RF and Microwave Semiconductor Device Handbook

Mike Golio

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351836203
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Electrical Engineering & Telecommunications
• Index: Technology & Engineering

Offering a single volume reference for high frequency semiconductor devices, this handbook covers basic material characteristics, system level concerns and constraints, simulation and modeling of devices, and packaging. Individual chapters detail the properties and characteristics of each semiconductor device type, including: Varactors, Schottky diodes, transit-time devices, BJTs, HBTs, MOSFETs, MESFETs, and HEMTs. Written by leading researchers in the field, the RF and Microwave Semiconductor Device Handbook provides an excellent starting point for programs involving development, technology comparison, or acquisition of RF and wireless semiconductor devices.

1
Varactors

Jan Stake
Chalmers University of Technology

1. 1.1 Introduction
2. 1.2 Basic Concepts
   1. Manley-Rowe Formulas
   2. Varactor Model
   3. Pumping
3. 1.3 Varactor Applications
   1. Frequency Multipliers
   2. Frequency Converters
   3. Parametric Amplifiers
   4. Voltage Tuning
4. 1.4 Varactor Devices
   1. Conventional Diodes
   2. The Heterostructure Barrier Varactor Diode
   3. The Si/SiO2/Si Varactor
   4. The Ferroelectric Varactor

1.1 Introduction

A varactor is a nonlinear reactive device used for harmonic generation, parametric amplification, mixing, detection, and voltage-variable tuning.¹ However, present applications of varactors are mostly for harmonic generation at millimeter and submillimeter wave frequencies, and as tuning elements in various microwave applications. Varactors normally exhibit a voltage-dependent capacitance and can be fabricated from a variety of semiconductor materials.² A common varactor is the reverse biased Schottky diode. Advantages of varactors are low loss and low noise. The maximum frequency of operation is mainly limited by a parasitic series resistance (see Fig. 1.1).

1.2 Basic Concepts

Many frequencies may interact in a varactor, and of those, some may be useful inputs or outputs, while the others are idlers that, although they are necessary for the operation of the device, are not part of any input or output. For instance, to generate high harmonics in a frequency multiplier it is more or less necessary to allow current at intermediate harmonics (idlers) to flow. Such idler circuits are usually realized as short-circuit resonators, which maximize the current at idler frequencies.

1.2.1 Manley-Rowe Formulas

The Manley-Rowe formulas³ for lossless nonlinear reactances are useful for intuitive understanding of multipliers, frequency converters, and dividers. Consider a varactor excited at two frequencies f_p and f_s; the corresponding general Manley-Rowe formulas are

Σm=1∞Σn=−∞∞mPm,nnfp+mfs=0Σm=−∞∞Σn=1∞nPm,nnfp+mfs=0

where m and n are integers representing different harmonics and P_m,n is the average power flowing into the nonlinear reactance at the frequencies nf_p and mf_s.

• Frequency multiplier (m = 0): if the circuit is designed so that only real power can flow at the input frequency, f_p, and at the output frequency, nf_p, the above equations predict a theoretical efficiency of 100%. The Manley-Rowe equation is P₁ + P_n = 0.
• Parametric amplifier and frequency converter: assume that the RF-signal at the frequency f_s is small compared to the pump signal at the frequency f_p. Then, the powers exchanged at sidebands of the frequencies nf_p and mf_s for m different from 1 and 0 are negligible. Furthermore, one of the Manley-Rowe formulas only involves the small-signal power as
  Σn=−∞∞P1,nnfp+fs=0
  Hence, the nonlinear reactance can act as an amplifying upconverter for the input signal at frequency f_s and output signal extracted at f_u = f_s + f_p with a gain of
  PuPs=P1,1P1,0=-(1+fpfs)=-fufs

1.2.2 Varactor Model

The intrinsic varactor model in Fig. 1.1 has a constant series resistance, R_s, and a nonlinear differential elastance, S(V) = dV/dQ = 1/C(V), where V is the voltage across the diode junction. This simple model is used to describe the basic properties of a varactor and is adequate as long as the displacement current is much larger than any conduction current across the junction. A rigorous analysis should also include the effect of a frequency- and voltage-dependent series resistance, and the equivalent circuit of parasitic elements due to packaging and contacting. The differential elastance is the slope of the voltage-charge relation of the diode and the reciprocal of the differential capacitance, C(V). Since the standard varactor model consists of a resistance in series with a nonlinear capacitance, the elastance is used rather than the capacitance. This simplifies the analysis and gives, generally, a better understanding of the varactor. The differential elastance can be measured directly and is used rather than the ratio of voltage to charge.

The elastance versus voltage for a conventional varact...

Table of contents

• Cover Page
• Half Title Page
• Title Page
• Copyright Page
• Preface
• Acknowledgments
• Editor-in-Chief
• Contents
• 1 Varactors
• 2 Schottky Diode Frequency Multipliers
• 3 Transit Time Microwave Devices
• 4 Bipolar Junction Transistors
• 5 Heterostructure Bipolar Transistors
• 6 Metal-Oxide-Semiconductor Field-Effect Transistors
• 7 Metal Semiconductor Field Effect Transistors
• 8 High Electron Mobility Transistors
• 9 RF Power Transistors from Wide Bandgap Materials
• 10 Monolithic Microwave IC Technology
• 11 Semiconductors
• 12 Metals
• 13 RF Package Design and Development
• 14 Thermal Analysis and Design of Electronic Systems
• 15 Low Voltage/Low Power Microwave Electronics
• 16 Technology Computer Aided Design
• 17 Nonlinear Transistor Modeling for Circuit Simulation
• Index