Pattern Imprinting in CMOS Static RAMs from Co-60 Irradiation

Abstract

Total dose irradiation of various CMOS SRAMs is shown to imprint the pattern stored in the memory during irradiation. This imprinted pattern is the preferred state of the memory at subsequent power-up. Imprinting can occur at dose levels significantly below the failure level of the devices and is consistent with the bias dependent radiation induced threshold shifts of the individual transistors of the memory cells. However, before total imprinting occurs, other unusual imprinting phenomena can occur, such as a reverse imprinting effect seen in SOS memories, which is probably related to the bias dependence of back-channel leakage.

Single event upset and charge collection measurements using high energy protons and neutrons

“…We attribute this to a dose imprinting effect which has been seen previously [16][17][18] in older and much smaller RAMS.…”

“…Previous researchers usually required dose of > 150 krads, to impart an imprint, but an early test on a commercial 4K bulk CMOS SRAM [17] showed imprinting effects for doses as low as 4-5 krads delivered by Co-60. A transistor threshold voltage shift and mobility imbalances induced by the radiation are thought to be the cause of the Table 3 contains the results of the proton tests in terms of the proton SEU cross sections.…”

Direct measurement and analysis of total ionizing dose effect on 130 nm PD SOI SRAM cell static noise margin*

“…, both data sides' SNM are decreased by TID, which is different from the conclusion obtained in the old generation of devices that one data side's SNM is decreased and the other data side's SNM is increased. [3][4][5][6][7][8] Figure 4 shows the extracted ∆SNM from butterfly curves as a function of TID levels, which reveals that radiation has a larger effect on Data 0 than Data 1. As discussed in Sec.…”

“…The impact of TID on the stability of SRAM cell has been investigated for several decades. [3][4][5][6][7][8][9][10][11][12][13] TID will result in a preferred state and non-preferred state in SRAM cell. That is, SNM of data applied on cell during TID exposure is increased, whereas SNM of TID complement data is decreased.…”

“…In general, SNM of SRAM before and after TID irradiation is determined by circuit simulation with the irradiated transistor model. [6,[9][10][11][12][13] Simulation results are experimentally verified by single event upset (SEU) characterization [3,[5][6][7][8] or background data [4,11] testing indirectly, according to the relationship between SNM and SEU cross section, and background data distribution. TID induced asymmetry in SRAM cell stability is experimentally verified by unbalanced SEU cross section for TID data and TID complement data, and TID pattern imprinting in background data.…”