Design and characterization of integrated varactors for RF applications

Varactors are passive semiconductor devices used in electronic circuits, as a voltage-controlled way of storing energy in order to boost the amount of electric charge produced. In the past, the use of low-cost fabrication processes such as complementary metal oxide semiconductor (CMOS) and silicon germanium (SiGe) were kept for integrated circuits working in frequency ranges below the GHz. Now, the increased working frequency of radio frequency integrated circuits (RF ICs) for communication devices, and the trend of system-on-chip technology, has pushed the requirements of varactors to the limit. As the frequency of RF applications continues to rise, it is essential that passive devices such as varactors are of optimum quality, making this a critical design issue.

Initially describing the physical phenomena that occur in passive devices within standard IC fabrication processes, Design and Characterization of Integrated Varactors for RF Applications goes on to:

present information on the design of wide band electrical varactor models (up to 5 GHz) which enable the accurate prediction of device performance; propose a specific methodology for the measurement of integrated varactors, covering on-wafer measurement structures, the calibration process, and detailed descriptions of the required equipment; explain de-embedding techniques and also analyse confidence level and uncertainty linked to the test set-up; examine the design of a voltage controlled oscillator (VCO) circuit as a practical example of the employment of methods discussed in the book.

Providing the reader with the necessary technical knowledge for dealing with challenging VCO designs, this book is an essential guide for practising RF and microwave engineers working on the design of electronic devices for integrated circuits. It is also a useful reference for postgraduate students and researchers interested in electronic design for RF applications.

Author Notes

Dr. Íñigo Gutiérrez , Faculty of Engineering, University of Navarra (TECNUN), Paseo Manuel Lardizabal 13, 20019 San Sebastien (Guipuzcoa), Spain

Íñigo Gutiérrez is currently a Lecturer in the Engineering Faculty of the University of Navarra (TECNUN), Spain. From 2002, he has held the post of Assistant Director of the RF Area of TECNUN and his research interests include integrated passive filters using varactors and integrated transformers for RF applications. Whilst at the University, Dr Gutiérrez has participated in several research projects involving varactors for industry and the Basque Government. He has also authored 4 technical publications and made 8 contributions to international congresses.

Dr. Juan Meléndez, Faculty of Engineering, University of Navarra (TECNUN), Paseo Manuel Lardizabal 13, 20019 San Sebastien (Guipuzcoa), Spain

Juan Meléndez is Assistant to the Director of the Communications Area of the Centro de Estudios e Investigaciones Técnicas de Guipúzcoa (CEIT), at the University of Navarra. He is also Assistant Professor in the Laboratory of Components and Elecromagnetic Compatibility at TECNUN. Since joining the CEIT, he has been Leader on a number of projects for international companies, developing wireless systems for domestic applications and implementing Six-Sigma methodology for the development and characterization of Wireless LAN applications in SiGe and CMOS. His research interests include system design level of RF transceivers. He is a member of the IEEE and has authored four technical publications.

Dr. Erik Hernández, Faculty of Engineering, University of Navarra (TECNUN), Paseo Manuel Lardizabal 13, 20019 San Sebastien (Guipuzcoa), Spain

Erik Hernández is currently a Researcher in the Communications Area of the Centro de Estudios e Investigaciones Técnicas de Guipúzcoa (CEIT), at the University of Navarra. He is also Assistant Professor in the Laboratory of Components TECNUN. Since joining the CEIT, he has been Leader for the project 'Passive Radiofrequency Link for ISM Bands' and has worked on different research initiatives for the company IKUSI. He has authored seven technical publications and has made 10 contributions to international congresses.

Acknowledgement

Summary

Contents

Chapter 1 Introduction

1.1 Passive Elements

1.2 Figures of Merit of Varactors

1.2.1 Quality factor

1.2.2 Tuning range

1.2.3 Self-resonance frequency (fr)

1.2.4 Effective silicon area

1.2.5 Absolute capacity value

1.3 Principal Types of Varactor Manufacture

1.3.1 Discrete Varactors

1.3.2 MEMS Varactors

1.3.3 BSTO Varactors

1.3.4 Integrated Varactors using Standard Technologies

Chapter 2 PN Junction Varactors

2.1 The Operating Principle of a PN-Junction Varactor

2.1.1 Electrical phenomena in a PN-junction varactor

2.2 Different Architectures of PN-Junction Varactors

2.2.1 Different configurations of pn-junction varactors

2.3 Influence of Bias Voltage on the Behaviour of a PN-Junction Varactor

2.4 Influence of Geometric Parameters on the Behaviour of a PN-Junction Varactor

2.4.1 Influence in the variation of the number of islands

2.4.2 Influence of the size of the islands

2.4.3 Influence of the distance between islands

2.4.4 Variation of the size of the N well

2.5 Influence of the Working Frequency on the Results

2.5.1 Influence of the frequency on the quality of varactor

2.5.2 Influence of the frequency on the capacitance of a varactor

2.6 Comparison Between the Different Types of PN-Junction Varactors

2.6.1 Comparison according to the effective silicon area

2.6.2 Comparison according to the quality factor

Chapter 3 Mos Varactors

3.1 Operating Principles of an Nmos Varactor

3.1.1 Operating ranges of the NMOS varactor

3.1.2 Electrical phenomena of an NMOS varactor in accumulation mode

3.1.3 Electrical phenomena of an NMOS varactor in depletion mode

3.2 NMOS Varactors

3.2.1 Operating ranges of the NMOS varactor

3.3 Influence of the Operating Mode of an NMOS Varactor

3.4 Influence of Bias Voltage on the Behaviour of an NMOS Accumulation Varactor

3.5 Influence of Geometric Parameters on the Behaviour of a NMOS Varactor

3.5.1 Influence on the variation of the varactor size

3.5.2 Influence of the varactor gate length on its performance

3.5.3 Influence of the varactor gate width on the variation

3.6 Influence of the Working Frequency on the Results

Chapter 4 Measurement Techniques for Integrated Varactors

4.1 Test System

4.2 Equipment Required for the On-Wafer Testing of Integrated Varactors

4.2.1 Test probes

4.2.2 Connectivity

4.3 Calibrating the Test System

4.4 Test Structures

4.4.1 Choosing the test structure configuration

4.4.2 Design of the test structures

4.4.2.1 Test Pads

4.4.2.2 Guard ring

4.4.3 Effects introduced by the test structures

4.4.3.1 Contact impedance ZC

4.4.3.2 Coupling between the two ports (Zf)

4.4.3.3 Autocoupling Yp

4.4.3.4 Connection track impedance Zi.

4.4.3.5 Coupling due to the connection tracks Yd.

4.4.3.6 Impedance to ground Zs.

4.5 Test Structure De-Embedding Techniques

4.5.1 Single-short structure

4.5.2 Single-open structure

4.5.3 Thru structure

4.6 Characterisation of Integrated Varactors

4.7 Test System Verification

4.7.1 Error introduced by positioning the test probes on the pads

4.7.2 Error introduced by the calibration reference tolerances

4.7.3 Error introduced by the test probes heating up

4.7.4 Error introduced by the degradation of the components

4.7.5 Analysis of the results

Chapter 5 Modelling Varactors

5.1 Introduction to the Modelling of Varactors

5.2 Modelling PN-Junction Varactors

5.2.1 Value of parameter L1

5.2.2 Value of parameter C1

5.2.3 Value of parameter R1

5.2.4 Value of parameter L2

5.2.5 Value of parameter C2

Available:*

On Order

Summary

Summary

Author Notes

Table of Contents