High-resistance ZrN thin film resistor for small and low-cost MMIC switch

GaAs monolithic microwave integrated circuit switch (MMIC SW) for cellular phones and WLAN are required to be smaller. The chip size can be smaller using a high-resistance thin film resistor (HR-TFR) because the resistance of the gate-resistor for the SW is very large. ZrN is thought to be one of the most promising materials for HR-TFRs. However, the ZrN TFRs have a thermal stability problem. In this study, we investigated the effect of thermal annealing on the ZrN film to improve the thermal stability. We found oxidized bumps in the ZrN TFR that are formed at the contact edge between the ZrN TFR and the electrode reduced the stability of the ZrN TFR. With an appropriate annealing condition, these oxidized bumps are suppressed and the stability of the ZrN TFR is improved. We developed a stable HR ZrN TFR of approximately 4000Ω/sq. to fulfill design requirements. We made the chip about 30% smaller in case of a single pole double throw (SPDT) MMIC SW for WLAN applications with the ZrN TFR.