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FiPInP: “Field-plated InGaAs-InAlAs high electron mobility transistors for emerging high-frequency applications”
Funding agency: Fondazione Cassa di Risparmio di Modena, Modena, Italy
Project members/Partners
University of Modena and Reggio Emilia, Italy
University of Manchester, UK
Project manager @ UniMORE: Giovanni Verzellesi
Start date: 01/12/2008
End date: 01/12/2011

InGaAs-InAlAs High-Electron Mobility Transistors (HEMTs) on InP substrates are being considered for a variety of emerging applications in the microwave, millimeter-wave and submillimeter-wave frequency ranges, including: next generation wireless communication systems, high bit rate optical communication systems, radars, active and passive millimeter-wave imaging,  radiometer and radio telescope systems, remote sensing instruments. All of these systems require power and/or low-noise amplifiers. InGaAs-InAlAs HEMTs have demonstrated the best high-frequency and low-noise performance of any transistor technology to date. This comes however at the cost of the low breakdown voltage resulting from the small critical electric field of the InGaAs channel. On the other hand, high voltage operation is amongst the most desirable solutions for achieving high power-density, high efficiency power amplifiers (PAs). High voltage capability is advantageous also for low-noise amplifiers (LNA), enabling more robust receiver with minimal protection circuitry.  The aim of the FiPInP project is to develop for the first time high-voltage InP HEMTs by introducing into the device structure a Field Plate (FP), i.e. an extension of the gate electrode on top of the passivation dielectric towards the drain contact, in order to effectively reduce the magnitude of the electric field at the drain side of the gate edge, thus resulting in higher breakdown voltage. The project has led to the successful fabrication of InGaAs-InAlAs pHEMTs on optimized epilayers  and incorporating field-plate structures of different dimensions.  Field-plate structures were designed relying on detailed TCAD simulations.  Measurements show that adopting the field plate enables the off-state breakdown voltage to be increased up to 17 V for 0.6-mm field-plates and to 19 V for 1.2-mm field plates. Moreover, field-plated pHEMTs exhibit a 10x lower gate leakage current than baseline pHEMTs without field plate. Finally, the field plate almost eliminates the dispersion between DC and 200-ns pulsed output characteristics. This can be attributed to the reduced electron injection into surface traps, leading to smaller gate-lag effects. The additional degree of freedom in the device design made available by the field plate can be exploited for (i) high voltage, high efficiency power amplifiers at millimeter-wave band, (ii) robust LNAs with simplified protection circuitry, (iii) integrated RF transceiver, including optimized devices for low-noise receivers and high-power devices for the transmitter PA.