During the last few years a number of different devices have been developed. MESFET was regarded as one of the earliest type of GaAs devices. The so-called ‘first generation’ of GaAs devices includes:
- Depletion-mode metal semiconductor field-effect transistor, D-MESFET
- Enhancement-mode metal-semiconductor field-effect transistor, E-MESFET
- Enhancement-mode junction field-effect transistor, E-JFET and
- Complementary enhancement-mode junction field-effect transistor, CE-JFET
First generation GaAs gates have exhibited switching delays as low as 70 to 80 psec for a power dissipation in the order of 1.5 mW to 150 microW.
There are other more sophisticated/second generation’ devices such as:
- High electron mobility transistor, HEMT
- Hetero-junction bipolar transistor, HBT
Electron mobility in second generation transistors can be up to five times greater than in the first generation. In consequence, very fast devices are possible.
However, in the following posts we will concentrate on establishing some of the fundamental principles of GaAs design methodology for the first generation devices only, particularly the predominant MESFETs, which are now at a stage of development that enables them to be incorporated in very fast VLSI systems.