# RHLP-18T: A Radiation-Hardened 18T SRAM with Enhanced Read Stability and Low Power Consumption
## 1 Introduction  
Aerospace systems and terrestrial applications operating at high altitudes face harsh environments, where high-energy particle interactions significantly threaten electronic component reliability. Sources like Galactic Cosmic Rays (GCR), solar particle events, and trapped radiation belts expose circuits to a flux of heavy ions, protons, and other energetic particles [1]. When such a particle passes through a Metal-Oxide-Semiconductor (MOS) transistor within a Static Random-Access Memory (SRAM) cell, it deposits energy along its path. This instantly generates a dense track of electron-hole pairs. The deposited charge can then be collected by sensitive nodes within the cell through mechanisms like drift and diffusion or the parasitic bipolar amplification effect [2]. If this collected charge exceeds a critical threshold, it can induce a transient pulse or cause a persistent state flip--a Single Event Upset (SEU)--altering the stored logic state (e.g., '0' flipping to '1') [3]. The charge collection dynamics induced by high-energy particles are critically dependent on the Linear Energy Transfer (LET)--a measure of energy deposition per unit path length by ionizing radiation--and device architecture. In advanced nanometer-scale FinFET (Field Effect Transistor) technologies, the three-dimensional gate structure enhances charge collection efficiency through pronounced funneling effects, consequently increasing SEU susceptibilitycompared to planar transistor architectures. These radiation-induced mechanisms must be rigorously addressed in radiation-hardened circuit design to ensure reliable operation in harsh environments [4]. Depending on the system's criticality, such SEUs in memory can lead to data corruption, erroneous computations, loss of control, and potentially mission failure. Therefore, SRAM cells used in these demanding applications must employ specialized Radiation-Hardened-by-Design (RHBD) approaches to ensure data integrity and system survivability [5]. RHBD technology is important not only for aerospace applications but also for nuclear power systems. Robots and control systems deployed inside nuclear power plants or at nuclear accident sites are continuously exposed to intense radiation, making them susceptible to radiation-induced errors such as SEUs, like in space environments. To mitigate these risks, RHBD techniques with robustness equivalent to those used in aerospace systems are indispensable [6]. To counter the harmful effects of radiation, the research community has spent decades developing a wide range of RHBD strategies [7; 8]. These strategies fall into several broad categories. Process-level hardening involves modifying the semiconductor manufacturing process itself, for instance, using Silicon-On-Insulator (SOI) substrates to reduce sensitive charge collection volume or employing specific doping profiles [9]. Layout-level techniques focus on the physical arrangement of transistors and interconnects; examples include implementing guard rings to suppress a Single Event Latch-up (SEL), increasing spacing between sensitive nodes to reduce charge sharing, and using redundant contacts. Complementary to these are circuit-level RHBD techniques, which modify the cell's electrical design to inherently tolerate or correct for SEUs [10]. These often involve adding transistors to create redundancy, implement error detection/correction, or enhance storage node stability. This work falls into the latter category, presenting a newly developed SRAM bit-cell architecture, which is designated as RHLP (Radiation-Hardened Low-Power)-18T in this paper. The RHLP-18T cell architecture presented in this paper is designed primarily for high SEU robustness, excellent read stability, and low static (hold) power consumption. While many established RHBD SRAM cells prioritize minimizing transistor count for area efficiency (e.g., various 12T or 14T designs), these approaches can involve compromises in noise margins or exhibit vulnerabilities to specific SEU scenarios or multiple-node charge collection events.