Papers by Author: Maher Soueidan

Abstract: In this study, the electrical properties of Ti₃SiC₂ based ohmic contacts formed on p-type 4H-SiC(0001) 4°-off substrates were studied. The Ti₃SiC₂ thin films were grown by thermal annealing (from 900°C to 1200°C) of Ti₅₀Al₅₀ layer deposited by magnetron sputtering. XRD analyzes were performed on the samples to further investigate the compounds formed after annealing. Using TLM structures, the Specific Contact Resistance (SCR) at room temperature of all contacts was measured. The temperature dependence (up to 600°C) of the SCR was studied to understand the current mechanisms at the interface and to determine the barrier height value by fitting the experimental results using the thermionic field emission theory. Aging tests showed that Ti₃SiC₂ based contacts were stable up to 200h at 600°C under Ar.

Abstract: In order to form Ti₃SiC₂ on 4H-SiC(0001) 8°-off, 200 nm of Ti₃₀Al₇₀ was deposited onto SiC substrates by magnetron sputtering from pure Ti₃₀Al₇₀ targets. The samples were then annealed at 1000°C for 10 min under Ar atmosphere in a Rapid Thermal Annealing (RTA) furnace. Structural analyses reveal the formation of epitaxial hexagonal Ti₃SiC₂ (0001) oriented. Elemental analyses show that high amount of Al and O elements are present inside the deposit. Obviously, the formation of Ti₃SiC₂ is accompanied by parasitic Al oxide, probably due to some unwanted oxygen residual in the RTA chamber. By using proper backing steps before the annealing, the deposit is not anymore composed of only Ti₃SiC₂ but accompanied with other compounds (Al₃Ti, and Al). On the oxide-free sample, the specific contact resistance ρ_c of the Ti₃SiC₂ based contact on p-type 4H-SiC (having N_a= 2×10¹⁹ cm^-3) was measured to be as low as 6×10^-5 Ω.cm².

Abstract: Spark plasma sintering has been used for decades in order to consolidate a wide variety of materials and permitting to obtain fully dense specimens. This technique has been mainly applied to ceramics. This paper concentrates on an unusual use of spark plasma sintering system: obtaining innovative materials especially architectured ones. Different applications are presented. Firstly, the SPS technique has been used to elaborate nanometers grain size materials or containing nanoscale microstructure. This is possible since the sintering temperature and the holding time are far lower in the SPS compared to other techniques. Then SPS has been used to realize diffusion bonding. In that case again, bonding can be realized at low temperature and for short time. It permits for example to realize bonding between two copper layers which is of a great importance for microelectronic applications. It is worth noting that this bonding can have the same mechanical strength as pure copper even for diffusion time of a few minutes. Secondly, bonding has been also carried out between a metallic layer and a ceramic one. This could lead to design of new layered materials combining interesting properties in terms of mechanical strength but also in terms of electrical resistance. The SPS machine has also been used to obtain porous materials (cobalt alloys or copper) with an adapted microstructure (porosity, tortuosity,). These structures could open new perspectives for biomedical or for microelectronic applications. All these examples lead to a better understanding of the physical processes which happen during spark plasma sintering.

Abstract: This paper presents the design, fabrication, and characterization of micro planar inductors on a microwave magnetic material (YIG). Planar spiral inductors were designed for monolithic DC-DC converters in System-In-Package with 100 MHz switching frequency (1 W, V_in= 3.6 V, V_out= 1 V). A microwave magnetic substrate (YIG) serves as mechanical support, and also presents a double purpose by increasing inductance value and reducing electromagnetic interferences (EMI). This last point is critical to improve the behavior of a switching mode power supply (SMPS). In order to obtain an optimal design for the inductor, geometrical parameters were studied using Flux2D simulator and an optimized 30 to 40 nH spiral inductor with expected 25 mΩ R_DC, 3 mm² footprint area was designed. Subsequently, samples have been fabricated by electroplating technique, and tested using a vector network analyzer in the 10 MHz to 100 MHz frequency range. Results were then compared to the predicted response of simulated equivalent model.

Abstract: Bonding of high purity polished copper was investigated using the Spark Plasma Sintering technique (SPS) showing the effect of SPS parameters (surface roughness, time, temperature and pressure) on the bonding strength behaviour. Mechanical characterization of the bonded samples was performed at room temperature using tensile test. Two surfaces roughnesses were studied (un-polished and polished samples). It was found that the bonding strength varied from 50 MPa to 233 MPa for un-polished and polished surfaces respectively The tensile strength of the used bulk copper-rod was found to be 365 MPa, while most results are over 122 MPa (a third of the bulk value).