Design flow of VLSI technology
Updated: Dec 1, 2020
VLSI technology has been developed mainly to integrate various logic devices such as transistors, and diodes in a smaller area. The concept of #VLSI began after the development of complex semiconductors and communication #technologies. CPU, RAM, ROM, glue logic are the essential properties for an electronic circuit. The VLSI helps us to integrate entire segments into a single chip.
The #electronics industry has achieved phenomenal growth over the last few decades, mainly due to the rapid advances in large scale #integration technologies and system design applications. The fundamental concept of VLSI is explained in another article and the link is given in the See also section. Do check it out. In this article, we are going to discuss the design flow of VLSI technology.
VLSI DESIGN FLOW
The VLSI design cycle starts with the formal specifications of a VLSI chip, followed by a series of steps and eventually, produces a packaged chip. The flow chart explains the process that is involved in the physical fabrication of VLSI chips.
A brief explanation of the flow chart is given below in the article.
The system specifications are nothing but the factors which are to be considered before fabricating a device or constructing any design. It is also perceived as the high-level representation of the concerned #system. The specifications of each and every component should be included in the design with the consideration of market requirements and economic viability.
The specification includes the size of the IC, the velocity of the current flow in it, the maximum amount of power that can be consumed by it. It also consists of the performance and the functionality of #transistors used in it. After determining the specifications, it is followed by the architectural design
This section serves as the building block of VLSI design. The concept by which IC chip van be fabricated is determined here. It may be either RISC [Reduced Instruction Set Computer] or CISC [Complex Instruction Set Computer]. It also includes the size of caches, the structure of pipelines employed, and floating-point numbers.
This represents the functional units involved in the #design and the interconnections between them. The functionality of all units is specified on the basis of their input, output, and time is taken for conduction. The functional design helps in improving the overall design of chips and reduces the complexity in the fabrication process. It also plays a vital role in debugging the errors of the system.
This section can also be stated as Register Transfer Level [RTL] description. This RTL can be expressed in Hardware Description Language such as Verilog, VHDL.
This logic design takes care of the word widths, register allocation, and also the control flow of the fabrication process.
It also carries out the necessary arithmetic operations. The logic design comprises the Boolean expressions which can be used in the process of simulation and verification.
Here, the #circuit representation is developed based on the logic design. It is usually expressed in circuit diagrams, that consist of circuit elements such as ICs, transistors, diodes, and the interconnection between them. By considering the speed and power requirement of the fabrication process, the above mentioned #Booleanexpressions are converted into a circuit design.
In this step, the circuit diagram is converted into a geometrical design called layout. A Layout is constructed by describing logic components such as diodes, transistors in their respective geometric models, and also the interconnections between them are also represented by various lines in multiple layers. This is a complex process and so it is operated as an automated function with the help of Layout synthesis tools.
After constructing the layout, it is verified and enters the fabrication process. A wafer which is about 20 cm long is the base of the fabrication process. Silicon crystals are used to produce wafers. Layout data is converted into photo-lithographic masks. Masks identify the spots, where the elements are needed to be deposited. The wafers are needed to be polished perfectly as the VLSI devices are in small dimensions.
PACKAGING AND TESTING
After fabricating, packaging should be done carefully in such a way, that the chips should ensure all the design specifications without any damage. Chips used in Multi-chip modules are not packaged since they use bare chips. Printed circuit boards use the chips that are packaged in the Dual In-Line package and Quad Flat package.
VLSI has been applied in diverse fields such as aerospace, consumer electronics, Bio-electronics, wireless communication, and also in defense. In aerospace, VLSI is applied in the takeoff, and landing of airplanes, weather monitoring and to control the operations inside the airplane. The future of the electronics industry is greatly dependent on the VLSI technology.