Short History of Integrated Circuits
At around 1940, computers consisted of thousands of vacuum tubes that were individually wired together in a very complex and expensive way. This design not only required a great deal of electricity, but it was also very maintenance-intensive. The ENIAC computer from 1946 had over 17.000 vacuum tubes and suffered a tube failure on average every two days, which was time-consuming to troubleshoot and repair. With the invention of the transistor in 1947 by Bell Labs, the components became significantly smaller, but the transistors were still wired together individually. This reduced power consumption of those computers and their overall size, but not their wiring complexity. It was not before the invention of integrated circuits before computers became way more efficient and easier to operate and maintain. Although an early concept for an integrated circuit goes back to 1949, it was ten years later when Robert Noyce (Fairchild Semiconductor) invented and patented the first monolithic integrated circuit chip based on a silicon substrate. At the same time, Jack Kilby (Texas Instruments) was working on a similar concept. In 1971, the Intel 4004 microprocessor was released. It is considered to be the first commercially produced microprocessor. It accomodated 2.250 transistors in a single chip, and came in a 16 pin Dual-Inline Package (DIP). Since that date, subsequent generations of microprocessors have been released with rapidly increasing transistor counts and operation speeds. An ever increasing demand for integrated circuits by consumers and businesses has allowed semiconductor production to grow to a global industry that made over 400 billion USD in annual sales in the year 2019.
History of IC Packaging Trends and Technologies
Since the 1970s, a large variety of IC packages has evolved. Although some package types have been introduced over 40 years ago, they are still widely used today. Dual InLine Packages (DIP), Small Outline Packages (SOP) or Quad Flat Packages (QFP) can still be found in today’s electronic devices. Land Grid Array (LGA) packages are still first choice in today’s high performance computer systems. Most recent developments including Interposer-based 2.5D ICs (2.5D IC) and 3D ICs (3D IC) are optimized packages for applications in tiny devices such as smartphones and smartwatches. The timeline below gives an overview of microchip packaging developments over the past years.
Advantages of Integrated Circuits
The large success of integrated circuits can be attributed to several different factors and advantages.
- Low size and weight: Integrated circuits may contain millions or billions of transistors in one silicon chip which dramatically reduces the size and weight of electronic devices compared to those built from discrete components.
- Low power consumption: Integrated circuits require less power than discrete circuit designs.
- Increased operating speed: Transistors that are located closer together can communicate faster. Therefore, densely packed integrated circuits operate faster than discrete circuits where components are further apart.
- Low production cost: Although integrated circuits are very complex in production, their mass production has greatly reduced the price of microchips. As the number of transistors in a microchip is typically very high, the cost per transistor is extremely low compared to the production of discrete transistors.
- High overall reliability: Integrated circuits have a very low failure rate due to the fact that they are produced in a highly controlled and clean environment. They do not rely on solder connections but only have a few micro-welded interconnections that are very durable. Also, they are sealed in a protective and shock-resistant epoxy package.
- High temperature stability: Integrated circuits can get hot and may need additional cooling, but they still operate at very high performance even at increased temperatures.
- Low maintenance cost: Damaged or faultly integrated circuits can easily be replaced by a new chip.
What’s inside a microchip?
Microchips come in various shapes and with various sizes. What they all have in common is that their outer appearance doesn’t reveal what’s inside. Looking at a cutaway diagram of a typical microchip in a Quad Flat Package (QFP), tiny structures become visible. Every package of a microchip accomodates an active device – the IC chip or IC die – the silicon centerpiece with countless circuits in it. The IC die is permanently attached to the package via a thin film of adhesive. Tiny bond wires connect the IC die with the lead wires of the IC package. The package itself protects the highly sensitive IC die from environmental attack, dissipates heat, and provides power and signal connections.
Moore’s Law is an observation that was issued in 1965 by Gordon Moore, the co-founder of Fairchild Semiconductor and CEO and co-founder of Intel. He observed that the number of transistors in an integrated circuit doubles roughly every year, and he predicted that this rate of growth would continue for at least another decade. Ten years later, he published an update, revising the doubling period to every two years. The figure below shows the validity of Moore’s Law until today. All data points indicate the release dates of Intel microprocessors.
Breaking down the complexity
The complexity within an integrated circuit that has millions or even billions of transistors is incredibly high. It is therefore impossible to look onto an IC chip through a microscope and to comprehend the range of functions the particular chip offers. The only conceivable way to understand integrated circuits is to focus on individual levels of abstraction and to understand the underlying electronical principles of that level before looking at another level.
Thinking in levels of abstraction greatly improves the understanding and readability of even complex digital systems. The following chapter starts at the level with the smallest units – transistors – which has the lowest complexity, and gradually abstracts to higher levels. Every new level of abstraction can be seen as a short summary of the previous level, often using short symbols that save space and carry more information. In this way, a total of six levels of abstraction will be described by using simple analogies and illustrations to break down the complexity.
- Transistor Level: This level of abstraction focuses on transistors, the smallest devices within an integrated circuit.
- Circuit Level: Technically not a separate level of abstraction, but helps to understand how transistors operate.
- Logic Gates Level: Circuit designs to create logic gates (AND, OR, others)
- Register Transfer Level: Combination of logic gates to create functional units (latches, flip flops, registers, encoders, decoders, multiplexers, demultiplexers, arithmetic logic units)
- Architecture Level: Also known as microarchitecture level. Interactions and data flows between functional units, control units.
- System Level: Design of what the chip is and how it behaves (central processing unit, graphics processing unit, memory, system-on-a-chip, others), definition of input and output.