Advances in integrated circuits






The integrated circuit from an Intel 8742, an 8-bit microcontroller that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of EPROM, and I/O in the same chip.
The integrated circuit from an Intel 8742, an 8-bit microcontroller that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of EPROM, and I/O in the same chip.

Among the most advanced integrated circuits are the microprocessors or "cores", which control everything from computers to cellular phones to digital microwave ovens. Digital memory chips and ASICs are examples of other families of integrated circuits that are important to the modern information society. While cost of designing and developing a complex integrated circuit is quite high, when spread across typically millions of production units the individual IC cost is minimized. The performance of ICs is high because the small size allows short traces which in turn allows low power logic (such as CMOS) to be used at fast switching speeds.

ICs have consistently migrated to smaller feature sizes over the years, allowing more circuitry to be packed on each chip. This increased capacity per unit area can be used to decrease cost and/or increase functionality—see Moore's law which, in its modern interpretation, states that the number of transistors in an integrated circuit doubles every two years. In general, as the feature size shrinks, almost everything improves—the cost per unit and the switching power consumption go down, and the speed goes up. However, ICs with nanometer-scale devices are not without their problems, principal among which is leakage current (see subthreshold leakage for a discussion of this), although these problems are not insurmountable and will likely be solved or at least ameliorated by the introduction of high-k dielectrics. Since these speed and power consumption gains are apparent to the end user, there is fierce competition among the manufacturers to use finer geometries. This process, and the expected progress over the next few years, is well described by the International Technology Roadmap for Semiconductors (ITRS).

[edit] Popularity of ICs

Main article: Microchip revolution

Only a half century after their development was initiated, integrated circuits have become ubiquitous. Computers, cellular phones, and other digital appliances are now inextricable parts of the structure of modern societies. That is, modern computing, communications, manufacturing and transport systems, including the Internet, all depend on the existence of integrated circuits. Indeed, many scholars believe that the digital revolution—brought about by the microchip revolution—was one of the most significant occurrences in the history of humankind.

[edit] Classification
A CMOS 4000 IC in a DIP
A CMOS 4000 IC in a DIP

Integrated circuits can be classified into analog, digital and mixed signal (both analog and digital on the same chip).

Digital integrated circuits can contain anything from a few thousand to millions of logic gates, flip-flops, multiplexers, and other circuits in a few square millimeters. The small size of these circuits allows high speed, low power dissipation, and reduced manufacturing cost compared with board-level integration. These digital ICs, typically microprocessors, DSPs, and micro controllers work using binary mathematics to process "one" and "zero" signals.

Analog ICs, such as sensors, power management circuits, and operational amplifiers, work by processing continuous signals. They perform functions like amplification, active filtering, demodulation, mixing, etc. Analog ICs ease the burden on circuit designers by having expertly designed analog circuits available instead of designing a difficult analog circuit from scratch.

ICs can also combine analog and digital circuits on a single chip to create functions such as A/D converters and D/A converters. Such circuits offer smaller size and lower cost, but must carefully account for signal interference.

[edit] Manufacture

[edit] Fabrication

Main article: Semiconductor fabrication

Rendering of a small standard cell with three metal layers (dielectric has been removed). The sand-colored structures are metal interconnect, with the vertical pillars being contacts, typically plugs of tungsten. The reddish structures are polysilicon gates, and the solid at the bottom is the crystalline silicon bulk.
Rendering of a small standard cell with three metal layers (dielectric has been removed). The sand-colored structures are metal interconnect, with the vertical pillars being contacts, typically plugs of tungsten. The reddish structures are polysilicon gates, and the solid at the bottom is the crystalline silicon bulk.

The semiconductors of the periodic table of the chemical elements were identified as the most likely materials for a solid state vacuum tube by researchers like William Shockley at Bell Laboratories starting in the 1930s. Starting with copper oxide, proceeding to germanium, then silicon, the materials were systematically studied in the 1940s and 1950s. Today, silicon monocrystals are the main substrate used for integrated circuits (ICs) although some III-V compounds of the periodic table such as gallium arsenide are used for specialized applications like LEDs, lasers, solar cells and the highest-speed integrated circuits. It took decades to perfect methods of creating crystals without defects in the crystalline structure of the semiconducting material.

Semiconductor ICs are fabricated in a layer process which includes these key process steps:

* Imaging
* Deposition
* Etching

The main process steps are supplemented by doping, cleaning and polarization steps.

Mono-crystal silicon wafers (or for special applications, silicon on sapphire or gallium arsenide wafers) are used as the substrate. Photolithography is used to mark different areas of the substrate to be doped or to have polysilicon, insulators or metal (typically aluminum) tracks deposited on them.

* Integrated circuits are composed of many overlapping layers, each defined by photolithography, and normally shown in different colors. Some layers mark where various dopants are diffused into the substrate (called diffusion layers), some define where additional ions are implanted (implant layers), some define the conductors (polysilicon or metal layers), and some define the connections between the conducting layers (via or contact layers). All components are constructed from a specific combination of these layers.

* In a self-aligned CMOS process, a transistor is formed wherever the gate layer (polysilicon or metal) crosses a diffusion layer.

* Resistive structures, meandering stripes of varying lengths, form the loads on the circuit. The ratio of the length of the resistive structure to its width, combined with its sheet resistivity determines the resistance.

* Capacitive structures, in form very much like the parallel conducting plates of a traditional electrical capacitor, are formed according to the area of the "plates", with insulating material between the plates. Owing to limitations in size, only very small capacitances can be created on an IC.

* More rarely, inductive structures can be built as tiny on-chip coils, or simulated by gyrators.

Since a CMOS device only draws current on the transition between logic states, CMOS devices consume much less current than bipolar devices.

A random access memory is the most regular type of integrated circuit; the highest density devices are thus memories; but even a microprocessor will have memory on the chip. (See the regular array structure at the bottom of the first image.) Although the structures are intricate – with widths which have been shrinking for decades – the layers remain much thinner than the device widths. The layers of material are fabricated much like a photographic process, although light waves in the visible spectrum cannot be used to "expose" a layer of material, as they would be too large for the features. Thus photons of higher frequencies (typically ultraviolet) are used to create the patterns for each layer. Because each feature is so small, electron microscopes are essential tools for a process engineer who might be debugging a fabrication process.

Each device is tested before packaging using automated test equipment (ATE), in a process known as wafer testing, or wafer probing. The wafer is then cut into rectangular blocks, each of which is called a die. Each good die (plural dice, dies, or die) is then connected into a package using aluminum (or gold) wires which are welded to pads, usually found around the edge of the die. After packaging, the devices go through final testing on the same or similar ATE used during wafer probing. Test cost can account for over 25% of the cost of fabrication on lower cost products, but can be negligible on low yielding, larger, and/or higher cost devices.

As of 2005, a fabrication facility (commonly known as a semiconductor fab) costs over a billion US Dollars to construct[10], because much of the operation is automated. The most advanced processes employ the following techniques:

* The wafers are up to 300 mm in diameter (wider than a common dinner plate).
* Use of 65 nanometer or smaller chip manufacturing process. Intel, IBM, NEC, and AMD are using 45 nanometers for their CPU chips, and AMD[1] and NEC have started using a 65 nanometer process. IBM and AMD are in development of a 45 nm process using immersion lithography.
* Copper interconnects where copper wiring replaces aluminum for interconnects.
* Low-K dielectric insulators.
* Silicon on insulator (SOI)
* Strained silicon in a process used by IBM known as strained silicon directly on insulator (SSDOI)

[edit] Packaging

Main article: Integrated circuit packaging

The earliest integrated circuits were packaged in ceramic flat packs, which continued to be used by the military for their reliability and small size for many years. Commercial circuit packaging quickly moved to the dual in-line package (DIP), first in ceramic and later in plastic. In the 1980s pin counts of VLSI circuits exceeded the practical limit for DIP packaging, leading to pin grid array (PGA) and leadless chip carrier (LCC) packages. Surface mount packaging appeared in the early 1980s and became popular in the late 1980s, using finer lead pitch with leads formed as either gull-wing or J-lead, as exemplified by small-outline integrated circuit -- a carrier which occupies an area about 30 – 50% less than an equivalent DIP, with a typical thickness that is 70% less. This package has "gull wing" leads protruding from the two long sides and a lead spacing of 0.050 inches.

Small-outline integrated circuit (SOIC) and PLCC packages. In the late 1990s, PQFP and TSOP packages became the most common for high pin count devices, though PGA packages are still often used for high-end microprocessors. Intel and AMD are currently transitioning from PGA packages on high-end microprocessors to land grid array (LGA) packages.

Ball grid array (BGA) packages have existed since the 1970s. Flip-chip Ball Grid Array packages, which allow for much higher pin count than other package types, were developed in the 1990s. In an FCBGA package the die is mounted upside-down (flipped) and connects to the package balls via a package substrate that is similar to a printed-circuit board rather than by wires. FCBGA packages allow an array of input-output signals (called Area-I/O) to be distributed over the entire die rather than being confined to the die periphery.

Traces out of the die, through the package, and into the printed circuit board have very different electrical properties, compared to on-chip signals. They require special design techniques and need much more electric power than signals confined to the chip itself.

When multiple dies are put in one package, it is called SiP, for System In Package. When multiple dies are combined on a small substrate, often ceramic, it's called an MCM, or Multi-Chip Module. The boundary between a big MCM and a small printed circuit board is sometimes fuzzy.

[edit] Other developments

In the 1980's programmable integrated circuits were developed. These devices contain circuits whose logical function and connectivity can be programmed by the user, rather than being fixed by the integrated circuit manufacturer. This allows a single chip to be programmed to implement different LSI-type functions such as logic gates, adders, and registers. Current devices named FPGAs (Field Programmable Gate Arrays) can now implement tens of thousands of LSI circuits in parallel and operate up to 550 MHz.

The techniques perfected by the integrated circuits industry over the last three decades have been used to create microscopic machines, known as MEMS. These devices are used in a variety of commercial and military applications. Example commercial applications include DLP projectors, inkjet printers, and accelerometers used to deploy automobile airbags.

In the past, radios could not be fabricated in the same low-cost processes as microprocessors. But since 1998, a large number of radio chips have been developed using CMOS processes. Examples include Intel's DECT cordless phone, or Atheros's 802.11 card.

Future developments seem to follow the multi-microprocessor paradigm, already used by the Intel and AMD dual-core processors. Intel recently unveiled a prototype, "not for commercial sale" chip that bears a staggering 80 microprocessors. Each core is capable of handling its own task independently of the others. This is in response to the heat-versus-speed limit that is about to be reached using existing transistor technology. This design provides a new challenge to chip programming. X10 is the new open-source programming language designed to assist with this task. [11]

[edit] Silicon graffiti

Ever since ICs were created, some chip designers have used the silicon surface area for surreptitious, non-functional images or words. These are sometimes referred to as Chip Art, Silicon Art, Silicon Graffiti or Silicon Doodling. For an overview of this practice, see the article The Secret Art of Chip Graffiti, from the IEEE magazine Spectrum and the Silicon Zoo.

[edit] Key industrial and academic data
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[edit] Notable ICs

* The 555 common multi-vibrator sub-circuit (common in electronic timing circuits)
* The 741 operational amplifier
* 7400 series TTL logic building blocks
* 4000 series, the CMOS counterpart to the 7400 series
* Intel 4004, the world's first microprocessor
* The MOS Technology 6502 and Zilog Z80 microprocessors, used in many home computers

[edit] Manufacturers

A list of notable manufacturers; some operating, some defunct:

* Agere Systems (now part of LSI Logic formerly part of Lucent, which was formerly part of AT&T)
* Agilent Technologies (formerly part of Hewlett-Packard, spun-off in 1999)
* Alcatel
* Altera
* AMD (Advanced Micro Devices; founded by ex-Fairchild employees)
* Analog Devices
* ATI Technologies (Array Technologies Incorporated; acquired parts of Tseng Labs in 1997; in 2006, became a wholly-owned subsidiary of AMD)
* Atmel (co-founded by ex-Intel employee)
* Broadcom
* Commodore Semiconductor Group (formerly MOS Technology)
* Cypress Semiconductor
* Fairchild Semiconductor (founded by ex-Shockley Semiconductor employees: the "Traitorous Eight")
* Freescale Semiconductor (formerly part of Motorola)
* Fujitsu
* Genesis Microchip
* GMT Microelectronics (formerly Commodore Semiconductor Group)
* Hitachi, Ltd.
* Horizon Semiconductors
* IBM (International Business Machines)
* Infineon Technologies (formerly part of Siemens)
* Integrated Device Technology
* Intel (founded by ex-Fairchild employees)
* Intersil (formerly Harris Semiconductor)
* Lattice Semiconductor
* Linear Technology
* LSI Logic (founded by ex-Fairchild employees)
* Maxim Integrated Products
* Marvell Technology Group
* Microchip Technology Manufacturer of the PIC microcontrollers
* MicroSystems International
* MOS Technology (founded by ex-Motorola employees)
* Mostek (founded by ex-Texas Instruments employees)
* National Semiconductor (aka "NatSemi"; founded by ex-Fairchild employees)
* Nordic Semiconductor (formerly known as Nordic VLSI)
* Nvidia (acquired IP of competitor 3dfx in 2000; 3dfx was co-founded by ex-Intel employee)
* NXP Semiconductors (formerly part of Philips)
* ON Semiconductor (formerly part of Motorola)
* Parallax Inc.Manufacturer of the BASIC Stamp and Propeller Microcontrollers
* PMC-Sierra (from the former Pacific Microelectronics Centre and Sierra Semiconductor, the latter co-founded by ex-NatSemi employee)
* Renesas Technology (joint venture of Hitachi and Mitsubishi Electric)
* Rohm
* Samsung Electronics (Semiconductor division)
* STMicroelectronics (formerly SGS Thomson)
* Texas Instruments
* Toshiba
* TSMC (Taiwan Semiconductor Manufacturing Company. semiconductor foundry)
* u-blox (Fabless GPS semiconductor provider)
* VIA Technologies (founded by ex-Intel employee) (part of Formosa Plastics Group)
* Volterra Semiconductor
* Xilinx (founded by ex-ZiLOG employee)
* ZiLOG (founded by ex-Intel employees)