The effect of mechanical stress on lateral-effect position-sensitive detector characteristics

Position-sensitive detectors (PSDs) are widely used in noncontact measurement systems. In order to minimize the size of such systems, interest has increased in mounting the PSD chip directly onto printed circuit boards (PCBs). Stress may be induced in the PSD because of the large differences in thermal expansion coefficients, as well as the long-term geometrical stability of the chip packaging. Mechanical stress has previously been shown to have an effect on the performance of semiconductors. The accuracy, or linearity, of a lateral effect PSD is largely dependent on the homogeneity of the resistive layer. Variations of the resistivity over the active area of the PSD will result in an uneven distribution of photo-generated current, and hence an error in the readout position. In this work experiments were performed to investigate the influence of anisotropic mechanical stress in terms of nonlinearity. PSD chips of 60×3 mm active area were subjected, respectively, to different amounts of compressive and tensile stress to determine the influence on the linearity.