Mark Tesauro

  • Effect of Process Variation on Pinch-Off Voltage of Depletion-Mode pHEMT

    Fred Pool, Qorvo
    Jinhong Yang, Qorvo
    Chang’e Weng, Qorvo
    Kaushik Vaidyanathan, Qorvo
    Moreen Minkoff, Qorvo
    Matthew Porter, Qorvo, Inc
    Michele Wilson, Qorvo
    Tertius River, Qorvo
    Mark Tesauro, Qorvo

    Pinch-off voltage is a key device characteristic of depletion-mode pseudomorphic high electron mobility transistors (pHEMT). Pinch-off voltage (Vp) shifts caused by manufacturing process variation were studied in this paper. Experimental results showed higher pinch-off voltage if the AlGaAs Schottky layer is oxidized or contaminated by metal. A significant increase in pinch-off voltage was observed when the Schottky layer was exposed to air for up to 2 hours after oxygen plasma treatment.  Investigation also revealed an increase in pinch-off voltage in relation to staging time and environment before gate contact metal deposition. In both cases, the effective thickness of the AlGaAs Schottky layer was reduced, and pinch-off voltage was increased. Models of metal cross-contamination and a “last wafer” effect in wet clean processing were also evaluated to address pinch-off voltage variation.

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