Switches

 Well, I don't have a specific topic to talk about today. Thus, I would like to share some knowledge on MOSFET. The acronym stands for Metal Oxide Semiconductor Field Effect Transistor. Yes, this is a type of transistor or let say in Laymen Term - a switch. Contrary to the mechanical switch, a MOSFET will switch on a soon as there is a voltage applied at the gate.

We have 2 different kind of switches. Either a voltage driven or current driven switches. MOSFET is a voltage driven switch. Meanwhile, a BJT (bipolar junction transistor) is a current driven switch. What does this mean? Basically, they will switch on once a voltage is being applied on the gate (MOSFET) or current at the base (BJT).

Let's go back to our MOSFET. I will touch the BJT in a separate post. The structure of a MOSFET is reflected by it's name in the 1st paragraph. At the gate area (G), we have a metal pad followed by an oxide (grey in photo) and silicon (brown area) as the semiconductor.

How does the MOSFET works? Simple. If a positive voltage supply is being applied at the gate, it will pull the negative electrons close to the oxide (positive charges will be repelled away from the oxide). In away, you have now a 'channel' of n electrons connecting between the Source (S) and Drain (D). The flow of electrons between source to drain will only happen if we have a potential difference between them. 

It is important to notice that the flow of current is in opposite direction to the flow of electrons. For easier understanding, the source indicating our electron source. The opposite direction would mean, current flow would be from drain.

You might noticed by now that the MOSFET is available either through NMOS or PMOS type. An NMOS, as example above is where a positive voltage being applied at the gate to get an n-channel. PMOS on the other hand, is vice versa.

I think this is sufficient for today. Hopefully this is not too confusing. I am looking forward to write more on this electronic related knowledge.

Titan - The Mars Moon.

G - connected to metal pad

Oxide - Gray area

S - source pad connected to n type material

D - drain pad connected to n type material

p - semiconductor from p type material