Wafer-scale integration

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Wafer-scale integration, WSI for short, is a rarely used system of building very-large integrated circuit networks that use an entire silicon wafer to produce a single "super-chip". Combining large size and reduced packaging, WSI was expected to lead to dramatically reduced costs for some systems, notably massively parallel supercomputers. The name is taken from the term very-large-scale integration, the current state of the art when WSI was being developed.

Integrated circuit electronic circuit manufactured by lithography; set of electronic circuits on one small flat piece (or "chip") of semiconductor material, normally silicon

An integrated circuit or monolithic integrated circuit is a set of electronic circuits on one small flat piece of semiconductor material that is normally silicon. The integration of large numbers of tiny transistors into a small chip results in circuits that are orders of magnitude smaller, faster, and less expensive than those constructed of discrete electronic components. The IC's mass production capability, reliability, and building-block approach to circuit design has ensured the rapid adoption of standardized ICs in place of designs using discrete transistors. ICs are now used in virtually all electronic equipment and have revolutionized the world of electronics. Computers, mobile phones, and other digital home appliances are now inextricable parts of the structure of modern societies, made possible by the small size and low cost of ICs.

Wafer (electronics) thin slice of semiconductor material used in the fabrication of integrated circuits

In electronics, a wafer is a thin slice of semiconductor, such as a crystalline silicon (c-Si), used for the fabrication of integrated circuits and, in photovoltaics, to manufacture solar cells. The wafer serves as the substrate for microelectronic devices built in and upon the wafer. It undergoes many microfabrication processes, such as doping, ion implantation, etching, thin-film deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated by wafer dicing and packaged as an integrated circuit.

In computing, massively parallel refers to the use of a large number of processors to perform a set of coordinated computations in parallel (simultaneously).


The concept

To understand WSI, one has to consider the normal chip-making process. A single large cylindrical crystal of silicon is produced and then cut into disks known as wafers. The wafers are then cleaned and polished in preparation for the fabrication process. A photographic process is used to pattern the surface where material ought to be deposited on top of the wafer and where not to. The desired material is deposited and the photographic mask is removed for the next layer. From then on the wafer is repeatedly processed in this fashion, putting on layer after layer of circuitry on the surface.

Multiple copies of these patterns are deposited on the wafer in a grid fashion across the surface of the wafer. After all the possible locations are patterned, the wafer surface appears like a sheet of graph paper, with grid lines delineating the individual chips. Each of these grid locations is tested for manufacturing defects by automated equipment. Those locations that are found to be defective are recorded and marked with a dot of paint (this process is referred to as "inking a die" however modern wafer fabrication no longer requires physical markings to identify defective die). The wafer is then sawed apart to cut out the individual chips. Those defective chips are thrown away, or recycled, while the working chips are placed into packaging and re-tested for any damage that might occur during the packaging process.

Flaws on the surface of the wafers and problems during the layering/depositing process are impossible to avoid, and cause some of the individual chips to be defective. The revenue from the remaining working chips has to pay for the entire cost of the wafer and its processing, including those discarded defective chips. Thus, the higher number of working chips or higher yield, the lower the cost of each individual chip. In order to maximize yield one wants to make the chips as small as possible, so that a higher number of working chips can be obtained per wafer.

The vast majority of the cost of fabrication (typically 30%-50%)[ citation needed ] is related to testing and packaging the individual chips. Further cost is associated with connecting the chips into an integrated system (usually via a printed circuit board). Wafer-scale integration seeks to reduce this cost, as well as improve performance, by building larger chips in a single package in principle, chips as large as a full wafer.

Printed circuit board Board to support and connect electronic components

A printed circuit board (PCB) mechanically supports and electrically connects electronic components or electrical components using conductive tracks, pads and other features etched from one or more sheet layers of copper laminated onto and/or between sheet layers of a non-conductive substrate. Components are generally soldered onto the PCB to both electrically connect and mechanically fasten them to it.

Of course this is not easy, since given the flaws on the wafers a single large design printed onto a wafer would almost always not work. It has been an ongoing goal to develop methods to handle faulty areas of the wafers through logic, as opposed to sawing them out of the wafer. Generally, this approach uses a grid pattern of sub-circuits and "rewires" around the damaged areas using appropriate logic. If the resulting wafer has enough working sub-circuits, it can be used despite faults.

Production attempts

Early WSI attempt by Trilogy Systems. Trilogy WSI Wafer.png
Early WSI attempt by Trilogy Systems.

Many companies attempted to develop WSI production systems in the 1970s and 80s, but all failed. TI and ITT both saw it as a way to develop complex pipelined microprocessors and re-enter a market where they were losing ground, but neither released any products.

Texas Instruments American semiconductor designer and manufacturer

Texas Instruments Incorporated (TI) is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, Texas, United States. TI is one of the top-10 semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which account for more than 80% of their revenue. TI also produces TI digital light processing technology and education technology products including calculators, microcontrollers and multi-core processors. To date, TI has more than 45,000 patents worldwide.

Microprocessor Computer processor contained on an integrated-circuit chip

A microprocessor is a computer processor that incorporates the functions of a central processing unit on a single integrated circuit (IC), or at most a few integrated circuits. The microprocessor is a multipurpose, clock driven, register based, digital IC that accepts binary data as input, processes it according to instructions stored in its memory and provides results as output. Microprocessors contain both combinational logic and sequential digital logic. Microprocessors operate on numbers and symbols represented in the binary number system.

Gene Amdahl also attempted to develop WSI as a method of making a supercomputer, starting Trilogy Systems in 1980 [1] [2] [3] and garnering investments from Groupe Bull, Sperry Rand and Digital Equipment Corporation, who (along with others) provided an estimated $230 million in financing. The design called for a 2.5" square chip with 1200 pins on the bottom.

Gene Amdahl American computer architect and high-tech entrepreneur

Gene Myron Amdahl was an American computer architect and high-tech entrepreneur, chiefly known for his work on mainframe computers at IBM and later his own companies, especially Amdahl Corporation. He formulated Amdahl's law, which states a fundamental limitation of parallel computing.

Trilogy Systems

Trilogy Systems Corporation was a computer systems company started in 1980. Originally called ACSYS, the company was founded by Gene Amdahl, his son Carl Amdahl and Clifford Madden. Flush with the success of his previous company, Amdahl Corporation, Gene Amdahl was able to raise $230 million for his new venture. Trilogy was the most well funded start-up company up till that point in Silicon Valley history. It had corporate support from Groupe Bull, Digital Equipment Corporation, Unisys, Sperry Rand and others. The plan was to use extremely advanced semiconductor manufacturing techniques to build an IBM compatible mainframe computer that was both cheaper and more powerful than existing systems from IBM and Amdahl Corporation.

Groupe Bull French-owned computer company

Bull SAS is a French-owned computer company headquartered in Les Clayes-sous-Bois, in the western suburbs of Paris. The company has also been known at various times as Bull General Electric, Honeywell Bull, CII Honeywell Bull, and Bull HN. Bull was founded in 1931, as H.W. Egli - Bull, to capitalize on the punched card technology patents of Norwegian engineer Fredrik Rosing Bull (1882–1925). After a reorganization in 1933, with new owners coming in, the name was changed to Compagnie des Machines Bull (CMB). Bull has a worldwide presence in more than 100 countries, and is particularly active in the defense, finance, health care, manufacturing, public and telecommunication sectors.

The effort was plagued by a series of disasters, including floods which delayed the construction of the plant and later ruined the clean-room interior. After burning through about 1/3 of the capital with nothing to show for it, Amdahl eventually declared the idea would only work with a 99.99% yield, which wouldn't happen for 100 years. He used Trilogy's remaining seed capital to buy Elxsi, a maker of VAX-compatible computers, in 1985. The Trilogy efforts were eventually ended and "became" Elxsi.

Elxsi was a minicomputer manufacturing company established in the late 1970s along with a host of other competitors in Silicon Valley, USA. The Elxsi processor was an Emitter Coupled Logic (ECL) design that featured a 50-nanosecond clock, a 25-nanosecond backpanel bus, IEEE floating-point arithmetic and a 64-bit architecture. It allowed multiple processors to communicate over a common bus called the Gigabus, believed to be the first company to do so. The operating system was a message based operating system called EMBOS. The Elxsi CPU was a microcoded design, allowing custom instructions to be coded into microcode.

VAX Computer architecture, and a range of computers

VAX is a discontinued instruction set architecture (ISA) developed by Digital Equipment Corporation (DEC) in the mid-1970s. The VAX-11/780, introduced on October 25, 1977, was the first of a range of popular and influential computers implementing that architecture.


Recently, a startup called Cerebras Systems is attempting WSI for the purpose of machine learning workload accelerator systems. [4]

See also

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