Semiconductor Design

Designing the chips that make our devices smart

This is the second of a three-part series on the semiconductor industry – from contextualizing the industry, to designing of a chip, to manufacturing and packaging it.

Part-1: https://www.dhirubhai.net/pulse/semiconductor-imperative-pvg-menon-l6avc/?trackingId=%2FML9MssTTRiFEwG7DUjedQ%3D%3D

The above diagram graphically illustrates the value chain in the electronic product. At the core is the integrated circuit or chip. It is manufactured or “fabricated” at a Semiconductor Foundry (aka “Fab”). The processed wafer, with multiple chips on it as individual “dies” is then further processed at an Assembly-Test-Mark-Package (ATMP) facility, where the individual dies are cut from the large wafer, pins attached to them (wire-bonding), then they are individually packaged and stamped. These are then soldered onto Printed Circuit Boards (PCB’s) by Electronic Manufacturing Services (EMS) providers (aka “contract manufacturers”) – who may provide this service to various brands. At the outer-most circle are the electronic systems makers – who make the (end) products that consumer can actually touch and feel and use – smartphones, laptops, medical devices, industrial devices, automotive electronics etc.

?The entire ecosystem can be conceived of like an onion – each successive peel represents a different part of the entire complex and multi-faceted electronics ecosystem. Each builds on the previous layer, and each adds value to the succeeding layer.

?And the beauty is that almost each layer is a mini ecosystem of its own. Each has its own innovations and key players. Each adds value.

?In this article, we examine the process by which a semiconductor chip is designed.

?Semiconductors – The core of an electronics product

Now let us focus on the innermost core of the onion – the chip. It is this tiny silicon device that provides the ‘intelligence’ or ‘brains’ to any electronic product. It is what makes smartphone ‘smart’, or powers the ‘intelligence’ behind AI-enabled products. They are ubiquitous and present everywhere – from a simple baby’s rattle (toy) to complex circuits powering aircraft or enabling cars to be driven. From powering mission-critical industrial systems to life-saving medical devices.

The design of a chip is a mix of cutting-edge innovation combined with engineering rigor. The design is done using CAD tools which literally hundreds of thousands of man years of design knowledge encapsulated in them. It would be no exaggeration to say that a semiconductor chip usually represents the finest realization of human innovation and engineering excellence – from the way it was designed, to the way it was manufactured, and ultimately to the functionality it enables in the equipment it powers. No wonder then it is called the “brains” of an electronic product.

Yet very little is known about the manner in which a chip is designed.

?What is an Integrated Circuit?

?Let us start by defining what a semiconductor chip or Integrated Circuit actually is.

Also known as a microchip, a semiconductor chip or integrated circuit (IC) is a small piece of semiconductor material made of silicon that is used to create a wide range of electronic devices and systems. They are the foundation of modern electronics and are used in a wide variety of products like computers, cell phones, medical devices, automotive products, industrial products etc.

These IC’s are made by etching small circuits, made up of a variety of electronic components, onto a piece of semiconductor material. Etching patterns into a thin slice of semiconductor material is done using photolithography -- a process that involves exposing the material to light through a mask or stencil. The patterns are then filled in with various conductive metals, to create the various components of the IC. The finished chip is then mounted on a circuit board and connected to other components using tiny wires or metal (copper) traces.

At a top level, the definition of a 4-step process for chip design, as enunciated by Synopsys Inc, a leading Electronic Design Automation (EDA) company, is worth repeating here.

1.???? Architectural design of the chip, wherein the parameters of the chip are determined including its size, desired function, level of power consumption, and preferred cost.

2.???? Logic and circuit design. After the parameters are outlined, engineers begin translating the required functions into circuit logic. Today, this process is done on automated logic simulators to verify that everything is in order before production.

3.???? Physical design phase. Here, the circuit logic is mapped onto a silicon wafer. Essentially, this is a plan of where each transistor, diode, or other component will sit on the chip.

4.???? Verification and sign-off phases are used to verify whether the designed chip is manufacture-able or not, and whether it can withstand the stresses and performance requirements of its assigned function. Specifically, added resistance from wiring, signal crosstalk, and variability are all factors to be considered.

What is meant by “designing a chip”?

Designing a semiconductor chip like say the Intel i7 microprocessor requires a combination of technical expertise, problem-solving skills, and the ability to work effectively in a multi-disciplinary team setting. Apart from a good grasp of technical skills, these are very complex development projects with many hundreds, even thousands of man years of development effort. Chips design tests every aspect of technical knowledge of the engineers and utilizes advanced project management tools and skills to make sure that all the different aspects are controlled, in time and on budget. A design and verification team for a complex chip can be quite large, with each team working on some esoteric part of the chip’s functionality. Hence managing the whole development process efficiently and tightly, ensuring adherence to the functional specifications etc, is a rigorous task.

The actual process of designing a semiconductor chip involves several different steps and can be quite complex. The actual design of chips is done using powerful and feature-rich Electronic Design Automation (EDA) tools, which are essentially very complex CAD tools used in chip design. Usually the chip design process includes licensing and integrating several IP (intellectual property) blocks. The process is expensive, rigorous and heavily monitored by professionally trained project managers. It is not uncommon to have several tens or even hundreds of millions of dollars in costs spent in this complex process of conceiving and designing a chip. All spent B-E-F-O-R-E the chip is sent for manufacturing!

Below, I try and give a simplified overview of the main steps involved in designing a chip:

1.???? Determine the desired functionality: The first step in designing a semiconductor chip is to define the desired functionality and performance requirements in as much detail as possible. This includes deciding on the specific circuits and components that will be included on the chip, as well as the required input/output and communication interfaces. The definition of functionality will also involve selection of various Intellectual Property (IP) blocks wherein specific functionality (eg USB or BlueTooth or WiFi connectivity, DRAM memory caches etc) are added from previously available sources.? Choices of the processor to be used (a RISC processor from say ARM, or an x86 series CISC processor etc), the bus to be used, the instruction set architecture (ISA) – all of these vital choices have to be made even before the project team is formed. Many times this is dictated by the set of customers or application area, and sometimes (very rarely) this is also dictated by the constraints of the production facilities available.

2.???? Create a circuit design: Once the desired functionality has been defined, the next step is to create a detailed circuit design. This typically involves using computer-aided design tools (known as EDA tools) to draw the circuit diagram, and to simulate and test the design to ensure that it meets the required specifications. A lot of time is spent in verifying the circuit design using verification tools which have rigorous rules coded into them. Based on the functionality and the application context, additional use-case specific test suites are also designed and run – for instance a SoC with similar architecture (but perhaps different peripherals) could be made for both say a telecom infra and a consumer electronics application. But the test plan and test suites would be very different for the two chips.

3.???? Create a layout: The next step is to create a layout of the chip, which defines the physical placement and interconnection of the various components and circuits on the chip. This is typically done using specialized layout tools and software.

4.???? Fabricate the chip: Once the chip design and layout are complete, the next step is to fabricate the chip. First a process called “tape out” is done to set the files to the (typically) commercial semiconductor foundry which will actually fabricate the chip. Consider this as the equivalent of taking the manuscript of a book after the page layout process is complete, and sending to the printer who will mass print the book using say offset printing technology. Fabricating a chip involves multiple stages. It starts with creating a photolithography mask, which is used to transfer the pattern of the chip layout onto a silicon wafer. The wafer is then subjected to various processing steps, such as doping and etching, to create the desired patterns and structures.

5.???? Test and verify the (finished) chip: After the chip has been fabricated, it must be tested to ensure that it functions correctly and meets the required specifications. This typically involves using specialized equipment to perform a variety of tests on the chip. If any defects are found, the chip design may need to be revised and the process repeated.

There is a lot of emphasis on testing and verification at each and every stage of the design process, since the cost of failure is catastrophic. Remember that (unlike software), once a chip is fabricated and (god forbid!) there is a mistake, then it is pretty much useless and becomes e-waste. Since it is hardware, a “patch” cannot be applied later on to correct it. Hence the emphasis on “first-time-right” for the silicon when it is finally manufactured.

As enabling technologies become more and more powerful, example Artificial Intelligence (AI), these tend to get used in the design process as well. For example, AI is now used extensively in designing of chips especially in optimizing physical design, power consumption etc. As end applications become more demanding (eg. an AI server farm), so too the chips powering the solution also becomes more complex. A lot of IP blocks are reused.

But, as a saying from the EPC industry goes, “No two construction projects are the same, even if it is a copy-exact from another project.” Similarly, each SoC/ASIC project is different, even if the IP blocks are reused and test cases are reused. Since no ASIC/SOC is a ‘copy-exact’ of another chip, the developer would need to meticulously test the entire chip to determine that t will work under all conditions of the software running on that chip.

The end result is a chip that is exactly suited for your end application, manufactured in the latest state-of-the-art Fab, and being integrated into a new (end) product which would bring happiness to its users. The designers of those systems will try and make the product cheaper-faster-better using this new improved chip.

In the next article, we will get into details of how semiconductor chips are manufactured – from Tape-out to packaging. The (slightly longer) article will look at cleanrooms, use of gases and chemicals, water treatment etc.

Author Bio: PVG Menon is a veteran of the electronics and semiconductor industry with over three and a half decades of experience spanning technology development and management, running global P&L, strategy consulting, and public policy advocacy. He is one of the few global executives with a comprehensive 360-degree experience of the entire lifecycle of a chip -- from design to manufacturing and design-in by a product company. He is also a passionate advocate of a strategy he calls "Innovation led Design. Design led Manufacturing".