A low-noise microwave HEMT using MOCVD

Low-noise high-electron-mobility Transistors (HEMT's) with AlGaAs/GaAs heterostructures have been successfully fabricated using normal pressure metal-organic chemical vapor deposition (MOCVD). Hall mobilities of the two-dimensional electron gas at the interface are 8030 and 14 8000 cm²/V . s at 300 and 77 K, respectively, with an undoped Al0.3Ga0.7As spacer layer of 100 Å. The HEMT's with 0.65-µm-long and 200-µm-wide gates have exhibited a noise figure of 1.13 dB with 10.8 dB of associated gain at 12 GHz, and a dc transconductance of 280 mS/mm. These values are comparable to other reported HEMT devices using molecular-beam epitaxy (MBE).     

Electron-beam fabrication of GaAs low-noise MESFET's using a new trilayer resist technique

A LO/HI/LO resist system has been developed to produce sub-half-micrometer T-shaped cross section metal lines using e-beam lithography. The system provides T-shaped resist cavities with undercut profiles. T-shaped metal lines as narrow as 0.15 µm have been produced. GaAs MESFET's with 0.25-µm T-shaped Ti/Pt/Au gates have also been fabricated on MBE wafers using this resist technique. Measured end-to, end 0.25-µm gate resistance was 80 ω/mm, dc transconductance gmas high as 300 mS/mm was observed. At 18 GHz, a noise figure as low as 1.4 dB with an associated gain of 7.9 dB has also been measured. This is the lowest noise figure ever reported for conventional GaAs MESFET's at this frequency. These superior results are mainly attributed to the high-quality MBE material and the advanced T-gate fabrication technique employing e-beam lithography.     

A high aspect ratio design approach to millimeter-wave HEMT structures

In MESFET and HEMT structures as the gate length is reduced below 0.5 µm in an attempt to achieve amplification at highest possible frequencies, it is essential that the depletion depth under the gate be also reduced in order to preserve a high aspect ratio that ensures a high device voltage gain factor (gm/g0) and a reasonable value of stable power gain at high frequencies. Results based on this design approach indicate that an n-A1GaAs/GaAs HEMT structure with 0.25-µm gate length could provide stable power gain in excess of 6 dB at the unity current gain frequency of 92.4 GHz, and for an aspect ratio of ten it is difficult to reduce the gate length below 0.25 µm.     

GaAs MESFET's by molecular beam epitaxy

The noise performance of "T" shaped Ti/W/Au gate GaAs Schottky-barrier field-effect transistors fabricated on channel layers grown by molecular-beam epitaxy (MBE) is reported. The nominal gate length was about 0.7 µm with a total gate width of 250 µm. Typical noise figure and the associated gain were 1.2 and 14 dB at 4 GHz, and 1.9 and 8.5 dB at 12 GHz. To out knowledge these are the best results reported to date on devices fabricated using MBE-grown GaAs. These preliminary results show the promise of MBE for high-quality GaAs FET's.     

Super low-noise GaAs MESFET's with a deep-recess structure

Super low-noise GaAs MESFET's for replacement of parametric amplifiers have been successfully developed by adopting a deep-recess structure. The structure of a 0.5-µm gate in a deeply recessed region with a cylindrical edge shape has enabled reduction of the source resistance to a half of that of conventional flat-type MESFET's. The noise figure was improved by more than 0.5 dB by this reduction of the source resistance, and less than 2.0-dB noise figure has been reproducibly obtained at 12 GHz. The best noise figures were 0.7 dB (14.9-dB gain) at 4 GHz and 1.68 dB (10.7-dB gain) at 12 GHz. The developed MESFET's were applied to two-stage amplifiers of 11.7-12.2-GHz band, and the noise figure obtained was 2.16 dB (T_{e}: 185K) at room temperature and 1.94 dB (T_{e}: 163K) at 0°C. This performance is good enough to replace some of parametic amplifiers.     

A low-noise GaAs MESFET made with graded-channel doping profiles

We have demonstrated that devices fabricated from epitaxially grown material with a graded-channel doping profile are capable of improved microwave performance. For operation at 12 GHz, graded-channel doping profile devices have an associated gain that is always 1 dB higher at the minimum noise-figure point compared to ion-implanted Gaussian-channel doping profile devices. A noise figure of 1.60 dB with 11-dB associated gain has been obtained at 12 GHz for 0.5-µm × 300-µm gate devices. A tranconductance of 200 mS/mm for this device has been achieved.     

GaAs MESFET's made by ion implantation into MOCVD Buffer layers

Low-noise GaAs metal-semiconductor field-effect transistors (MESFET's) have been made using ion-implanted metal organic chemical vapor deposition (MOCVD) buffer layers. A noise figure of 1.46 dB with 10.20 associated gain has been achieved at 12 GHz for a 0.5-µm gatelength by 300-µm gatewidth FET device. This result demonstrates that excellent GaAs LNFET's can be made by ion implantation into MOCVD buffer layers, comparable to the best results obtained from similar devices made by AsCl3vapor-phase epitaxy and molecular-beam epitaxy.     

110-120-GHz monolithic low-noise amplifiers

The authors discuss the development of 110-120-GHz monolithic low-noise amplifiers (LNAs) using 0.1-mm pseudomorphic AlGaAs/InGaAs/GaAs low-noise HEMT technology. Two 2-stage LNAs have been designed, fabricated, and tested. The first amplifier demonstrates a gain of 12 dB at 112 to 115 GHz with a noise figure of 6.3 dB when biased for high gain, and a noise figure of 5.5 dB is achieved with an associated gain of 10 dB at 113 GHz when biased for low-noise figure. The other amplifier has a measured small-signal gain of 19.6 dB at 110 GHz with a noise figure of 3.9 dB. A noise figure of 3.4 dB with 15.6-dB associated gain was obtained at 113 GHz. The authors state that the small-signal gain and noise figure performance for the second LNA are the best results ever achieved for a two-stage HEMT amplifier at this frequency band     

Very high gain millimeter-wave InAlAs/InGaAs/GaAs metamorphicHEMT's

We report the first demonstration of W-band metamorphic HEMTs/LNA MMICs using an AlGaAsSb lattice strain relief buffer layer on a GaAs substrate. 0.1×50 μm low-noise devices have shown typical extrinsic transconductance of 850 mS/mm with high maximum drain current of 700 mA/mm and gate-drain breakdown voltage of 4.5 V. Small-signal S-parameter measurements performed on the 0.1-μm devices exhibited an excellent f_T of 225 GHz and maximum stable gain (MSG) of 12.9 dB at 60 GHz and 10.4 dB at 110 GHz. The three-stage W-band LNA MMIC exhibits 4.2 dB noise figure with 18 dB gain at 82 GHz and 4.8 dB noise figure with 14 dB gain at 89 GHz, The gain and noise performance of the metamorphic HEMT technology is very close to that of the InP-based HEMT     

Submicron T-shaped gate HEMT fabrication using deep-UV lithography

A new combination of low/high/low sensitivity tri-layer (PMMA/PMIPK/PMMA) resist system was used for deep UV lithography to-fabricate submicron T-shaped gate. Gate length as narrow as 0.2 μm is achieved. GaAs HEMTs with 0.3 μm T-shaped Ti/Pt/Au gate are fabricated using this technology. The HEMT demonstrated a 0.6 dB noise figure and 13 dB associated gain at 10 GHz. This deep UV lithography process provides a high throughput and low cost alternative to E-beam lithography for submicron T-gate fabrication     

Super low-noise HEMTs with a T-shaped WSix gate

A T-shaped quarter-micron gate structure composed of WSi_x /Ti/Pt/Au has been developed for low-noise AlGaAs/GaAs HEMTs. The gate resistance R_g was reduced to 0.3 Ω for devices with 200 μm-wide gates despite using WSi_x, and the source resistance R_s reached 0.28 Ω mm by minimising the source-gate distance using a self-alignment technique. This HEMT exhibited the lowest reported noise figure of 0.54 dB with an associated gain of 12.1 dB at 12 GHz     

Improved noise performance of GaAs MESFET's with selectively ion-implanted n+source regions

Superior microwave performance of 0.5-µm-gate GaAs MESFET's has been attained by a structure with selectively ion-implanted n⁺source regions. The source series resistance is reduced and the noise figure of 2.1 dB is observed at 12 GHz.     

New technology towards GaAs LSI/VLSI for computer applications

For future large-scale computer applications, new device technologies towards GaAs LSI/VLSI have been developed: self-aligned fully implanted planar GaAs MESFET technology and high electron mobility transistor (HEMT) technology by molecular beam epitaxy (MBE). The self-aligned GaAs MESFET logic with 1.5-µm gate length exhibits a minimum switching time of 50 ps and the lowest power-delay product of 14.5 fJ at room temperature. The enhancement/depletion (E/D) type direct coupled HEMT logic has achieved a switching time of 17.1 ps with 1.7-µm gate length at liquid nitrogen temperature and more recently a switching time of 12.8 ps with 1.1-µm gate HEMT logic, which exceeds the top speed of Josephson Junction logic and shows the highest speed of any device logic ever reported. Optimized system performances are also projected to system delay of 200 ps at 10-kilogate integration with GaAs MESFET VLSI, and 100 ps at 100-kilogate with HEMT VLSI. These values of system delay correspond to the computer performance of over 100 million instructions per second (MIPS).     

GaAs dual-gate MESFET's

Performance of GaAs dual-gate MESFET, including high-frequency noise behavior, was analyzed on the basis of Statz's model. Under the design considerations developed from the analysis, fabrication and characterization of a prototype device were carried out. The present analysis was confirmed to reproduce satisfactorily the performance observed. Minimum noise figure and associated gain observed in the device with two 1-µm gates were; 1.2 dB and 16.7 dB at 4 GHz, 2.2 dB and 16.3 dB at 8 GHz, and 3.2 dB and 12.6 dB at 12 GHz, respectively. More than 35-dB gain controllability was also obtained at 8 GHz.     

Microwave performance of 0.25-µm gate length high electron mobility transistors

The performance of 0.25-µm gate length high electron mobility transistors (HEMT's) is reported. Devices were fabricated on layers grown by MBE. One of the heterostructures had no undoped AlGaAS spacer layer (wafer A), whereas the other had a 40-Å spacer layer (wafer B). The maximum stable gain on both wafers was ∼ 12 dB at 18 GHz. The minimum noise figure measured was 0.60 dB at 8 GHz and 1.3 dB at 18 GHz. Wafer A yielded devices with a unity current gain cutoff frequency ftof 65 GHz whereas wafer B gave an ftof 70 GHz. These results can be attributed primarily to the high quality material, low parasitic resistance, and short gate length.     

Correlation of undoped, in-alloyed, and whole-ingot annealed semi-insulating GaAs substrates for low-noise microwave amplifiers

The quality of LEC grown GaAs substrates critically affects the final low-noise microwave device and circuit performance as evidenced by comparing Si-implanted undoped, In-alloyed, and whale-ingot annealed semi-insulating substrates. We investigated differences in Si implant activation, electrical profiles, and uniformity of material, device, and circuit parameters. The best noise figure of 1.33 dB at 10 GHz was measured on a 0.5-µm low-noise FET fabricated on a high-pressure whole-ingot annealed LEC wafer. A noise figure of 2.0 dB with associated gain of 24 dB at 10 GHz was achieved for a monolithic two-stage low-noise amplifier fabricated on the standard high-pressure LEC substrate.     

New Technology Towards GaAs LSI/VLSI for Computer Applications

For future large-scale computer applications, new device technologies towards GaAs LSI/VLSI have been developed self-aligned fully implanted planar GaAs MESFET technology and high electron mobility transistor (HFMT) technology by molecular beam epitaxy (MBE). The self-aligned GaAs MESFET logic with 1.5-µm gate length exhibits a minimum switching time of 50 ps and the lowest power-delay product of 14.5 fJ at room temperature. The enhancement/depletion (E/D) type direct coupled HEMT logic has achieved a switching time of 17.1 ps with 1.7-µm gate length at liquid nitrogen temperature and more recently a switching time of 12.8 ps with 1.1-µm gate HEMT logic, which exceeds the top speed of Josephson Junction logic and shows the highest speed of any device logic ever reported. Optimized system performances are also projected to system delay of 200 ps at 10-kilogate integration with GaAs MESFET VLSI, and 100 ps at 100-kilogate with HEMT VLSI. These values of system delay correspond to the computer performance of over 100 million instructions per second (MIPS).     

0.1-µm Gate-length pseudomorphic HEMT's

AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistors (HEMT's) with a gate length of 0.1 µm have been successfully fabricated. The HEMT's exhibit a maximum transconductance of 540 mS/mm with excellent pinch-off characteristics. A maximum stable gain (MSG) as high as 18.2 dB was measured at 18 GHz. At 60 GHz the device has demonstrated a minimum noise figure of 2.4 dB with an associated gain of ∼6 dB. These are the best gain and noise results reported to date for HEMT's.     

Whole-ingot annealed semi-insulating GaAs substrates for low-noise microwave amplifiers

The quality of liquid-encapsulated Czochralski (LEC) grown GaAs substrates critically affects the final low-noise microwave device and circuit performance as evidenced by comparing Si-implanted undoped, In-alloyed, and whole-ingot annealed semi-insulating substrates. We investigated differences in Si-implant activation, electrical profiles, and uniformity of material, device, and circuit parameters. The best noise figure of 1.33 dB at 10 GHz was measured on a 0.5-µm low-noise FET fabricated on the high-pressure whole-ingot annealed LEC wafer. A noise figure of 2.0 dB with associated gain of 24 dB at 10 GHz was achieved for a monolithic two-stage low-noise amplifier (LNA) fabricated on the standard high-pressure LEC substrate.     

Very low-noise HEMTs using a 0.2?m T-gate

A very low-noise, high-electron-mobility transistor has been fabricated using a 0.2 ?m T-shaped gate. At 12 GHz, a noise figure of 0.61 dB with an associated gain of 12.58dB has recently been measured. This is the lowest noise figure ever reported for an HEMT at this frequency