Statistical VTH shift variation self-convergence scheme using near threshold VWL injection for local electron injected asymmetric pass gate transistor SRAM

A 6T-SRAM macro with the V_TH shift variation self-convergence scheme of the asymmetric pass gate transistor by the local electron injection is proposed. The statistical V_TH shift variation of the pass gate (PG) transistor is measured and the positive correlation between the PG transistor V_TH shift and its original V_TH due to V_D effect is self-compensated by the negative correlation between those by I_D effect. As a result, the measured PG transistor V_TH shift is less correlated with the V_TH of PG before injection. In order to enhance I_D effect and reduce V_D effect for a self-convergence in V_TH shift, near threshold V_WL self-convergence injection scheme is proposed. The proposed scheme reduces V_D effect by 38% and enhances I_D effect by 20%. Furthermore, the fabricated SRAM macro demonstrates 3 times larger word-line operation voltage window, 41% less read margin variation and 80mV lower V_CCMIN after the local electron injection.