Chapter 6 The Use and Design of Passive Circuit Elements in IC Technologies

Chapter Chapter 6 The Use and Design of Passive Circuit Elements in IC Technologies

Radio Frequency Integrated Circuit Design Second Edition Book
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Radio Frequency Integrated Circuit Design Second Edition Book

  • c h a p t e r 6the Use and Design of passive circuit elements in Ic technologies6.1 IntroductionIn this chapter, passive circuit elements will be discussed. First, metalization and back-end processing (away from the silicon) in integrated circuits will be described. this is the starting point for many of the passive components. then, design, model-ing, and use of passive components will be discussed. these components are inter-connect lines, inductors, capacitors, transmission lines, and transformers. Finally, there will be a discussion of the impact of packaging.passive circuit elements such as inductors and capacitors are necessary compo-nents in rF circuits, but these components often limit performance, so it is worth-while to study their design and use. For example, inductors have many applications in rF circuits, as summarized in table 6.1. an important property of the inductor is that it can simultaneously provide low impedance to dc while providing nite ac impedance. In matching circuits or tuned loads, this allows active circuits to be biased at the supply voltage for maximum linearity. however, inductors are lossy, resulting in increased noise when used in an LNa or oscillator. When used in a power amplier, losses in inductors can result in decreased efciency. also, sub-strate coupling is a serious concern because of the typically large physical dimen-sions of the inductor.6.2 the technology Back end and Metalization in Ic technologiesafter all the front-end processing is complete, the active devices are connected using metal (the back end), which is deposited above the transistors as shown in Figure 6.1. the metals must be placed in an insulating layer of silicon dioxide (SiO2 ), to prevent different layers of metal from shorting with each other. Most processes have several layers of metal in their back end. these metal layers can also be used to build capacitors, inductors, and even resistors.the bottom metal is typically connected to the front end with tungsten plugs, which are highly resistive. however, unlike aluminum, gold, or copper, this metal has the property that it will not diffuse into the silicon. When metals such as copper diffuse into silicon, they cause the junction to leak, seriously impairing the perfor-mance of transistors. a contact layer is used to connect this tungsten layer to the active circuitry in the silicon. higher levels of metal can be connected to adjacent layers using conductive plugs that are commonly called vias. Whereas metal can be made in almost any shape desired by the designer, the vias are typically limited to