Papers by Keyword: TLM

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Authors: Lilyana Kolaklieva, V. Chitanov, Roumen Kakanakov
Abstract: Al-Free Nanolayered Metallizations Based on the Transition Metals Ti, Mo, Ni and Pd, with Varied Ti Content, Have Been Developed as an Alternative of the Al-Based Contacts for Sub-Micron Hemts. the Electrical, Morphological and Thermal Properties of the Metallization Schemes Have Been Studied with the Aim of Obtaining the Most Suitable Combination of Low Resistivity, a Smooth Surface and an Acute Edge. the Lowest Resistivity of 8.8x 10-6 Ω.cm2 Has Been Determined with the Ti/Mo/Ti/Au Contact, while the Lowest Surface Roughness of 6 Nm Has Been Measured for the Ti/Ni/Ti/Au Metallization. these Contact Schemes Have Shown much Better Edge Acuity in Comparison to the Al-Based Metallizations.
Authors: Katarina Smedfors, Luigia Lanni, Mikael Östling, Carl Mikael Zetterling
Abstract: Extreme temperature measurements of Ni/Ti/Al contacts to p-type SiC (Na = 1∙1018cm-3), with a specific contact resistivity ρc = 6.75∙10-4 Ωcm2 at 25 °C, showed a five time increase of the specific contact resistivity at -40 °C (ρc = 3.16∙10-3 Ωcm2), and a reduction by almost a factor 10 at 500 °C (ρc = 7.49∙10-5 Ωcm2). The same response of ρc to temperature was seen for contacts on lower doped epitaxial layer. Also N-type nickel contacts improved with higher operational temperature but with a considerably smaller variation over the same temperature interval. No degradation of the performance was seen to either the Ni/Ti/Al or the Ni contacts due to the high temperature measurements.
Authors: Duy Minh Nguyen, Christophe Raynaud, Mihai Lazar, Heu Vang, Dominique Planson
Abstract: N+ 4H-SiC commercial substrates with n-type epilayers have been used to realize bipolar diodes and TLM structures. The p-type emitter of diodes was realized by Al implantations followed by a post-implantation annealing with or without a graphite capping layer. Ohmic contacts were formed by depositing Ti/Ni on the backside and Ni/Al on the topside of the wafer. It appears that capping the sample during the annealing reduces considerably the surface roughness and the specific contact resistance. Sheet resistance and specific contact resistance as low as 2kΩ/□ and respectively 1.75×10-4 Ωcm² at 300 K have been obtained. I-V measurements as a function of temperature have been performed from ~100 to ~500 K. The variations of the series resistance vs. temperature can be explained by the freeze-out of carriers and by the variation of carrier mobility.
Authors: Lilyana Kolaklieva, Roumen Kakanakov, Plamen Stefanov, Volker Cimalla, S. Maroldt, Oliver Ambacher, Katja Tonisch, Florentina Niebelschütz
Abstract: Electrical, thermal and chemical properties of Ti/Al/Ti/Au ohmic contacts with different former Ti-Al ratio are investigated for application in GaN HEMTs. Lowest resistivity of 4.22x10-5 Ω.cm2 has been obtained to the channel of the HEMT structure. It is found out that the initial Ti/Al ratio influences the optimal annealing temperature at which the lowest resistivity is obtained and the element distribution and interface chemistry of the annealed contacts. XPS analysis revealed two compounds contributing to ohmic properties: an intermetal compound AlAu2 in the contact layer and a semimetal TiN at the interface with GaN.
Authors: Ferdinando Iucolano, Fabrizio Roccaforte, Filippo Giannazzo, A. Alberti, Vito Raineri
Abstract: In this work, the structural and electrical properties of Ti/Al/Ni/Au contacts on n-type Gallium Nitride were studied. An ohmic behaviour was observed after annealing above 700°C. The structural analysis showed the formation of an interfacial TiN layer and different phases in the reacted layer (AlNi, AlAu4, Al2Au) upon annealing. The temperature dependence of the specific contact resistance demonstrated that the current transport occurs through thermoionic field emission in the contacts annealed at 600°C, and field emission after annealing at higher temperatures. By fitting the data with theoretical models, a reduction of the Schottky barrier from 1.21eV after annealing at 600°C to 0.81eV at 800°C was demonstrated, together with a strong increase of the carrier concentration at the interface. The reduction of the contact resistance upon annealing was discussed by correlating the structural and electrical characteristics of the contacts.
Authors: Uwe Zimmermann, Anders Hallén, Bo Breitholtz
Authors: Fabrizio Roccaforte, Francesco La Via, Vito Raineri, Paolo Musumeci, Lucia Calcagno
Authors: Marilena Vivona, Giuseppe Greco, Raffaella Lo Nigro, Salvatore di Franco, Filippo Giannazzo, Simone Rascunà, Mario Saggio, Fabrizio Roccaforte
Abstract: The mechanism of Ohmic contacts formation to p-type SiC is a fundamental and technological concern continuously under debate. Typically, Ti/Al-based contacts are a good choice for Ohmic contacts to p-type SiC, even though some aspects strictly related to the specific nature of Al (susceptibility to oxidation, low melting temperature, etc.) remain to be optimized. In this work, the evolution of the electrical properties of a Ti/Al/W multiple-layer contact has been studied by TLM characterization and correlated to the changes in the morphology and microstructure upon thermal annealing. The formation of an Ohmic contact has been observed after a thermal annealing at 1100°C, discussing the possible reasons determining the transition to an Ohmic behavior.
Authors: Farah Laariedh, Mihai Lazar, Pierre Cremillieu, Jean Louis Leclercq, Dominique Planson
Abstract: Transfer Length Method (TLM) based-structures were fabricated on 0.8 µm-thick epitaxial p-type Silicon Carbide (4H-SiC) layers. TLM mesas were defined by a 2 µm height using an SF6/O2 reactive ion etching. TLM metal patterns were obtained by a lift-off procedure and electron beam deposition of Ni, Ti, Al and Pt. The patterned samples were annealed in Argon ambient at temperature ranging from 700°C up to 1000°C in a RTA furnace with a rapid heating ramp (up to 50°C/s) to complete the ohmic contact with the p-type SiC layer. Specific contact resistances were extracted from current/voltage measurements. To identify and follow the profile evolution of constituting element in the contacts and at the SiC/contact interface, the ohmic contacts were characterized using Secondary Ion Mass Spectrometry and Energy-Dispersive X-Ray spectroscopy before and after annealing. Ohmic contacts are obtained only for the Ni/Ti/Al and Ni/Ti/Al/Ni stacking layers and not for the Ti/Al/Ti/Ni and Ti/Al/Ti/Pt/Ni compositions. The specific contact resistance of Ni/Ti/Al/Ni stacking layers was observed to decrease from 2.7×10-4 Ω.cm2 at 700°C and 6.3×10-5 Ω.cm2 at 750°C to a minimal value of 1.5×10-5 Ω.cm2 at 800°C. Ohmic contacts are obtained with a reproducibility of 80 %.
Authors: Liliana Kassamakova, Roumen Kakanakov, Ivan Kassamakov, Konstantinos Zekentes, Katerina Tsagaraki, Genoveva Atanasova
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