10.1. Current Flow in the Device

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

In this part, we are discussing how voltage is applied to a device. When we apply voltage V (let’s say to the gate), and maintain the source and body connections, it sets up conditions for current to flow within the device. This is the first essential step in understanding how electrical devices operate — they require voltage to function.

Think of voltage like water pressure in a pipe. Just as higher water pressure causes more water to flow through a pipe, applying voltage makes the electrical current flow through the device. Without it, there wouldn't be any flow, similar to how turning off the tap stops water from coming out.

So, we call this is V and this is DS DS V 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.

Even though there is insulation preventing direct current flow through certain terminals, current can still flow through the circuit due to the voltage differences established. This is crucial as it means that not all parts of the device will conduct electricity — only specific pathways will allow current to pass, which creates a controlled flow through the device.

Imagine a city's water supply system where some pipes are insulated to prevent leaks. Water (current) still flows through the main pipeline (the conductive path), while insulated pipes only serve as boundaries without allowing any water to seep through, ensuring the flow remains contained in specific areas.

So, this I 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.

Here, current (I) flows due to the movement of electrons, which move from one terminal to another. The applied voltage creates an electric field that pushes these electrons through the device, allowing current to flow. Understanding the role of electrons provides a deeper insight into how electricity operates at a microscopic level.

Think of electrons as tiny cars on a road (the conductive path). When there’s a traffic signal (voltage) at a junction, the cars start moving from one side to the other, creating a flow of traffic (current) across the bridge (the device).

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

This segment highlights two important fields: the vertical field created by V (gate voltage) affects how many electrons are present in the device, while the horizontal field created by V (drain-source voltage) directs the movement of electrons. Understanding these fields helps us comprehend how voltage levels impact electron behavior and thus, the current.

Imagine a park with two playing fields: the vertical field represents the space where kids can play (the electron concentration), while the horizontal field is like the pathway connecting the two sides of the park (drain-source). The kids move between the fields based on how they are encouraged (by the voltages).

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.

Current flow is significantly impacted by the dimensions of the device including length, width, and the thickness of the oxide layer. These physical parameters affect how easily electrons can flow through the device, which in turn influences overall performance. Understanding the geometry of devices can lead to better designs in electronics.

Imagine a narrow versus a wide pipe: a narrow pipe allows less water to flow through than a wider one. In electron flow, if the width or length of the conductive pathway is increased, it allows for more electrons (or current) to flow through, similar to how a wider pipe facilitates higher water flow.

As a circuit designer what will be looking for if the device it is already fabricated... we may assume that these parameters are given to us and we may consider they are fixed.

For circuit designers, especially when working with pre-fabricated devices, it's crucial to understand how fixed parameters influence current flow. Designers focus on how variations in voltage affect performance without altering the device’s physical characteristics, as these are often set during fabrication.

Consider a cookie recipe where certain ingredients are pre-measured. While you can adjust the baking time (voltage), you cannot change the amount of flour or sugar (device dimensions) once the cookies are in the oven, so the final product's quality will depend on how well you manage the baking conditions.

On the other hand if it is you are a VLSI circuit designer where the device yet to be implemented... whenever we say technology is fixed device parameters are fixed.

Device engineers have the flexibility to alter certain parameters (like thickness or surface quality) during production to improve performance. On the other hand, VLSI (Very Large Scale Integration) circuit designers work with established device parameters, focusing instead on how to optimize upon these through voltage and geometry changes since the technology has already been defined.

It's like an architect versus a builder: the architect (circuit designer) works with predefined blueprints (fixed parameters) to create a building (circuit) while the builder (device engineer) can still choose varied materials or methods to enhance the overall quality of the structure.

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