MEMS hotplates with TiN as a heater material

Titanium nitride has been investigated as a heater material for hotplates and microreactors. TiN is CMOS compatible, and has a higher melting point (2950 /spl deg/C) than conventional heaters of Pt and poly-Si. For the first time, TiN is tested inside a conventional membrane of LPCVD SiN/sub x/. Two types of TiN are considered: high stress and low stress. Their performance is compared with that of Pt. The maximum temperature of TiN coils is 11% higher than Pt coils with the same layout and over 700 /spl deg/C. For high-stress TiN, the TCR is almost constant and close to that of Pt, making it very suitable for temperature sensing. In the case of low-stress TiN the TCR becomes nonlinear and changes sign. The large differences between the nitrides are explained by the grain structure. Low-stress TiN contains many voids. They relax stress but strongly scatter the conduction electrons. The different grain structures are related to the sputtering parameters according to the Thornton model.