Large-scale integration

Large-scale integration (LSI) is the process of creating MOS integrated circuits (MOS IC) by combining thousands of MOS transistors onto a single integrated circuit (IC) chip. LSI began in the early 1970s when MOS integrated circuit chips were widely adopted, enabling complex semiconductor and telecommunication technologies to be developed. The microprocessor and memory chips are LSI devices. Before the introduction of LSI technology, most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU, ROM, RAM and other glue logic. LSI lets IC designers add all of these into one chip.

History

Background

The history of the transistor dates to the 1920s when several inventors attempted devices that were intended to control current in solid-state diodes and convert them into triodes. Success came after World War II, when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication and theory. Scientists who had worked on radar returned to solid-state device development. With the invention of the first transistor at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state devices.

With the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits. However, as the complexity of circuits grew, problems arose. One problem was the size of the circuit. A complex circuit like a computer was dependent on speed. If the components were large, the wires interconnecting them must be long. The electric signals took time to go through the circuit, thus slowing the computer.

The invention of the integrated circuit solved this problem by making all the components and the chip out of the same block (monolith) of semiconductor material. The circuits could be made smaller, and the manufacturing process could be automated. This led to the idea of integrating all components on a single-crystal silicon wafer, which led to small-scale integration (SSI) in the early 1960s, and then medium-scale integration (MSI) in the late 1960s.

LSI

Further information: MOS integrated circuit and MOS transistor

MOS transistor, the basic building block of LSI MOS chips.

Mohamed M. Atalla invented the MOS transistor (1959) and MOS integrated circuit chip (1960), the basis for LSI technology.

Large-scale integration was made possible with the wide adoption of the MOS transistor, originally invented by Mohamed M. Atalla and Dawon Kahng at Bell Labs in 1959. Atalla first proposed the concept of the MOS integrated circuit chip in 1960, followed by Kahng in 1961, both noting that the MOS transistor's ease of fabrication made it useful for integrated circuits. General Microelectronics introduced the first commercial MOS integrated circuit in 1964. In the early 1970s, MOS integrated circuit technology allowed the integration of more than 10,000 transistors in a single chip. This paved the way for LSI in the 1970s and VLSI in the 1980s, with tens of thousands of MOS transistors on a single chip (later hundreds of thousands, then millions, and now billions).

The first semiconductor chips held two transistors each. Subsequent advances added more transistors, and as a consequence, more individual functions or systems were integrated over time. The first integrated circuits held only a few devices, perhaps as many as ten diodes, transistors, resistors and capacitors, making it possible to fabricate one or more logic gates on a single device. Now known retrospectively as small-scale integration (SSI), improvements in technique led to devices with hundreds of logic gates, known as medium-scale integration (MSI). Further improvements led to large-scale integration (LSI), i.e. systems with at least a thousand logic gates. Current technology has moved far past this mark and today's microprocessors have many millions of gates and billions of individual transistors.

Further development, driven by the same MOSFET scaling technology and economic factors, led to "large-scale integration" (LSI) by the mid-1970s, with tens of thousands of transistors per chip.

The masks used to process and manufacture SSI, MSI and early LSI and VLSI devices (such as the microprocessors of the early 1970s) were mostly created by hand, often using Rubylith-tape or similar. For large or complex ICs (such as memories or processors), this was often done by specially hired professionals in charge of circuit layout, placed under the supervision of a team of engineers, who would also, along with the circuit designers, inspect and verify the correctness and completeness of each mask.

Integrated circuits such as 1K-bit RAMs, calculator chips, and the first microprocessors, that began to be manufactured in moderate quantities in the early 1970s, had under 4,000 transistors. True LSI circuits, approaching 10,000 transistors, began to be produced around 1974, for computer main memories and second-generation microprocessors.

Some SSI and MSI chips, like discrete transistors, are still mass-produced, both to maintain old equipment and build new devices that require only a few gates. The 7400 series of TTL chips, for example, has become a de facto standard and remains in production.

VLSI

Main article: VLSI

The final step in the development process, starting in the 1980s and continuing through the present, is very large-scale integration (VLSI). The development started with hundreds of thousands of transistors in the early 1980s, since 2016, transistor counts continue to grow beyond ten billion transistors per chip.

Multiple developments were required to achieve this increased density. Manufacturers moved to smaller MOSFET design rules and cleaner fabrication facilities so that they could make chips with more transistors and maintain adequate yield. The path of process improvements was summarized by the International Technology Roadmap for Semiconductors (ITRS), which has since been succeeded by the International Roadmap for Devices and Systems (IRDS). Electronic design tools improved enough to make it practical to finish these designs in a reasonable time. The more energy-efficient CMOS replaced NMOS and PMOS, avoiding a prohibitive increase in power consumption. Modern VLSI devices contain so many transistors, layers, interconnections, and other features that it is no longer feasible to check the masks or do the original design by hand. Instead, engineers use EDA tools to perform most functional verification work.

In 1986 the first one-megabit random-access memory (RAM) chips were introduced, containing more than one million transistors. Microprocessor chips passed the million-transistor mark in 1989 and the billion-transistor mark in 2005. The trend continues largely unabated, with chips introduced in 2007 containing tens of billions of memory transistors.

At one time, there was an effort to name and calibrate various levels of large-scale integration above VLSI. Terms like ultra-large-scale integration (ULSI) were used. But the huge number of gates and transistors available on common devices has rendered such fine distinctions moot. Terms suggesting greater than VLSI levels of integration are no longer in widespread use.

In 2008, billion-transistor processors became commercially available. This became more commonplace as semiconductor fabrication advanced from the then-current generation of 65 nm processes. Current designs, unlike the earliest devices, use extensive design automation and automated logic synthesis to lay out the transistors, enabling higher levels of complexity in the resulting logic functionality. Certain high-performance logic blocks like the SRAM (static random-access memory) cell, are still designed by hand to ensure the highest efficiency.

See also

• System on a chip (SoC)
• Neuromorphic engineering
• Application-specific integrated circuit
• Caltech Cosmic Cube
• Design rules checking
• Electronic design automation
• Mead & Conway revolution
• Polysilicon

Further reading

• Baker, R. Jacob (2010). CMOS: Circuit Design, Layout, and Simulation, Third Edition. Wiley-IEEE. p. 1174. ISBN 978-0-470-88132-3. http://CMOSedu.com/
• Weste, Neil H. E.; Harris, David M. (2010). CMOS VLSI Design: A Circuits and Systems Perspective, Fourth Edition. Boston: Pearson/Addison-Wesley. p. 840. ISBN 978-0-321-54774-3. {{cite book}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help) http://CMOSVLSI.com/
• Chen, Wai-Kai (ed) (2006). The VLSI Handbook, Second Edition (Electrical Engineering Handbook). Boca Raton: CRC. ISBN 0-8493-4199-X. {{cite book}}: |author= has generic name (help)
• Mead, Carver A. and Conway, Lynn (1980). Introduction to VLSI systems. Boston: Addison-Wesley. ISBN 0-201-04358-0.{{cite book}}: CS1 maint: multiple names: authors list (link)

External links

• Lectures on Design and Implementation of VLSI Systems at Brown University
• List of VLSI companies around the world
• Design of VLSI Systems
• Complete VLSI Design Flow