10.2.1. Transition to I-V Characteristics

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

In this section, we begin by discussing how voltage is applied to a device and how it influences current flow. When voltage, denoted as V, is applied to a terminal while keeping the source connected, it establishes conditions under which current can flow. It's important to note that although there may be insulators present, preventing current from passing through certain terminals, current can still flow through the device due to the conductive paths available.

Think of this scenario like water flowing through pipes. Imagine when you open a faucet (applying voltage), water (current) starts moving through a connected hose (the conductive path) to the garden. The hose can have bends or blockages (insulators), preventing flow in certain areas, but when there's a clear path, water can flow freely.

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, you may say this is lateral field. 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 DS right and as a result we do have the I .

This chunk focuses on how electric fields created by the applied voltages influence electron movement, which is responsible for carrying current. In particular, the vertical field due to voltage VG modifies electron density, while the horizontal field due to voltage VDS facilitates the movement of these electrons from the source to the drain. Thus, understanding how these fields operate is crucial for predicting and managing current flow in electronic devices.

Imagine the electric fields as invisible highways. The vertical field is like constructing new lanes (increasing electron density), while the horizontal field is the smooth road that allows cars (electrons) to move quickly from one point (source) to another (drain). Both of these factors play a crucial role in ensuring that traffic flows smoothly.

So, note that these electrons are coming from this side. So, that is why you call this is source and it is getting drained to this terminal that is why you call drain. Now, it is very clear that why you call this is drain and source.

In electronic devices, it's essential to identify the roles of different terminals. The one from which the electrons originate is referred to as the 'source', while the terminal into which electrons flow is known as the 'drain'. Understanding this concept is fundamental for distinguishing the functioning of various components in a circuit.

Consider a water system where a reservoir acts as the source of water, and the end of a pipe where the water exits is the drain. Just like in electronics, the reservoir (source) supplies water (electrons), and the drain is where the water ultimately flows out. This analogy helps clarify the directional flow of electrons in a circuit.

So, this current flow I it is a strong function of this V , V and also it is strong function of the spacing from here to here namely the length of the device.

The current flowing through the device is affected by several variables, including the applied voltages (VG and VDS) and the physical dimensions of the device, particularly the length. The spacing between the source and drain influences how easily electrons can move, defining the overall current behavior.

If we return to the water analogy, think of the pipe diameter as the device's length—the longer the pipe, the harder it is for water to flow through. Similarly, if the voltage increases (like increasing pressure at the reservoir), it can push more water through the pipe, analogous to the higher current flow in electronics.

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. Maybe it is referred as t , then dielectric constant here of this portion it is referred as ε and of course, the mobility of the electrons in the channel region.

In addition to length, other design parameters such as the width of the device, oxide thickness, dielectric constant, and electron mobility play significant roles in determining current flow. Designers must consider all these parameters to optimize devices for better performance based on their intended applications.

Think of optimizing a garden to grow plants. The width of the garden bed is like the device's width; the depth of soil (oxide thickness) affects root growth. If we improve the soil's quality (dielectric constant) and ensure roots can grow freely (mobility), the plants (electrons) will thrive better!

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 as function of V and V .

From a circuit designer's perspective, once a device has been fabricated, they work with established parameters such as the width (W) and length (L) of the device. Their focus shifts to analyzing how the current (I) varies with changes in voltages applied (VG and VDS). Understanding this dependency is essential for effectively integrating the device into circuits.

Think of a chef preparing a dish with a fixed recipe (established parameters). While the chef cannot change the ingredients (fabrication parameters), they can vary cooking times (voltages) to adjust the dish's flavor (current) to achieve the best possible outcome.

On the other hand if it is you are a VLSI circuit designer where the device yet to be implemented. However, technology is fixed; that means, these parameters are fixed.

VLSI circuit designers typically have a fixed set of technology parameters to work with when implementing devices. However, they do have flexibility in defining the width and length of the transistors, allowing them to optimize performance within the constraints of the technology. This design flexibility is crucial for modern electronic devices.

Consider a custom car builder who must use a certain chassis type (fixed technology). While the chassis' dimensions are set, the builder can choose the engine size and tire width (W and L) to tailor performance. This highlights how VLSI designers optimize under fixed constraints.

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