Managing test coverage uncertainty due to thermal noise in nano-CMOS: A case-study on an SRAM array

Vikram B. Suresh, S. Kundu
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引用次数: 3

Abstract

From system-on-a-chip to high performance processors, SRAM is a critical component. In highly scaled CMOS devices, process variation is a major concern as it affects SRAM stability which often sets the floor on supply voltage and the ceiling on operating temperature of a semiconductor chip. Consequently, low-voltage and high temperature testing are often part of manufacturing test flow. In this paper, we show that for marginal cells, thermal noise is a major corrupting factor that affects the outcome of testing. A cell with large process variation which should ordinarily fail during memory test may pass due to impact of thermal noise at high temperature. To address this uncertainty during testing, we propose a stochastic metric for test coverage. We also propose application of N-detect and Multi-level Word Line (WL) techniques to improve test coverage based on this stochastic metric. Simulation studies on 32nm PTM models indicate varying probability of faulty bit detection across the spectrum of random thermal noise that lead to erroneous test results. Multiple accesses to each bit cell during test increases the fault coverage from -10% to near ideal 100%. Boosting WL voltage during read test and scaling it below nominal voltage during write test accelerates fault detection. Simulation of a 1KB SRAM array test case shows an improvement in fault coverage from -88% to 100% by increasing the number of detects to 100.
纳米cmos中热噪声引起的测试覆盖不确定性管理:SRAM阵列的案例研究
从单片系统到高性能处理器,SRAM都是关键部件。在高规模的CMOS器件中,工艺变化是一个主要问题,因为它会影响SRAM的稳定性,这通常会设置电源电压的下限和半导体芯片的工作温度的上限。因此,低压和高温测试通常是制造测试流程的一部分。在本文中,我们表明,对于边缘电池,热噪声是影响测试结果的主要破坏因素。由于高温下热噪声的影响,在记忆测试中通常会失败的工艺变化较大的电池可能会通过。为了在测试期间处理这种不确定性,我们为测试覆盖率提出了一个随机度量。我们还提出应用N-detect和多级词线(WL)技术来提高基于该随机度量的测试覆盖率。对32nm PTM模型的仿真研究表明,在随机热噪声频谱中,错误位检测的概率不同,从而导致错误的测试结果。在测试期间对每个位单元的多次访问将故障覆盖率从-10%提高到接近理想的100%。在读测试期间提高WL电压,在写测试期间将其降至标称电压以下,可以加速故障检测。对1KB SRAM阵列测试用例的仿真表明,通过将检测次数增加到100次,故障覆盖率从-88%提高到100%。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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