Remarkable developments in bipolar technology over the past decade have seen the silicon germanium heterojunction bipolar transistor emerge from research labs to enter production in radio frequency technologies. These developments have allowed SiGe BiCMOS transistors to address high frequency wireless and optical communications applications that were previously only possible in III/V and II/VI devices. This book brings together for the first time all the new developments and describes in a unified manner the physics, materials science and technology of silicon bipolar transistors and SiGe heterojunction bipolar transistors.

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SiGe Heterojunction Bipolar Transistors

In the quasi-static approach the cut-off frequency or unity-gain bandwidth f T of a one-dimensional bipolar transistor can readily be calculated from the doping profile by means of a numerical device simulation program. The physical interpretation of such results in terms of the usual regional model is greatly facilitated by a new partition of the small-signal charge distribution. Only two region boundaries remain to be determined. The criterion employed for this purpose is unambiguous. The total transit time from emitter contact to collector contact (inversely proportional to f T ) is subdivided into five physically meaningful components. The method can readily be implemented in device simulation programs, making these easier to use as a design tool. It provides more detailed insight into the influence of the emitter doping gradient on f T . Examples illustrate the three effects that can cause the f T fall-off at high collector current densities: high injection in the base, base widening and quasi-saturation. In all cases the emitter transit time turns out to dominate the total transit time at very high current densities, albeit beyond the limit of practical interest.

A simple regional analysis of transit times in bipolar transistors

This paper investigates high-current and electrostatic discharge (ESD) phenomena in pseudomorphic epitaxial-base silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) in base-collector, base-emitter, collector-emitter and collector-to-substrate configurations. Transmission line pulse (TLP) and ESD human body model (HBM) wafer-level reliability testing of SiGe HBTs is completed for high-current characterization and evaluation of the ESD robustness of a BiCMOS SiGe technology.

Electrostatic discharge characterization of epitaxial-base silicon-germanium heterojunction bipolar transistors

The effects of vertical and lateral structures on cutoff frequency and breakdown voltage are investigated for high-speed bipolar transistors. The cutoff frequencies are examined in the range from 2.5 to 80 GHz by analysis and from 3 to 20 GHz by experiment. To attain the maximum cutoff frequency, it is predicted that the collector width, the base width, and the collector concentration should be 0.12 mu m, 0.07 mu m, and 1.2*10/sup 16/ cm/sup -3/, respectively, and that in this scaled transistor, breakdown voltages, BV/sub CE0/ and BV/sub C8O/ should be reduced below 3 and 7.7 V respectively. >

An analytical and experimental investigation of the cutoff frequency f/sub T/ of high-speed bipolar transistors

Achieving radio frequency (RF) performance circuit objectives and electrostatic discharge (ESD) protection will continue to challenge future technology. In this study, we use the ultimate limitation of the transistor (e.g., known as the Johnson Limit) as a means to provide an ESD power clamp by providing a first low breakdown trigger device and a second high breakdown clamp device. Using the inverse relationship between unity current gain cutoff frequency and breakdown voltage, ESD power clamps are constructed using epitaxial base pseudomorphic Silicon Germanium heterojunction transistors in a common-collector Darlington configuration. ESD experimental test results from human body model (HBM), machine model (MM) and transmission line pulse (TLP) testing demonstrate the scaling of ESD power clamps. Design studies of alternative implementations, resistor ballasting and alternative triggers will be discussed. As a comparative analysis, the SiGe-based ESD power clamps will be compared to CMOS MOSFET-based ESD power clamps. A new dimensionless group is defined to quantify the relationship between the power-to-failure and the maximum Johnson limit power.

Silicon Germanium heterojunction bipolar transistor ESD power clamps and the Johnson Limit

The effect of the emitter doping gradient on the transit time in microwave bipolar transistor structures has been investigated. The range of gradients was chosen to cover those typically found in shallow phosphorus- and arsenic-emitter diffusions. The results show that there is appreciable free carrier storage in the emitter space charge layer. The Storage decreases when the doping gradient in the junction is increased. This effect can account for the improved f T values of arsenic emitter transistors. The free carrier storage in the emitter space charge layer is compared with predictions deduced from the theoretical analysis of Morgan and Smits [1].

J.A. Kerr

Papers

The effect of emitter doping gradient on f T in microwave bipolar transistors