K. Kamei

Growth of high-purity GaAs epilayers by MOCVD and their applications to microwave MESFET's

Abstract In an attempt to obtain high-purity GaAs epilayers for microwave device applications by a (CH3)3Ga/AsH3 MOCVD technique, effects of starting materials quality and growth parameters were investigated. It was found that the epilayer quality is mainly limited by the (CH3)3Ga purity. Analyses using flameless atomic absorption spectrophotometry showed that the (CH3)3Ga sources contained a large amount of Si as compared with other metallic impurities. By using refined (CH3)3Ga with reduced impurity contents and by optimizing growth conditions, a layer with an electron mobility at 77 K of 139,000 cm2/V · s at an electron concentration of 3.7 × 1014/cm3 was obtained. For low-noise MESFET applications, n- − n − n+ epilayers were grown successively on semi-insulating GaAs substrates. Improvement of the layer purity has made it possible to grow n- buffer layers thick enough to avoid substrate effects. Al gate MESFETs fabricated with gate dimensions of 0.5 μm × 300 μm showed a noise figure of 2.0 dB with an associated gain of 8.2 dB, and a maximum optimized gain of 12 dB at 12 GHz.

GaAs Monolithic MIC's for Direct Broadcast Satellite Receivers

A 12-GHz low-noise amplifier (LNA), a 1-GHz IF amplifier (IFA), and an 11-GHz dielectric resonator oscillator (DRO) have been developed for DBS home receiver applications by using GaAs monolithic microwave integrated circuit (MMIC) technology. Each MMIC chip contains FETs as active elements and self-biasing source resistors and bypass capacitors for a single power supply operation. It also contains dc-block and RF-bypass capacitors. The three-stage LNA exhibits a 3.4-dB noise figure and a 19.5-dB gain over 11.7-12.2 GHz. The negative-feedback-type three-stage IFA shows a 3.9-dB noise figure and a 23-dB gain over 0.5-1.5 GHz. The DRO gives 10-mW output power at 10.67 GHz, with a frequency stability of 1.5 MHz over a temperature range from -40-80° C. A direct broadcast satellite (DBS) receiver incorporating these MMICs exhibits an overall noise figure of ≤ 4.0 dB for frequencies from 11.7-12.2 GHz.

Super low noise AlGaAs/GaAs HEMT with one tenth micron gate

Low-noise AlGaAs/GaAs HEMTs (high-electron-mobility transistors) with a 0.1- mu m gate length have been developed. State-of-the-art low noise figures of 0.51 dB and 1.9 dB were obtained at 18 GHz and 40 GHz at room temperature, with associated gains of 10.8 dB and 5.3 dB, respectively. This performance has been achieved by shortening the gate length to 0.1 mu m and also by lowering the gate resistance drastically with a T-shaped gate structure. The effects of gate length and gate resistance on microwave performance are experimentally shown.<<ETX>>

Broadband HEMT and GaAs FET Amplifiers for 18 - 26.5 GHz

Two types of broadband amplifiers operating over 18 to 26.5 GHz have been developed by using newly developed 0.4-µm gate HEMTs and conventional 0.25-µm gate GaAs FETs. The four-stage EEMT amplifier exhibits a noise figure of <= 7.2 d.B and a gain of 19.3 +- 1.8 dB and the five-stage GaAs FET amplifier exhibits a noise figure of <= 12 dB and a gain of 22.7 +- 2.2 dB over 18 to 26.5 GHz. The minimum noise figures in the measured frequency ranqe are 5.0 dB and 7.5 dB for the HEMT and GaAs FET amplifiers, respectively. No essential difference is found between the amplifiers in input/output VSWR, output power and temperature variation of noise figure and gain.

Direct-Coupled GaAs Monolithic IC Amplifiers

A two-stage GaAs FET monolithic amplifier has been developed that exhibits a noise figure of 2dB and a gain of 20dB at frequencies from 0.3 to 1.5 GHz. The FET gate width is optimized to 1mm to lower the noise figure for a 50 Omega signal source impedance. A direct-coupled scheme is used for chip size reduction. All the circuit elements such as FETs, Schottky diodes and resistors are fabricated by using selective ion-implantation for realizing a planar structure.

20 GHz-Band Low-Noise HEMT Amplifier

A 20 GHz-band low-noise amplifier has been developed by using newly developed 0.25-µm gate HEMTs. The amplifier has been fabricated by cascading six single-ended unit amplifiers without any isolators at the interstages. The HEMT amplifier exhibits a noise temperature of 170 K (NF = 2.0 dB) and a gain of 47 dB over 17.5 to 19.5 GHz in an uncooled operation. Noise temperatures of 130 K (NF = 1.6 dB) and 110 K (NF = 1.4 dB) have been obtained at -20°C and -50°C, respectively.

Broadband HEMT Amplifier for 26.5 - 40.0 GHz

A broadband amplifier operating over 26.5 to 40 GHz has been developed by using 0.25-µm gate HEMTs. The amplifier has been fabricated by cascading five unit amplifiers. Two balanced-type unit amplifiers are used in an input and an output stages to realize good input/output VSWRs . Three single-ended unit amplifiers are installed in the intermediate stages to achieve higher gain. The developed amplifier shows a noise figure of <= 7.0 dB, a gain of 18.2 +- 1.6 dB and inputfoutput VSWRs of <= 2.0 over 26.5 to 40 GHz.

Ka-band 1 watt power GaAs MMICs

High-power and high-gain Ka-band GaAs monolithic microwave integrated circuits (MMICs) were developed using a Be coimplantation technique. At 29.5 GHz, an output power of 1 W with 4.2 dB gain was obtained for a 4.8-mm width MMIC. An intercept point of +42 dBm has been obtained from the third-order intermodulation distortion measurement.<<ETX>>

Quarter micron gate low noise GaAsFET's operable up to 30 GHz

Quarter micron gate low noise GaAs MESFETs have been developed by delineating gate electrodes with an electron beam lithography technique and by reducing parasitic source and gate resistances. At 18GHz, a noise figure of 1.9dB with an associated gain of 7dB and a maximum available gain of 11dB were obtained at drain currents of 10mA and 30mA, respectively. At 30GHz, a noise figure of 4dB with an associated gain of 5dB and a maximum available gain of 8dB were obtained. The measured noise figures are the best values reported so far, and this work has demonstrated the feasibility of utilizing GaAs MESFETs up to millimeter-wave regions.

GaAs low-noise MESFET prepared by metal-organic chemical vapor deposition

High performance GaAs MESFETs have been fabricated on epitaxial layers grown by MO-CVD (metal-organic chemical vapor deposition). At 8 GHz, a NF (noise figure) of 1.8 dB with an associated gain of 11 dB has been obtained for Al-gate MESFETs with gate dimensions of 0.5 × 300 µm. The NF at 8 GHz is lower by 1 dB than the previously reported results on MESFETs prepared by MO-CVD (1). The substantial improvement of the device performance is due to the first successful growth of thick enough buffer layer, together with an extremely sharp interface profile of electron concentration between a buffer and an active layers.