Nondestructive, Self-Contained Extraction Method of Parasitic Resistances in HEMT Devices

This article addresses the classical problem of determining the extrinsic resistances (RG, RS, and RD) of field-effect transistors (FETs) and, in particular, of high-electron-mobility transistors (HEMTs). The presented approach relies on small-signal measurements of open-channel transistors, as often proposed both for traditional metal-semiconductor FETs (MESFETs) and HEMTs. Unlike what is common practice with HEMTs, the method proposed here does not oversimplify the model of the active channel. On the contrary, we retrieve from the literature a possible analytical model for the open-channel HEMT and use it to determine the triplet of extrinsic resistances without the need of stressing the gate junction with too high currents. Another result of the approach, valid both for MESFETs and HEMTs, is a deterministic way to remove the contribution of the gate junction from the small-signal parameters of the measured devices. All extractions process data that are available on suitable ranges in frequency or in bias voltage, without taking to the limit the sweep parameters or seeking specific resonances. Also, optimizations are only allowed to refine the nominal values, not as the main technique of extraction. These goals are achieved by setting up different subproblems in the form of overdetermined linear systems and then solving by pseudoinversion. The validity of the approach is demonstrated on the measurements of devices from advanced HEMT technologies realized by OMMIC, both GaAs-based (40-nm gate length) and GaN-based (100 and 60 nm).