7.3 A 28nm embedded SG-MONOS flash macro for automotive achieving 200MHz read operation and 2.0MB/S write throughput at Ti, of 170°C

Accelerated advances in automotive technology, such as sophisticated real-time engine controls for higher fuel efficiency and advanced driver-assistance systems (ADAS), are expanding the application range of Flash MCUs, microcontrollers with embedded Flash memory (eFlash). In addition to consistent demands for faster random access, shorter rewrite time and larger memory capacity in eFlash, there are increasingly intense requirements for robust operations and high data reliability under extremely high junction temperature (T_i,) of 170°C. On the other hand, along with device scaling beyond 40nm generation, the reliability of eFlash systems is constrained by not only eFlash memory cells but also peripheral transistors and metal interconnections. As oxide films in transistor devices and between metal interconnections are getting thinner, their time-dependent dielectric breakdown (TDDB) lifetime is critically degraded, which poses a great challenge in advanced eFlash design. This paper presents 28nm eFlash macros for automotive with four key features. The first feature is a 28nm split-gate (SG)-MONOS cell array with temperature-adjusted overdrive wordline (WL) voltage control to realize both 200MHz random access and more than 10× longer TDDB lifetime of WL drivers. Second, we implement a high-voltage control technique to relax electrical stress on memory cells and peripheral devices by temperature-adaptive step pulse erase control (TASPEC). Third, we achieve high write throughput of 2.0MB/s by source-side injection (SSI) programming with negative back-bias achieving 63% reduction of program pulse time. Finally, we reduce RF noise by 19dB with a spread-spectrum phase-shifted clock-generation technique for over-the-air program updates while achieving a high write throughput.