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.     

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.     

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.     

Low-noise HEMT fabricated by MOCVD

Low-noise HEMTs with GaAlAs/GaAs heterostructures have been successfully fabricated using metal organic chemical vapour deposition (MOCVD). Hall mobilities of the two-dimensional electron gas at the interface are 8000 and 148 000 cm2/Vs at 300 and 77 K. These are comparable to the best results yet reported using molecular beam epitaxy (MBE). The HEMTs fabricated by MOCVD with a 0.8 ?m-long gate have exhibited a noise figure of 1.47 dB with 9 dB associated gain at 12 GHz and transconductance of 190 mS/mm.     

Ultra low noise characteristics of AlGaAs/InGaAs/GaAs pseudomorphicHEMT's with wide head T-shaped gate

The fully passivated low noise AlGaAs/InGaAs/GaAs pseudomorphic (PM) HEMT with 0.13 μm T-shaped gate was fabricated using dose split electron beam lithography method (DSM). This device exhibited low noise figures of 0.31 and 0.45 dB at 12 and 18 GHz, respectively. These noise figures are the lowest value ever reported for the GaAs based HEMT's. These results are attributed to the extremely low gate resistance which results from wide head T-shaped gate having the higher ratio more than 10 of gate head length to gate footprint     

0.2 Micron length T-shaped gate fabrication using angle evaporation

A new technique has been developed to generate sub-half-micron T-shaped gates in GaAs MESFET's. The technique uses a single-level resist and an angle evaporation process. By using this technique, T-shaped gates with lengths as short as 0.2 µm near the Schottky interface have been fabricated. Measured gate resistance from this structure was 6.1 Ω/mm gate width which is the lowest value ever reported for gates of equal length. GaAs single- and dual-gate MESFET's with 0.3 µm long T-shaped gates have also been fabricated. At 18 GHz, maximum available gain of 9.5 dB in the single-gate FET and maximum stable gain of 19.5 dB in the dual-gate device have been measured.     

First successful fabrication of high-performance all-refractory-metal (Ta-Au) GaAs FET using very highly doped N+-layers and nonalloyed ohmic contacts

An all-refractory-metal GaAs MESFET (ARFET) making use of a Ta Schottky barrier with a thick gold overlayer for the source, gate and drain, and very highly doped N+-layers (2x1019 cm-3) to achieve low-resistivity nonalloyed ohmic contacts, has been successfully fabricated. These have a 400 ?m gate periphery and 0.6 ?m gate length and measured an associated gain of 10.22 dB and a noise figure of 2.14 dB at 8 GHz. The ARFETs were fabricated on epitaxial layers grown by MBE. Only one mask was used to simultaneously define source, gate and drain regions via a plasma dry-etch technique.     

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).     

A novel camel diode gate GaAs FET

A novel device utilizing the "camel diode" in place of a Schottky barrier gate has been demonstrated in GaAs grown by molecular beam epitaxy (MBE). The devices have a 7.5 µm channel length, 3 µm gate length, and a 280 µm gate width. The layers from which the devices are fabricated consist of a 0.15 µm GaAs layer doped to a level of 1.5 × 10¹⁷cm^-3to form the channel, and a 100 Å p+GaAs and a 400 Å n+ region to form the gate. Because of the long gate length, the electron velocity does not reach saturation, thus a transconductance of 80 mS/mm is obtained. A simple theory describing the device operation has also been developed.     

A study of high-speed normally off and normally on Al0.5Ga0.5As heterojunction gate GaAs FET's (HJFET)

The dc, small-signal microwave, and large-signal switching performance of normally off and normally on Al0.5Ga0.5As gate heterojunction GaAs field-effect transistors (HJFET) with submicrometer gate lengths are reported. The structure of both types of devices comprises an n-type 10¹⁷-cm^-3Sn-doped active layer on a Cr-doped GaAs substrate, a p-type 10¹⁸-cm^-3Ge-doped Al0.5Ga0.5As gate layer and a p⁺-type 5 × 10¹⁸-cm^-3Ge-doped GaAs "contact and cap" layer on the top of the gate. The gate structure is obtained by selectively etching the p⁺-type GaAs and Al0.5Ga0.5As. Undercutting of the Al0.5Ga0.5As layer results in submicrometer gate lengths, and the resulting p⁺-GaAs overhang is used to self-align the source and the drain with respect to the gate. Normally off GaAs FET's with 0.5- to 0.7-µm long heterojunction gates exhibit maximum available power gains (MAG) of about 9 dB at 2 GHz. Large-signal pulse measurements indicate an intrinsic propagation delay of 40 ps with an arbitrarily chosen 100-Ω drain load resistance in a 50-Ω microstrip circuit. Normally on FET's with submicrometer gate lengths (∼0.6 µm) having a total gate periphery of 300 µm and a corresponding dc transconductance of 20-30 mmhos exhibit a MAG of 9.5 dB at 8 GHz. The internal propagation delay time measured under the same conditions as above is about 20 ps.     

Performance of power FET's fabricated on MBE-Grown GaAs layers

Power GaAs FET's of various sizes have been fabricated using MBE material containing a 1 µm-thick semi-insulating buffer layer. These devices, when operated between 6 and 12 GHz, exhibited state-of-the-art microwave performance. For example, the 3 mm devices gave an output power of 1.5 W with 10.9 dB associated gain at 6.4 GHz, a power-added efficiency of 42.6% with 1.4 W output power and 6.4 dB associated gain at 8 GHz. The results confirm the capability of MBE for producing high quality material with a sharp active layer/buffer interface.     

High performance ion-implanted low noise GaAs MESFET's

Low noise GaAs MESFET's fabricated by ion-implanting into AsCl3VPE buffer layers have demonstrated not only excellent dc and RF performance, but also a highly reproducible process. The average noise figure and associated gain of four device lots at 12 GHz are 1.6 dB and 10.0 dB, respectively. The standard deviation of noise figure and associated gain from device lot to lot are 0.03 dB and 0.19 dB, respectively. And the standard deviation of noise figure and associated gain from device to device for 35 devices over four lots are 0.13 dB and 0.47dB, respectively. The best device performance includes a 1.25 dB noise figure with 10.46 dB associated gain at 12 GHz for a 0.5 µm × 300 µm FET structure. These results demonstrate the excellent performance and process consistency of ion implanted MESFET's.     

InGaAs／GaAs异质结构材料及器件应用

概述了ＩｎＧａＡｓ／ＧａＡｓ异质结构材料用于制作微波器件的优越性，叙述了材料的ＭＢＥ生长、输运特性和掺杂分布，以及用于制作Ｋｕ波段低噪声高增益ＨＦＥＴ的结果：栅长０．５μｍ，１２ＧＨｚ下噪声系数０．９３ｄＢ，相关增益９ｄＢ。     

Highly selective reactive ion etching applied to the fabrication of low-noise AlGaAs GaAs FET's

Selective dry etching of GaAs to AlGaAs (x = 0.25) using pure CCl2F2etching gas has been achieved. During reactive ion etching (RIE), the discharge has been analyzed by optical emission and mass spectroscopy. A high-selectivity ratio up to 1000, associated with a clean and anisotropic etching or an undercut of GaAs can be obtained by adjustment of the pressure. Selective RIE has been used to etch the n⁺GaAs cap layer of an n⁺GaAs/AlGaAs/GaAs heterostructure and to define the gate recess of discrete two-dimensional electron-gas FET's (TEGFET's). Results on low-noise TEGFET's fabricated by this technique are reported for the first time. Thanks to the reduction of side etching, very low source resistances have been obtained (less than 1 Ω . mm) for a source-to-gate distance up to 2 µm. Noise figures of 2 dB have been measured at 12 GHz with an associated gain of 8.3 dB for a gate length of 0.7 µm.     

Half-micrometer gate-length ion-implanted GaAs MESFET with 0.8-dBnoise figure at 16 GHz

Ion-implanted GaAs MESFETs with half-micrometer gate length have been fabricated on 3-in-diameter GaAs substrates. At 16 GHz, a minimum noise figure of 0.8 dB with an associated gain of 6.3 dB has been measured. This noise figure is believed to be the lowest ever reported for 0.5- and 0.25-μm ion-implanted MESFETs, and is comparable to that for 0.25-μm HEMTs at this frequency. By using the Fukui equation and the fitted equivalent circuit model, a K_f factor of 1.4 has been obtained. These results clearly demonstrate the potential of ion-implanted MESFET technology for K-band low-noise integrated circuit applications     

Low-noise HEMT using MOCVD

Low-noise HEMT AlGaAs/GaAs heterostructure devices have been developed using metal organic chemical vapor deposition (MOCVD). The HEMT's with 0.5-µm-long and 200-µm-wide gates have shown a minimum noise figure of 0.83 dB with an associated gain of 12.5 dB at 12 GHz at room temperature. Measurements have confirmed calculations on the effect of the number of gate bonding pads On the noise figure for different gate Widths. Substantial noise figure improvement was observed Under low-temperature operation, especially compared to conventional GaAs MESFET's. A two-stage amplifier designed for DBS reception using the HEMT in the first stage has displayed a noise figure under 2.0 dB from 11.7 to 12.2 GHz.     

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.     

Noise figure characteristics of 1/2-µm gate single-heterojunction high-electron-mobility FET's at 35 GHz

In this letter, we report room-temperature noise figure performance of Gallium Arsenide single-heterojunction high-electron-mobility transistors (HEMT's). We have measured a noise figure of 2 dB at 35 GHz with 5 dB of associated gain. The devices tested were 150 µm wide with 0.5-µm-long gates. The active layers were grown by molecular beam epitaxy (MBE). These values are the best reported results for either HEMT's or MESFET's at these frequencies, regardless of their geometry.     

Ka-band monolithic amplifier using 0.5 mu m gate length ion-implanted GaAs/AlGaAs heterojunction FET technology

Monolithic, two-stage amplifiers using 0.5*80 mu m/sup 2/ gate GaAs/AlGaAs heterojunction FETs have been developed for Ka-band operation. These monolithic two-stage amplifiers were fabricated using ion implantation for the active layer and optical lithography for the 0.5 mu m gate length. MMIC two-stage amplifiers achieved average gains of 12.6+or-1.4 dB at 30 GHz and 8.8+or-2.0 dB at 40 GHz, respectively, for all 39 sites across a three inch diameter wafer. These are the first reported results for MMIC two-stage amplifiers using 0.5 mu m gate length ion-implanted GaAs/AlGaAs heterojunction FETs achieving over 10 dB gain at Ka band.<>     

Low-Noise MESFET's for Ion-Implanted GaAs MMIC's

Fabrication considerations for low-noise FET's in ion-implanted GaAs monolithic microwave integrated circuits (MMIC'S) are presented. Processes that can deteriorate FET performance have been identified and some solutions proposed. Low-noise MMIC FET's fabricated along these lines show good microwave performance tbrongh 18 GHz, approaching the performance available from similar discrete FET's. 0.8- µm gate-length MMIC FET's with a noise figure of 2.9 dB and associated gain of 6.1 dB at 18 GHz have been fabricated. These devices are suitable for low-noise applications in ion-implanted GaAs MMIC's.