What is the need of scaling? Mention the merits and demerits of constant voltage scaling?
Answers
The most important point in this scaling is the supply voltage is scaled but the electric field remains constant hence the same constant field scaling is given.
Advantages of scaling:
1. Increases the switching speed.
2. Reduces chip size.
3. Reduces power dissipation.
Disadvantages of scaling:
Effect on SiO2 thickness – on scaling oxide thickness eventually a sage will reach when oxide will lose its dielectric property.
Subthreshold current – For smaller device, in addition to VGS voltage, VDS voltage also has greater influence on the carrier flow in the channel. The carrier in the channel can be increased by increasing VDS voltage & also potential barrier can be reduced even VGS < VT. Thus, resulting current through the channel for higher values of VDS is called sub-threshold current.
Noise problem – Scaling process inevitably results in noise problem, which degrades the reliability of high density chip.
Answer:
scaling is a technique to make them closer to each other or in simpler words
Explanation:
scaling is needed for the reduction in the parameters (like current, voltage, electric field etc.) due to reduction in length of the transistor with the advancement in technology.
Merits of constant voltage scaling are as follow-
Packaging Density: The packing density of the device improves as a result of scaling hence we can fit more transistors in the same space as before.
Size Chip: As we can pack more number of transistors in the same space hence we can decrease the overall area of the chip
Multifunction of Chip: As transistor size is reduced we can make multifunctional chips by reducing the area of chips.
Demerits of constant voltage scaling are as follow-
voltage scaling is that the electric field increases as the minimum feature length is reduced.
This leads to velocity saturation, mobility degradation, increased leakage currents and lower breakdown voltages.
After scaling, the different Mosfet parameters will be converted as given by table below: Before Scaling After Constant Field Scaling After Constant Voltage Scaling