Integrated passive elements

Passive components are ubiquitous in electronics, from the simplest to the most complex applications. As passive elements are bulky devices when compared to active devices such as transistors, it is attractive to seek to integrate them within chips. However, the integration of passive elements is a challenge in terms of the manufacturing process, since each passive component thus produced must have performance at least equivalent to that of its discrete counterpart to be of interest from an economic point of view.

The issues raised by the integration of passive components have not always aroused the same interest as for active components, particularly those integrated with CMOS technologies. Indeed, for the past 40 years, the world of microelectronics has been governed by Moore's Law, which has been in force since 1973, and is likely to remain so for a few more years before stalling due to parasitic physical effects. Most integration efforts have been focused on active components, and transistors in particular. Since 2004, the trend towards miniaturization has been slowed down by a wide range of technical difficulties, such as thermal dissipation, which prevents components from increasing in frequency despite their smaller size. These physical limitations make miniaturization increasingly difficult. The semiconductor industry cannot count on dividing transistor size from generation to generation, and must therefore find a new paradigm to continue reducing sizes and costs. At each technological node (180 nm, 90 nm, 65 nm, 45 nm, 32 nm, 22 nm...), previously negligible limitations become preponderant, and the slightest non-uniformity in the manufacturing process exponentially increases the dispersion of component characteristics.

The integration of passive elements is therefore less advanced than that of active elements, but the need for miniaturization in certain fields is tending to reduce the differences.

Certain fields of application increasingly require high-value passive components, which would benefit from a higher level of integration. This is the case for radio-frequency applications with decoupling capabilities, or for circuit power supply functions.

In this issue, we look at the problems associated with integration, with the various technological options and their influence on electrical performance. The technological aspect defines the main characteristics and electrical performance of these integrated elements. Next, the main passive components are reviewed, both from a manufacturing process point of view, with the materials commonly used and the structure of the components, and from an electrical point of view, with the main characteristics and performance achieved. The basic passive elements - resistors,...