Novel Magnetic Burn-In for Retention and Magnetic Tolerance Testing of STTRAM

Abstract

Spin-transfer torque RAM (STTRAM) is considered as one of the most promising candidates among the emerging memory technologies. However, it brings new test challenges such as characterizing retention time and magnetic tolerance. STTRAM retention time needs to range from few seconds to years depending on its application. This is further aggravated by a significant shift in retention time under static (process variation) and dynamic (voltage, temperature fluctuation) variations. Conventional test-flows lack the capability to characterize STTRAM retention time while maintaining a reasonable test time. We propose the magnetic burn-in (MBI) test, which can be incorporated in the existing test flow with minimal changes to enable STTRAM retention testing with shorter test times ( $3.71\times 10^{{^{13}}}\text{X}$ reduction with 220 Oe at 25 °C). MBI is also combined with standard thermal burn-in (MBI+BI) for further compression of retention time and test time ( $1.97\times 10^{^{14}}\text{X}$ reduction with 220 Oe at 125 °C). We also propose MBI to certify the magnetic tolerance of STTRAM bits during write/read/retention modes with minimal changes in the existing test flow. For the STTRAM employed in this paper, we have found 86, 370, and 319 Oe to be the write, the read, and the retention tolerance, respectively.