10.1.1. Role of Voltage V_GS and V_DS

So, here what you see it is that, suppose if we apply the voltage here V_GS and also we apply V_DS keeping body and source they are connected. So, we call this is V_GS and this is V_DS.

In this chunk, we're introduced to the key voltages in a transistor: V_GS (gate-source voltage) and V_DS (drain-source voltage). V_GS is applied between the gate and source terminals, while V_DS is applied between the drain and source terminals. The connection between the body and source is also highlighted, indicating that these terminals influence the behavior of the transistor significantly.

Think of the transistor as a water pipe system. V_GS acts like a valve that controls the water (electrons) flow. If the valve is partially open, some water can flow, but if it's fully closed (no V_GS), no water will flow through the pipe (no current). V_DS is like the pressure pushing the water from the reservoir (drain) through the pipe (channel) towards the outlet (source).

The current it will be of course, we do have insulator. So, through this terminal there will not be any current, but then there will be a current flow. So, this I_DS it is flowing here. And, of course, this current it is carried by electrons. So, these electrons are really moving from left to right by this field or by this voltage, you may say this is lateral field.

This chunk explains that while there are insulative layers preventing current from leaking directly through certain terminals, current (I_DS) still flows through the transistor channel. This flow is primarily due to the movement of electrons. The 'lateral field' refers to the electric field established in the channel as a result of the applied V_DS, guiding the electrons from the source to the drain.

Imagine a crowded street (the channel) where people (electrons) are flowing from one end (source) to the other (drain). The pressure of a crowd (the electric field created by V_DS) encourages people to move in one direction. Even if there are barriers (insulators), the crowd still finds ways to move along the path provided.

So we can say this vertical field it is getting created by V_GS, which is changing the concentration of the electron on the other hand the horizontal field getting created by V_DS, which is helping for the movement of the electron from left to right.

The electric fields created by the voltages V_GS and V_DS have distinct roles. V_GS affects the concentration of electrons in the transistor channel, affecting how easily they can flow, while V_DS creates a lateral electric field that facilitates the movement of these electrons. Together, they determine the current that flows through the transistor.

Consider a highway where V_GS is akin to traffic lights controlling how many cars (electrons) can enter the road (channel) at any given time. When the light is green (V_GS is applied), more cars can enter. V_DS is like a downhill slope that propels cars forward, making it easier for them to travel from one point to another.

So, this current flow I_DS it is a strong function of this V_GS, V_DS and also it is strong function of the spacing from here to here, namely the length of the device. So, it is a strong function of the length it is strong function of the other geometry namely width of the device and also it is strong function of the device parameter, which includes the thickness of this oxide.

The current flowing through the transistor (I_DS) is influenced not only by the applied voltages (V_GS and V_DS) but also by the physical dimensions of the device, such as length and width. Additionally, device parameters like the thickness of the insulating oxide layer and the dielectric constant impact the current's behavior, indicating that both electrical and physical factors are interconnected in determining transistor performance.

Imagine trying to pour water from different shaped containers. A wider container (wider device) allows more water (current) to flow out than a narrower one. Similarly, if the pipe (channel) is long versus short, it affects how quickly water can exit. In this case, V_GS and V_DS are like the pressure and size of the opening dictating the flow.

So as a circuit designer what will be looking for if the device it is already fabricated. So, W’s and L’s they are already defined then we will be looking for the dependency of I_DS as function of V_GS and V_DS. As a device engineer you may try to change this t_ox or change probably in the surface so that the mobility it will be better.

This chunk differentiates between the roles of a circuit designer and a device engineer. A circuit designer typically works with fixed device parameters (like widths and lengths), focusing on how current (I_DS) depends on the applied voltages (V_GS and V_DS). In contrast, a device engineer may modify the physical structure (such as oxide thickness) to improve electron mobility, hence enhancing device performance.

Think of a chef (circuit designer) who can only use fixed ingredients (set device parameters) to create a recipe (circuit) based on what’s available. Meanwhile, a food scientist (device engineer) might experiment with fresh ingredients or try new cooking methods (alter device structure) to improve the dish's taste or presentation (device functionality).

On the other hand if you are a VLSI circuit designer where the device yet to be implemented. However, technology is fixed; that means, these parameters are fixed. So, you may say that whenever we say technology is fixed device parameters are fixed, but then you also have the flexibility to change the W’s and L’s of the devices.

In this final chunk, the focus is on VLSI circuit designers who work with fixed technologies. Although the fundamental parameters may be set by technology, they still have flexibility regarding device geometry (width W and length L) to optimize performance. This adaptability is crucial in creating efficient integrated circuits using the fixed technology’s framework.

Imagine building a house (VLSI design) using a set blueprint (fixed technology) that outlines certain dimensions and materials. Even though you can't change the blueprint itself, you can choose how to arrange the rooms (modify W and L) within those constraints to maximize space and functionality.

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