Development of 2T-SONOS Cell Using a Contamination-Free Process Integration for a Highly Reliable Code Storage eNVM

We report a low-cost and highly reliable 2T-SONOS embedded nonvolatile memory (eNVM) using a novel contamination-free process integration. The proposed 2T-SONOS cell is fabricated on a 90-nm high-voltage CMOS process for a touch screen controller embedded display driver IC applications. For a code storage purpose, eNVM with moderate memory density, simple integration, platform logic and process compatibility, and sufficient retention lifetime are critically important. Thanks to the contamination-free charge trap layer and optimized junction, we have achieved enough retention lifetime without using any special materials for the charge trap layer. The 120 °C data retention lifetime of over 10 years is verified using 77 × 3 samples of 32-kB memory density intellectual property. By correlating high-temperature retention bake results with technology computer-aided design simulations, we can understand long-term charge redistribution behavior inside trap nitride, which is significantly different from floating gate type NVM.