Ageing behavior of polysilicon heaters for CMOS microstructures operated at temperatures up to 1200 K

We report the operation of micro test structures at temperatures up to 1200 K. The structures realized by a standard CMOS process consist of dielectric membranes which are heated resistively by an integrated, degenerately n-doped polysilicon heater. The heater itself serves as temperature monitor and as object of interest to characterize the ageing behavior of polysilicon. The structures are cycled thermally to temperatures up to 1200 K by increasing the electrical heating power stepwise to 124 mW. Depending on the cooling rate of the thermal cycles, the resistance of the heater can reversibly be changed between +33% (cooling rate 0.02 K/s) and -17% (cooling rate 12.1 K/s) of its initial value. During the constant power steps of the heating/cooling cycles exponential resistance changes vs. time with time constants in the range of seconds to a few minutes are observed.