D.K. Umemoto

GaAs heterojunction bipolar transistor device and IC technology for high-performance analog and microwave applications

GaAs-AlGaAs n-p-n heterojunction bipolar transistor (GaAs HBT) technology and its application to analog and microwave functions for high-performance military and commercial systems are discussed. In many applications the GaAs HBT offers key advantages over the alternative advanced silicon bipolar and III-V compound field-effect-transistor (FET) approaches. TRWs GaAs HBT device and IC fabrication process, basic HBT DC and RF performance, examples of applications, and technology qualification work are presented and serve as a basis for addressing general capability issues. A related 3- mu m emitter-up, self-aligned HBT IC process provides excellent DC and RF performance, with simultaneous gain-bandwidth product, f/sub T/, and maximum frequency of oscillation, f/sub max/, of approximately 20-40 GHz and DC current gain beta approximately=50-100 at useful collector current densities approximately=3-10 kA/cm/sup 2/, early voltage approximately=500-1000 V, and MSI-LSI integration levels. These capabilities facilitate versatile DC-20-GHz analog/microwave as well as 3-6 Gb/s digital applications, 2-3 G sample/s A/D conversion, and single-chip multifunctions with producibility. >

High-reliability GaAs-AlGaAs HBTs by MBE with Be base doping and InGaAs emitter contacts

The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5*10/sup 8/ h at 125 degrees C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology.<<ETX>>

Monolithic HEMT-HBT integration by selective MBE

We have achieved successful monolithic integration of high electron mobility transistors and heterojunction bipolar transistors in the same microwave circuit. We have used selective molecular beam epitaxy and a novel merged processing technology to fabricate monolithic microwave integrated circuits that incorporate both 0.2 /spl mu/m gate-length pseudomorphic InGaAs-GaAs HEMTs and 2 /spl mu/m emitter-width GaAs-AlGaAs HBTs. The HEMT and HBT devices produced by selective MBE and fabricated using our merged HEMT-HBT process exhibited performance equivalent to devices fabricated using normal MBE and our baseline single-technology processes. The selective MBE process yielded 0.2 /spl mu/m HEMT devices with g/sub m/=600 mS/mm and f/sub T/=70 GHz, while 2/spl times/10 /spl mu/m/sup 2/ HBT devices achieved /spl beta/>50 and f/sub T/=21.4 GHz at J/sub c/=2/spl times/10/sup 4/ A/cm/sup 2/. The performance of both a 5-10 GHz HEMT LNA with active on-chip HBT regulation and a 20 GHz Darlington HBT amplifier are shown to be equivalent whether fabricated using normal or selective MBE. >

Monolithic GaAs HBT p-i-n diode variable gain amplifiers, attenuators, and switches

The authors report on monolithic circuits integrating HBTs and p-i-n diode using a common HBT MBE structure. An HBT variable gain amplifier using p-i-n diode as a variable resistor achieved a gain of 14.6 dB, a bandwidth out to 9 GHz, a gain control range of >15 dB, and an IP3 of 28 dBm. A two-stage HBT p-i-n diode attenuator from 1-10 GHz and an X-band one-pole two-throw HBT p-i-n diode switch were also demonstrated. The two-stage p-i-n attenuator has over 50 dB dynamic range at 2 GHz and a maximum IP3 of 9 dBm. The minimum insertion loss is 1.7 dB per stage and has a flat response to 10 GHz. The X-band switch has an insertion loss of 0.82 dB and an off-isolation of 25 dB. The bandwidth is greater than 35% and the IP3 is greater than 34.5 dBm. These circuits consist of p-i-n diodes constructed from the base-collector MBE layers of a baseline HBT process. This is the first monolithic integration of p-i-n diode switch, variable gain control, and attenuation functions in an HBT technology without additional processing steps or MBE material growth. >

Reliability analysis of GaAs/AlGaAs HBTs under forward current/temperature stress

The reliability of GaAs/AlGaAs heterojunction bipolar transistors is investigated by accelerated life-testing of discrete devices under forward bias stress at elevated temperatures. The DC device characteristics are monitored to evaluate the effect of bias/temperature stress on a large number of devices fabricated on MBE (molecular beam epitaxy) grown material. The primary degradation observed in some devices is a reduction in the current gain which appears to be due to an electric field-aided diffusion of interstitial Be from the base into the base-emitter graded region. Other devices with optimal epitaxial material show stable current gain after DC bias stress at high temperature. Ohmic contact degradation, with or without bias, is also observed at the emitter contact, resulting in an increased emitter series resistance.<<ETX>>

GaAs HBT wideband matrix distributed and Darlington feedback amplifiers to 24 GHz

The designs and performances of a 2-24 GHz distributed matrix amplifier and 1-20 GHz 2-stage Darlington coupled amplifier based on an advanced HBT MBE profile that increases the bandwidth response of the distributed and Darlington amplifiers by providing lower base-emitter and collector-base capacitances are presented. The matrix amplifier has a 9.5 dB nominal gain and a 3-dB bandwidth to 24 GHz. This result benchmarks the highest bandwidth reported for an HBT distributed amplifier. The input and output VSWRs are less than 1.5:1 and 2.0:1, respectively. The total power consumed is less than 60 mW. The chip size measures 2.5*2.6 mm/sup 2/. The 2-stage Darlington amplifier has 7 dB gain and 3-dB bandwidth beyond 20 GHz. The input and output VSWRs are less than 1.5:1 and 2.3:1, respectively. This amplifier consumes 380 mW of power and has a chip size of 1.66*1.05 mm/sup 2/. >

High-linearity, low DC power monolithic GaAs HBT broadband amplifiers to 11 GHz

Two broadband monolithic amplifiers based on GaAs heterojunction bipolar transistors (HBT) have been developed covering the 0.05-11-GHz frequency band. The hybrid designs reported by B.L. Nelson et al. (1989 IEEE GaAs IC Symp. Digest, Oct. 1989, p.79-82) have been successfully implemented with monolithic microwave IC (MMIC) technology. These amplifiers are the first reported balanced and distributed MMIC HBT amplifiers and represent a significant improvement over MESFET and HEMT approaches in high-linearity, low-DC-power performance for communication and electronic warfare applications. A 5-11-GHz MMIC balanced amplifier designed for high linearity produces +33-dBm third-order output intercept point (IP3) with 7.5-dB associated gain and less than 160-mW DC-power consumption. A 0.05-9-GHz distributed amplifier designed for low DC power and high gain consumes less than 50-mW and provides 6-10-dB gain at nominal bias. Device fabrication and characteristics are described.<<ETX>>

GaAs HBT 0.75-5 GHz multifunctional microwave-analog variable gain amplifier

We report on a GaAs HBT 3-stage variable gain amplifier operating over a 0.75-5 GHz frequency band. The amplifier is broken up into a single-ended HBT LNA pre-amplifier, an analog current steering differential cascode cell for variable gain control, and a differential amplifier output stage. The broadband pre-amplifier is required to reduce the inherently noisy differential cascode stage, and an output differential amplifier is used to provide output drive capability and differential to single-ended conversion. The VGA has a maximum gain of 23.8 dB gain, an IP3>18 dBm, and a noise figure of 6.5 dB. The variable gain control range is >35 dB. This chip demonstrates the versatility of HBT IC technology which can integrate digital, analog, and microwave circuit functions to achieve high performance in a single monolithic chip. >

Integrated complementary HBT microwave push-pull and Darlington amplifiers with p-n-p active loads

The authors report the microwave results of complementary heterojunction bipolar transistor (HBT) amplifiers that integrate both n-p-n and p-n-p devices on the same chip using selective molecular beam epitaxy (MBE). An HBT wideband amplifier utilizing the Darlington configuration and implementing a p-n-p active load has a gain of 7.5 dB and a bandwidth from DC to 2.5 GHz. A complementary push-pull amplifier has a saturated output power of 7.5 dBm at 2.5 GHz. >

GaAs heterojunction bipolar transistor MMIC DC to 10 GHz direct-coupled feedback amplifier

A DC-to-10-GHz fixed-gain amplifier implemented with a GaAs heterojunction bipolar transistor (HBT) monolithic microwave integrated circuit (MMIC) technology is described. The wideband amplifier design is based on Darlington-connected transistors with resistive feedback. A 3- mu m-emitter self-aligned-base ohmic metal HBT IC process (f/sub max/ approximately=30-40 GHz) with a simplified MBE growth structure is used to fabricate the amplifier. The feedback amplifier exhibits a flat 11-dB gain response to 6 GHz with a -3-dB roll-off at 10 GHz, 5-6-dB noise figure over the 10-GHz band, and 1-dB power compression of 11 dBm at midband. Compared to similar 0.5- mu m-gate GaAs MESFET wideband amplifiers, the HBTs third-order intercept point (IP3)/DC power ratio is two times greater and the chip size seven times smaller. Compared to similar advanced silicon bipolar and previously reported HBT direct-coupled amplifier designs, the GaAs HBT amplifier reported has twice the bandwidth.<<ETX>>