MICROWAVE CHARACTERSTICS OF SiGe HBT

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In this thesis, I described about the basic introduction to SiGe Hetero-junction bipolar transistors, evaluation of SiGe HBT, SiGe HBT advantages over Si BJT‘s, the characteristics of Linearly Graded base doping and uniform base doping. Derived the S- parameters from the Complete Small Signal hybrid-pi Model of SiGe HBT. S-parameters of the Complete Small Signal hybrid-pi model of SiGe HBT calculated by using model equations of the Small Signal Model of intrinsic SiGe HBT within the frequency range of0.2-50-GHz using parasitic effects

Transcript of MICROWAVE CHARACTERSTICS OF SiGe HBT

MICROWAVE CHARACTERSTICS OF SiGe HBT

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

Master of Technology InVLSI Design & Embedded Systems by SANDEEP PONTATI

Roll No: 209EC2133

Department of Electronics & Communication Engineering National Institute of Technology Rourkela 2011

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MICROWAVE CHARACTERSTICS OF SiGe HBT

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

Master of Technology InVLSI Design & Embedded Systems by

Sandeep Pontati Roll No: 209EC2133 Under the guidance of Dr. Neti.V.L.Narasimha Murty

Department of Electronics & Communication Engineering National Institute of Technology Rourkela 2011

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National Institute Of Technology Rourkela

CERTIFICATEThis is to certify that the thesis entitled, MICROWAVE CHARACTERISTICS OF SiGe HBT submitted by SANDEEP PONTATI (209EC2133) in partial fulfilment of the requirements for the award of Master of Technology degree in Electronics and Communication Engineering with specialization in VLSI Design and Embedded Systems at National Institute of Technology, Rourkela (Deemed University) and is an authentic work by her under my supervision and guidance. To the best of my knowledge, the matter embodied in the thesis has not been submitted to any other university/institute for the award of any Degree or Diploma.

Date:

Dr. Neti.V.L.Narasimha MurtyDept. of E.C.E, National Institute of Technology Rourkela-769008

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ACKNOWLEDGMENT

I would like to express my gratitude to my thesis guide Dr. Neti.V.L.Narasimha Murty for his guidance, advice and constant support throughout my thesis work. I would like to thank him for being my advisor here at National Institute of Technology, Rourkela. Next, I want to express my respects to Prof. S.K. Patra , Prof. K. K. Mahapatra, Prof. G S Rath, Prof. S. Meher , Prof. D. P. Acharya , Prof. Poonam Singh and Prof. Samit ari for teaching me and also helping me how to learn. They have been great sources of inspiration to me and I thank them from the bottom of my heart. I would like to thank all faculty members and staff of the Department of Electronics and Communication Engineering, N.I.T. Rourkela for their generous help in various ways for the completion of this thesis. I would like to thank all my friends and especially my classmates for all the thoughtful and mind stimulating discussions we had, which prompted us to think beyond the obvious. Ive enjoyed their companionship so much during my stay at NIT, Rourkela. I am especially indebted to my parents for their love, sacrifice, and support. They are my first teachers after I came to this world and have set great examples for me about how to live, study, and work.

Sandeep Pontati

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ABSTRACT

In this thesis, I described about the basic introduction to SiGe Hetero-junction bipolar transistors, evaluation of SiGe HBT, SiGe HBT advantages over Si BJTs, the characteristics of Linearly Graded base doping and uniform base doping. Derived the Sparameters from the Complete Small Signal hybrid-pi Model of SiGe HBT. S-parameters of the Complete Small Signal hybrid-pi model of SiGe HBT calculated by using model equations of the Small Signal Model of intrinsic SiGe HBT within the frequency range of 0.2-50-GHz using parasitic effects. Intrinsic SiGe HBT model is having higher cutoff frequency than extrinsic SiGe HBT model because extrinsic SiGe HBTs having parasitic effects. The linearly graded-base SiGe HBT doping has smaller base transit time and larger cutoff frequency than the uniformly-base HBT doping. S-parameters of the intrinsic small signal SiGe HBT and complete Small Signal of SiGe HBT are calculated by using various base widths. S-parameters of the Complete small signal hybrid-pi model of SiGe HBT are calculated by using different Ge concentrations. Further SiGe HBT are used to MMIC (Millimeter Microwave Integrated Circuit) Technology.

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ContentsACKNOWLEDGMENT ...................................................................................... iii ABSTRACT........................................................................................................... iv CHAPTER-1............................................................................................................1 INTRODUCTION ..................................................................................................11.1Introduction: .................................................................................................................. 2 1.1.1 SiGe HBT: .......................................................................................................... 2 1.1.2 History of SiGe Technology .................................................................................. 3 1.1.3 Applications of SiGe HBT: ...................................................................................... 4 1.1.4 SiGe HBT vs GaAs HBT: ........................................................................................ 4 1.2 Literature review:.......................................................................................................... 5 1.3 Scope of Thesis:............................................................................................................ 11

CHAPTER-2..........................................................................................................12 Material Properties & .......................................................................................12 S-parameters of SiGe HBT ..................................................................................122.1 Material Properties of SiGe HBT: ................................................................................ 13 2.1.1 Critical thickness:................................................................................................... 14 2.1.2 Band Structure of SiGe: ......................................................................................... 15 2.1.3 Dielectric Constant:................................................................................................ 15 2.2 Small Signal model of SiGe HBT: ............................................................................ 18 2.2.1 Base resistance: ...................................................................................................... 19 2.3 Intrinsic Small Signal of SiGe HBT: .......................................................................... 20 2.3.1 Introduction: ........................................................................................................... 20 2.3.2 Intrinsic base resistance: ........................................................................................ 21 2.3.3 Collector-Base Capacitance (C) : ........................................................................ 22 2.3.4 Emitter-Base Capacitance (C):............................................................................. 29 2.3.5 Transconductance (gm):.......................................................................................... 32 2.3.6 Base-Emitter Resistance: ....................................................................................... 33v

2.3.5 S-Parameters of Intrinsic HBT:............................................................................ 33 2.3.6 Device Parameters: ................................................................................................ 34 2.3.7 Simulation Results: ................................................................................................ 35 2.4 Extrinsic Small signal SiGe HBT: ............................................................................... 42 2.4.1 Simulation Results: ................................................................................................ 44 2.5 Comparison of intrinsic and extrinsic SiGe HBT ......................................................... 51 2.6 SiGe HBT for Different Ge Concentrations ................................................................ 52

CHAPTER 3 ..........................................................................................................54 CONCLUSION .....................................................................................................543.1 Conclusion: ................................................................................................................... 55 3.2 Scope for Future Work ................................................................................................. 55

REFERENCES : ...................................................................................................56

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List of Figures:FIGURE 1.1 Block Diagram of SiGe HBT................................................................................. 3 Figure 2. 1 Strain and relaxed SiGe on Si substrate .................................................................... 13 Figure 2. 2 Critical thickness vs Ge fraction .......................................................................... 14 Figure 2. 3 Bandgap as a function of Ge percentage for Strained and unstrained SiGe ....... 15 Figure 2. 4 Energy band diagram for a Si BJT and graded-base SiGe HBT.......................... 16 Figure 2. 5 Small Signal model of SiGe HBT hybrid-pi model ............................................. 19 Figure 2. 6 The cross section view of components of base and collector resistance ............ 20 Figure 2.7 Intrinsic small signal model of SiGe HBT........................................................... 21 Figure 2. 8 Graded junction Space charge distribution .......................................................... 22 Figure 2.9Abrupt junction a) Space charge distribution b) electric field profile .................. 26 Figure 2