2.3 nm barrier AlN/GaN HEMTs with insulated gates (original) (raw)
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High-Performance AlN/GaN HEMTs on Sapphire Substrate With an Oxidized Gate Insulator
IEEE Electron Device Letters, 2011
This letter presents transistor device results on ultrathin AlN/GaN high-electron mobility transistors grown on a sapphire substrate with high dc/RF performance, including low gate leakage and high transconductance. Devices with 80-and 180-nm T-gates are compared, which demonstrate drain-induced OFF-state gate leakage currents below 10 −6 A/mm and extrinsic transconductance g m ∼ 500 mS/mm by utilizing a ∼2-3 nm amorphous oxide layer formed under the T-gate during processing. In addition, excellent dc results such as R C < 0.50 Ω • mm and pulsed I DS,max ∼ 1.75 A/mm are reported. Small-signal RF performance using an 80-nm T-gate achieved f t > 100 GHz operation, which is among the best so far reported for AlN/GaN technology.
AlN/GaN Insulated-Gate HEMTs With 2.3 A/mm Output Current and 480 mS/mm Transconductance
IEEE Electron Device Letters, 2008
High-electron mobility transistors (HEMTs) based on ultrathin AIN/GaN heterostructures with a 3.5-nm AlN barrier and a 3-nm Al2O3 gate dielectric have been investigated. Owing to the optimized AIN/GaN interface, very high carrier mobility (~1400 cm2/V ldr s) and high 2-D electron-gas density (~2.7times1013/cm2) resulted in a record low sheet resistance (~165 Omega/sq). The resultant HEMTs showed a maximum dc output current density of ~2.3 A/mm and a peak extrinsic transconductance gm,ext~480 mS/mm (corresponding to gm,int~1 S/mm). An fT/fmax of 52/60 GHz was measured on 0.25times60 mum2 gate HEMTs. With further improvements of the ohmic contacts, the gate dielectric, and the lowering of the buffer leakage, the presented results suggest that, by using AIN/GaN heterojunctions, it may be possible to push the performance of nitride HEMTs to current, power, and speed levels that are currently unachievable in AlGaN/GaN technology.
High Electron Velocity Submicron AlN/GaN MOS-HEMTs on Freestanding GaN Substrates
AlN/GaN heterostructures with 1700-cm2/V·s Hall mobility have been grown by molecular beam epitaxy on freestanding GaN substrates. Submicrometer gate-length (LG) metal-oxide-semiconductor (MOS) high-electron-mobility transistors (HEMTs) fabricated from this material show excellent dc and RF performance. LG = 100 nm devices exhibited a drain current density of 1.5 A/mm, current gain cutoff frequency fT of 165 GHz, a maximum frequency of oscillation fmax of 171 GHz, and intrinsic average electron velocity ve of 1.5 ×107 cm/s. The 40-GHz load-pull measurements of LG = 140 nm devices showed 1-W/mm output power, with a 4.6-dB gain and 17% power-added efficiency. GaN substrates provide a way of achieving high mobility, high ve, and high RF performance in AlN/GaN transistors.
Fabrication and Characterization of Thin-Barrier AlGaN/AlN/GaN HEMTs
IEEE Electron Device Letters, 2011
The growth, fabrication, and performance of Al 0.5 Ga 0.5 N/AlN/GaN high-electron-mobility transistors (HEMTs) with a total barrier thickness of 7 nm are reported. An optimized surface passivation and an Ohmic recess etch yield HEMTs exhibiting 0.72 S/mm peak extrinsic DC transconductance at a current density of 0.47 A/mm. Devices with a gate length of 90 nm achieve 78 GHz unity-current-gain frequency and up to 166 GHz maximum frequency of oscillation. The minimum noise figure at 10 GHz is 0.52 dB with an associated gain of 9.5 dB.
Very high channel conductivity in low-defect AlN/GaN high electron mobility transistor structures
Applied Physics Letters, 2008
Low defect AlN/GaN high electron mobility transistor ͑HEMT͒ structures, with very high values of electron mobility ͑Ͼ1800 cm 2 / V s͒ and sheet charge density ͑Ͼ3 ϫ 10 13 cm −2 ͒, were grown by rf plasma-assisted molecular beam epitaxy ͑MBE͒ on sapphire and SiC, resulting in sheet resistivity values down to ϳ100 ⍀ / ᮀ at room temperature. Fabricated 1.2 m gate devices showed excellent current-voltage characteristics, including a zero gate saturation current density of ϳ1.3 A / mm and a peak transconductance of ϳ260 mS/ mm. Here, an all MBE growth of optimized AlN/GaN HEMT structures plus the results of thin-film characterizations and device measurements are presented.
Advanced Design of Ultrathin-Barrier AlN/GaN HEMTs
Of the III-Nitride family the AlN/GaN heterojunction has demonstrated the largest combined polarization charge and energy band o sets available in the system. Engineering the polarization fields through varying the AlN thickness leads to two-dimensional electron gas densities (2DEGs) that may be tailored between 0.5 - 5 x1013 cm2. Furthermore, the ultra-thin (< 5 nm) barrier and excellent transport properties of this all binary heterostructure make it well suited for high electron mobility transistor applications where high frequency and high current are required. This work encompasses various design aspects of GaN-based High Electron Mobility Transistors (HEMTs) which ultimately result in the realization of several generations that utilize the AlN/GaN heterostructure. HEMTs fabricated from high-mobility, low sheet resistance heterostructures have achieved drain current densities up to 2.3 A/mm and transconductance of 480 mS/mm, which set new benchmarks for GaN-based HEMTs. Ultra-thin pre-metallization etching has been employed for the rst time to reduce ohmic contact resistance for AlN/GaN HEMTs and has enabled small signal frequency performance in excess of 100 GHz. Moll's method for delay time extraction has been utilized to extract an effective electron velocity in the intrinsic region of the AlN/GaN HEMT and was found to be 1.2 x107 cm/s. By leveraging the allowable thickness window of the AlN barrier along with the high density 2DEGs that result, several novel HEMT devices have been designed and realized. High Al-content AlxGa1xN back barriers have been employed for improved 2DEG con finement in several new variations of the ultra-thin AlN/GaN HEMT. A dual, parallel-channel AlN/GaN-based HEMT structure is designed and realized for the first time as an epitaxial approach to mitigating DC-RF frequency dispersion. These structures emphasize the facilitation of new device designs that are made possible through the particular qualities the AlN/GaN heterostructure possesses.
MBE-grown ultra-shallow AlN/GaN HFET technology
2007
Due to large polarization effects, two-dimensional electron gas (2DEG) concentrations higher than 1x10 13 cm-2 can be produced at the AlN/GaN heterojunction with AlN barriers as thin as 2 nm. This ultra-shallow channel together with the wide bandgap of AlN (6.2 eV) makes AlN/GaN heterojunction field effect transistors (HFET) extremely attractive for high frequency (>100 GHz) high power applications. At Notre Dame, these structures have been grown using molecular beam epitaxy and the record transport properties among III-V nitrides are achieved: a sheet resistance of ~ 170 ohm/square for a single heterostructure at room temperature. HFETs have been fabricated with optical lithographically defined gates. At present the device dc characteristics show a maximum drain current of 800 mA/mm and transconductance of 180 mS/mm for 3 μm long gate. This clearly demonstrates its value toward high speed devices. The development as well as challenges of this technology will be discussed here.
A series of six ultrathin AlN/GaN heterostructures with varied AlN thicknesses from 1.5 - 6 nm have been grown by molecular beam epitaxy on free-standing hydride vapor phase epitaxy (HVPE) GaN substrates. High electron mobility transistors (HEMTs) were fabricated from the set in order to assess the impact of barrier thickness and homo-epitaxial growth on transistor performance. Room temperature Hall characteristics revealed mobility of 1700 cm2/Vs and sheet resistance of 130 Ω/sqr. for a 3 nm thick barrier, ranking amongst the lowest room-temperature sheet resistance values reported for a polarization-doped single heterostructure in the III-Nitride family. DC and small signal HEMT electrical characteristics from submicron gate length HEMTs further elucidated the effect of the AlN barrier thickness on device performance.
Micromachines
The emergence of gallium nitride high-electron-mobility transistor (GaN HEMT) devices has the potential to deliver high power and high frequency with performances surpassing mainstream silicon and other advanced semiconductor field-effect transistor (FET) technologies. Nevertheless, HEMT devices suffer from certain parasitic and reliability concerns that limit their performance. This paper aims to review the latest experimental evidence regarding HEMT technologies on the parasitic issues that affect aluminum gallium nitride (AlGaN)/GaN HEMTs. The first part of this review provides a brief introduction to AlGaN/GaN HEMT technologies, and the second part outlines the challenges often faced during HEMT fabrication, such as normally-on operation, self-heating effects, current collapse, peak electric field distribution, gate leakages, and high ohmic contact resistance. Finally, a number of effective approaches to enhancing the device’s performance are addressed.