A. Gruhle

MBE-grown Si/SiGe HBTs with high beta , f/sub T/, and f/sub max/

Si/SiGe heterojunction bipolar transistors (HBTs) were fabricated by growing the complete layer structure with molecular beam epitaxy (MBE). The typical base doping of 2*10/sup 19/ cm/sup -3/ largely exceeded the emitter impurity level and led to sheet resistances of about 1 k Omega / Square Operator . The devices exhibited a 500-V Early voltage and a maximum room-temperature current gain of 550, rising to 13000 at 77 K. Devices built on buried-layer substrates had an f/sub max/ of 40 GHz. The transit frequency reached 42 GHz.<<ETX>>

Noise modeling of microwave heterojunction bipolar transistors

Analytical expressions of microwave heterojunction bipolar transistors minimum noise figure and noise parameter are reported in this paper. These expressions are derived from a noise model including nonideal junctions, emitter and base resistances and have been compared with measured data obtained on a Si-SiGe HBT. An agreement between theoretical and experimental data was as observed up to 20 GHz for several bias conditions. The limits of the model or the range of validity of the proposed equations have been also examined with the help of an appropriate CAD software. The analysis of the influence of parasitic elements on noise parameters has shown a strong influence of the extrinsic base collector capacitance at microwave frequencies. >

Growth of 100 GHz SiGe-Heterobipolar Transistor (HBT) Structures

The transit frequency f T of SiGe-heterobipolar transistors (HBTs) was increased from 20 GHz to 100 GHz. This was mainly achieved by thickness reduction of the double heterojunction SiGe-base from 65 nm to 25 nm. The complete vertical structure of the SiGe-HBTs (collector, base, emitter, emitter contact) was grown in one run by Si molecular beam epitaxy (Si-MBE). The growth temperature was varied from 650° C at the collector side to 325° C at the emitter contact side. The different n-type doping levels (1017/ cm3, 1018/ cm3, 1020/ cm3) were obtained by applying three different Sb-doping techniques (secondary implantation, adatom pre build-up, low temperature doping). The p-type base was doped with boron. The doping level in the base (6×1019/ cm3) exceeded the emitter doping level by a factor of 30 (doping level inversion).

Recent advances with SiGe heterojunction bipolar transistors

Abstract In the last few years Si/SiGe/Si heterostructures grown by molecular beam epitaxy (MBE) with its high precision and reproducibility have been used to build high-frequency and low-noise heterojunction bipolar transistors (HBTs). The latest optimization of layer design led to a SiGe HBT with an f max value of 160 GHz. As a circuit demonstrator a DC-18 GHz low power wideband amplifier was integrated showing a gain of 9.5 dB at only 18 mW power consumption. Several monolithically integrated 26 GHz and 40 GHz VCOs were fabricated on high-resistivity substrates using SiGe HBTs and on-chip varactors built from the same MBE layers. A multi-finger power HBT exhibited 100 mW at 5.7 GHz in a hybrid class A amplifier with 30% efficiency. At 2 GHz, 1 W output power was obtained with 44% power-added efficiency. Mesa-type research transistors as well as fully passivated devices will be compared. A high-quality oxide passivation results in excellent low-frequency noise performance of SiGe HBTs with corner frequencies down to 300 Hz. At the same time the high-frequency noise is kept low due to the small base resistance leading to a measured noise figure of 0.5 dB at 1 GHz. In future a large number of circuit applications, in particular for mobile communications will profit from the high performance of SiGe HBTs.

Mesa and planar SiGe-HBTs on MBE-wafers

SiGe-HBTs have the potential for outstanding analog and digital or mixed-signal high frequency circuits widely based on standard Si technology. Here we review on MBE grown transistors and circuits. Processes and results of a research-like SiGe HBT and two possible production relevant HBT versions are presented. The high frequency results with fmax and fT up to 120 GHz and a minimum noise figure of 0.9 dB at 10 GHz demonstrate the advantage of using MBE samples with steep and high base doping and high germanium contents. A comparison to the concept of reported low doped, low germanium and triangular profiled SiGe base layers, realized by UHV-CVD, is given. In addition, some circuit demonstrators of SiGe-ICs will be presented.

The influence of emitter-base junction design on collector saturation current, ideality factor, Early voltage, and device switching speed of Si/SiGe HBT's

In advanced Si/SiGe HBTs the base is doped much higher than emitter and collector. Base outdiffusion becomes a problem because of the formation of parasitic barriers that degrade device performance. The simulations and experiments of this paper show that a strong correlation exists between (a) the drop of the collector saturation current, (b) an increase of its ideality factor and (c) a rise of the switching time due to an additional emitter delay which can no longer be neglected. Curves of these three parameters as a function of Si/SiGe heterointerface position and outdiffusion at the base-emitter interface have been calculated and indicate that only a few nm shift may cause severe device degradation. An important result is that the collector current ideality factor or the inverse Early voltage is a very sensitive indicator for the quality of the emitter-base interface. Application of these results have yielded experimental SiGe HBTs with transit frequencies above 60 GHz. >

1/f noise in self-aligned Si/SiGe heterojunction bipolar transistor

The first characterization of the low-frequency noise in a self-aligned Si/SiGe heterojunction bipolar transistor (HBT) is reported. The observed low-frequency noise exhibits a pure 1/f shape, probably related to carrier number fluctuations at the pseudomorphic emitter-base heterointerface.<<ETX>>

50 GHz Si1 − xGex heterobipolar transistor: growth of the complete layer sequence by molecular beam epitaxy

Abstract The six-layer structure of a Si1 − xGex heterobipolar transistor (HBT) with flat doping levels and abrupt junctions is grown by a silicon molecular beam epitaxy (MBE) process in one run. The process, the MBE equipment used and analytical results (secondary-ion mass spectrometry) are described. The growth temperature is reduced from 650 °C at the collector to 325 °C at the emitter contact. A Si1 − xGex base doping level of 5 × 1019 cm−3 is obtained by coevaporation of silicon, germanium and boron from an electron beam evaporator, a BN effusion cell and a high temperature graphite cell respectively. The n-type doping of 1016–1020 cm−3 (collector, emitter and emitter contact) is obtained by applying three different antimony dopant incorporation methods. Test transistors fabricated from these structures exhibited low noise, good high frequency performance (fT,fmax > 50 GHz) and low base sheet resistance (less than 1 kΩ/□).

Collector-up SiGe heterojunction bipolar transistors

SiGe heterojunction bipolar transistors (HBTs) in a collector-up version have been built. This configuration has the advantage of a very low collector-base capacitance. In addition, because the substrate is the emitter, extremely low emitter series inductances may be achieved, e.g., in the case of packaged discrete devices. This is particularly interesting for RF power amplifiers. Transistors fabricated on MBE-grown layers with an emitter size of 1.6 /spl mu/m showed near-ideal Gummel plots, DC current gains of up to 485, an S/sub 21/ gain of 20 dB at 2 GHz and an f/sub max/ of 33 GHz. A problem to be solved is the large parasitic C/sub BE/ capacitance which degrades the transit frequency.

Multi emitter finger SiGe-HBTs with f/sub max/ up to 120 GHz

Multi emitter finger silicon germanium heterojunction bipolar transistors (SiGe-HBTs) grown by MBE have been investigated by varying the collector design. No current crush effects have been observed for different transistor geometries. SiGe-HBTs with a 400 nm 2/spl times/10/sup 16/ cm/sup -3/ doped collector layers and 10 emitter fingers of 1 /spl mu/m/spl times/10 /spl mu/m exhibit a maximum oscillation frequency of 120 GHz and a power gain of 20 dB at 10 GHz. These are presently the highest values reported for silicon based transistors.<<ETX>>