Cost-Effective Test Screening Method on 40-nm Embedded SRAMs for Low-Power MCUs

Embedded static random access memories (SRAMs) with cost-effective test screening circuitry are demonstrated for low-power microcontroller units (MCUs). The probing test step at the low temperature (LT) of −40 °C is obviated by imitating pseudo-LT (PLT) conditions in the package test, where a sample is measured at room temperature (RT). Monte Carlo simulation is carried out considering local <inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {t}}$ </tex-math></inline-formula> variations as well as contact soft open failure (high resistance), confirming good minimum operating voltage (<inline-formula> <tex-math notation="LaTeX">$V_{\mathrm {min}}$ </tex-math></inline-formula>) correlation between LT and PLT conditions. Test chips with two types of 4-Mbit single-port SRAM macros and 1-Mbit dual-port SRAM macro are designed and fabricated using low-power 40-nm CMOS technology. Measurement results demonstrate that the proposed test method reproduces LT conditions and screens out LT failures with less overscreening. The proposed test method eliminates 1/3 or more of the test costs.

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