H.Q. Tserng

Millimeter-wave power operation of an AlGaAs/InGaAs/GaAs quantum well MISFET

The authors have developed state-of-the-art millimeter-wave power transistors using quantum-well MISFETs. MISFETs with both undoped InGaAs wells and doped InGaAs wells have been built. The f/sub t/ of the MISFETs with doped well was higher than that of MISFETs with undoped wells, indicating that the device speed does not degrade when the charge transport layer is doped. The power performance of the MISFETs with doped wells was far superior. The best device delivered a power density of 1.0 W/mm with 3.2-dB gain and 27% power-added efficiency at 60 GHz. >

AlGaAs/GaAs Heterojunction Bipolar Transistors with 4W/mm Power Density at X-Band

Fabrication and microwave characterization of X-band AIGaAs/GaAs heterojunction bipolar transistors are described. MBE was used to prepare the device structure with heavily doped (1x10/sup 19/cm/sup -3/) 1000A thick base layers. Two 2 µm x 10 µm emitter fingers separated by 2 µm (total emitter periphery of 40 µm) were used in a self-aligned emitter-base configuration. From the S-parameter measurements f/sub t/ and f/sub max/ values of 25 and 20 GHz respectively were determined. Devices operating under CW conditions produced 80 mW CW output power (2W/mm of emitter periphery) with 4 dB gain and 23% power added efficiency at 10 GHz. Under 0.25 µs pulses, 160 mW output power (4 W/mm) was obtained with 4 dB gain and 35% power added efficiency.

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.

Embedded transmission line (ETL) MMIC for low-cost, high-density wireless communication applications

A new embedded transmission line (ETL) MMIC approach which allows flexibility in mixing different transmission line types (i.e., coplanar and striplines) for maximum MMIC (Monolithic Microwave Integrated Circuits) design flexibility and permits the elimination of back-side processing for low production cost is described. This ETL MMIC approach is an enabling technology allowing for low-cost, batch fabrication, and high-density integration of microwave and RF components (including silicon mixed signal products) for emerging wireless communication applications.

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.

A low loss, 5.5 GHz-20 GHz monolithic balun

A low-loss monolithic Marchand balun has been designed and fabricated using polyimide as the inter-metal dielectric. The measured return loss is less than -10 dB from 5.5 GHz to 28 GHz. The balun loss is less than 0.7 dB over the 6 GHz to 21 GHz operating band. This is the lowest loss ever reported for such a balun. The excellent loss is the result of using a relatively thick polyimide layer (10 /spl mu/m) as the inter-metal dielectric. This balun has been applied to HBT and pHEMT amplifiers with second harmonic components suppressed >40 dB, even in compression, demonstrating very good push-pull operation.

A heterostructure FET with 75.8-percent power added efficiency at 10 GHz

The authors report the performance of a new AlGaAs/GaAs heterostructure FET (HFET) designed to have very high efficiency at the X-band with high drain bias. The combination of low doped AlGaAs under the gate and highly doped GaAs channel and superlattice buffer layers allows high gate-drain and source-drain breakdown voltage, constant transconductance, and moderate-to-high maximum channel current. These characteristics make the devices ideal for Class B and Class F operation. The 1200*0.25- mu m HFET devices have demonstrated a power-added efficiency (PAE) of 75.8% with 603 mW of output power and 8.8 dB of gain with a 9-V drain bias at 10 GHz. Other 1200*0.25- mu m HFET devices have demonstrated a 63.2% PAE with 8.3 dB of gain and 851 mW of output power with a 12-V drain bias. At 14 volts, 50% PAE was measured with 7.4-dB gain and 1.1 W of output power.<<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>>