Analysis of localized polarization in GaAs substrates and shift in threshold voltage of a transistor caused by Intrinsic stress in passivation thin films

Effect of stress in passivation films on shift in the threshold voltage of GaAs transistors is analyzed using a finite element method. Stress field devoloped in the transistor structure is analyzed by considering thermal stress and intrinsic stress of thin films. Localized polarization and the stress-induced-charge density devoloped in the transistor structure are calculated by considering both the piezoelectric effect of GaAs and the predicted stress field in the transistor structure. It is possible to quantitatively predict the shift in the threshold voltage of the transistor, which is mainly caused by the passivation-film stress, by integrating the calculated density of the stress-induced charge in the transistor area. The minimum shift of about 0.1 V is obtaine d when the film stress is -50 MPa. The predicted shift in the threshold voltage agrees well with the measured result.