Abstract
We report a systematic study of nickel chrome (NiCr) thin film resistors (TFRs) used as resistors in InP-based monolithic microwave integrated circuits (MMICs). The effects of fabrication process parameters (such as surface treatments or thermal cycles) and substrate materials on the electrical properties of NiCr TFRs are discussed. After completion of MMIC fabrication, the NiCr thin film resistors were found to exhibit lower sheet resistance (Rsh) as compared to the as-deposited films. The origin of this variation has been found to be mainly related to the post-NiCr thermal cycles involved in the IC process technology. In contrast, the Rsh values of NiCr TFRs deposited on GaAs or SiNx coated substrates were almost unaffected by thermal annealing. Hence, a thin SiNx passivation layer on the InP substrate has been integrated in the InP-based MMIC process to avoid the NiCr-InP interaction. As a result, NiCr thin film resistors with high sheet resistance uniformity and reproducibility, as well as low temperature coefficient of resistance (TCR) have been achieved. Moreover, the use of a SiNx layer on the InP substrate was also found to improve the inter-device isolation.
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