Context: FETs are divided into two families: junction FET (JFET) and insulated gate FET (IGFET). The IGFET is more commonly known as a metal–oxide–semiconductor FET (MOSFET), reflecting its original construction from layers of metal (the gate), oxide (the insulation), and semiconductor. Unlike IGFETs, the JFET gate forms a p–n diode with the channel which lies between the source and drain. Functionally, this makes the n-channel JFET the solid-state equivalent of the vacuum tube triode which, similarly, forms a diode between its grid and cathode. Also, both devices operate in the depletion mode, they both have a high input impedance, and they both conduct current under the control of an input voltage.

Question: How many groups are FETs split into?
Answer: two

Question: What are the names of the groups of FETs
Answer: junction FET (JFET) and insulated gate FET (IGFET)

Question: What is the common term for an IFGET?
Answer: a metal–oxide–semiconductor FET (MOSFET)

Question: How is a JFET different from an IGFET?
Answer: the JFET gate forms a p–n diode with the channel

Question: What mode do both JFET and IGFET operate in?
Answer: depletion mode

Question: What is a vacuum tube triode made from?
Answer: Unanswerable

Question: What controls the amount of input voltage?
Answer: Unanswerable

Question: How many layers of metal are in the gate of an IGFET?
Answer: Unanswerable

Question: What kind of FET is mass produced?
Answer: Unanswerable