Selective Flip-Flop Optimization for Circuit Reliability

AbstractThis chapter proposes a selective flip-flop optimization method (Golanbari et al., IEEE Trans Very Large Scale Integr VLSI Syst 39(7):1484–1497, 2020; Golanbari et al., Aging guardband reduction through selective flip-flop optimization. In: IEEE European Test Symposium (ETS) (2015)), in which the timing and reliability of the VLSI circuits are improved by optimizing the timing-critical components under severe impact of runtime variations. As flip-flops are vulnerable to aging and supply voltage fluctuation, it is necessary to address these reliability issues in order to improve the overall system lifetime. In the proposed method, we first extend the standard cell libraries by adding optimized versions of the flip-flops designed for better resiliency against severe Bias Temperature Instability (BTI) impact and/or supply voltage fluctuation. Then, we optimize the VLSI circuit by replacing the aging-critical and voltage-drop critical flip-flops of the circuit with optimized versions to improve the timing and reliability of the entire circuit in a cost-effective way. Simulation results show that incorporating the optimized flip-flops in a processor can prolong the circuit lifetime by 36.9%, which translates into better reliability.This chapter is organized as follows. Section 1 introduces wide-voltage operation reliability issues and motivates the proposed selective flip-flop optimization approach. The impacts of runtime variations on flip-flops are explained in Sect. 2. Consequently, Sect. 3 presents cell-level optimization of the flip-flops. The proposed selective flip-flop optimization methodology is described in Sect. 4, and optimization results are discussed in Sect. 5. Finally, Sect. 7 concludes the chapter.