12.4. Indian Institute of Technology, Kharagpur

So, the overall plan what is as, I said that we have discussed in the previous class about these 4 topics. So, these things we already has been discussed. And, today we are first we are going to discuss about the similar kind of things, but for p-type MOSFET.

In this section, we outline the focus of our discussion, which today is about the p-channel MOSFET (p-type MOSFET). This is a continuation of the previous lecture, where we covered n-channel MOSFETs (n-MOSFETs). Understanding both types is crucial for efficient circuit design, as p-MOS and n-MOS devices often work together in integrated circuits. The intent is to draw comparisons between n-MOS and p-MOS technologies to clarify their distinct functionalities.

Imagine you have a pair of shoes, one for rainy weather (n-MOS) and one for sunny weather (p-MOS). Just like each shoe serves a specific purpose, both p-MOS and n-MOS transistors have unique roles in electronic circuits. Knowing when to use each type ensures you have the right 'footwear' for your circuit's needs.

So, to start with let we go for the basic structure of the p-MOSFET keeping in mind that n-MOSFET in as background information. So, here the MOSFET for p-MOS type I should say where the channel it is and the channel it is supposed to be p-type and this is the cross sectional view of p-type MOSFET.

Here, we introduce the basic structure of the p-MOSFET, emphasizing the channel type, which is p-type. It is positioned alongside a reference of the n-MOSFET structure. The p-MOSFET features p-type islands that serve as the source and drain, whereas the body is lightly doped with n-type material. Understanding this structure is vital because it dictates how the device operates electrically.

Consider a water pipe: the p-type region represents water flowing in one direction with easy passage, whereas the n-type serves as the walls that support the pipe's structure. For the device to work efficiently, it’s crucial that the 'water' (current) flows through the 'pipe' (transistor) correctly.

And then, we will see that what are the things are happening in detail, but this is what the cross sectional view.

This segment reiterates the significance of understanding the cross-sectional view of the p-MOSFET, as this helps visualize how the device creates its operational 'channel'. The behavior of voltage applied at the gate with respect to the source is essential for channel formation, which allows the flow of charge carriers (holes in this case) that results in current flow.

Think of a river (current) that requires a riverbed (channel) to flow. The thickness and slope of the riverbed can change how fast and efficiently water moves. Similarly, the channel in a p-MOSFET must be properly established for efficient current flow.

Now, here at the gate we like to prefer to apply some voltage. So, that the channel supposed to be getting created and we want to convert this channel from n-type to p-type. So, definitely we required applying -ve potential with respect to source as well as body.

In this section, we discuss how biasing the p-MOSFET works. To activate or 'turn on' the p-MOS device, a negative voltage (with respect to the source) must be applied at the gate. This action creates a p-type channel from the p-type body, allowing holes to move and ultimately enabling current to flow from source to drain.

Consider flipping a toggle switch to turn on a light. Just as you need to switch it in the right direction to get light, you need to apply the correct voltage to the gate of a p-MOSFET to allow current to flow, illuminating your circuit just like the light in your room.

As a result it produces a current in the same direction. And, now this current since it is flowing from source to drain just to have proper convention of the +ve current flow, we may call this is I.

This segment describes how current flows in a p-MOSFET, which is conventionally defined as moving from the source to the drain. This current comprises holes moving through the channel created when the gate voltage is appropriately applied. Establishing this current flow is crucial for understanding how the p-MOSFET operates within a circuit.

Imagine a racetrack where runners (holes) move from the starting point (source) to the finish line (drain). Just like runners need a proper path (channel) to follow to complete their race successfully, holes in a p-MOSFET need a correctly biased channel to flow efficiently.

So, what kind of reorientation shall we do? First thing is that we will flip the p-MOS transistor, because here we do have lower potential and here we do have higher potential.

This section explains how device orientation impacts circuit design. Proper orientation is essential in a circuit with multiple devices, ensuring consistent behavior and simplifying connections. Flipping the p-MOSFET helps align its source and drain with the appropriate potential levels in the circuit.

Think of arranging furniture in a room for optimal space usage. Just as you need to position sofas (transistors) for easy movement (current flow), you must align the p-MOSFET correctly for it to function well within the circuit.

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