Electrical/piezoresistive effects in bent Alpide MAPS

Abstract

The ITS3 upgrade baseline design employs MAPS (Monolithic Active Pixel Sensor) in bent state. Bending experiments with the existing ITS2 MAPS (=Alpide chip) show it remains functional but with relative large analog supply current changes. It is shown that by the piezoresistive effect, rotation of current mirror FETs can be responsible which was confirmed after validating the layout. Measured Gauge Factor has proper sign but is 3 times lower than typical values derived from literature. The magnitude of the measured strain induced PMOS V$_{th}$ shift is as expected but the sign differs for compressive strain with some of the literature.