A new CMOS stress sensor ratiometric readout for in-plane stress magnitude and angle detection

This paper presents a new CMOS stress sensor readout method based on the ratiometric measurement principle. A unique feature of this method is to simultaneously detect the in-plane stress magnitude and angle. The sensor core is a cascoded current mirror structure consisting of a reference input branch and four output branches with MOSFETs in 0°, 45°, 90° and 135° layout orientations. Current ratios of orthogonal pairs (0°, 90°) and (45°, 135°) are examined to derive the stress magnitude and angle information. The ratiometric measurement principle improves the readout accuracy by weakening the dependency on the absolute current value. The proposed method is verified by the 4-point bending measurement of a P-Type MOSFET sensor core on a silicon stripe. The non-bending related gain error is compensated. The measured stress changes linearly with the applied displacement, showing the correct trend. Both tensile and compressive stress measurements give consistent results. Angle detection accuracy of +/-1° is measured.