Gate Length Scales Down
MOSFET scaling refers to the process of reducing the critical parameter of a MOS transistor according to a specific criterion, in order to enhance performance features such as speed, application range, power dissipation, and more while maintaining the fundamental operational characteristics.
Advantages of Gate Length Scales Down
Packaging Density: Scaling improves the packing density of the device, allowing for more transistors to be accommodated within the same space.
Chip Size Reduction: With increased packing density, the overall area of the chip can be decreased, leading to smaller-sized chips.
Multifunctionality: Scaling enables the creation of multifunctional chips by reducing the chip’s area, thereby incorporating multiple functions within a smaller space.
Disadvantages of Gate Length Scales Down
Increased Leakage Current: Scaling down the gate length can lead to an increase in leakage current, particularly sub-threshold leakage. This rise in idle current can result in higher power dissipation and reduced efficiency.
Short Channel Effects: As the gate length scales down, short channel effects such as drain-induced barrier lowering (DIBL) and sub-threshold leakage become more pronounced. These effects can deteriorate transistor performance and introduce variability.
Manufacturing Challenges: Scaling down gate lengths necessitates the utilization of advanced lithography techniques and tighter process controls. This, in turn, leads to increased complexity and costs in the manufacturing process.
Reliability Concerns: Smaller gate lengths can make transistors more susceptible to various reliability issues, including hot carrier injection, electrostatic discharge (ESD), and process variations. It is essential to address these challenges to ensure the long-term reliability of VLSI circuits.
Types of MOSFET Scaling
Constant Field Scaling or Full Scaling: This type of scaling maintains a constant electric field in the channel region while reducing the device dimensions. It helps to improve transistor performance by enhancing speed and reducing power dissipation.
Constant Voltage Scaling: In constant voltage scaling, the gate oxide thickness is scaled down to maintain a constant voltage threshold. This allows for improved device performance and power efficiency.
Lateral Scaling: Lateral scaling involves reducing the transistor dimensions uniformly in all directions, including length and width. It helps in achieving overall device miniaturization and performance enhancement.