# An 8 kb RRAM-Based Nonvolatile SRAM with Pre-Decoding and Fast Storage/Restoration Time
## 1 Introduction  
Recently, with the popularity and continuous development of portable electronic products such as smart phones, digital cameras, tablet computers and mobile memory devices, the memory market has been expanding. At the same time, the rapid increase in data has presented new challenges for the development of memory. Under the influence of advanced technology, the development of flash memory has also reached a bottleneck on the 32 nm node [1]. People are gradually turning to nonvolatile memory (NVM) technology. New memory based on new materials and technologies, especially nonvolatile memory, is gradually being developed. At present, the main nonvolatile devices include EEPROM, FeRAM, RRAM, etc. [2; 3; 4].  
SRAM has the same operation speed as a logic circuit and has low power consumption in static mode. It also utilizes a manufacturing process similar to that for logic circuits without additional cost, so it is widely used in logic ICs. The disadvantage of SRAM is that data cannot be stored in the event of power failure, which places certain restrictions on its development [5; 6; 7]. RRAM has the advantages of high integration density, fast operation speed, low power consumption, and non-volatile, multi-value storage [8; 9], which provides practical solutions for analog storage [10], computing in memory [11], artificial intelligence [12], etc.  
The research on nvSRAM started in 1984. Fujitsu of Japan adopted ferroelectric components to carry out a series of research and development on nvSRAM [13]. In the 1990s, Cypress of the United States developed nvSRAM based on SONOS technology [14]. In 2006, Toshiba of Japan studied nvSRAM based on MRAM, focusing on the application of MRAM and RRAM in nvSRAM [15]. With the fast progress in technology, nonvolatiledevices have been directly integrated with SRAM, and high-density nvSRAM has become the mainstream development focus [16]. nvSRAM is composed of SRAM and NVM. NVM can store and restore data, so as to realize the function of nonvolatile memory. nvSRAM can store data in non-volatile components in case of system power failure. When the power is restored, the data can be restored to SRAM. Compared with traditional SRAM, nvSRAM has the same performance as well as nonvolatile functionality, which ensures that high-end instruments and equipment can store data in real time. Nowadays, nvSRAM products are gradually finding use in ATMs, automotive electronics, printing equipment, industrial control and other fields [17; 18].  
RRAM uses the different resistance states of some thin-film materials under the action of electrical excitation to store data [19; 20; 21; 22]. Compared with three other mainstream NVMs such as FeRAM, MRAM and PCM, RRAM has high integration, fast reading and writing speed [22; 23], low writing power consumption and high compatibility with the current traditional CMOS process. In 2015, [PERSON] proposed an nvSRAM of 7T1R, which effectively reduced the energy consumption in the data restoration phase by using DSI technology [24]. The next year, [PERSON] proposed a high-speed and low-power 8T1R nvSRAM architecture, which improved speed and power consumption by sharing RRAM cells [25]. Therefore, nvSRAM, which integrates RRAM and SRAM, has the functions of both traditional SRAM and nonvolatile memory. It is one of the nonvolatile memories that are the focus of current research.