D.L. Miller

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

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 ftof 55 GHz and maximum frequency of oscillationf_{\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.

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.

GaAs/(Ga,Al)As heterojunction bipolar transistors with buried oxygen-implanted isolation layers

A simple self-aligned technique using oxygen implants to reduce the extrinsic base-collector capacitance in GaAs/(Ga,Al)As heterojunction bipolar transistors (HBTs) is described. This technique has been used to achieve nonthreshold logic ring-oscillators with propagation delays down to 30 ps per gate, the lowest reported to date for any bipolar transistor circuit.

GaAs/(GaAl)As heterojunction bipolar transistors using a self-aligned substitutional emitter process

This paper describes the first self-aligned heterojunction bipolar transistor (HBT) process which includes ion implantation to reduce the base resistance. With this substitutional emitter technique, the base implant and the emitter contact patterns are defined with the same mask. Arbitrary contact materials can be used allowing optimization of the contact resistances. Transistors with emitter width down to 1.5 µm have been fabricated. Nonthreshold logic (NTL) ring oscillators made with these transistors had propagation delay times down to 27.2 ps. This is the lowest reported to date for bipolar transistors.

Multiple-channel GaAs/AlGaAs high electron mobility transistors

Multiple-channel high electron mobility transistors (HEMTs) have been designed and fabricated on GaAs/AlGaAs heterostructural material grown by molecular beam epitaxy (MBE). The sheet carrier density of the two-dimensional electron gas (2-DEG) measured at 77 K was linearly proportional to the number of high mobility electron channels, and reached 5.3 × 1012cm-2for six-channel HEMT structures. Depletion-mode devices of the double-heterojunction HEMT were operated between negative pinchoff voltage and forward-biased gate voltage without any transconductance degradation. A peak extrinsic transconductance of 360 mS/mm at 300 K and 550 mS/mm at 77 K has been measured for a 1-µm gate-length double-heterojunction enhancement-mode device. An extremely high drain current of 800 mA/mm with a gate-to-drain avalanche breakdown voltage of 9 V was measured on six-channel devices.

A 20-GHz frequency divider implemented with heterojunction bipolar transistors

This paper reports a high-speed frequency divider implemented with AlGaAs/InGaAs/GaAs heterojunction bipolar transistors (HBTs). The divide-by-four static frequency divider was fabricated with a fully self-aligned dual-lift-off HBT process. A maximum operating frequency of 20.1 GHz was achieved. This is the highest frequency ever reported for static frequency dividers.

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.

Nonthreshold logic ring oscillators implemented with GaAs/(GaAl)As heterojunction bipolar transistors

The first nonthreshold logic (NTL) ring oscillators implemented with GaAs/(GaAl)As heterojunction bipolar transistors (HBTs) are reported. Propagation delay times down to 52 ps per gate were achieved, using transistors with emitter dimensions of 1.2 µm × 5 µm. Numerical simulations of the circuits were also done, which agreed closely with the experimental results.

VA-2 GaAs/(Ga,Al)As heterojunction bipolar transistors with buried oxygen-implanted isolation layers

junction capacitances are necessary to improve f ~ . This HBT f~ can be as high as 50 GHz by reducing only the emitter contact resistance. To interpret the experimentally deduced short intrinsic transit time, we discuss hot-electron transport in base and collector layers. Finally, it has been confirmed that HBT’s have the ultrahigh cutoff frequencies without limits due to the emitter crowding effect and base diffusion transit time as Si-bipolar transistors always have. Therefore, IlBTs are most promising devices for ultrahigh-speed IC’s.

Low-noise high electron mobility transistors for monolithic microwave integrated circuits

High electron mobility transistors (HEMTs) for monolithic microwave integrated circuits have been fabricated that have demonstrated excellent performance. External transconductance of 300 mS/mm is observed and noise figures of 1 and 1.8 dB with associated gains of 16.1 and 11.3 dB at 8 and 18 GHz, respectively, have been measured. These are comparable to the best reported noise figures for either HEMTs or MESFETs and are the highest associated gains reported for such low-noise figures. Analysis of these devices indicates that further improvements in these results is possible through optimization of HEMT layers and fabrication technology to reduce gate-source parasitic resistance.