Polysilicon sensors for CMOS-MEMS electrothermal probes

Abstract

We describe multiple embedded polysilicon resistive sensors in CMOS-MEMS electrothermal probes as a step toward creating probe arrays for passing current on ICs to reconfigure resistance change (RC) vias. When not in contact, a low-resistivity unsilicided polysilicon (LP) resistor detects probe displacement indirectly through the temperature coefficient of resistance (TCR) effect. When in contact with a load force, the difference of two LP resistors, one under stress in the flexure and the other cantilevered, cancels the TCR and extracts the piezoresistive (PZR) change, thus working as a force sensor. With a 10 V, 37.15 mW drive, at loads less than 10 µN, the achieved force sensitivity is constant and matches within 3.1% to the sensitivity extracted by mechanically pushing on the tip. The sensitivity decreases at large loads due to the unequal thermal boundary conditions of the two LP resistors. A third silicided polysilicon (SP) resistor having near zero piezoresistance is added to detect the thermal boundary condition change thereby extending the maximum detectable load.