It is also valid to point out that it is entirely the result of scaling; being able to fabricate features in a semiconductor substrate with increasingly smaller dimensions. This is possible because the physical attributes of the substrate offer advantages only when scaling. It is best illustrated in terms of speed of operation, as well as the more obvious reduction in area required. The transistor's functionality is a result of the substrate's characteristics, which are influenced by - but not dependent upon - physical area.
For passive components, Moore's Law isn't really applicable; in fact, the reverse is nearer the truth. Physical area has much more influence on the functionality of passive components, based on the materials used. However, while the semiconductor industry is intrinsically tied to silicon dioxide for its substrate, manufacturers of passive components have a much more colourful palette from which to paint - and it is this ability to modify and improve on the materials used that is delivering benefits in discrete, passive components.
Playing their part
Discrete components remain fundamental to the design of electronic equipment, in many ways. As semiconductor integration forges ahead, the relative proportion of passive components in a BoM (bill of materials) continues to grow. Typically, passives can now represent 80% of a BoM's component count and 20% of the total cost. Without doubt it is the transistor, in the form of integrated circuits, that empowers the electronics industry, but it is its symbiotic relationship with passive components and the principals they embody which provides the structure for its success. Consequently, it is improbable that any electronics device today is capable of operating without the support of resistors, capacitors and inductors. From filters to suppressers and from charge pumps to circuit protection, passive components are an essential element of any design. In turn, it is also essential that their role in a design be given due consideration, as without it the benefits provided through highly integrated semiconductors could easily be eroded.
As with many aspects of electronics design, the exact solution will rely heavily on the requirements. This is, perhaps, even more relevant when selecting passive components than it is when designing-in semiconductors. Capacitors, for instance, fall into two broad categories; electrostatic, for lower-capacitance values, and electrolytic, for higher capacitance. Within each of these groups there are two sub-groups, based on the materials used: ceramic and film within electrostatic, and aluminium and tantalum for electrolytic.
Capacitors can be further sub-divided based on their application, for instance electrolytic capacitors operate under DC conditions and are polarised, while electrostatic ones are suitable for both AC and DC operation and are non-polarised. This is important because the application immediately imposes limitations on the level of capacitance available.
In terms of volumes shipped, ceramic capacitors represent the largest slice of this market and are used extensively in transient protection or power-supply decoupling for ICs and other circuit-protection applications. This also makes them the lowest-cost option, while tantalum-based electrolytic capacitors have seen continued price rises over recent years. Ceramic capacitors also offer larger capacitance and low ESR values in smaller package sizes, however, which can be an important factor in today's portable electronic equipment.
Along with ceramic capacitors, aluminium electrolytic capacitors are likely to feature highly on any BoM. They provide an optimised solution for decoupling, bulk storage, filtering and suppression tasks. However, they also come with some restrictions on their use, which many engineers may not be aware of. For example, when designing lighting ballasts, designers are encouraged to use aluminium electrolytic capacitors due to their large capacitance and relatively low cost. But because in lighting applications, such devices are typically subjected to elevated temperatures over very long periods of time, designers need to understand how ESR, capacitance and leakage current are affected. Electrolytic capacitors are also subject to variations in leakage current and capacitance within each manufacturing batch. These characteristics can result in operational variations from unit to unit and over the service life of a piece of OEM equipment.
Integrated passives
As with capacitors, there is a similar breakdown in resistors, in terms of materials used: carbon, metal, metal oxide are common for leaded devices. Demand for both resistors and capacitors manufactured using surface-mount technology, however, is increasing, and manufacturers such as NIC Components are meeting this demand through innovations in the materials used and the packaging developed, particularly with single-in-line and chip-level packaging.
Thick-film arrays of resistors offer massive savings in PCB area and are applicable to a growing number of designs. The same is being seen for both capacitors and inductors, as the pressure for ever-smaller hand-held devices grows.
The foundation of electronic engineering is built on principles that remain as important today as they were when first discovered. Like Moore's Law, the terms used are constant reminders of the pioneers to whom the industry owes so much: Alessandro Volta, André-Marie Ampère, James Watt, Michael Faraday, and Georg Ohm. These "natural philosophers" may have had some idea of how important their discoveries were in the early 19th century, but perhaps little appreciation for how significant they would remain nearly 200 years later.
Figure 1: NIC's NRSG radial leaded miniature aluminum electrolytic capacitors.
Figure 2: The NPI and NPIS series of surface-mount power inductors.
Figure 3: The NSHC and NSPU series of stacked film chip capacitors.
