SiGe Base Research Articles

(Invited) On the Potential of Lateral BJTs and SiGe HBTs in Advanced CMOS Technologies

State-of-the-art SiGe HBTs have achieved astonishing performance demonstrating record fT /fmax of 505/720 GHz in bipolar-only process [1] and fT /fmax in the 300-400 GHz range in the commercial BiCMOS technologies [2-4], making them suitable for RF and millimeter wave applications as well as for high-performance analog and mixed-signal circuits. A number of fabrication steps must be added to CMOS backbone technology to obtain such high-performance self-aligned SiGe HBTs that generally include at least two polysilicon layers, one or more epitaxial growths, deep trenches, multiple spacers and other isolation and/or sacrificial layers. Although SiGe HBTs can be implemented several technology nodes behind CMOS with competitive or better RF performance, the addition of those fabrication steps and lithography masks notably increases the cost of technology. Furthermore, high-breakdown voltage HBTs are beneficial for higher-swing applications, such as RF power amplifiers, and their fabrication with high-speed transistors in the same process usually requires various collector implantation schemes, increasing the number of added masks and steps further. Lateral bipolar transistors (LBTs) could principally provide a viable solution for a tradeoff between technological complexity and high-performance due their compact structure where intrinsic transistor regions are more easily accessible from the silicon surface. However, their electrical characteristics in pure-silicon are inferior to those of standard vertical-current transistors so far [5, 6]. As the most advanced lateral-current-flow device, Horizontal Current Bipolar Transistor (HCBT) (Fig. 1.a) [7] has optimum doping profile with low parasitics and is the highest-speed implanted-base Si BJTs, integrated with CMOS in low-cost technology and with the capability to adjust breakdown voltage without any increase in process complexity [8], just by layout manipulation. Due to lateral current flow, the electric field from collector can be shielded in various ways: by recessed CMOS p-well region (Fig. 1.b) increasing BV CEO above 10 V; by double emitter structure with BV CEO>12 V (Fig. 1.c); by double emitter structure with recessed p-well with BV CEO>36 V (Fig. 1.d); and by floating field plates with BV CEO>45 V (Fig. 1.e). Such a wide range of breakdown voltages in the same technology enables: (i) the implementation of high-voltage circuits currently covered by Bipolar-CMOS-DMOS (BCD) process in HCBT technology, (ii) integration of such high-voltage, i.e. power-management and/or analog circuits with RF circuits.The potential of HCBT concept with SiGe base is examined by TCAD simulations. SiGe base stack is placed on the sidewall of the active collector region, as shown in Fig. 2, instead of implanted intrinsic base. The extrinsic base p+ region is implanted into the top part of the grown stack. The electrical characteristics are consistently compared to the self-aligned vertical-current SiGe HBT with the geometry corresponding to the most advanced devices from literature (Fig. 3). Both structures have the same intrinsic doping profile, shown in Fig. 4. Since the extrinsic base overhangs the active collector region in HCBT introducing extrinsic C BC and affecting the collector current distribution, its doping profile shape critically impacts the high-frequency performance. The fT and fmax of the HCBT structure in Fig. 2 are similar to those of vertical current HBT with f T lower by 11 GHz and f max basically equal, whereas the HCBT with more realistic extrinsic base shape results in the improved fT /fmax up to 358/490 GHz (Fig. 5), without impacting β and BV CEO, as shown in Table I. Due to the one-sided base contact, HCBT has higher RB and lower CBC per emitter length and for a given IC HCBT has to be twice longer resulting in a smaller RB and a bit higher CBC than in vertical-current HBT. The interface resistance between the base polysilicon and intrinsic base in vertical-current HBTs is not accounted for in simulations, but has been identified as significant contributor to total RB [1,3]. This RB component is eliminated in SiGe HCBT since the extrinsic base is directly metal-contacted without p+ polysilicon, implying a further improvement of RB in favor of HCBT in actual devices. The fT /fmax can be increased by reducing wbext as can be expected in down-scaling, as shown in Fig. 6, reaching fT /fmax of 375/505 GHz for wbext =45 nm and converging to an ideal 1D transistor. Applying the same concept to SOI substrate, fT /fmax are decreased (Fig. 7) due to denser current distribution in collector boosting the Kirk effect and increasing RC .Simulation study clearly show that HCBT concept can provide state-of-the-art high-frequency performance with vertical-current HBTs as a reference, while implemented in lower-cost technology with simpler integration schemes, that include high-voltage transistors, with both bulk and SOI advanced CMOS. Figure 1

Dynamic SIMS, spectroscopic ellipsometry and x-ray diffractometry analysis of SiGe HBTs with Ge grading

In this paper, SiGe heterojunction bipolar transistors (HBTs) with Ge concentrations up to 40 atomic percent (at%) and different slopes of Ge gradients are characterized by comparing dynamic secondary ion mass spectrometry (D-SIMS) and multi-angle spectroscopic ellipsometry (SE). X-ray diffractometry (XRD) was used as reference. D-SIMS results show that sputter rate and Ge content calibration have major impact on depth profile measurements of HBTs with graded SiGe. Strained and relaxed SiGe show differences in Ge content calibration and no difference in sputter rate calibration. Jiang’s protocol was used for Ge content calibration and proven to be valid up to ∼50 at% Ge. SE with a combination of 3 angles of incidence (AOIs) (59, 65, 71°) in comparison with the single AOI (71°) realized in industrial setup for semiconductor manufacturing environment was analyzed to find a more stable solution for revealing the thickness of plateau and gradient parts of SiGe base. SE with 71° AOI and rotating compensator is the best choice for in-line HBT with Ge grading characterization. The determination of gradient shape continues to be a challenging task for SE, due to high parameter correlations and the need to use some fixed parameters within the fitting procedure. D-SIMS remains the favorite for graded profile determination. Results of D-SIMS and SE with fixed parameters are in good agreement with XRD for HBTs with Ge grading.

Performance improvement for epitaxially grown SiGe on Si solar cell using a compositionally graded SiGe base

Silicon germanium (SiGe) is a material with high mobility and relatively low bandgap making it an attractive candidate for the bottom subcell in a III-V tandem solar cell grown on silicon (Si) substrate. This paper reports on the performance improvement of an epitaxially grown SiGe on Si solar cell by growing a higher Ge composition SiGe layer in the base. The purpose of growing a higher Ge composition SiGe layer in the base is to improve the light absorption. The first iteration of this structure was an Si0.18Ge0.82 solar cell fabricated with a 1 μm thick Si0.12Ge0.88 layer in the base. This solar cell had a lower efficiency compared with the reference solar cell without the Si0.12Ge0.88 layer. One of the main reasons for the lower efficiency is believed to be the high threading dislocation density (TDD) caused by the abrupt change of lattice constant between Si0.18Ge0.82 and Si0.12Ge0.88 in the base. In order to reduce the TDD, the second iteration of the structure was fabricated with a compositionally graded SiGe base. With the new structure, an SiGe on Si solar cell with an efficiency of 3.1%, when filtered by a GaAs0.79P0.21 top cell, was fabricated. The Ge composition in the base of this solar cell gradually increased from 82% to 85% and then decreased again to 82%. The developed SiGe solar cell with graded base provides more flexibility for a highly efficient GaAsP/SiGe dual junction solar cell grown on an Si substrate.

Two-zone SiGe base heterojunction bipolar charge plasma transistor for next generation analog and RF applications

For next generation terahertz applications, heterojunction bipolar transistor (HBT) with reduced dimensions and charge plasma (CP) can be a potential candidate due to simplified and inexpensive process. In this paper, a symmetric lateral two-zone SiGe base heterojunction bipolar charge plasma transistor (HBCPT) with an extruded (extended) base is proposed and its performance at circuit level is studied. The linearly graded electric field in the proposed HBCPT provides improved self gain (β) and cut-off frequency (fT). Two-dimensional (2-D) TCAD and small-signal model based simulations of the proposed HBCPT demonstrates high self gain β 35–172.93 and fT of 1–4 THz for different device parameters. Moreover, fT of 1104.9 GHz and β of 35 can be achieved by decreasing Nb up to 8.2×1017cm−3. Although, fT of 2 THz and 4 THz can also be achieved by reducing the base resistance up to 10 Ω and increasing the emitter/collector length up to 63 nm, respectively. The small-signal analysis of common-emitter amplifier based on the proposed HBCPT demonstrate high voltage gain of 50.11 as compared to conventional HBT (18.1).

Investigation of Disilane-Based SiGe-HBT Layers for Low External Base Resistances

In the past decade there has been increased interest in utilizing SiGe-heterojunction bipolar transistors (SiGe-HBT) and in particular SiGe-BiCMOS technologies for applications in the mm-and sub-mm-wave range. High data rate communication systems and optical networks for >100Gb/s, industrial and automotive sensors at 120 GHz for velocity and position control as well as imaging systems at >160 GHz for medical and security systems are some examples for these fields of application. Key elements for the continuous improvement of the high frequency performance of SiGe-HBTs are the scaling of vertical and lateral dimensions as well as design optimization to achieve reduced parasitics. In particular the maximum oscillation frequency fmax could be increased in the last years above 0.5 THz. Beside a sufficient high cut-off frequency fT, a reduced base-collector capacitance CBC and low base resistance RB are beneficial for the fmax performance of a SiGe-HBT. In this work we investigate the behavior of the external base resistance RBext for two different epitaxial processes used in SiGe-HBTs with a silane- (SiH4) and disilane-based (Si2H6) precursor. The SiGe-layers were treated by various rapid thermal annealing (RTA). We processed different wafers with an oxide stack usually used in a standard SiGe-BiCMOS process. After the release of certain silicon regions by reactive-ion-etching the epitaxial layers were deposited. First a selective epitaxial silicon buffer was grown within oxide-free windows followed by non-selective growth of a silicon layer, the in-situ boron doped SiGe base layer and an on top silicon cap layer. For the disilane-based process the SiGe layer grows in an amorphous phase whereas for the silane-based process a poly-crystalline film is formed. The growth of the whole Si-SiGe-Si stack was adapted for disilane process in order to reach the same layer thicknesses for both variants inside oxide free windows (single-crystalline regions) as for the original silane-based process. Sheet resistance (Rs) measurements were performed on 49 points across a wafer on the poly crystalline SiGe layer on an oxide. Figure 1 shows the Rs of silane-based (#1) and disilane-based (#3) SiGe-layer after a rapid thermal annealing at 1010°C for 12s. We observe a decrease of Rs by 60% in comparison to the silane-based SiGe-layer. Even for a reduced annealing temperature of 950°C (#2) the Rs dropped down around 30% in comparison to the silan-based variant. Moreover the standard deviation of the sheet resistance in the poly-crystalline regions across the wafer becomes significantly smaller and decreased by a factor of six down to approximately 50 Ohm/square for the disilane-based SiGe stack. Secondary-ion-mass-spectroscopy (SIMS) measurements were used to characterize the boron doping and SiGe-profile inside the crystalline and poly-crystalline regions of the wafers. In the poly crystalline region the germanium and boron concentration of the disilane-based process corresponds to the distribution of the single crystalline region. However we obtain a difference in the doping distribution after epitaxy (Fig. 2a) in comparison to the silane-based process. This difference becomes more significant after the RTA and we observe a quite homogeneous distribution of Ge and boron for the silane-based SiGe-stack whereas a steeper doping is within poly-crystalline layers for the disilane-based process (Figure 2b). We address this disparity in the Ge and boron distribution to differences in the diffusion behavior for the disilane-based layer stack due to i) the deposition as an amorphous Si/SiGe/Si layer and ii) the grain size of the poly-crystals after the final RTA. For our operation point the loading effect during the disilane-based epi-process leads to a 40% increased boron dose in the external base region compared to the silane-based process and without increasing the B doping inside the single crystalline region. This is beneficial for the behavior of RBext. Finally we applied both variants in a standard SiGe-BiCMOS flow. The overall performance of the SiGe-HBT depends of course on several other aspects like base-emitter and base-collector capacitances and the influence of changing one parasitic component has to be carefully evaluated. Nevertheless the external base resistance as well as the contact resistance dropped by 55% and 45%, respectively, for the disilane-based process and show the benefits for the use of this type of epitaxial layer depositions in advanced SiGe-HBTs. Figure 1

Impact of Lateral Scaling on Silicon Germanium High Breakdown Power Amplifier Device Performance

Silicon Germanium (SiGe) Heterojunction Bipolar Transistors (HBTs) in Bipolar Complementary Metal Oxide Semiconductor (BiCMOS) technologies have in recent years, emerged as a viable alternative to Gallium Arsenide (GaAs) [1] for commercial development of linear power amplifier (PA) modules for wireless communications. The explosion in WLAN applications at 2.4GHz has provided ample opportunity for SiGe BiCMOS to substantially penetrate the PA market [2]. SiGe HBTs offer several benefits compared to it’s GaAs HBT counterparts including the ability to provide high integration at a reduced cost [3]. The higher thermal conductivity associated with the silicon substrate enables reduced chip areas, smaller packages and provides improvements in chip robustness. Additionally, SiGe BiCMOS integration facilitates improved power densities, on-chip matching and bias chokes, temperature compensated power detector and a CMOS compatible interface [2]. SiGe HBT PA device design limits have traditionally been constrained by the performance tradeoff described by the Johnson limit, which states that the product of the current gain, fT and the DC open-base breakdown voltage, BVceo, should be relatively constant[3]. However, it is now generally accepted that DC emitter-open breakdown voltage, BVcbo is a more useful indicator of device ruggedness for PA applications. This arises since SiGe HBT operation in PA applications have been demonstrated at voltages significantly higher than BVceo, [1,4]. Furthermore, power-gain cut-off frequency, fMAX , has also been cited as relevant a device metric for PAs as fT , [1,3] and several authors have suggested that improvements in fMAX will enhance PA device performance. Typically, improvements in device fMAX are achieved by lateral scaling to accomplish a reduction in the base resistance and collector-base capacitance. Since SiGe HBT device physics do not demand rigid tradeoff between BVcbo and fMAX, , several potential device optimization opportunities exist for PA applications. Technology computer-aided design (TCAD) has been used to optimize the PA design performance relative to the base technology. The TCAD methodology was based on a detailed strategy which entailed developing a process and device model calibration for an existing 0.35um SiGe HBT device that features non-self-aligned emitter-base integration, with a carbon doped SiGe base layer and an implanted extrinsic base region [2]. The model calibration featured a close match of both process and electrical characteristics to the measured data. An important element to matching the electrical characteristics of the device, was simulating key artifacts of the process related to epitaxial growth of the SiGe base layer, which defined the final device topology. The calibration served as the baseline simulation for the optimization study and provided insight into the device performance limitations. The simulations demonstrated the device breakdown, BVcbo, occurs along the extrinsic region of the collector and the base, and is correspondingly set by the thickness of the collector n-epitaxial layer and the vertical diffusion of the extrinsic base into the collector. Several lateral scaling strategies were therefore investigated, which addressed optimization of collector-base capacitance, Ccb and base resistance, Rb for improvements in fMAX and BVcbo. Scaling the lateral dimension of the device resulted in improvements in the performance metrics peak fT , peak Ic and fMAX . Improvements in fT and Ic are explained by the reduced surface field effect, whereby a more uniform field distribution delays base push out effect in the transistor[5]. The AC and DC characteristcs will be reviewed.

A novel approach for justification of box-triangular germanium profile in SiGe HBTs

This work presents a unique and robust approach for validation of using the box-triangular germanium profile in the base of SiGe heterojunction bipolar transistors, where the methodology considers the simultaneous optimization of the p-type base doping profile in conjunction with the germanium profile in the base. The study analyses the electron motion across the SiGe base in SiGe HBTs, owing to different accelerating electric fields. The analysis first presents a figure of merit, to achieve the minimum electron transit time across the base in conjunction with the increased current gain in n—p—n-SiGe HBTs, which shows a general trend vis-à-vis the advantage of a trapezoid germanium profile, but with additional accuracy as we considered simultaneously optimized p-type base doping. The effect of minority carrier velocity saturation is then included to make the study more detailed. The analysis then investigates the shifted germanium profile in the base to further minimize the base transit time. Finally, it is shown that a shifted germanium profile eventually evolves into a box-triangular Ge-profile in the SiGe base, which could simultaneously minimize the base transit time and reduce emitter delay by virtue of the high current gain. The analysis verifies that for an average Ge-dose of 7.5% Ge across the base, a box-triangular germanium profile in conjunction with an optimum base doping profile has an approximately identical base transit time and a 30% higher current gain, in comparison with an optimum base doping and triangular Ge-profile across the whole base.

A Perspective on Symmetric Lateral Bipolar Transistors on SOI as a Complementary Bipolar Logic Technology

Recently published reports suggest that symmetric lateral bipolar transistors on semiconductor-on-insulator (SOI) is CMOS compatible in fabrication process, and can be much denser than CMOS due to their much larger (5-10× larger) drive-current capability. When used in traditional bipolar circuits, SOI bipolar offers much lower power dissipation and/or much higher maximum speed. With both NPN and PNP devices of comparable characteristics, SOI lateral bipolar suggests the possibility of complementary bipolar (CBipolar) circuits in configurations analogous to CMOS. In this paper, the performance versus power dissipation of CBipolar circuits is examined using analytic equations. It is shown that for CBipolar to be superior to CMOS in both performance and power dissipation, narrow-gap-base heterojunction structures, such as Si emitter with Ge base or Si emitter with SiGe base, are required.

Effects of carbon on phosphorus diffusion in SiGe:C and the implications on phosphorus diffusion mechanisms

The use of carbon (C) in SiGe base layers is an important approach to control the base layer dopant phosphorus (P) diffusion and thus enhance PNP heterojunction bipolar transistor (HBT) performance. This work quantitatively investigated the carbon impacts on P diffusion in Si0.82Ge0.18:C and Si:C under rapid thermal anneal conditions. The carbon molar fraction is up to 0.32%. The results showed that the carbon retardation effect on P diffusion is less effective for Si0.82Ge0.18:C than for Si:C. In Si0.82Ge0.18:C, there is an optimum carbon content at around 0.05% to 0.1%, beyond which more carbon incorporation does not retard P diffusion any more. This behavior is different from the P diffusion behavior in Si:C and the B in Si:C and low Ge SiGe:C, which can be explained by the decreased interstitial-mediated diffusion fraction fIP, SiGe to 95% as Ge content increases to 18%. Empirical models were established to calculate the time-averaged point defect concentrations and effective diffusivities as a function of carbon and was shown to agree with previous studies on boron, phosphorus, arsenic and antimony diffusion with carbon.

Effect of High Performance SiGe HBT Design Parameters on the Minimum Gate Delay of an ECL Inverter

In this paper, we focus on ECL inverter delay analysis through approximate analytical equations. We highlight its dependence on design parameters of SiGe HBT device as well as on electrical parameters. The advantage of this approach is to correlate the physical device parameters to the dominant time constant of this ECL gate. The simulated results show that good performances were derived from well-balanced SiGe HBT characteristics achieved through the fully-self aligned SiGe base structure with a fast forward transit time and low collector capacitance. Strict control at all stages of the technological process in the development of the device, allows the control of all these factors, and it will be possible to optimize the switching performance. 

Lithography Solutions in Novel High Frequency SiGe HBT Device

Advanced vertical NPN SiGe HBT device integrated in a CMOS technology are widly used in RF application such as LNA, PA, Mixer circuit. It can be fabricated by different architectures. HHNEC novel SiGe HBT device with non-EPI collector, borderless emitter and deep contact structures is one of them. It can offer scalable break down volatages, smaller device area and low manufactering cost. For SiGe HBT device, SiGe base, EW (emmitter window) and EP (Emitter poly) are most critical. The device performance is very sensitive to their CD, pattern fidelity and miss-alignment. On the other sides, SiGe film optical characteristics are very sensitive to its formulation process such as Ge concentration, thermal temperature, crystal lattice and so on. How to setup a robust base to emmiter loop is most important. In this paper, we will introduce our study result on 150G high frequency SiGe HBT device. The key design rule is comprable to sub 110nm design rule. Pure KrF process with maximum 0.82NA scanner tools is used. SiGe film impact to lithograhpy process is studied. New lithography and OPC solutoins are demostrated. The device sensitivity is aslo discussed with different solutions.

Effect of bandgap engineering on thermal characteristic of radiofrequency power SiGe heterojunction bipolar transistor

As is well known, direct-current (DC) characteristic, frequency characteristic and noise characteristic of SiGe heterojunction bipolar transistor(HBT) can be improved by "bandgap engineering"(by Ge composition). However, the effect of "bandgap engineering" on the thermal characteristic of HBT has not been reported. In this paper, the effect of "bandgap engineering" is analyzed by the use of 3D thermal-electric feedback model. Considering the temperature dependence of emitter junction voltage and current gain, the expression of the minimum emitter ballasting resistance (REmin), which is necessary for SiGe HBT thermal stability, is presented. Furthermore, non-uniform ballasting resistance design is given so as to further enhance the thermal stability of device. It is found that the surface temperature of the device decreases with the increase of Ge composition in SiGe base. This is because SiGe HBT internally possesses the thermal-electrical negative feedback. For the same dissipated power, the REmin decreases as Ge composition increases, which is beneficial to the improvment of the performance of radio frequancy(RF) power SiGe HBT. These results provide a good guide to further optimization of RF power SiGe HBT performance, especially thermal design.

TCAD modeling of NPN-SI-BJT electrical performance improvement through SiGe extrinsic stress layer

The impact of introducing a SiGe stress layer formed over the extrinsic base and adjacent to the intrinsic base of NPN-Si-BJT device on the electrical properties and frequency response has been studied using TCAD modeling. Approximately 42% improvement in f t and 13% improvement in f max have been achieved for the strained NPN-Si-BJT device in comparison with an equivalent standard conventional BJT device. In addition to that, an enhancement of the collector current by almost three times has been achieved. The same approach has been applied for NPN-SiGe-HBT device to clarify the impact of the extrinsic SiGe stress on the device's performance using TCAD modeling. Simulation results have shown that applying the SiGe stress layer on the base region of the HBT device is less efficient in comparison with the BJT device, as the SiGe base is already stressed due to the existence of Ge at the base. Approximately 5% improvement in f max and 3% improvement in f t have been achieved for the strained HBT device in comparison with an equivalent standard conventional HBT device.

F T × BV cbo product modeling for SiGe:C HBTs

The specific aspects of SiGe:C HBT process and device simulation using TCAD are discussed. Cut-off frequency fT and collector junction breakdown voltage BVcbo dependences on carbon concentration in SiGe base area are investigated. The boron and carbon profiles in SiGe base are obtained to provide a trade-off between gain, cut-off frequency and break-down voltage. High values of fT × BVcbo product were achieved.

Design of High Efficiency Multi-GHz SiGe HBT Electro-Optic Modulator

We design and theoretically analyze a heterojunction bipolar transistor (HBT) electro-optic (EO) modulator with a composition graded SiGe base. The waveguide has a large cross-section of 1 microm for ease of fiber alignment. At a base-emitter bias of V BE = 2.5 V, a pi-phase shift requires 74.5 microm interaction length for TM polarization at lambda = 1.55 microm. The total optical attenuation is 3.9 dB to achieve a pi-phase shift in this condition. This device is expected to operate at a switching speed of 2.4 GHz.

Effect of silicidation on silicon-based thin film resistors in SiGe integrated circuits

The resistance variation of the silicon–germanium (SiGe) thin film resistor caused by the fabrication process of SiGe integrated circuits (ICs) was investigated. The SiGe resistor and the Si resistor were made of the thin films identical with the p-type SiGe base layer and the n-type Si emitter layer of the SiGe hetero-junction bipolar transistor, respectively. The range of the resistance value of the SiGe resistor was much larger than that of the Si resistor, and an abnormally high resistance of the SiGe resistor was often observed. Ti–B precipitates and Ti(Si1−xGex)2 protrusions were created as the result of the Ti silicidation of the p-type SiGe layer, whereas no precipitates and protrusions were generated in the case of the n-type Si layer. It was confirmed by scanning electron microscopy that the nonuniform resistance of the SiGe resistor was induced by the removal of the protrusions and underlying field oxides in the contact window. Resistance uniformity of the SiGe resistor was much improved by increasing the contact size. The simulation result of the detrimental influence of the resistance change on ICs indicated that the fabrication process and the structure of the thin film resistor should be optimized for enhancing IC reliability.

SiGe HBTs With Normal High-Speed Emitter-Up and Reverse Low-Power Collector-Up Operation

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> SiGe heterojunction bipolar transistors (HBTs) are usually optimized to obtain best performance in the forward operation mode. In this paper, we demonstrate that a simultaneous excellent performance in the reverse mode of operation can be obtained as well. A <formula formulatype="inline"><tex>$f_{T}/f_{\max}$</tex></formula> combination of 50/100 GHz is obtained, which is, to our knowledge, the best value reported for a Si-based HBT operating in the reverse mode. This excellent performance is analyzed and explained by studying the different delay components of the device in the reverse operation mode. It is shown that the extrinsic SiGe base region plays a crucial role. Additionally, good low-power performance in the reverse operation mode is obtained as well, which is attributed to a reduction in the device parasitic contributions. The simultaneous availability of a high-speed performance in the forward mode and a low-power performance in the reverse mode offers additional flexibility to optimize circuit performance in terms of speed, power, and area. </para>

Modeling of the inverse base width modulation effect in HBT transistor with graded SiGe base

A model of the position of the edge of emitter-base junction in the base and collector current pre-exponential ideality factor in HBT transistor with a SiGe base is presented. The model is valid for transistors with nonuniform profiles of doping and Ge content. The importance of taking into account the dependence of the effective density of states in SiGe on local Ge content and that of electron diffusion coefficient in SiGe on drift field for modeling accuracy is studied.

In-Line Characterization of Heterojunction Bipolar Transistor Base Layers by High-Resolution X-Ray Diffraction

The suitability of high-resolution X-ray diffraction (HRXRD) as an in-line measurement tool for the characterization of heterojunction bipolar transistor SiGe base layers and Si cap layers was investigated. We showed that despite of polycrystalline Si on the mask material of patterned wafers, HRXRD measurements performed on an array of small windows yield results which are comparable to those that were obtained on a window which is larger than the size of the source beam, regarding the thickness and the Ge content of the SiGe layers. The possibility to extract layer parameters for active device windows of different sizes was therefore demonstrated. The suitability of HRXRD for in-line measurement of the Si cap thickness was also assessed and the sensitivity of this technique for determining the substitutional boron concentration in SiGe was studied. The detection limit in the monitoring of the active dopant concentration was about 2.7 x 10^19 cm-3.

Bottom 컬렉터와 단일 금속층 구조로 설계된 SiGe HBT의 전기적 특성

This paper presents the electrical properties of SiGe HBTs designed with bottom collector and single metal layer structure for RF power amplifier. Base layer was formed with graded-SiGe/Si structures and the collector place to the bottom of the device. Bottom collector and single metal layer structures could significantly simplify the fabrication process. We studied about the influence of SiGe base thickness, number of emitter fingers and temperature dependence <TEX>$(<200^{\circ}C)$</TEX> on electrical properties. The feasible application in <TEX>$1{\sim}2GHz$</TEX> frequency from measured data <TEX>$BV_{CEO}{\sim}10V,\;f_T{\sim}14GHz,\;{\beta}{\simeq}110,\;NF{\sim}1dB$</TEX> using packaged SiGe HBTs. We will discuss the temperature dependent current flow through the e-b, b-c junctions to understand stability and performance of the device.