Quantitative study of photoelectric laser stimulation for logic state imaging in embedded SRAM

The use of optical techniques for attacking integrated circuits (ICs) at the silicon level is increasingly being reported. Although these attacks can be complex to set and require skilled attacker that can access expensive equipment, they are nonetheless very powerful. Among the different applications described in literature, there has been a focus on extracting data directly from embedded SRAM. Such attacks can provide access to highly sensitive information such as encryption keys and bypass various security strategies. An attacker usually exploits one of the several interactions that exist between light and semiconductor to generate an image where content can be directly qualified by the data in memory (Logic State Image – LSI). Thermal laser stimulation (TLS) and laser probing (EOFM-Electro-Optical Frequency Mapping) have been reported in the literature recently but Photoelectric Laser Stimulation (PLS) did not get as much attention. Considering the potential advantages of PLS over other techniques (e.g. lower power requirements to generate current/voltage change, effect can be triggered at shorter wavelength which may lead to an improved spatial resolution), we investigate in this paper if logic state images can be generated with PLS on a variety of devices and do a comparative assessment with state-of-the-art technologies to assess potential benefits and limitations.