From the foundry to the model - A fully automated system for on-wafer MESFET characterization

The fabrication of microwave integrated circuits requires several tests to be carried out on wafer in order to check the effectiveness of the process. That is accomplished by measuring some param­eters of a small group of test devices named PCM (Process Control Monitor), located on the same wafer and fabricated with the same process. In this paper a system is presented which integrates in a single workstation the experimental procedures, and the data processing which allow to carry out on line the more significant parameters of microwave GaAs FET. In order to achieve significant results in MMIC device modeling, a proper design of the PCM layout is required. This is accomplished by using special metallized patterns on GaAs, for the network analyzer calibration, which allow to define the reference planes very close to the active area of the device. A software package drives the user through all the operations up to the development of a small signal MESFET model, so that the procedure overcomes the peculiarity of laboratory experiment and gains the characteristic of a more general and operative tool, useful for recurrent applications.