Test and diagnosis of resistive bridges in multi-Vdd designs

Abstract

A key design constraint of circuits used in hand-held devices is the power consumption, mainly due to battery life limitations. Adaptive power management (APM) techniques aim to increase the battery life by adjusting the supply voltage (Vdd) and operating frequency, according to the workload. APM-enabled devices raise a number of challenges for existing manufacturing test and diagnosis techniques, as certain defects exhibit Vdd dependent detectability. This means that to achieve 100% fault coverage, APM-enabled devices should be tested at all operating voltages using repetitive tests. Repetitive tests at several Vdd settings are undesirable as it increases the cost of manufacturing test. This thesis provides two new and cost-effective Design for Test (DFT) techniques to avoid repetitive tests thereby reducing test cost. The first technique uses test point insertion (TPI) to reduce the number of test Vdd settings. TPI capitalizes on the observation that each resistive bridge defect consists of a large number of logic faults, including detectable and non-detectable logic faults. It targets resistive bridges requiring test at higher Vdd settings, and converts un-detectable logic faults at the lowest Vdd setting, into detectable logic faults by using test points. Test points provide additional controllability and observability at the fault site. TPI has shown encouraging results in terms of reducing the number of test Vdd settings, however it does not achieve single Vdd test for all designs. Taking this issue into account, another gate sizing (GS) based DFT technique is proposed. It targets bridges that require multi-Vdd test and increases the drive strength of gates driving such bridges. The number of test Vdd settings are reduced minimizing test cost. Experimental results show that for all designs, the proposed GS technique achieves 100% fault coverage at a single Vdd setting; in addition it has a lower overhead than the TPI in terms of timing, area and power.

The Vdd dependent detectability of resistive bridges demands re-evaluation of existing diagnosis techniques, as all existing techniques use a single voltage setting for fault diagnosis, which may have a negative impact on diagnosis accuracy, affecting subsequent design cycle and yield. This thesis proposes a novel and cost-effective technique to improve diagnosis accuracy of resistive bridges in APM-enabled designs. It evaluates the impact of varying supply voltage on the accuracy of diagnosis and demonstrates how additional voltage settings can be leveraged to improve the diagnosis accuracy through a novel multi-voltage diagnosis algorithm. The diagnosis cost is reduced by identifying the most useful voltage settings and by eliminating tests at other voltages thereby achieving high diagnosis accuracy at reduced cost. All developed test and diagnosis techniques have been validated using simulations with ISCAS and ITC benchmarks, realistic fault models and actual bridges extracted from physical layouts.

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Identifiers

ORCID for Mark Zwolinski: orcid.org/0000-0002-2230-625X

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