Simplifying Semiconductors for You

The Structure Of Industry – I

The semiconductor industry popularly known as VLSI industry or hardware industry is based on the development of Integrated Circuits (or ICs). These ICs are sometimes referred as ‘chips’, and are made up of small circuits fabricated over a semiconductor material (mostly silicon). The unique property of semiconductors to provide a range of conductivity makes it an indispensable part of electronics, and hence, our life. Why such semiconductor materials are used for IC fabrication is a vast topic which requires a different discussion.

Since the development of ICs, engineers all over the world are working on developing more features on a reduced size of chip. However, the process of chip design is far from simple. The industry in itself has extremely specialized fields, where engineers with expertise in different domains work together to introduce a new technology in the market. The article will discuss the major distribution of chip development process, specifically ASIC¹ development. This will provide you a glimpse into the insides of semiconductor industry. However, the details of the individual fields will be discussed in further articles.

Let’s start from a specific requirement. This requirement can be the development of a completely new application, or an enhancement over an old application (in terms of power, area, speed). This requirement is presented by the marketing teams of the  organization based on their market research. This includes customer analysis, competitive analysis and studying the market trends to understand the placement of the desired product to have a profitable business. The technical feasibility of the product is discussed with engineers at different levels to set the right expectations. Finally, the product requirements are fixed and the design or production process starts.

Design Architecture: The first step in the actual chip-design starts with development of a design architecture. The engineers share deep design and production knowledge to build an architectural model of the functionally working design along with its specifications (power, performance and area). The teams of design architects mainly consists of experienced design engineers who have gained significant experience and know-how of entire chip-making process.

Design Implementation: Once the architecture is finalized, the team of digital and analog design engineers start working on the implementation (assuming most of the ICs are mixed-signal ICs, having both digital and analog parts). Analog design engineers deal with continuous signals that vary over time, focusing on fidelity, precision, consistency and performance of signals.  Digital design engineers deal with binary signal values ‘0’ and ‘1’ and develop the code using HDLs (Hardware Description Languages like Verilog/VHDL). Both analog and digital engineers require different tools and expertise to implement the design, but work together to achieve the result.

Design Verification: The process of design verification starts shortly after the design implementation. Design Verification engineers start reading the specifications alongside design development and develop testcases. This involves extensive testing of all corner cases with an aim to detect potential bugs in the design. It requires several iterations of design changes based on the bugs found by DV engineers. When the design verification cycle is complete, with no more bugs detected, the design is finalized. This is generally termed as RTL freeze, where RTL refers to the design code.

Synthesis/STA (Static Timing Analysis) : Once the first draft of verified design is ready, STA engineers start working on timing closure, synthesis and static timing analysis. This is the process where RTL code is converted into gate level design (referred as gate-netlist). STA engineers work with design engineers for some changes that might be needed and verification engineers to verify the gate netlist as well. The process repeats until the final RTL freeze. If there is any design change request after RTL freeze, the change is done in the gate-level netlist to avoid further iteration of design and verification cycle and minimize the effort.

Physical Design: This process starts when the gate-netlist is released by the STA engineers. They collaborate with design and STA teams and develop circuit layouts. The placement of the circuit components is planned and visualized in this process, like in actual IC.

Design for test: This is the process which starts shortly after design implementation. This is fairly new practice, used in large designs, where testing structures are added in the design. These special testing structures allow the generation of patterns which have the ability to detect manufacturing defects. They work closely with all the above teams and finally release a set of patterns to be used by test teams, after the actual fabrication.

The above steps constitute the pre-silicon development phase of an ASIC. When all the above teams perform their functions with proper testing at each level, the design is ‘taped out’ and sent to the fabrication units (commonly known as ‘fabs’).

The post-silicon flow will be discussed in next article.