and S = 420 V/dec, respectively. This enhancement in transistors performance was attributed to the reduction of charge density in the depletion region of Ru-Si-O/In-Ga-Zn-O Schottky contacts, which we assigned to the densification of a-IGZO films fabricated at higher I_c.

Continuous wavelet transform for d-space distribution analysis in nanocrystallic materials

We present a novel application of the continuous wavelet transform (CWT) for quantitative analysis of electron diffraction fringe patterns for material science research. With this method unsupervised analysis of large data sets can be performed, to determine statistical distribution of fringe periods, corresponding to the spacing between the planes in the atomic lattice. It is more robust and less time consuming than typical manual approach. Obtained information can be further utilized for characterization and identification of the crystallographic structures present in the sample. The proposed method is applied to analysis of high resolution transmission electron microscope (HRTEM) images of Iridium-Zinc-Silicon-Oxide thin films, which reveal nanocrystallic structures dispersed in an amorphous matrix.

Influence of capping SiO 2 layer on stability of NiO thin film under thermal stress

NiO thin films deposited by RF reactive magnetron sputtering at room temperature were characterized by low optical transmittance, high acceptors concentration and low mobility of carriers. Storage of NiO films in air atmosphere and at elevated temperature leads to degradation of semiconducting conductivity of NiO. To improve NiO film stability the samples were preserved from air by covering them with thin SiO2 film. Influence of SiO2 capping layer on mentioned properties after annealing in argon and oxygen ambient at temperatures from 200°C up to 600°C were examined. High temperature was applied to study thermal bleaching of NiO films with SiO2 capping layer. Optical transmittance as well as bandgap are increased after subsequent annealing at 350°C and rise much more significantly after annealing at higher temperature. The electrical parameters of NiO film without cap are drastically changed after annealing in Ar even leading to huge resistivity, but these SiO2 covered films reveal increased resistivity and improved mobility above 1 cm2/V·s after annealing at 350°C.