H.D. Shih

Microwave power GaAs MISFET's with undoped AlGaAs as an insulator

A metal-insulator-semiconductor field-effect transistor using an undoped AlGaAs layer as an insulator has been fabricated and RF tested. Due to the higher breakdown field of the wide-band-gap AlGaAs, the gate breakdown voltage has been greatly improved as compared with a conventional GaAs MESFET. The prebreakdown gate leakage current of this new device structure is also much lower than that of the MESFET. The presence of the gate insulator also reduces the gate capacitance. All these factors result in a GaAs power FET structure with potentials for high power, efficiency, and frequency of operation. An unoptimized 750-µm gate-width device achieved an output power of 630 mW with 7-dB gain and 37-percent power-added efficiency at 10 GHz. At reduced output power levels, power-added efficiency as high as 46-percent was obtained at X-band.

Millimeter Wave Monolithic GaAs Power FET Amplifiers

Millimeter-wave monolithic GaAs power FETs with total gate widths of up to 400 pm and output powers up to 200 mW have been developed. These amplifiers were fabricated using sub-half-micrometer gate length FETs on MBE-grown epitaxial layers with n+ contact layers. A source overlay structure with via groundings has been used for the FET design. Power densities of 0.53 W/mm, 0.45 W/mm, and 0.25 W/mm were obtained at 34 GHz, 41 GHz, 54 GHz, respectively. Power-added efficiency of 33% was obtained at 35 GHz with 0.53 W/mm power density.

Millimeter-wave GaAs power FET with a pulse-doped InGaAs channel

Performance of a GaAs power MESFET has been improved significantly by incorporating a pulse-doped InGaAs layer in the GaAs n-channel. InGaAs provides electron transport properties superior to those of GaAs. The doping level of the GaAs layer can be very high, making it a very-high-transconductance device. Moreover, the conduction-band discontinuity at the heterointerface acts as a potential barrier for electron confinement; therefore, the power gain of the FET is significantly improved. The resulting device delivered a power density of 0.6 W/mm with 14% power-added efficiency and 3.5-dB gain at 60 GHz. At a gain of 5.1 dB, power density was 0.4 W/mm.<<ETX>>

Ka-band monolithic GaAs FET power amplifier modules

Monolithic GaAs FET power amplifiers consisting of several power-combined devices are fabricated and evaluated. The baseline monolithic chip design consists of a single stage 400- mu m FET amplifier and a six-way traveling-wave power divider/combiner with a single-stage amplifier in each of the six arms. Several chip combinations were used to make a 1-W amplifier with 5-dB gain and a 0.55-W amplifier with 27-dB gain at 34 GHz. A two-way hybrid combining scheme making use of 0.6-W monolithic chips producing 1 W of output power is also described.<<ETX>>

A high efficiency Ka-band monolithic GaAs FET amplifier

A monolithic three-stage Ka-band GaAs FET power amplifier has been designed and fabricated on MBE (molecular-beam epitaxy)-grown material with a highly doped (8*10/sup 17/ cm/sup -3/) channel. Devices with gate length of 0.25 mu m and gate width of 50 mu m, 100 mu m, and 250 mu m were cascaded. The gate and drain bias networks were also integrated. A maximum small-signal gain of 26 dB was obtained with 4 V on the drain and 0 V on the gate. When biased for large-signal operation, the amplifier was capable of generating 112 mW output power with 16-dB gain and 21.6% power-added efficiency at 34 GHz. It is believed that this is a record efficiency for a GaAs MMIC (microwave monolithic integrated circuit) amplifier at this frequency.<<ETX>>

GaAs power MESFET with 41-percent power-added efficiency at 35 GHz

A GaAs power MESFET has been optimized for Ka-Band operation. The device has an n/sup +/ ledge channel structure with a 0.25- mu m gate on MBE-grown material. An output power density of 0.71 W/mm was achieved with 5.2-dB gain and 34% power-added efficiency. When tuned for maximum efficiency, a power-added efficiency of 41% was obtained with a power density of 0.61 W/mm and a gain of 5.6 dB.<<ETX>>

Millimeter-wave GaAs FET's prepared by MBE

GaAs MESFETs suitable for operation in the millimeter-wave frequency range have been developed. These devices feature electron-beam-defined sub-half-micrometer gates with MBE grown materials. With an active-layer doping of 6 × 1017/cm3, an extrinsic transconductance of 330 mS/mm was obtained. A 75-µm gate-width device has achieved a gain of 13, 9.5, and 6.5 dB at 35, 44, and 60 GHz, respectively.

44-GHz monolithic GaAs FET amplifier

Millimeter-wave monolithic GaAs FET amplifiers have been developed. These amplifiers were fabricated using FETs with MBE-grown active layers and electron-beam defined sub-half-micrometer gates. Source groundings are provided through very low inductance via holes. The single-stage amplifier has achieved over a 10-dB gain at 44 GHz. A 300-µm gate-width amplifier has achieved an output power of 60 mW with a power density of 0.2 W per millimeter of gate width.

High Power Distributed Amplifier Using MBE Synthesized Material

The main limitations of the output power of a distributed amplifier are the gate line loss and the gate-to-drain breakdown voltage. A novel circuit concept to reduce the gate loss using series capacitors on the gate feeding lines has been implemented. The device breakdown voltage has been improved by using an MBE grown material with two layers (low doped gate buffer layer and usual active layer). A monolithic GaAs distributed amplifier using 6 x 300 µm FETs has achieved an output power of 800 mW with 4dB gain. The power added efficiency was about 15%.

High-performance In/sub 0.08/Ga/sub 0.92/As MESFETs on GaAs

In/sub 0.08/Ga/sub 0.92/As MESFETs were grown in GaAs