Total ionizing dose effects on innovative silicon-on-insulator static random access memory cell

Abstract

The static random access memory (SRAM), as a common and important high-speed storage module in modern digital circuit systems, plays an important role in improving the performances of electronic systems. The data about the total ionizing dose (TID) radiation effect of SRAM cell have not been rich in the literature so far. In this work, a novel 6-transistor SRAM cell (6T LB SRAM cell) based on L-type gate body-contact (LB) MOSFET device is designed and fabricated by 130nm silicon-on-insulator (SOI) process. The LB MOSFET follows the center-symmetric layout design of the SRAM cell, reducing the area by approximately 22% compared with the SRAM cell using the T-type gate MOSFET contact device (6T TB SRAM cell) of the same device size. The electrical performance difference between LB MOSFET and other devices is compared. Besides this, the variations of the leakage current and the reading static noise margin (RSNM) of SRAM cells based on different MOSFETs under various total ionizing doses are also investigated. The test results indicate that the LB MOS successfully suppresses the floating body effect (FBE), and that the drain-induced barrier lowing (DIBL) and drain-to-source breakdown voltage (BVds) characteristics are improved. The performance of this device is similar to that of TB MOS device, but due to the special body contact design, the former has an advantage of smaller area. Due to the use of the body contact device, the leakage current of the 6T LB SRAM cell is significantly smaller than that of the conventional floating device SRAM cell (6T FB SRAM cell), which has lower static power consumption. After ⁶⁰Co-γ ray irradiation, the 700 krad(Si) radiation dose only increases the leakage current of 6T LB SRAM cell by 21.9%, which is better than 41.4% of 6T FB SRAM cell. In addition, the 6T LB SRAM cell has an RSNM value similar to that of the 6T TB SRAM cell, and this is 1.93 times higher than the that of 6T FB SRAM cell. The radiation experiment causes the butterfly curve of the 6T FB SRAM cell to be asymmetrically deformed, and the stability of the SRAM cell is deteriorated due to the TID effect. However, the test results show that when the radiation dose reaches 700 krad (Si), the RSNM value of the 6T LB SRAM cell is reduced only by 11.2%. Therefore, 6T LB SRAM cell has stable and reliable practical value.