10.1.3. Function of Current (I_DS) in Relation to Device Geometry

Suppose if we apply the voltage here V and also we apply V_GS keeping body and source they are connected. So, we call this is V_D and this is V_GS. 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.

In a transistor, we apply voltages at different terminals, typically the gate (V_GS) and the drain (V_D), to control the flow of current through the device. Though part of the device may be insulated and not allow current to pass directly, current can still flow between the source and the drain terminals. This flow of current is denoted as I_DS.

Think of a water pipe system: applying voltage is like turning on a faucet. Even if there are areas in the pipe that are sealed (insulated), water (current) can still flow through the open sections (from source to drain) when pressure is applied (voltage is activated).

These electrons are really moving from left to right by this field or by this voltage, which may be said this is lateral field. So, we can say this vertical field is created by V_GS, which is changing the concentration of the electrons. On the other hand, the horizontal field is created by V_D, which helps the movement of the electrons from left to right.

Electrons flow through the channel in a transistor due to electric fields created by applying voltages. The vertical field, produced by the gate voltage (V_GS), influences the density of electrons in the channel, while the horizontal field, generated by the drain voltage (V_D), aids their movement from the source to the drain. Collectively, these fields arrange the electron flow necessary for current I_DS to exist in a controlled manner.

Imagine a crowded room where people (electrons) need to move from one door (source) to another (drain). If the lights (V_GS) change, more people might be encouraged to enter the room, and the push from a line (V_D) helps them move swiftly toward the exit. The combination of attraction and push enables a steady flow of movement.

This current flow I_DS is a strong function of V_GS, V_D, and also it is a strong function of the spacing from here to here namely the length of the device. It is also a strong function of the other geometry namely width of the device, and also the thickness of this oxide layer, referred to as t_ox.

The amount of current (I_DS) flowing through a transistor depends on several factors. The voltages applied at the gate (V_GS) and drain (V_D) influence how much current flows. Additionally, the physical dimensions of the device, such as its length (L) and width (W), also play a crucial role, alongside the electrical properties of the materials used in the device, including the thickness of the oxide layer (t_ox).

Think of a river where the amount of water (current) flowing depends on several things: the width of the river (device width), the steepness of the banks (voltage applied), and the overall length of the river (device length). A wide, steep river will have more water flowing than a narrow, flat river.

As a circuit designer, if the device is already fabricated, then W’s and L’s are already defined. You will be looking for the dependency of I_DS as a function of V_GS and V_D. In contrast, a device engineer may try to change t_ox to improve mobility.

In the field of electronics, circuit designers often work with pre-designed devices, focusing on how to optimize the performance of these circuits by adjusting voltage levels (V_GS, V_D). On the other hand, device engineers have the ability to alter material properties and physical dimensions of the transistors, such as adjusting oxide thickness, to enhance performance metrics like electron mobility.

Consider a chef (circuit designer) who must create a dish using available ingredients (fixed device parameters). The chef must figure out the best combination of flavors (voltages) to optimize the meal. Meanwhile, a food scientist (device engineer) can experiment with modifying the ingredients themselves (changing oxide thickness) to enhance the meal's overall tastiness.

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