The influence of well contact on multiple-cell upsets in 28nm SRAM

In order to study the effects of the feature size reduction and well contact placement on the topology patterns characterization and the charge collection mechanism of device heavy ion single event multiple upset at the nanometer scale, heavy ion single event effect experiment investigation on the domestic 28nm SRAM was carried out on the experimental platform of HI-13 heavy ion accelerator in Beijing. Based on the mapping relationship between the logical address and physical address of the device, the experiment data were processed to obtain the 28nm SRAM heavy ion single event upset cross section curves, multiple upset percentage and multiple upset topology patterns, and the results were compared with those of heavy ion single event effect experiments in 65nm SRAM. The results show that, under the influence of factors such as feature size reduction and lower operating voltage, the heavy ion single event upset threshold and the bit upset saturation cross section of 28nm SRAM decreases significantly. In the direction perpendicular to the well, due to the reduced 28nm SRAM feature size, even if the single nucleon energy of the incident high LET heavy ion is low, its deposited charge is sufficient to affect the three SRAM cells across the well direction due to the combined effect of ion track coverage, well potential modulation caused by the parasitic bipolar amplification effect and carrier diffusion, resulting in the 28 nm SRAM topology pattern has a shape of n rows × 3 columns, which poses new challenges and requirements for the anti-radiation hardened technology with scrubbing and EDAC(Error Detection And Correction). Due to the global well contact deployment, the charge deposited by the incident ions in the well far away from the well contact is difficult to be discharged quickly, and the parasitic bipolar amplification effect lasts longer. The charge sharing competition between two PMOS in SRAM cell causes the single event upset recovery, which is the fundamental reason that causes the discontinuity of multiple upset topology pattern in 28nm SRAM . This provides a new anti-radiation hardened idea for the suppression of single event upset by the use of parasitic bipolar amplification in the future.