3D GaN nanoarchitecture for field-effect transistors

The three-dimensionality of 3D GaN field-effect transistors (FETs) provides them with unique advantages compared to their planar counterparts, introducing a promising path towards future FETs beyond Moore's law. Similar to today's Si processor technology, 3D GaN FETs offer multi-gate structures that provide excellent electrostatic control over the channel and enable very low subthreshold swing values close to the theoretical limit. Various concepts have been demonstrated, including both lateral and vertical devices with GaN nanowire (NW) or nanofin (NF) geometries. Outstanding transport properties were achieved with laterally contacted NWs that were grown in a bottom-up approach and transferred onto an insulating substrate. For higher power application, vertical FETs based on regular arrays of GaN nanostructures are particularly promising due to their parallel integration capability and large sidewall surfaces, which can be utilized as channel area. In this paper, we review the current status of 3D GaN FETs and discuss their concepts, fabrication techniques, and performances. In addition to the potential benefits, reliability issues and difficulties that may arise in complex 3D processing are discussed, which need to be tackled to pave the way for future switching applications

Capacitance-voltage characterization of Al 2 O 3 /GaN-on-insulator (GaNOI) structures with TMAH surface treatment

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Capacitance-voltage characterization of Al 2 O 3 /GaN-on-insulator (GaNOI) structures with TMAH surface treatment

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Comparison for 1/ f Noise Characteristics of AlGaN/GaN FinFET and Planar MISHFET

International audienceDC and 1/f noise performances of the AlGaN/GaN fin-shaped field-effect transistor (FinFET) with fin width of 50 nm were analyzed. The FinFET exhibited approximately six times larger normalized drain current and transconductance, compared to those of the AlGaN/GaN planar metal-insulator-semiconductor heterostructure field-effect-transistor (MISHFET) fabricated on the same wafer. It was also observed that the FinFET exhibited improved noise performance with lower noise magnitude of 8.5×10 -15 A 2 /Hz when compared to the value of 8.7×10 -14 A 2 /Hz for the planar MISHFET. An intensive analysis indicated that both devices follow the carrier number fluctuation model, but the FinFET suffers much less charge trapping effect compared to the MISHFET (two orders lower charge trapping was observed). Moreover, the FinFET did not exhibit the Lorentz-like components, which explains that the depleted fin structure effectively prevents the carriers from being trapped into the underlying thick GaN buffer layer. On the other hand, the slope of the noise is 2 irrespective of drain voltage and apparently showed the Lorentz-like components, especially at high drain voltage in MISHFET device. This explains that the carrier trapping/detrapping between the 2-D electron gas channel and the GaN buffer layer is significant in MISHFET

Fabrication of AlGaN/GaN Ω-shaped nanowire fin-shaped FETs by a top-down approach

International audienceAn AlGaN/GaN-based Ω-shaped nanowire fin-shaped FET (FinFET) with a fin width of 50 nm was fabricated using tetramethylammonium hydroxide (TMAH)-based lateral wet etching. An atomic layer deposited (ALD) HfO2 side-wall layer served as the etching mask. ALD Al2O3 and TiN layers were used as the gate dielectric and gate metal, respectively. The Ω-shaped gate structure fully depletes the active fin body and almost completely separates the depleted fin from the underlying thick GaN buffer layer, resulting in superior device performance. The top-down processing proposed in this work provides a viable pathway towards gate-all-around devices for III–nitride semiconductors

Fabrication of normally-off GaN nanowire gate-all-around FET with top-down approach

International audienceLateral GaN nanowire gate-all-around transistor has been fabricated with top-down process and characterized. A triangle-shaped GaN nanowire with 56 nm width was implemented on the GaN-on-insulator (GaNOI) wafer by utilizing (i) buried oxide as sacrificial layer and (ii) anisotropic lateral wet etching of GaN in tetramethylammonium hydroxide solution. During subsequent GaN and AlGaN epitaxy of source/drain planar regions, no growth occurred on the nanowire, due to self-limiting growth property. Transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping reveal that the GaN nanowire consists of only Ga and N atoms. The transistor exhibits normally-off operation with the threshold voltage of 3.5 V and promising performance: the maximum drain current of 0.11 mA, the maximum transconductance of 0.04 mS, the record off-state leakage current of ∼10−13 A/mm, and a very high Ion/Ioff ratio of 108. The proposed top-down device concept using the GaNOI wafer enables the fabrication of multiple parallel nanowires with positive threshold voltage and is advantageous compared with the bottom-up approach

Performance enhancement of AlGaN/GaN nanochannel omega-FinFET

International audienceNovel AlGaN/GaN omega-shaped nanochannel FinFETs with fin width of 50 nm were successfully fabricated using TMAH lateral wet etching with ALD HfO2 sidewall spacer. This fin structure apparently exhibited the current spreading in the access region, which results in the suppression of the drain lag effect at high drain voltage and sharp switching performance with subthreshold swing of 57–65 mV/decade. Excellent on- and off-state state performances for the fabricated device prove that the omega-shaped gate structure not only exhibits excellent gate controllability, but also decouples the active nano-channel region from the underlying thick buffer. The proposed device is very promising candidate for high-performance device applications

1/f -noise characteristics of AlGaN/GaN omega shaped nanowire FETs

session 4: Frequency Phenomena and NoiseInternational audienceThe AlGaN/GaN omega-shaped nanowire FETs with different nanowire widths (W) have been fabricated. The effects of varying W on the performance of AlGaN/GaN omega-shaped nanowire FETs were investigated using low frequency noise (LFN) measurement. It was found that the noise characteristics of the device with narrow W show improved noise performances due to the accumulation of electrons in the volume of the nanowire which constricts the electron trapping in GaN layer. This volume accumulation of electrons is responsible for the mobility fluctuations because it decreases the probability of channel electrons at surface being captured into the surface traps, and also high carrier concentration screens the effective trapping of electrons in the volume of the nanowire. Whereas, width increases the LFN characteristics tended to be dominated by the carrier number fluctuation because the fin is too wide for volume accumulation and are subjected to the bulk trapping

Temperature-dependent characteristics of AlGaN/GaN FinFETs with sidewall MOS channel

International audienceAlGaN/GaN fin-shaped field-effect transistors (FinFETs) with variable fin width have been fabricated and characterized. Low-temperature measurements reveal distinct operation modes for wide FinFET, narrow FinFET and planar FET. The wide fin device exhibits broad transconductance (gm) that decreases sublinearly with increasing temperature due to the existence of the sidewall metal–oxide–semiconductor (MOS) channel. By comparison, the conventional planar AlGaN/GaN metal–insulator–semiconductor heterostructure FET (MISHFET) features relatively narrow gm curve and near-exponentially decay of gm with temperature. The effect of the sidewall channel becomes more prominent for the narrow fin device and leads to two distinct gm peaks. The first peak at negative gate voltage corresponds to the two-dimensional electron gas (2-DEG) channel, while the second peak at positive gate voltage is related to the sidewall MOS channel. Measurements also show that the electrons in 2-DEG channel experience polar-optical-phonon scattering unlike the electrons in the sidewall MOS channel which are mainly subject to Coulomb scattering

1/f-Noise in AlGaN/GaN Nanowire Omega-FinFETs

International audienceThe low-frequency noise (LFN) characteristics of AlGaN/GaN FinFETs with omega-gate and combined two-dimensional electron gas (2DEG) and MOS conduction are investigated. It is found that LFN is dominated by carrier number fluctuations whatever the width of the fin. Charge trapping in narrow devices is one order of magnitude lower than in wide fin device. In narrow devices, the sidewall conduction prevails and the noise mainly stems from the carrier trapping in the sidewall Al2O3 gate dielectric. Instead, in wide fin devices, the top gate AlGaN/GaN HEMT structure dominates and the LFN is mostly governed by the carrier trapping in the GaN layer close to 2DEG channel