E.A. Sovero

Heterojunction Bipolar Transistors for Microwave and Millimeter-Wave Integrated Circuits

This paper reviews the present status of GaAIAs/ GaAs HBT technology and projects the impact of these devices on microwave and millimeter-wave integrated circuits. Devices with f/sub max/ above 100 GHz are described. Differential amplifiers are shown to have offset voltages with standard deviation below 2 mV and voltage gain of 200 per stage. Breakdown voltages (BV/sub CBO/) above 20 V are demonstrated. Frequency dividers operating above 20 GHz are described.

Ultrahigh power efficiency operation of common-emitter and common-base HBT's at 10 GHz

The DC and RF characteristics of microwave power HBTs are described. Ultrahigh power-added efficiency is reported for AlGaAs-GaAs HBTs operating at 10 GHz in common-emitter (CE) and common-base (CB) modes. A record high 67.8% power-added efficiency with 11.6 dB associated gain was achieved with a CE HBT at a CW output power of 0.226 W, corresponding to a power density of 5.6 W/mm. With a CB HBT, 62.3% power-added efficiency with 11.85 dB gain and 0.385 W total CW power was demonstrated. Power saturation characteristics of CE and CB HBTs are compared. The importance of bias schemes is discussed. High-efficiency operation in near class B mode is described and compared with FET operation. An advantage of HBT over FET is the low leakage current during the off half cycle in class B operation. Stability conditions for CE and CB HBTs are discussed. >

High power GaAlAs/GaAs HBTs for microwave applications

This paper reports the attainment of high microwave output, up to 0.4 W cw at 10 GHz, with GaAlAs/ GaAs heterojunction bipolar transistors. In addition to high power, the HBTs displayed excellent power-added efficiency (4896) and power gain (7 dB). A key factor in obtaining these high powers and efficiencies is the ability to support high collector-emitter voltages without breakdown. Breakdown voltage was up to 23 V (BVcbo) in the devices reported here. The experimental data are in good agreement with a theoretical model of I-V characteristics near breakdown. The cutoff frequency ftwas found to vary with Vceas expected for electron-drift at a saturation veloclty of 1 × 107cm/s across the base-collector depletion region.

Monolithic GaAs PHEMT MMICs integrated with high performance MEMS microrelays

We report the successful integration of MEMS microrelays with PHEMT MMIC in a single monolithic structure. The process we describe here allows us to build MEMS microrelays along GaAs PHEMT devices without any sacrifice in performance or yield to either device. The test structure used the switches to activate one of two X-band LNAs. The switches have an insertion loss of less than 0.3 dB up to 50 GHz while the LNAs have a gain of 20 dB and 1.1 dB NF at 9 GHz.

A Ka-band monolithic quasi-optic amplifier

Recent advances in the development of a Ka-band quasi-optic amplifier are reported. The amplifier consists of a two-dimensional array of PHEMT power amplifiers, each of which is coupled to individual input and output slot antennas. The array of 112 amplifiers (49 mm total gate periphery) is organized into pairs operating in push-pull between a 7/spl times/8 array of input slots and an 8/spl times/8 array of orthogonal output slots. The total chip size is 12.8 mm by 13.4 mm and has a thickness of 75 /spl mu/m. It is fabricated with standard MMIC processing techniques. The amplifier provided gain from 37.5 GHz to 39.5 GHz with a peak gain approaching 9 dB at 38.6 GHz. The maximum measured output power is 29 dBm.

High-performance Ka-band monolithic low-noise amplifiers using 0.2-/spl mu/m dry-recessed GaAs PHEMTs

Ka-band ultra-low-noise amplifiers fabricated with a manufacturable dry-recess process are presented. Low-damage selective dry etching was used for gate recess to achieve uniform threshold voltage (Vth) and saturation current (I/sub dss/). Threefold improvement in Vth uniformity was achieved in comparison with the wet recess process. Fabricated PHEMT low-noise amplifiers (LNAs) employing 0.2-/spl mu/m mushroom gates showed an average noise figure of 2.2 dB from 31-36 GHz with an associated gain of 22.5 dB. At the design frequency of 35 GHz, the noise figure was less than 2 dB. This is among the best results ever reported for Ka-band LNAs.

Fast thin film vanadium dioxide microwave switches

A new concept in microwave and millimeter-wave switching structures is demonstrated. The switch is built on a GaAs substrate and is compatible with IC technology. The approach used to implement the concept is to place a variable-resistance element spanning a very short gap (compared to the width of the line) on a metal transmission line. Switching the gap material from the high resistance state to the low resistance state turns the line from an open circuit to the connected state. The topics discussed include the material system used, a specific demonstration of a microwave switch using this system, possible applications of the switch, and its present limitations and how they could be overcome. A switch is built which at 40 GHz has an insertion loss of less than 1 dB in the on-state and more than 12 dB in the off-state. Switching time is under 30 ns.<<ETX>>

44-GHz monolithic plane-wave amplifiers

A Plane Wave Amplifier is an array of small power amplifiers that accept input signals via input antennas and radiate amplified output signals from an output antenna. Such array amplifiers promise a method of efficient power at EHF. This concept has been experimentally explored in the 40-50 GHz band and gain over acceptable bandwidths has been measured. >

A millimeter-wave multifunction HEMT mixer

A monolithic chip with a single 80 μm HEMT device, 1.25×3.0 mm2 in size, has been tested as both a fundamental and a subharmonic mixer. With input filter networks for K- and Q-bands providing two separate radio frequency/local oscillator (RF/LO) channels to the gate, the chip produces an IF signal from DC to 4 GHz at the drain. The mixer operates in three independent modes with the highest conversion gain of 6.9 dB in K-band fundamental mode, the best DSB noise figure of 4.4 dB in Q-band fundamental mode, and better than 20 dB of on-chip LO-to-RF isolation in Q-band subharmonic mode. In all three modes, the active mixer has shown positive conversion gain.

High power efficiency X-band GaAlAs/GaAs HBT

Excellent power performance from a common-emitter GaAlAs/GaAs HBT (heterojunction bipolar transistor) at 10 GHz is reported. Record high added efficiency of 67.8% and 11.6-dB associated gain were obtained, with 0.226-W output power. HBTs of various sizes were tested, and 55% added efficiency and 10-dB associated gain were obtained regularly. From the largest available device 0.63 W with 8-dB gain was obtained. The base current crowding effect does not appear in the HBTs tested. The operation of the HBT is analyzed and shown to be close to that of the class-B amplifier. The collector-current behavior with respect to the power level is explained. Harmonic content is found to be very low. Compared with other solid-state power devices at 10 GHz the HBT demonstrates the highest added efficiency and associated gain at high-output-power condition. In addition, the low HBT input Q factor eases broadband matching, making it the best candidate for microwave power application.<<ETX>>