Integrated Passives for High-Frequency Applications

Abstract

1.1 Definitions of Integrated Passives Passive elements are indispensable in RF systems and are used for matching networks, LC tank circuits, attenuators, filtering, decoupling purposes and so on (Tilmans H. A C et al., 2003). Passive elements can be simply classified into distributed elements including transmission lines and waveguides, and lumped elements including inductors, capacitors and resistors. The distributed circuits take into account the phase shift occurring when the signal wave propagates along the circuits. As the operating frequency moves into the microwave spectrum, the distributed circuits have a higher Q factor, and thus they are usually used for high-frequency applications. Lumped elements are zero-dimensional by definition. In other words, the lumped elements have no physical dimensions which are significant with respect to the wavelength at the operating frequency, so that the phase shift that arises can be ignored. Discrete lumped elements are conventionally used in electronic circuits that work at a lower frequency. This is because the sizes of the discrete lumped elements become comparable to the wavelength at microwave frequencies. With the advent of new photolithography and passive integration technologies, the three basic building blocks for circuit design-inductors, capacitors, and resistors can be made small enough to be available in lumped form (Tummala R. R. et al., 2000). Lumped passive components may be discrete, integrated or embedded. The discrete is a singular device in a leaded or surface mount technology (SMT) case. This includes screen-printed resistors, capacitors, and inductors. Passive integration technologies allow several passive components to be integrated, either into a substrate (embedded) or onto a substrate (integrated). Integrated passive devices usually come in a compact SMT package or chipscale package (CSP) as a stand-alone component with input, output and ground terminations, which is much smaller than the operating wavelength providing some complete circuit functions, such as impedance-matching, filtering and so on, for highfrequency applications up to several tens of GHz (Tilmans H. A C et al., 2003). The lumped element circuits have the advantage of a smaller size, lower cost, and wide-band characteristics, though the Q factor is generally lower than distributed circuits. Integrated lumped passive circuits with a small form factor are especially suitable for some RF and microwave applications where real estate or wide-band requirements are of prime importance, for example mobile phones or other handheld wireless products. The choice 13