VLSI Technology: History, Usage and Design Process

VLSI Technology

Very large-scale integration is a process of embedding or integrating hundreds of thousands of transistors onto a singular silicon semiconductor microchip. VLSI technology's conception dates back to the late 1970s when advanced level processor (computer) microchips were also in their development stages. Two of the most common VLSI devices are the microprocessor and the microcontroller.

VLSI refers to an integrated circuit technology with numerous devices on a single chip. The remarkable growth of the electronics industry is primarily due to the advances in large-scale integration technologies. With the arrival of VLSI designs, the number of possibilities for ICs in control applications, telecommunications, high-performance computing, and consumer electronics as a whole continues to rise.

Presently, technologies like smartphones and cellular communications afford unprecedented portability, processing capabilities, and application access due to VLSI technology. The forecast for this trend indicates a rapid increase as demands continue to increase.

The Advantages of VLSI Technology

The following are the primary advantages of VLSI technology:

Reduced size for circuits

Increased cost-effectiveness for devices

Improved performance in terms of the operating speed of circuits

Requires less power than discrete components

Higher device reliability

Requires less space and promotes miniaturization

The Design Process of a VLSI IC

Overall, VLSI IC design incorporates two primary stages or parts:

1. Front-End Design: This includes digital design using a hardware description language, for example, Verilog, System Verilog, and VHDL. Furthermore, this stage encompasses design verification via simulation and other verification techniques. The entire process also incorporates designing, which starts with the gates and continues through to design for testability.

2. Back-End Design: This consists of checking the manufacturability of the chip. It involves placement, routing, clock tree synthesis, timing closure, LVS/DRC checks and a mask creation that can be delivered to the fabrication unit for manufacturing.

3. Fabrication: This consists of the processes involved in manufacturing a chip out of a piece of silicon.

The entire design process follows a step-by-step approach, and the following are the front-end design steps:

Problem Specification: This is a high-level interpretation of a system. We address the key parameters, such as design techniques, functionality, performance, fabrication technology, and physical dimensions. The final specifications include the power, functionality, speed, and size of the VLSI system.

Architecture Definition: This includes fundamental specifications such as floating-point units and which system to use, such as RISC or CISC and ALU's cache size.

Functional Design: This recognizes the vital functional units of a system and, thus, enables identification of each unit's physical and electrical specifications and interconnect requirements.

Logic Design: This step involves control flow, Boolean expressions, word width, and register allocation.

Circuit Design: This step performs the realization of the circuit in the form of a netlist. Since this is a software step, it utilizes simulation to check the outcome.

The following are the back-end design steps for hardware development:

Physical Design: In this step, we create the layout by converting the netlist into a geometrical depiction. This step also follows some preconceived static rules, such as the lambda rules, which afford precise details of the ratio, spacing between components, and size.

The following are the steps followed in a foundry for manufacturing a chip:

Wafer Processing: This step utilizes pure silicon melted in a pot at 1400º C. Then, a small seed comprising the required crystal orientation is injected into liquefied silicon and gradually pulled out, 1mm per minute. We manufacture the silicon crystal as a cylindrical ingot and cut it into discs or wafers before polishing and crystal orientation.

Lithography: This process (photolithography) includes masking with photo etching and a photographic mask. Next, we apply a photoresist film on the wafer. A photo aligner then aligns the wafer to a mask. Finally, we expose the wafer to ultraviolet light, thus highlighting the tracks through the mask.

Etching: Here, we selectively remove material from the surface of the wafer to produce patterns. With an etching mask to protect the essential parts of the material, we use additional plasma or chemicals to remove the remaining photoresist.

Ion Implantation: Here, we utilize a method to achieve a desired electrical characteristic in the semiconductor, i.e., a process of adding dopants. The process uses a beam of high-energy dopant ions to target precise areas of the wafer. The beam's energy level determines the depth of wafer penetration.

Metallization: In this step, we apply a thin layer of aluminum over the entire wafer.

Assembly and Packaging: Every one of the wafers contains hundreds of chips. Therefore, we use a diamond saw to cut the wafers into single chips. Afterward, they receive electrical testing, and we discard the failures. In contrast, those that pass receive a thorough visual inspection utilizing a microscope. Finally, we package the chips that pass the visual inspection as well as recheck them.

VLSI technology is ideally suited to the demands of today's electronic devices and systems. With the ever-increasing demand for miniaturization, portability, performance, reliability, and functionality, VLSI technology will continue to drive electronics advancement.