Cedric Lacam - Academia.edu (original) (raw)

Papers by Cedric Lacam

2022 IEEE International Reliability Physics Symposium (IRPS)

2018 International Workshop on Integrated Nonlinear Microwave and Millimetre-wave Circuits (INMMIC), 2018

This paper presents the simulated results and first small-signal on-wafer measurements of two MMI... more This paper presents the simulated results and first small-signal on-wafer measurements of two MMIC power amplifiers (PA), based on InAlGaN/GaN HEMT technology, for Ka band applications. The two three-stages MMIC1 & MMIC2 are operating within a bandwidth of [27.5–31]GHz and [37–39.5]GHz, respectively and demonstrate over these bandwidths a saturated output power of 40dBm and 38dBm, respectively. Each stage use 8×50μm gate width HEMTs fabricated with a 0.15μm gate length on 70μm thick SiC substrate.

IEEE Electron Device Letters, 2016

2016 11th European Microwave Integrated Circuits Conference (EuMIC)

We report on the performances of 0.1-μm gate length InAl(Ga)N/GaN HEMT devices on SiC substrate. ... more We report on the performances of 0.1-μm gate length InAl(Ga)N/GaN HEMT devices on SiC substrate. Measurements results of DC, pulsed I-V, S-parameters and load-pull power performances are presented. Devices exhibited a maximum DC transconductance of 400mS/mm and drain current of 1.2A/mm at Vgs=1V. Cut-off frequencies Ft and Fmag of 60GHz and 140 GHz were obtained. Load-pull power measurements at 30GHz allowed us to achieve an output power density of 3W/mm with 40% of PAE at Vds=15V. Biased at Vds=20V, a maximum saturated output power density of 5W/mm was achieved.

HAL (Le Centre pour la Communication Scientifique Directe), Sep 19, 2016

International audienc

2019 14th European Microwave Integrated Circuits Conference (EuMIC), 2019

This article presents the performances obtained on a 0.15mumathrmm0.15 \mu \mathrm{m}0.15mumathrmm gate length InAlGaN/Ga... more This article presents the performances obtained on a 0.15mumathrmm0.15 \mu \mathrm{m}0.15mumathrmm gate length InAlGaN/GaN HEMT technology on SiC substrate. This technology uses a back-barrier buffer layer to ensure the confinement of electrons in the channel, which minimizes variations of the drain current when the HEMT devices are submitted to DC or RF pulses. Measurements of the drain current recovery time are shown when the devices are submitted to VDS, VGS or microwave RF pulses. A comparison with an AlGaN/GaN HEMT structure designed with an iron doped buffer layer is proposed.

2019 49th European Microwave Conference (EuMC), 2019

This paper presents the measurement results of a MMIC power amplifiers (PA), based on InAlGaN/GaN... more This paper presents the measurement results of a MMIC power amplifiers (PA), based on InAlGaN/GaN HEMT technology, for Ka band applications. The three-stages MMIC is operating within a bandwidth of [25-31]GHz and demonstrate over this bandwidth a saturated output power of 40dBm. Each stage uses 8x50µm gate width HEMTs fabricated with a 0.15µm gate length on 70µm thick SiC substrate.

GaN-based HEMTs are excellent candidates for next-generation high-power microwave applications. N... more GaN-based HEMTs are excellent candidates for next-generation high-power microwave applications. Nevertheless, due to the spontaneous n-type conductivity of GaN crystals, devices equipped with unintentionally-doped buffer experience detrimental short-channel effects, undermining both the device performances and their long-term stability. Technological solutions involve the introduction of carbon and/or iron compensating species which compensate the unintentional donor species, render the GaN buffer layer semi-insulating, and improve the confinement of electrons in the 2DEG. Nevertheless, the presence of foreign impurities and the related peculiar growth conditions, may give rise to enhanced crystallographic defect density. Within this work, we comprehensively investigate the static and dynamic parasitic effects related to the GaN-buffer design, and we discuss the implications on the rf performance and reliability

Physica Status Solidi A-applications and Materials Science, 2017

2018 22nd International Microwave and Radar Conference (MIKON), 2018

Recent results obtained using InAlGaN/GaN HEMT technology. Material advantages of this heterostru... more Recent results obtained using InAlGaN/GaN HEMT technology. Material advantages of this heterostructure are depicted and some technological aspects are described. Low lagging effects and high electric field capability is presented. Power densities up to 10W.mm−1 have been obtained at 30GHz. MMIC power amplifiers are briefly reported.

IEEE Transactions on Electron Devices, 2019

This paper reports on sub-10 nm quaternary barrier InAlGaN/GaN High Electron Mobility Transistors... more This paper reports on sub-10 nm quaternary barrier InAlGaN/GaN High Electron Mobility Transistors (HEMTs) grown by Metal-Organic-Vapor-Phase-Epitaxy (MOVPE) with an in situ SiN passivation layer, and ultra-short gate length of 200 nm. Two batches of HEMTs with two SiN thicknesses (t SiN) of 14 and 22 nm are studied. Low Frequency Noise (LFN) measurements of the drain current have been carried out in the linear regime and showed that the in situ SiN thickness has no impact on the noise performance. S ID /I D 2 in the linear regime dependence over the gate overdrive shows that the channel noise is located under the gate and that the noise is not impacted by the thickness of the in situ SiN layer.

Journal of Applied Physics, 2019

Due to its intrinsic properties and the possible lattice match to GaN, InAlN is expected to allow... more Due to its intrinsic properties and the possible lattice match to GaN, InAlN is expected to allow the fabrication of optimal high electron mobility transistors for high power and high frequency applications. However, the crystal quality of InAlN nearly lattice-matched to GaN degrades when the layer thickness is increased, and this is a strong limitation for the fabrication of devices in which thick barriers need to be used. In this work, we have carried out a detailed theoretical investigation of the behavior of indium atoms in the alloy. It is clearly shown that in the presence of nitrogen vacancies, which are common defects in these materials, indium nitride clusters will present excess formation energy up to diameters around 1.4 nm. In parallel, Z contrast TEM observations close to the InAlN/GaN interface show that 2-5 nm size indium rich areas form and are systematically connected to the vertical degradation channels. This is at variance with published results, which concluded that the observed degradation was due exclusively either to the underlying threading dislocations or to a characteristic three-dimensional growth mode.

Journal of Vacuum Science & Technology A, 2019

This paper reports on atomic layer etching of several III-N materials such as GaN, AlN, AlGaN, an... more This paper reports on atomic layer etching of several III-N materials such as GaN, AlN, AlGaN, and InAlGaN based on a sequential surface modification by chlorine adsorption followed by a low energy Ar plasma exposure to remove the modified layer using a reactive ion etching system. A study on the influence of several parameters, such as gas flow rates, removal step duration, RIE power and number of cycles on the etch per cycle, and the root-mean-square roughness, is performed. Low etch per cycle from 0.17 to 1.85 nm/cycle, respectively, for AlGaN and GaN and surfaces as smooth as the as-grown samples were obtained. The developed process is intended to be used for normally off GaN-based high electron mobility transistor processing.

International Journal of Microwave and Wireless Technologies, 2017

This paper presents performances achieved with InAlGaN/GaN HEMTs with 0.15 µm gate length on SiC ... more This paper presents performances achieved with InAlGaN/GaN HEMTs with 0.15 µm gate length on SiC substrate. Technology Computer Aided Design simulations were used to optimize the heterostructure. Special attention was paid to the design of the buffer structure. I-V measurements with DC and pulsed bias voltages were performed. CW measurements at millimeter waves were also carried out and are detailed in the following sections. The technology, optimized for power applications up to 45 GHz, demonstrates a current gain cut-off frequency FTof 70 GHz and a maximum available gain cut-off frequency FMAGof 140 GHz. CW Load-pull power measurements at 30 GHz enable to achieve a maximum PAE of 41% associated with an output power density of 3.5 W/mm when biased at VDS= 20 V. These devices, with an improved buffer structure show, reduced recovery time in pulsed operating conditions. These improved characteristics should have a positive impact for pulsed or modulated signal applications.

IEEE Transactions on Electron Devices, 2018

The impact of varying the GaN channel layer thickness (t ch) in InAlGaN/AlN/GaN HEMTs with C-dope... more The impact of varying the GaN channel layer thickness (t ch) in InAlGaN/AlN/GaN HEMTs with C-doped AlGaN back barriers is investigated. t ch was 50, 100, and 150 nm, and the gate length of the fabricated HEMTs ranged from 50 to 200 nm. It is found that short-channel effects (SCEs) are significantly mitigated with a small t ch. For HEMTs with a gate length of 50 nm, the drain-induced barrier lowering changes from 40 to 93 mV/V as t ch is increased from 50 to 150 nm. On the other hand, it is shown that dispersive effects are more severe for a smaller t ch , as demonstrated by a sixfold increase in the dynamic ON-resistance for t ch = 50 nm compared to t ch = 150 nm. The tradeoff between dispersion and SCEs is reflected in large-signal measurements at 30 GHz. The 50-nm channel, mainly limited by dispersion, exhibits an output power of 3.5 W/mm. The thicker channels reach a maximum of around 5 W/mm, but for different gate lengths due to the difference in severity of the SCEs. This paper elucidates the interplay between SCEs and dispersion related to t ch , its consequences for the largesignal performance and for the limitation in downscaling of the gate length. Index Terms-Back barrier (BB), channel thickness, double heterojunction (DH) HEMT, dispersion, GaN HEMT, InAlGaN, large signal, short-channel effects (SCEs).

Microelectronics Reliability, 2018

On-wafer short term step-stress tests were carried out to evaluate InAlGaN/GaN HEMT devices. Thre... more On-wafer short term step-stress tests were carried out to evaluate InAlGaN/GaN HEMT devices. Three types of transistor were studied, each one having a specific two dielectric layer passivation. The results of these tests demonstrate that the upper layer of the passivation has a strong impact on the ageing of the devices. When the upper layer is an Al 2 O 3 Atomic Layer Deposited one, the transistors show a better stability of their electrical parameters than those passivated with the other stacks.

Journal of microscopy, 2017

Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morph... more Defects in quaternary InAlGaN barriers and their effects on crystalline quality and surface morphology have been studied. In addition to growth conditions, the quality of the GaN template may play an important role in the formation of defects in the barrier. Therefore, this work is focused on effects caused by threading dislocations (TDs) and inversion domains (IDs) originating from the underlying GaN. The effects are observed on the crystalline quality of the barrier and characteristic surface morphologies. Each type of TDs is shown to affect the surface morphology in a different way. Depending on the size of the corresponding hillock for a given pinhole, it was possible to determine the dislocation type. It is pointed out that the smallest pinholes are not connected to TDs whereas the large ones terminate either mixed type or edge type TDs. At sufficiently large layer thickness, the IDs originating from the GaN template lead to the formation of concentric trenches at the layer sur...

Journal of Crystal Growth, 2017

This work presents the growth of quaternary barrier InAlGaN/GaN HEMT structures with in-situ SiN ... more This work presents the growth of quaternary barrier InAlGaN/GaN HEMT structures with in-situ SiN passivation by MOVPE. Five heterostructures with different SiN thicknesses, ranging from 0 to 22 nm, were realized. We observed that the growth of SiN onto the InAlGaN barrier results in smooth films, without formation of extended defects and without degradation of the structural properties of the barrier layer, even in the case of a SiN growth times as long as 90 min. In agreement with these findings, the sheet resistance of the heterostructures was found to be independent on the SiN deposition time, proving also that the SiN layer does not introduce additional strain into the heterostructure. The passivation effect of the SiN cap was demonstrated through Hall measurements. A significant increase of the sheet resistance after ohmic contacts realization was observed on the sample without SiN in-situ passivation and related to surface charges. This change was not observed on the HEMT structures with in-situ passivation, regardless the SiN layer thickness, showing that the SiN cap is an effective way to reduce the density of electronically active states at the interface between the III-N layers and the passivation. In addition, the structures show state of the art transport properties with 2DEG densities of 1.6×10 13 cm −2 and electron mobilities as high as 1800 cm 2 V −1 s −1 .