“System on a Chip”, or SOC, refers to the integration of all the necessary electronic circuits of diverse functions onto a single chip, to come up with a complete electronic system that performs the more complex but more useful final product function.  Thus, instead of building an electronic product by assembling various chips and components on a circuit board, SOC technology will allow all of these parts to be fabricated together on a single chip, which can function as the final product itself. 

For instance, an SOC for electronic control of an automobile's suspension system will have the following distinct parts: 1) an accelerometer for detecting the car's motion; 2) an ADC for converting the accelerometer's analog output into digital data; 3) a digital signal processor for analyzing the digital data; 4) and an output driver system for controlling the mechanical behavior of the suspension system.  In an SOC, all of these functionally individual circuits will be contained on a single integrated circuit.

System-on-a-Chip (SOC) must not be confused with System-in-a-Package (SIP), which is a device that consists of multiple individually fabricated chips that make up a complete electronic system housed in a single package. Thus, SIP pertains to an advanced type of packaging technology, while SOC deals with microchip fabrication technology.

The advantages offered by SOC technology include:  1) higher performance, since all the circuits will be on a single chip; 2) smaller space requirements; 3) lower memory requirements;  4)  higher system reliability; and 5) lower consumer costs.

The challenges posed by SOC technology include:  1) larger design space; 2) higher design and prototyping costs; 3) longer design and prototyping cycle time; 4) more complex debugging; 5) lower IC yields and higher wafer fab costs due to the relatively larger die sizes involved; 6) integration of intellectual property from multiple (and possibly independent) sources. 

Figure 1. An acoustic SOC from Akustica, Inc. composed of

microphones, support electronics, and software on a standard

CMOS chip; source: http://www.archive.chipcenter.com

Aside from these challenges, the task of electrically testing SOC's is daunting as well. Automatic testers today are built along specific specialty areas, and only the most expensive test systems cater to a wide variety of device technologies. An SOC, in essence being composed of many different devices, requires a test system that can perform electrical testing on all its analog and digital circuit components.  SOC testing, therefore, generally requires high-end and consequently more expensive ATE systems.

Due to the complexities and high costs of developing viable SOC technologies, even large semiconductor companies have opted to co-develop SOC-based products with partner companies instead of going about it on their own.  For instance, Motorola, Philips and STMicroelectronics have started working together with TSMC to develop SOC processors that will power a wide variety of products - from set-top boxes to MP3 players to networking equipment.

IBM has also formed an alliance with Sony and Toshiba to create a new SOC processor architecture called Cell, which are expected to end up in Sony's PlayStation 3 game console.  AMD, on the other hand, has formed its 'Personal Connectivity Solutions' group, which will focus on SOC's for home-networking products.  Intel is doing the same thing with its XScale processor.

SOC development is a complicated activity that encompasses many disciplines, from circuit design to thermal management to test engineering.  Building an SOC from the design library of your own company is one thing, building one from several design libraries from different suppliers is another.  Making the various blocks from these different design libraries work together, even if they're not designed to be compatible with each other in the first place, is indeed a big challenge by itself already.

A high level of design reuse among design groups is needed to attain high productivity rates in SOC design. A common approach for design reuse is 'source reuse', which consists of reusing designs created elsewhere. Unfortunately, source reuse is not a very effective system in many cases, since it still involves understanding and redesigning of IP (intellectual property) blocks on the part of the SOC designer to make them useable in a new product.

A more effective reuse methodology, known as integration-driven reuse, allows the SOC designer to reuse an IP block without having to make changes to it. One approach for this is to use an integration platform, which is an SOC design environment that includes architectural specifications and pre-qualified IP blocks designed to work together on that platform. Philips is an example of a semiconductor company that employs integration platforms to meet their design productivity goals.

Given the high cost of SOC development, it is certainly not the solution for everything in the semiconductor industry.  SOC may be appropriate for high-volume production of not-too-complex systems, but not for low-volume production of complex systems that require different technologies. For the latter case, SIP may be a better choice.