41. Fundamentals of Field Effect Transistors (FETs)
In Field-Effect Transistor (FET: Field Effect Transistor),
There
are two types by the difference of the structure. One is the
joining type.
FET (JFET: Junction gateFET)、
The
other one is MOSFET( Metal Oxide Semiconductor FET).
Elementary action (n channel type)
Elementary action will be explained by taking the example of MOSFET of n channel. At first, the electron gathers around the joining region of the oxide film and p type substrate when the voltage is applied to the gate electrode. Therefore, the electrical characteristic of p type semiconductor around the oxide film changes, and it becomes a thin n channel layer. On the other hand, the source electrode and the drain electrode are composed of n type semiconductor, and the current flows between the drain electrode and the source electrode through a thin n channel layer when the voltage is applied between drain-source.In other words, the current that flows between drain-source can be controlled by controlling the size of the voltage applied to the gate electrode.
Main characteristic of MOSFET
Main maximum rating
| Voltage between drain-source |
|
It shows the maximum voltage that can be applied between drain-source. It is sometimes called the withstand voltage. |
|---|---|---|
| Voltage between gate-source |
|
It shows the maximum voltage that can be applied between gate-source. |
| Drain current |
|
The maximum current that can be supplied to drain. (Mainly used in MOSFET) |
| Gate current |
|
It shows the maximum current that can flow in the gate
when the gate voltage |
is made positive in case of using in JFET. It shows
the maximum value of drain current
Main electrical characteristic
| Gate breaking current |
|
The leakage current between source to gate when applied negative voltage to gate from source and short-circuit between drain-source. It is gate current in the normal operatino of the JFET or leakage current through oxide film in case of MOSFET which is relatively extreme small to JFET case. |
|---|