Cerdanyola del Vallès, Spain
Cerdanyola del Vallès, Spain

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Fontsere A.,IMB CNM CSIC | Perez-Toms A.,IMB CNM CSIC | Placidi M.,IMB CNM CSIC | Llobet J.,IMB CNM CSIC | And 10 more authors.
Applied Physics Letters | Year: 2011

As GaN technology continues to gain popularity, it is necessary to control the ohmic contact properties and to improve device consistency across the whole wafer. In this paper, we use a range of submicron characterization tools to understand the conduction mechanisms through the AlGaN/GaN ohmic contact. Our results suggest that there is a direct path for electron flow between the two dimensional electron gas and the contact pad. The estimated area of these highly conductive pillars is around 5 of the total contact area. © 2011 American Institute of Physics.


Perez-Tomas A.,IMB CNM CSIC | Fontsere A.,IMB CNM CSIC | Sanchez S.,IMB CNM CSIC | Jennings M.R.,University of Warwick | And 2 more authors.
Applied Physics Letters | Year: 2013

Here, using a frequency dependent conductance analysis, we map the parallel conductance vs gate bias/frequency and further analyze the slow and fast traps as a function of the Fermi level for different gate architectures of analogous AlGaN/GaN heterojunction transistors with Schottky and SiNx metal-insulator-semiconductor (MIS) gate. The density of interface traps (D it)-MIS reducing Dit-, the characteristic trap constant and the variance of the band-bending (σs) have been investigated for slow and fast traps. Additional gate stress appears to have a notable effect on the MIS fast trap profile with σs increasing up to 2.5 kT/q. © 2013 American Institute of Physics.


Perez-Tomas A.,IMB CNM CSIC | Placidi M.,IMB CNM CSIC | Fontser A.,IMB CNM CSIC | Gammon P.M.,University of Warwick | Jennings M.R.,University of Warwick
Microelectronics Reliability | Year: 2011

The behavior of an ohmic contact to an implanted Si GaN n-well in the temperature range of 25-300 °C has been investigated. This is the sort of contact one would expect in many GaN based devices such as (source/drain) in a metal-oxide-semiconductor transistor. A low resistivity ohmic contact was achieved using the metal combination of Ti (350 )/Al (1150 ) on a protected (SiO2 cap) and unprotected samples during the post implantation annealing. Sheet resistance of the implanted layer and metal-semiconductor contact resistance to N+ GaN have been extracted at different temperatures. Both, the experimental sheet resistance and the contact resistance decrease with the temperature and their characteristics are fitted by means of physical based models. © 2011 Elsevier Ltd. All rights reserved.


Fontsere A.,IMB CNM CSIC | Fontsere A.,Polytechnic University of Catalonia | Perez-Tomas A.,IMB CNM CSIC | Banu V.,IMB CNM CSIC | And 5 more authors.
Proceedings of the International Symposium on Power Semiconductor Devices and ICs | Year: 2012

Innovative 800V/300°C AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) fabricated with a 4-inch Si CMOS compatible technology are presented in this paper. High performance AlGaN/GaN MIS gated HEMT (MIS-HEMT) and passivated HEMT (i-HEMT) were fabricated using 5nm-thick HfO 2, and 30nm-thick CVD Si 3N 4 as the gate and passivation insulator, respectively. Contact resistance maps yield reduced R c of 1.32±0.26 Ωmm for Au-free compared to 0.86±0.58 Ωmm for conventional Au-based Ohmic metallization. The off-state breakdown voltage is around 800V with a specific on-resistance of 2 mΩcm 2. Gate and drain leakage currents as well as dynamic I/V trapping are significantly improved with the MIS-HEMT architecture with almost no trade-off to the on-state. © 2012 IEEE.


Perez-Tomas A.,IMB CNM CSIC | Fontsere A.,IMB CNM CSIC | Llobet J.,IMB CNM CSIC | Placidi M.,IREC | And 5 more authors.
Journal of Applied Physics | Year: 2013

The vertical bulk (drain-bulk) current (Idb) properties of analogous AlGaN/GaN hetero-structures molecular beam epitaxially grown on silicon, sapphire, and free-standing GaN (FS-GaN) have been evaluated in this paper. The experimental Idb (25-300 °C) have been well reproduced with physical models based on a combination of Poole-Frenkel (trap assisted) and hopping (resistive) conduction mechanisms. The thermal activation energies (Ea), the (soft or destructive) vertical breakdown voltage (V B), and the effect of inverting the drain-bulk polarity have also been comparatively investigated. GaN-on-FS-GaN appears to adhere to the resistive mechanism (Ea 0.35 eV at T 25-300 °C; VB 840 V), GaN-on-sapphire follows the trap assisted mechanism (Ea 2.5 eV at T > 265 °C; VB > 1100 V), and the GaN-on-Si is well reproduced with a combination of the two mechanisms (Ea 0.35 eV at T > 150 °C; VB 420 V). Finally, the relationship between the vertical bulk current and the lateral AlGaN/GaN transistor leakage current is explored. © 2013 AIP Publishing LLC.


Oria L.,IMB CNM CSIC | Ruiz De Luzuriaga A.,Cidetec | Alduncin J.A.,Cidetec | Perez-Murano F.,IMB CNM CSIC
Microelectronic Engineering | Year: 2013

Block co-polymer (BCP) lithography is becoming an established technique for patterning beyond optical lithography limitations. It is based on combining the intrinsic property of block co-polymers to phase separate at the molecular scale with the capabilities of conventional top-down lithographic methods for patterning surfaces. Guiding the self-assembly of block co-polymers by surface chemical modification is one of the most used processes to drive the self-assembly in a convenient way. It consists on using lithography and oxygen plasma to create different wettability regions on a polymer brush grafted on the surface. However, the optimal conditions for obtaining a good guiding pattern in chemical surface modification are difficult to find since the ultimate mechanism that causes the guiding is not completely known. We present an investigation about the use of hydroxyl-terminated polystyrene (PS-OH) as a single polymer brush layer for multiple patterning directed self-assembly DSA of PS/PMMA block co-polymers. We achieve pattern multiplication with density increase factors up to 12 and we demonstrate pattern transfer to silicon. © 2012 Elsevier B.V. All rights reserved.


Eichler A.,Institute Catala Of Nanotecnologia | Del Alamo Ruiz M.,Institute Catala Of Nanotecnologia | Plaza J.A.,IMB CNM CSIC | Bachtold A.,Institute Catala Of Nanotecnologia
Physical Review Letters | Year: 2012

We report on the nonlinear coupling between the mechanical modes of a nanotube resonator. The coupling is revealed in a pump-probe experiment where a mode driven by a pump force is shown to modify the motion of a second mode measured with a probe force. In a second series of experiments, we actuate the resonator with only one oscillating force. Mechanical resonances feature exotic line shapes with reproducible dips, peaks, and jumps when the measured mode is commensurate with another mode with a frequency ratio of either 2 or 3. Conventional line shapes are recovered by detuning the frequency ratio using the voltage on a nearby gate electrode. The exotic line shapes are attributed to strong coupling between the mechanical modes. The possibility to control the strength of the coupling with the gate voltage holds promise for various experiments, such as quantum manipulation, mechanical signal processing, and the study of the quantum-to-classical transition. © 2012 American Physical Society.


Torras N.,IMB CNM CSIC | Zinoviev K.E.,IMB CNM CSIC | Marshall J.E.,University of Cambridge | Terentjev E.M.,University of Cambridge | Esteve J.,IMB CNM CSIC
Applied Physics Letters | Year: 2011

Liquid crystal elastomers (LCE) containing embedded carbon nanotubes (CNTs) contract when exposed to light, due to LC disordering induced by the ability of CNTs to absorb light and convert it into thermal energy. A cantilever made of LCE-CNTs exposed to light demonstrates dynamic bending due to inhomogeneous strain distribution caused by exponential heat generation across the cantilever width. Analysis of bending dynamics helps to extract parameters that are important for designing actuators based on these materials. In this work, we have carried out direct measurements of temperature evolution inside the cantilever and related its kinetics to the applied irradiation power. © 2011 American Institute of Physics.


Banu V.,IMB CNM CSIC | Godignon P.,IMB CNM CSIC | Jorda X.,IMB CNM CSIC | Alexandru M.,IMB CNM CSIC | Millan J.,IMB CNM CSIC
Proceedings of the International Semiconductor Conference, CAS | Year: 2012

This work presents thermal analysis results of surge current test performed on pressed-pack encapsulated SiC Schottky Diodes. An original method for temperature evaluation during high current pulses, based on behavioural SPICE models, was used to approach the analysis. Silicon Carbide (SiC) is one of the most adequate wide bandgap (WBG) material for manufacturing high temperature and high power electronics. However, the actual generation of commercially available SiC power diodes (Schottky and JBS) shows a maximum junction temperature of only 175°C. This important derating of the SiC devices, which theoretically are capable to sustain much higher temperatures, is due to the packaging limitation. The aim of our investigations is to overcome the actual limitations of SiC device packaging and to obtain reliable SiC devices able to operate at temperatures over 300°C. © 2012 IEEE.


Banu V.,IMB CNM CSIC | Godignon P.,IMB CNM CSIC | Perpina X.,IMB CNM CSIC | Jorda X.,IMB CNM CSIC | Millan J.,IMB CNM CSIC
Microelectronics Reliability | Year: 2012

This work presents experimental comparative results of power cycling capability of SiC Schottky diodes performed on various encapsulation technologies. For the analysis, we used an original concept based on the device self-heating and a dedicated workbench. The aim of our studies is to obtain reliable Silicon Carbide (SiC) devices able to operate at temperatures over 300 °C. Various technological approaches have to be considered, mainly on the interconnection technique and metallization layers in order to improve the temperature operation of the power diodes. Our investigation showed the most suitable packaging technology for SiC devices sustaining high temperature swing. Special attention is dedicated to the press-pack contact. © 2012 Elsevier Ltd. All rights reserved.

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