Model of NBTI combined with mobility degradation *Project supported by the Shenzhen Science and Technology Project (Nos. ZDSYS201703031405137, JCYJ20170810163407761, (JCYJ20170818114156474), the PhD Start-up Fund of Natural Science Foundation of Guangdong Province (No. 2015A030310499), and the China Postdoctoral Science Foundation Funded Project (No. 2015T80023). (December 2018)