The development of MMIC switch FET models for the Philips Microwave D07M foundry process

Microwave switches are generally fabricated in MMIC form using FETs, since these devices are the most easily integrated into the standard MMIC processes. The RF path is between the drain and source with control being provided at the gate. The switch FETs used were different from conventional FETs in that a high value resistor was placed in the gate circuit to provide isolation between the control signal and the RF, and much greater unit gate widths were used. In all cases, the standard Philips Microwave D07M implant was used and good switch behaviour was obtained from the layout of the device. A range of switch FET test patterns were defined on GaAs wafers and were RF-on-wafer probed at frequencies between 45 MHz and 26.5 GHz. The unit gate widths explored were between 50 μm and 300 μm with devices having one, two, four and eight gate fingers. A physically sensible model was created, having twelve elements whose values were fitted to the measured data for every combination of unit gate width and number of fingers, such that the elements of the model varied with these physical parameters in a manner that would be expected. The great benefit to the user of this kind of model is that the parameterised data set developed allows complete freedom in the design of switches, without the constraints of having to use data from a limited discrete data base. In general, excellent agreement was obtained between simulation and measurement