M.E. Kim

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. >

12-40 GHz low harmonic distortion and phase noise performance of GaAs heterojunction bipolar transistors

GaAs-AlGaAs heterojunction bipolar transistors (HBTs) have been used to demonstrate the capability of low harmonic distortion with high efficiency and low-phase-noise performance in the 12-40-GHz frequency regime. A simplified 3- mu m emitter, self-aligned base metal HBT process is used to fabricate transistors with f/sub max/ approximately=30-50 GHz, high linearity, and low 1/f noise, yielding significantly improved third-order intermodulation product intercept point (IP3) and oscillator performance. The HBT IP3 ranges from 20-35 dBm for 12-20 GHz with a linearity figure-of-merit ratio, IP3(mW)/input DC power (mW), approximately=4 to 20 times higher than comparable HEMTs (high-electron-mobility transistors) and MESFETs at 12 to 37.7 GHz with -82 dBc/Hz phase noise at 100-kHz offset. It is concluded that these capabilities make HBTs attractive for high-IP3 amplifiers and mixers and low-phase-noise voltage-controlled oscillators in advanced receiver applications.<<ETX>>

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>>

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>>

Effects of neutron irradiation on GaAs/AlGaAs heterojunction bipolar transistors

The effects of neutron irradiation on 3- mu m-emitter, self-aligned-base, ohmic metal GaAs/AlGaAs heterojunction bipolar transistors and ICs based on molecular beam epitaxy have been experimentally and analytically investigated at fluence levels up to 1.3*10/sup 14/ n/cm/sup 2/. Devices with high DC current gain, beta , exhibited higher sensitivity to neutron irradiation than those with low beta . At 1.3*10/sup 14/ n/cm/sup 2/, DC beta was degraded by 25% for high- beta devices and by 7% for low- beta devices. Parasitic base current components such as the emitter edge recombination seem to be the key factor determining the neutron sensitivity. The functional dependence of beta on neutron fluence seems to follow the Messenger-Spratt relation, manifested by a linear increase of the base current with fluence. No deterioration was seen either in transistor RF characteristic or in digital circuit high-speed performance due to neutron irradiation up to a fluence of 1.3*10/sup 14/ n/cm/sup 2/. >

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>>

Picosecond optoelectronic measurement of S parameters and optical response of an AlGaAs/GaAs HBT

The S parameters of an AlGaAs/GaAs heterojunction bipolar transistor (HBT) are measured using a picosecond optoelectronic system. The measured S parameters show qualitatively good agreement with those obtained using a conventional vector network analyzer. The optical response of the HBT is also measured using this system by directly illuminating the base-collector region. Used as a phototransistors, the HBT shows pulse widths with full-width half-maximum (FWHM) as short at 15 ps. >

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

Two broadband hybrid amplifiers based on GaAs heterojunction bipolar transistors (HBTs) have been developed covering the 0.05-11-GHz frequency band. These amplifiers represent the first reported balanced and distributed HBT amplifiers and offer significant improvement over MESFET and HEMT approaches in high linearity, low DC power performance for space communication applications. A 5-11-GHz balanced amplifier designed for high linearity produces +32-dBm third-order output intercept point (IP3) with a 8-dB associated gain and less than 150-mW DC power consumption. The balanced architecture permits easy cascadability and allows optimum impedance match design within the Lange couplers. A 0.05-9-GHz distributed amplifier designed for low DC power and high gain consumes only 50 mW and provides 10-dB flat gain. On the basis of these hybrid designs, monolithic heterostructure bipolar transistor (HBT) amplifiers have been designed which offer the potential for improved capabilities.<<ETX>>

Improved current gain and f/sub T/ through doping profile selection in linearly graded heterojunction bipolar transistors

Analytical and experimental results are used to show that extension of a thin p-doped layer of base doping into the graded-gap region, close to the base, of an n-p-n AlGaAs/GaAs heterojunction bipolar transistor and removing n-type dopant from the rest of the linearly graded AlGaAs region improves current gain beta and unity gain cutoff frequency f/sub T/. Current gain is significantly improved by reducing recombination near the metallurgical interface and using the effective electric field from the grading to accelerate electrons as they are injected into the p-base. The doping profile also inhibits the formation of a potential minimum in which electrons can be stored in close proximity to the base. This greatly improves f/sub T/, and does not hamper the current injection or increase the turn-on voltage. Space-charge recombination current is also reduced, due to the carrier density reduction associated with the effective electric field due to the graded gap. >

Effect of exponentially graded base doping on the performance of GaAs/AlGaAs heterojunction bipolar transistors

The authors have fabricated n-p-n GaAs/AlGaAs heterojunction bipolar transistors (HBTs) with base doping graded exponentially from 5*10/sup 19/ cm/sup -3/ at the emitter edge to 5*10/sup 18/ cm/sup -3/ at the collector edge. The built-in field due to the exponentially graded doping profile significantly reduces base transit time, despite bandgap narrowing associated with high base doping. Compared to devices with the same base thickness and uniform base doping of 1*10/sup 19/ cm/sup -3/, the cutoff frequency is increased from 22 to 31 GHz and maximum frequency of oscillation is increased from 40 to 58 GHz. Exponentially graded base doping also results ill consistently higher common-emitter current gain than uniform base doping, even though the Gummel number is twice as high and the base resistance is reduced by 40%.<<ETX>>