Andrei Avram

Low stress PECVD amorphous silicon carbide for MEMS applications

We present a characterization of PECVD (plasma-enhanced chemical vapour deposition) amorphous silicon carbide films for MEMS/BioMEMS applications. For this applications a high deposition rate and a controllable value of the residual stress is required. The influence of the main parameters is analyzed. Due to annealing effect, the temperature can decrease the compressive value of the stress. The RF frequency mode presents a major influence on residual stress: in low frequency mode a relatively high compressive stress is achieved due to ion bombardment and, as a result, densification of the layer achieved. The PECVD amorphous silicon carbide layers presents a low etching rate in alkaline solutions (around 13 A/min in KOH 30% at 80°C) while in HF 49% the layer is practically inert. Amorphous silicon carbide can be used as masking layer for dry etching in XeF2 reactors (etching rate of 7 A/min). Finally, applications of PECVD amorphous silicon carbide layers for MEMS/BioMEMS applications are presented.

Contributions to development of high power SiC-IGBT

The IGBT is a device that combines the advantages of simplicity of drive due to the voltage-controlled device with high impedance gate and low power dissipation due to the conductivity modulation effect. For that reason, the SiC-IGBT is used for applications that require a high breakdown voltage of 5 kV and more. The IGBT presented in this paper has one epilayer, a buffer layer between substrate and epilayer to improving the dynamic characteristics and a guard ring/epilayer junction to increase the saturation current. The SiC-IGBT is used in applications that require: higher current conduction capability, power losses efficiently dissipated, operation at higher temperatures, up to 600 degC, and in very harsh environment

Gold Nanoparticle Uptake by Tumour Cells of B16 Mouse Melanoma

Because of their photo-optical distinctiveness and biocompatibility, gold nanoparticles have proven to be powerful tools in various nanomedical applications. In this article, we discuss the advantage of gold nanoparticles in image diagnostic application of melanoma. It has demonstrated the potential role of gold nanoparticles in the study of tumour tissue architecture and the utility of gold nanoparticles in the hystopathological exam of B16 melanoma with the benefit of fluorescence emission of gold nanoparticles in UV spectrum. The optical properties of colloidal gold nanoparticles allow spectroscopic detection and identification of melanoma cells. The method proposed is easy, inexpensive and reliable for hystopathological analysis of melanoma. The fluorescence images in the cryosections of tissues depicted a strong luminescence property of gold nanoparticles uptaken in melanoma, results that confirm the role of the gold nanoparticles in biological labelling and imaging applications. To emphasize the AuNPs influence over the biological tissues, a study of the chemical bonds configuration was performed using Raman spectrometry.

Design and fabrication of a MEMS chevron-type thermal actuator

This paper presents the design and fabrication of a MEMS chevron-type thermal actuator. The device was designed for fabrication in the standard MEMS technology, where the topography of the upper layers depends on the patterns of structural and sacrificial layers underneath. The proposed actuator presents some advantages over usual thermal vertical chevron actuators by means of low operating voltages, high output force and linear movement without deformation of the shaft. The device simulations were done using COVENTOR software. The movement obtained by simulation was 12 μm, for a voltage of 0.2 V and the current intensity of 257 mA. The design optimizes the in-plane displacement by fixed anchors and beam inclination angle. Heating is provided by Joule dissipation. The material used for manufacture of chevron-based actuator was aluminum due to its thermal and mechanical properties. The release of the movable part was performed using isotropic dry etching by Reactive Ion Etching (RIE). A first inspection wa...

Burried hot wire anemometer for fluid velocity measurements

Hot wire thermal anemometers are the most reliable devices when measuring fluid flow velocity. When combined with suitable materials, they can provide accurate information in real time. Our current project requires a hot wire anemometer to detect and localize accurately the turbulences which appear during the flow of viscoelastic fluids in obstructed microchannels. The present paper presents the study of a hot wire design for detecting and measuring turbulent fluid flow in microchannels and proposes a fabrication technology suitable for detecting turbulences within the flow.

Detection of Circulating Tumor Cells Using Microfluidics

Metastasis is the main cause of death in cancer patients worldwide. During metastasis, cancer cells detach from the primary tumor and invade distant tissue. The cells that undergo this process are called circulating tumor cells (CTCs). Studies show that the number of CTCs in the peripheral blood can predict progression-free survival and overall survival and can be informative concerning the efficacy of treatment. Research is now concentrated on developing devices that can detect CTCs in the blood of cancer patients with improved sensitivity and specificity that can lead to improved clinical evaluation. This review focuses on devices that detect and capture CTCs using different cell properties (surface markers, size, deformability, electrical properties, etc.). We also discuss the process of tumor cell dissemination, the biology of CTCs, epithelial-mesenchymal transition (EMT), and several challenges and clinical applications of CTC detection.

Fabrication of spiral phase plates for optical vortices

This work presents a reproductible fabrication process of spiral phase plates (SPPs) based on microfabrication techniques such as photolithography and reactive ion etching (RIE). The fabricated SPPs operate in the reflection mode in order to generate optical vortices with topological charge m = 2 and m = 4. Structural and functional characterizations prove the optical quality of the fabricated SPP.

160 GHz silicon micromachined folded slot antenna array

This paper describes the design, electromagnetic (EM) modeling and experimental results obtained for a 160 GHz double folded slot antenna array processed through silicon micromachining. Initial simulations showed reflection losses (RL) of -17 dB at 160 GHz and a fractional bandwidth of ~18.7% (with RL<;-10dB between 148.65 GHz and 178.59 GHz). The simulated directivity was larger than 4 dBi in the working frequency band and ~6.8 dBi at 160 GHz. The structure was processed through deep reactive ion etching (DRIE), and resulted in a thinner substrate than designed. The experimental results for this thinner substrate of about 140 μm showed a ultra wideband behavior, with measured RL<;-10dB for almost the whole 140-210 GHz band and -17 dB at 160 GHz. The free space transmission parameter was measured and the results were compared with the simulated directivity showing a frequency shift of the curve, but otherwise a very good agreement in the trend of the two curves.

220 GHz membrane supported folded slot antenna array

This paper presents the design, electromagnetic modeling, fabrication and characterization of a Folded Slot Antenna Array (FSAA) working at 220 GHz. The structure was processed on a 2.1 μm thick SiO2/Si3N4 dielectric membrane released through deep reactive ion etching (DRIE) of low-resistivity (p = 10 Ω ·cm) silicon. The antenna was characterized on wafer, showing good agreement with simulated results. The measured calibrated gain is 5.5 dB at 220 GHz, and is greater than 0 dB between 200-250 GHz.

On manipulation and detection of biomolecules using magnetic carriers

We performed micromagnetic simulations regarding the detection of magnetic microbeads using spin-valve sensors. Detection of magnetic fields generated by these magnetic particles encapsulated in plastic, carbon or ceramic spheres which are coated with chemical or biological species such as DNA or antibodies that selectively bind to the target analyte can be made using giant magnetoresistive (GMR) or planar Hall effect (PHE) sensors made from spin-valve structures. This detection concept is suitable to biomolecular recognition, and in particular to single molecule detection. The concept and the realization of a magnetohydrodynamic micro pump are presented.