The influence of width of mesa-piezoresistors on their characteristics

The influence of width of polysilicon mesa-piezoresistors with dielectric insulation on their surface resistivity and piezosensitivity is studied experimentally when forming the passivating layer of thermal silicon oxide. It is demonstrated that the surface resistivity strongly increases when decreasing the width of mesa-piezoresistors in the interval of 3 ≤ W ≤ 10 μm. This fact concerns the decrease of the cross section and the impurity segregation during oxidation. It is found out that decrease of the width results in the increase of the longitudinal piezosensitivity and the decrease of the transverse one. For the concentration in question the temperature resistance coefficient of polysilicon resistors doped with boron decreases slightly with the decrease of width, and it remains constant if the dopant is phosphor. Simple model explaining the behavior of the surface resistivity and piezosensitivity is proposed in the paper.