Selectively Implanted Collector Research Articles

Design of a 250-Gbit/s SiGe HBT Electrooptic Modulator

We present a rigorous electrical and optical analysis of a highly scaled, graded-base, SiGe heterojunction bipolar transistor (HBT) electrooptic (EO) modulator. In this study, we propose a 2-D electrical model and a 3-D optical model for a graded-base SiGe HBT structure that is capable of operating at a data bit rate of 250 Gbit/s or higher. In this structure, apart from a polysilicon/low doped emitter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$( \hbox{width} = 90\ \hbox{nm})$</tex></formula> and a strained SiGe graded base <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$( \hbox{depth} = 8.5\ \hbox{nm})$</tex></formula> , a selectively implanted collector (SIC) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{depth} = 26\ \hbox{nm})$</tex></formula> is introduced. Furthermore, at a base-emitter swing of 0 to 1.0 V, this model predicts a rise time of 3.48 ps and a fall time of 0.55 ps. Optical simulations predict a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pi$</tex></formula> phase shift length <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(L_{\pi})$</tex></formula> of 204 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu \hbox{m}$</tex></formula> , with an extinction ratio of 13.2 dB at a wavelength of 1.55 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">$\mu\hbox{m}$</tex></formula> .

Modeling and Analysis of an 80-Gbit/s SiGe HBT Electrooptic Modulator

We present a rigorous electrical and optical analysis of a strained and graded base SiGe Heterojunction Bipolar Transistor (HBT) electrooptic (EO) modulator. In this paper, we propose a 2-D model for a graded base SiGe HBT structure that is capable of operating at a data bit rate of 80 Gbit/s or higher. In this structure, apart from a polysilicon/monosilicon emitter <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{Width} = 0.12\ \mu\hbox{m})$</tex> </formula> and a strained SiGe graded base <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{Depth} = 40\ \hbox{nm})$</tex> </formula> , a selectively implanted collector (SIC) <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$(\hbox{Depth} = 0.6\ \mu \hbox{m})$</tex></formula> is introduced. Furthermore, the terminal characteristics of this new device modeled using MEDICI are closely compared with the SiGe HBT in the IBM production line, suggesting the possibility of fast deployment of the EO modulator using established commercial processing. At a subcollector depth of 0.4 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> and at a base-emitter swing of 0 to 1.1 V, this model predicts a rise time of 5.1 ps and a fall time of 3.6 ps. Optical simulations predict a <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\pi$</tex></formula> phase shift length <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({ \rm L}_{\pi})$</tex></formula> of 240.8 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> with an extinction ratio of 7.5 dB at a wavelength of 1.55 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu\hbox{m}$</tex></formula> . Additionally, the tradeoff between the switching speed, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$L_{\pi}$</tex></formula> and propagation loss with a thinner subcollector is analyzed and reported.

Influence of the Selectively Implanted Collector Integration on +400 GHz fMAX Si/SiGe:C HBTs

Optimization of SiGe HBT performances towards very high cut-off frequencies fT and fMAX requires high collector doping level together with low collector/base junction capacitance CBC. This compromise is usually achieved by localizing a dedicated collector implant (so-called SIC implant) under the intrinsic emitter/base region of the device. In this paper, we present the influence of the integration choice of the Selectively Implanted Collector (SIC) on the performance of +400 GHz fMAX Si/SiGe:C HBTs featuring a selective epitaxy of the base [1]. We describe in the first part of this paper the different process flows investigated for the SIC integration. Second part is dedicated to the analysis of the electrical results obtained for the different SIC modules and to the understanding of these results. We conclude on the perspectives to further improve hf performances.

Low-Frequency Noise Properties of SiGe Heterojunction Bipolar Transistors

In this study, we investigated the low-frequency noise in SiGe heterojunction bipolar transistors (HBTs) with and without a selectively implanted collector (SIC). By comparing the magnitude of 1/ f noise, collector current, and current gains of the SiGe HBTs with and without SIC, we show that the impurities at the collector produced by the incomplete activation of the implanted ions cause an increase in the collector current 1/ f noise spectrum. Thus, SiGe HBT with SIC exhibits higher collector noise current spectra due to the inactive ions in the collector. The figures-of-merit of noise corner frequency ( fC) to cutoff frequency ratio ( fT), fC/ fT, indicates that the SiGe HBT without SIC has a better low-frequency noise property for circuit application prior to the fT roll-off. Furthermore, at the onset of high injection effect, the conspicuous degradation of high-frequency properties also deteriorates the fC/ fT ratio of SiGe HBT without SIC.

The influence of collector designs on fmax versus ft characteristics for different types of Si-based RF bipolar transistors

The cut-off frequency ft, the maximum frequency of oscillation fmax and the collector–emitter breakdown voltage BVCEO are computed for various types of Si-based bipolar transistors with different selectively implanted collector (SIC) profiles. In particular, the influence of SIC profiles on ft versus BVCEO and fmax versus BVCEO characteristics is investigated. Subsequently, the fmax versus ft behaviour is discussed. It is shown that for slow transistors (BJTs) there is a trade-off between ft and fmax. However, in the case of faster HBTs this trend can be reversed.

SiGe HBT Without Selectively Implanted Collector (SIC) Exhibiting$f_max = hbox310 hboxGHz$and$hboxBV_rm CEO = hbox2 hboxV$

Device characteristics for SiGe heterojunction bipolar transistors fabricated by a simplified process without selectively implanted collector (SIC), which exhibit peak fmax of 310 GHz at the collector-current density of 7 mA/mum2 and BVCEO of 2 V, are reported. For comparison, the characteristics of devices with various SIC doses are also presented, and the observed trends are discussed

RF power characteristics of SiGe HBTs at cryogenic temperatures

This paper investigates the temperature dependence (from 77 to 300 K) of dc, ac, and power characteristics for n-p-n SiGe heterojunction bipolar transistors (HBTs) with and without selectively implanted collector (SIC). In SiGe HBTs without SIC, the valance band discontinuity at the base-collector heterojunction induces a parasitic conduction band barrier while biasing at saturation region and high current operation at cryogenic temperatures. This parasitic conduction band barrier significantly reduces the current gain and cutoff frequency. For transistors biased with fixed collector current, the measured output power, power-added efficiency, and linearity at 2.4 GHz decrease significantly with decreasing operation temperatures. The temperature dependence of output power characteristic is analyzed by Kirk effect, current gain, and cutoff frequency at different temperatures. The parasitic conduction band barrier in SiGe HBTs with SIC is negligible, and thus the device achieves better power performance at cryogenic temperatures compared with that in SiGe HBT without SIC.

Small-Signal Characterization of SiGe-HBT&lt;tex&gt;$f_T$&lt;/tex&gt;-Doubler up to 120 GHz

In this brief, small-signal characterizations of selectively implanted collector (SIC) and non-SIC SiGe-heterojunction bipolar transistors (HBT) f/sub T/-doublers up to 120 GHz are measured, analyzed, and compared with those of the corresponding single devices. The measured results confirm a great improvement in transit frequency with almost no considerable decrease in the maximum stable gain/maximum available gain, and maximum oscillation frequency. Since the f/sub T/-doubler can be used easily instead of a single transistor, a much higher transit frequency and RF power can be achieved while using a technology with a moderate f/sub T/.

A submicrometer 252 GHz f/sub T/ and 283 GHz f/sub MAX/ InP DHBT with reduced C/sub BC/ using selectively implanted buried subcollector (SIBS)

The selectively implanted buried subcollector (SIBS) is a method to decouple the intrinsic and extrinsic C/sub BC/ of InP-based double-heterojunction bipolar transistors (DHBTs). Similar to the selectively implanted collector (SIC) used in Si-based bipolar junction transistors (BJTs) and HBTs, ion implantation is used to create a N+ region in the collector directly under the emitter. By moving the subcollector boundary closer to the BC junction, SIBS allows the intrinsic collector to be thin, reducing /spl tau//sub C/, while simultaneously allowing the extrinsic collector to be thick, reducing C/sub BC/. For a 0.35 × 6 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> emitter InP-based DHBT with a SIBS, 6 fF total C/sub BC/ and >6 V BV/sub CBO/ were obtained with a 110-nm intrinsic collector thickness. A maximum f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 252 GHz and f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 283 GHz were obtained at a V/sub CE/ of 1.6 V and I/sub C/ of 7.52 mA. Despite ion implantation and materials regrowth during device fabrication, a base and collector current ideality factor of /spl sim/2.0 and /spl sim/1.4, respectively, at an I/sub C/ of 100 μA, and a peak dc /spl beta/ of 36 were measured.

Evaluating and designing the optimal 2D collector profile for a 300 GHz SiGe HBT

An optimally designed selectively implanted collector (SIC) doping profile allows keeping a SiGe-HBT's current in a vertical flow under the emitter while minimizing the parasitic collector-base capacitance ( C cb). TCAD simulations were used to provide insight into a 300 GHz HBT's current flow lines and to derive design guidelines for the optimal mask width of the SIC implant. This boosted the HBT's transit frequency ( f t) by 6.5% and the unity power gain ( f max) by 23%.

Impact-ionization-induced avalanche multiplication effect and Early effect in the selectively implanted collector n–p–n bipolar junction transistors

The impact-ionization-induced avalanche multiplication effect and Early effect in the selectively implanted collector (SIC) bipolar junction transistors are investigated in this paper. The multiplication factor M−1 and the Early effect factor E−1 are characterized by a proposed novel technique capable of separating those two contributions to the increment of collector current with collector–base bias of the transistors with and without SIC technology. The collector–base threshold voltage of multiplication factor M−1=10 −5 is shifted from 5 V to below 1 V and the voltage of the Early effect factor E−1=10 −1 is shifted from 5.2 to 2.2 V by the SIC technology with dose of 4×10 12 cm −3 and energy of 360 keV phosphorus implantation.