Temperature-dependent characteristics of polysilicon and diffused resistors

The temperature-dependent characteristics of polysilicon and diffused resistors have been studied. By using the 0.18-mum CMOS technology, a cobalt salicide process is employed and silicide is formed at the ends of resistors. Based on a simple and useful model, some important parameters of resistors including bulk sheet resistance (R-bulk) and interface resistance (R-interface) are obtained at different temperature. For diffused resistors, the R-bulk and R-interface values are increased and decreased with the increase of temperature, respectively. Positive values of temperature coefficient of resistance (TCR) are observed. Furthermore, TCR values are decreased with the decrease of resistor size. For polysilicon resistors, the R-interface values are decreased with the increase of temperature. In addition, negative and positive TCR values of R-bulk are found in n(+) and p(+) polysilicon resistors, respectively. In conclusion, by comparing the studied diffused and polysilicon resistors, the negative trends of TCR are observed when the resistor sizes are decreased.