# Total Ionizing Dose Effects in Advanced 28 nm Charge Trapping 3D NAND Flash Memory
## 1 Introduction  
With the development of storage technology, a large number of new types of memory have been developed [1]. NAND Flash memories represent one of the most rapidly evolving sectors in the semiconductor market. As a type of non-volatile storage, NAND Flash memory can be electronically erased and reprogrammed. Over the last decade, developments in planar NAND Flash cells have progressed swiftly, approaching their scaling limits [2]. To accommodate the demand for higher capacities, the industry has transitioned from planar to 3D NAND technologies, necessitating advanced technological innovations [3, 4]. Three-dimensional NAND emerges as a promising solution for large-scale data storage in future memory systems. Extensive research into 3D NAND has led to the proposal of various memory architectures, including BiCS [5], TCAT [6], DC-SF [7], and SMArT [8]. While the adoption of 3D structures enhances storage density and generally improves reliability--owing to the increased electron storage capacity compared to planar configurations--it also poses new challenges associated with the polysilicon channel and floating body effects [9].  
The current mainstream 3D NAND Flash structure is a vertical-channel structure where memory cells are located at the intersection between vertical pillars and horizontal word lines [10]. Three-dimensional NAND Flash can be divided into two categories according to the different storage layer materials: floating gate (FG) and charge trapping (CT). The charge storage layer material of FG flash is polysilicon, which is isolated from adjacent cells through a dielectric layer. CT 3D NAND Flash is an emerging flash memory structure; thestorage layer material of charge trapping flash is silicon nitride (SiN), which stores charge through a trap inside the material. In addition, since charge trapping technology supports higher pillars, it allows for denser storage.  
With the continuous advancement of technology, a variety of 3D NAND Flash memories have been commercialized, leading to an increase in the number of layers from the initial 32 to the current 128 or even higher [11]. Three-dimensional NAND Flash faces several reliability challenges in ionizing radiation environments. Ionizing radiation affects the threshold voltage of memory cells, leading to bit flip events [11; 12; 13]. Radiation introduces defective states in the oxide layers of memory cells, reducing their reliability in terms of durability and data retention [14; 15; 16]. Additionally, TID affects the standby current and the time required for read, write, and erase operations [17; 18; 19]. Annealing time also plays a crucial role in memory performance [17]. However, the above studies on radiation effects mainly focus on FG flash. There are few studies on CT flash; only [PERSON] et al. published a study on the TID effect of X-ray on CT flash [10].  
This article assesses the performance of a 128-layer CT 3D NAND Flash memory exposed to Co-60 sources in different operating modes. Memory operating in Single-Level Cell (SLC) mode and Triple-Level Cell (TLC) mode exhibits varying degrees of TID resistance. Moreover, different bias states demonstrate varied resistance to radiation. Performance parameters such as standby current, RBER, operating current, threshold voltage, and multi-bit flipping were evaluated under various operating conditions in both TLC and SLC modes to thoroughly assess the TID resistance of this 128-layer CT 3D NAND Flash memory. This work will explore the worst bias of CT 3D NAND Flash operating in space and provide guidance for space applications of the device.  
The remainder of this article is structured as follows: Section 2 introduces the technical specifications of the 3D NAND Flash discussed in this study and the experimental design details. Section 3 presents and analyzes the findings on RBER, standby and read currents, threshold voltage, and the performance timing after radiation. Section 4 concludes the article.