Olivier Noblanc

Characterization of ohmic and Schottky contacts on SiC

The interface chemistry of nickel and tungsten based contacts on SiC has been investigated by XPS on as-deposited samples and after contact formation. After annealing at 950 °C for 10 min, Ni/SiC and Ni/Si/SiC ohmic contacts are formed due to the chemical reactions, as a result of which Ni2Si appears. However, Ni/Si (instead of pure Ni) deposition on SiC leads to modification of the diffusion processes and formation of a contact layer free of carbon. After annealing at 1200 °C for 4 min, the WN (W)/SiC systems are characterized by strong interface reactions resulting in W5Si3 and W2C formation in the contact layer. The 800 °C annealed WN/SiC contact is characterized by a chemically inert interface, and is found to be of a Schottky type.

High-Performance 15-V Novel LDMOS Transistor Architecture in a 0.25-

The optimization of the small and large signal performances of a radio frequency (RF)-LDMOS is presented via the achievement of a novel LDMOS architecture. Specific process steps are introduced into a 0.25-mum BiCMOS technology and precisely described to realize a fully salicided gate RF-LDMOS architecture. Significant improvement is obtained on the small-signal - fT and Fmax - and power performances while maintaining good dc characteristics

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The interface chemistry of WN/4H–SiC structures has been studied by means of X-ray photoelectron spectroscopy (XPS). XPS investigations have been performed on as deposited, 800°C and 1200°C annealed (4 min) samples. The as deposited and 800°C annealed samples are characterized by chemically inert interfaces. Complete nitrogen out-diffusion from the WN layer, significant carbon diffusion into the contact layer, tungsten carbide and tungsten silicide formation occur during the 1200°C annealing process. The 800°C annealed WN/4H–SiC contacts are found to be of a Schottky type with a barrier height of 0.91 eV. The Schottky barrier height and the ideality factor show no significant changes during 100 h storage at 500°C under nitrogen and during operation at increasing temperature up to 350°C in air.

BiCMOS Process for RF-Power Applications

The electrical properties and interface chemistry of Ti/Au/Pt/Ti Schottky contacts to n-type 4H-SiC have been investigated with respect to their utilization for MESFETs operated at high temperatures. The electrical properties of these contacts were studied at room temperature as well as during thermal treatment. The barrier height determined from I-V characteristics was calculated to be 1.17 eV with an ideality factor of 1.09. These parameters were examined by ageing and temperature dependence tests as criteria for the thermal stability and reliability of the contacts. The barrier height and ideality factor did not change after prolonged heating at a constant temperature of and operating temperatures up to , which confirmed the contact stability. Diodes used in the measurements showed a low leakage current at 100 V reverse voltage and room temperature ( A) as well as at ( A) and breakdown voltage above 400 V. The chemical interface properties were studied by x-ray photoelectron spectroscopy for as-deposited, annealed and heated contacts. Annealing at for 10 min led to formation of TiC and in a restricted region close to the SiC interface. The data revealed a chemically stable Ti/SiC interface after annealing, which is of importance for stable rectifying characteristics during long-term operation.

Interface chemistry of WN/4H-SiC structures

Annealed W (WN)/4H–SiC interfaces have been compared on the basis of X-ray photoelectron spectroscopy (XPS) studies. The 1200°C annealed W (WN)/4H–SiC structures are characterized by intense interface reactions leading to tungsten carbide and tungsten silicide formation in the contact layers. The 800°C annealed WN/4H–SiC structure exhibits a chemically inert interface, and the 800°C annealed WN/4H–SiC contact is found to be of a Schottky type with a barrier height of 0.94 eV and an ideality coefficient of 1.09.

Thermostable Ti/Au/Pt/Ti Schottky contacts to n-type 4H-SiC

Thomson Silicon Carbide MESFET was characterised in DC, small signal and load-pull conditions. Several amplifiers were designed to be used in communication systems (digital television, DAB) and were measured. A comparison with a LDMOS amplifier showed that SiC is a very promising material for microwave and RF power amplification.

XPS characterization of tungsten-based contact layers on 4H–SiC

X-ray photoelectron spectroscopy (XPS) is used to investigate the chemical reactions and diffusion processes at Ti/Au/Pt/Ti/SiC interfaces for as deposited and annealed at 575°C for 10 min structures. The distribution of the elements and the change in their chemical state has been studied. The XP spectra indicate titanium carbide and platinum silicides formation at the SiC interface, which is preceded by the dissociation of SiC due to the reactivity of Ti at 575°C. TiC represents a barrier to the further diffusion of Ti to the SiC bulk and the Ti layer makes the diffusion of Pt into SiC difficult. The element distribution of the annealed structure demonstrates that Pt has diffused through almost the whole gold layer to the surface, an alloy of the two metals being formed.

Silicon Carbide amplifiers for communication applications

In this paper we present static measurements fand defects analysis performed on 4H-SiC MESFETs on semi-insulating (SI) substrates containing vanadium. I d-Vds -T and I d-Vgs -T characteristics show anomalies (Threshold voltage shift, leakage current, degradation in saturation current...). Deep defects analysis performed by capacitive transient spectroscopy (C-DLTS) proves the presence of one deep defect called E1 with an activation energy 0.32eV. The studies of C-DLTS signal with pulse duration (t p) and polarization voltage (V r) confirm that E 1 trap is a point defect. Current transient spectroscopy (I-DLTS) performed in the same devices confirm E1 defect and shows the presence of six levels with activation energies ranging from 0.09eV to 1.01eV. The localization and the identification of these defects is presented. Finally, the correlation between the anomalies observed on output characteristics and defects is discussed.