The present invention relates to active monolithic microwave devices.
Previous monolithic microwave integrated circuits (MMICs) have used GaAs FETs in a common-source configuration. In this case, the source regions (usually three or more regions) are connected to ground potential areas of the circuit in a low-inductance manner, the input signal is applied to the gate, and the output signal is taken from the drain. In the prior art of such monolithic FET configurations, the source regions are connected to the expanded ground areas at the top and bottom of the photograph using plated gold air bridges when it is necessary to cross over the gate feeds. The input gate transmission line is split into two or more feeds as is the output drain transmission line. The submicrometer gate itself is a single line located vertically between the source and drain regions. This "pi-gate" device design provides low output-to-input feedback capacitance and uniform phasing along the device.
A monolithic common-gate amplifier was published in 1981, in the preceedings of the MTT Symposium. See Peterson et al, "A Monolithic GaAs 0.1 to 10 GHz Amplifier", MTT Symposium Proceedings at page 354. However, this device did not teach the innovative air bridge configuration which is used to achieve the advantages of the present invention.
A key requisite in realizing a common-gate amplifier monolithically is a low and repeatable gate inductance. If the gate inductance is not low, it may lead to instability. If the gate inductance is not repeatable, the resulting device inconsistency will not permit economical integrated circuit fabrication techniques.
Thus it is an object of the present invention to provide a monolithic common-gate device structure which can be monolithically realized with low and repeatable gate to ground inductance.