Highly scaled indium phosphide (InP) heterojunction bipolar transistor (HBT) technologies have been demonstrated with maximum frequencies of oscillation ( $f_{\max}$ ) of >1 THz and circuit operation has been extended into the lower end of the terahertz (THz) frequency band. InP HBTs offer high radio-frequency (RF) output power density, millivolt (mV) threshold uniformity, and high levels of integration. Integration with multilevel thin-film wiring permits the realization of compact and complex THz monolithic integrated circuits (TMICs). Circuit results reported from InP HBT technologies include: 200-mW power amplifiers at 210 GHz, 670-GHz amplifiers and fundamental oscillators, and fully integrated 600-GHz transmitter circuits. We review the state of the art in THz-capable InP HBT devices and integrated circuit (IC) technologies. Challenges in extending transistor bandwidth and in circuit design at THz frequencies will also be addressed.

InP HBT Technologies for THz Integrated Circuits

A 100-element 10-GHz grid amplifier has been developed. The active devices in the grid are chips with heterojunction-bipolar-transistor (HBT) differential pairs. The metal grid pattern was empirically designed to provide effective coupling between the HBTs and free space. Two independent measurements, one with focusing lenses and the other without, were used to characterize the grid. In each case, the peak gain was 10 dB at 10 GHz with a 3-dB bandwidth of 1 GHz. The input and output return losses were better than 15 dB at 10 GHz. The maximum output power was 450 mW, and the minimum noise figure was 7 dB. By varying the bias, a signal could be amplitude modulated with a modulation index as large as 0.65. Tests show that the grid was quite tolerant of failures-the output power dropped by only 1 dB when 10% of the inputs were detuned. The grid amplifier is a multimode device that amplifies beams of different shapes and angles. Beams with incidence angles up to 30 degrees were amplified with less than a 3-dB drop in gain. >

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A 100-element HBT grid amplifier

A linearity study of the propagation delay of bipolar circuits carried out using a SPICE program is discussed. It is found that the behavior of the propagation delay is quite linear, and therefore analytical propagation delay expressions for ECL and CML circuits are derived using a sensitivity analysis. The validity of the expressions is checked by SPICE simulations and comparison to experimental data published in the literature, and agreement is within 5%. The expressions indicate that there is an optimum value of load resistance for logic circuits in order to achieve a minimum propagation delay. For present technology, logic circuits for silicon transistors can operate at the current density corresponding to maximum f/sub T/, and logic circuits for AlGaAs-GaAs heterojunction bipolar transistors (HBTs) should operate at a current density lower than that of maximum f/sub T/. Therefore, it is important to increase the collector current density of maximum f/sub T/ for silicon bipolar circuits, or to decrease the base resistance R/sub B/ and the forward transit time tau /sub F/ for HBT circuits, in order to increase the circuit speed. >

Accurate analytical delay expressions for ECL and CML circuits and their applications to optimizing high-speed bipolar 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 120 GHz are described. Differential amplifiers are shown to have offset voltages with standard deviation below 2 mV and voltage gain as high as 200 per stage. Breakdown voltiages (BV/sub CB0/) above 20 V are demonstrated. Frequency dividers operating above 20 GHz are described.

Heterojunction Bipolar Transistors for Microwave and Millimeter-Wave Integrated Circuits

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. >

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

This paper describes a self-aligned heterojunction-bipolar-transistor (HBT) process based on a simple dual-lift-off method. Transistors with emitter width down to 1.2 µm and base doping up to 1 × 1020/cm3have been fabricated. Extrapolated current gain cutoff frequency f t of 55 GHz and maximum frequency of oscillation f_{\max} of 105 GHz have been obtained. Current-mode-logic (CML) ring oscillators with propagation delays as low as 14.2 ps have been demonstrated. These are record performance results for bipolar transistors. The dual-lift-off process is promising for both millimeter-wave devices and large-scale integrated circuit fabrication.

AlGaAs/GaAs heterojunction bipolar transistors fabricated using a self-aligned dual-lift-off process

http://ieeexplore.ieee.org/iel5/9943/31771/01479383.pdf

Modeling, fabrication and performance of ion implanted low-noise GaAs FETs

The authors report the first demonstration of completely MOMBE (metal-organic molecular beam epitaxy) grown carbon-doped base self-aligned AlGaAs/GaAs HBTs (heterojunction bipolar transistors) operating at microwave frequencies. Excellent DC and RF characteristics have been achieved. For a 1400-AA-thick base doped at a level of 1*10/sup 19/ cm/sup -3/, cutoff frequency f/sub T/ of 45 GHz and f/sub max/ of 90 GHz were measured from common emitter HBTs. Common base HBTs with total emitter area of 360 mu m/sup 2/ delivered 560 mW output power with 43% of power-added efficiency and 8.9 dB gain at 10 GHz. A high-power MMIC (monolithic microwave integrated circuit) amplifier operating in 8-11 GHz bandwidth has achieved 2 W output power. The device modeling based on measured S-parameters indicates that the performance can be further improved with optimal layer structure and doping profiles. >

http://ieeexplore.ieee.org/iel5/606/6055/00235303.pdf

J.A. Higgins

Papers

AlGaAs/GaAs heterojunction bipolar transistors fabricated using a self-aligned dual-lift-off process

Modeling, fabrication and performance of ion implanted low-noise GaAs FETs

MOMBE-grown carbon-doped base self-aligned AlGaAs/GaAs heterojunction bipolar transistors for microwave applications