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A GaN high electron mobility transistor monolithic microwave integrated circuit (MMIC) designer typically has to choose a device design either for high-gain millimeter-wave operation with a short gate length, or for high-power-density X-band operation with a much larger gate/field-plate structure. We provide the designer the option of incorporating two different devices by implementing a 0.14-µm gate length GaN MMIC process capable of high-efficiency Ka-band operation while simultaneously achieving high power density in the same process flow.The key process enabler simply uses the capacitor top plate in the MMIC process as a field plate on the passivation layer. On two separate devices on the same chip using the same MMIC process flow, we demonstrate 7.7 W/mm at 35 GHz and V DS = 30 V on a standard 4 × 65-µm T-gated FET and then 12.5 W/mm at 10 GHz and V DS = 60 V on a 4 × 75-µm T-gated FET by adding a field plate. These are the highest reported power densities achieved simultaneously at X-band and Ka-band in a single wideband GaN MMIC process.

Abstract:The purpose of this work was to investigate the validity of Arrhenius accelerated-life testing when applied to gallium nitride (GaN) high electron mobility transistors (HEMT) lifetime assessments, where the standard assumption is that only critical stressor is temperature, which is derived from operating power, device channel-case, thermal resistance, and baseplate temperature. We found that power or temperature alone could not explain difference in observed degradation, and that accelerated life tests employed by industry can benefit by considering the impact of accelerating factors besides temperature. Specifically, we found that the voltage used to reach a desired power dissipation is important, and also that temperature acceleration alone or voltage alone (without much power dissipation) is insufficient to assess lifetime at operating conditions.

Optical pulse sources with repetition rate approaching Terahertz is very import for many photonics applications including ultra-high speed optical communication and generation of sub-mm waves. Both active and passive mode locked fiber lasers are the appropriate choice for this purpose because of the availability ofErbium doped fiber amplifier. In general, the mode locking occurs with a repetition rate of nf, where n is an integer and f, is the longitudinal mode frequency spacing. This is called harmonic mode locking. In the case ofrational harmonic mode locking, the repetition rate is (np + 1) f,, where p is also another integer. For the case ofactive mode locking, this is obtained when the modulation frequency to the amplitude or phase modulator used for mode locking is given by (n + l/p) f. For the case of passive mode-locking, the rational harmonic mode-locking occurs when the saturable absorber in a ring laser is offset by a fraction p/L from the center where L is the length of the cavity. We have developed a theory of the rational mode locked fiber laser. The results of the theory are compared with experimental results obtained from a l.5p fiber laser actively mode-locked with a LiNbO3 electro-optic phase modulator.