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

Abstract

In order to study the effects of the feature size reduction and well contact placement on the characterization of topology patterns and the charge collection mechanism of device heavy ion single event multiple upset on a nanometer scale, the heavy ion single event effect experiment on the domestic 28 nm static random-access memory (SRAM) is 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 experimental data are processed, and the 28 nm SRAM heavy ion single event upset cross section curves, multiple upset percentage, and multiple upset topology patterns are obtained. The results are compared with those of heavy ion single event effect experiments in 65 nm SRAM, showing that under the influences 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 28 nm SRAM decrease significantly. In the direction perpendicular to the well, owing to the reduced 28 nm SRAM feature size, even if the single nucleon energy of the incident high LET (linear energy transfer) 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 fact that the 28 nm SRAM topology pattern has a shape of <i>n</i> rows × 3 columns, which poses new challenges and requirements for the anti-radiation hardened technology with scrubbing and EDAC (error detection and correction). Owing 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 discharge quickly, and the parasitic bipolar amplification effect lasts longer. The charge sharing competition between two p-channel metal oxide semiconductor in SRAM cell causes the single event upset recovery, which is the fundamental reason why the discontinuity of multiple upset topology pattern appears in 28 nm SRAM. This study provides a new anti-radiation hardened idea for suppressing the single event upset by using the parasitic bipolar amplification in the future.