Renesas Electronics, a premier provider of advanced semiconductor solutions, introduced 5 new product versions in the RMLV0816B and RMLV0808B series of Advanced Low-Power SRAM (Advanced LP SRAM), the company’s flagship SRAM (static random access memory) devices. The new memory devices have a density of 8 megabits (Mb) and utilize a fine fabrication process technology with a circuit linewidth of 110 nanometers (nm).
In the Advanced LP SRAM Series, which can achieve soft error (Note 1) free and latch-up (Note 2) free operation, Renesas started mass production of 4 Mbit products fabricated in a fine feature size process with a 110 nm circuit line width in December 2013 and now has launched the 8 Mbit products in this series. The new devices are high-reliability products that achieve the same soft error rate as Renesas' earlier products that were fabricated in a 150 nm process. They also achieve low-power operation with a standby current of maximum of 2 microamperes (µA) at 25°C, making them suitable for data storage in battery-backup devices.
Renesas low-power SRAM products are used extensively in a wide range of products including industrial, office automation, communication, automotive, and consumer applications, and earned the industry's largest market share in 2013 (Note 3). As in the past, along with increased performance and functionality in user systems, the reliability of the system as a whole is critically important. This is why high reliability is required in the SRAM, which stores important information such as the system software and data. In particular, measures to deal with soft errors due to alpha rays and neutrons in cosmic radiation are seen as critical.
Since Renesas has added a capacitor (Note 5) to the memory node (Note 4) in the cell of the Advanced LP SRAM devices, these devices have an extremely high resistance to soft errors. A common method for dealing with soft errors is to correct the errors that occur using an ECC (error correcting code) circuit embedded in the SRAM or user system. There are, however, limits to such techniques, such as not being able to correct multiple bit errors depending on the performance of the ECC itself. To deal with this issue, the Renesas Advanced LP SRAM adopts structural measures that suppress soft error occurrence itself. The results of system soft error testing in Renesas currently mass produced 150 nm process Advanced LP SRAM has shown that these devices are essentially soft error free.
Additionally, the load transistors (p channel) in the SRAM cell are formed as polysilicon TFT (note 6) devices, and since they are stacked in the upper layer of the n-channel MOS transistors that are formed on the silicon substrate, only n-channel transistors are formed on the underlying silicon substrate. As a result, there are no parasitic thyristor structures in the memory area and thus these devices have a structure in which latch-up cannot, in principle, occur.
As a result of these design aspects, these products are SRAM devices with extremely high reliability compared to full CMOS type (Note 7) devices that have the ordinary memory cell structure. Thus they can contribute to even higher performance and reliability in equipment that requires high reliability, such as FA equipment, test equipment, smart grid related equipment, and transportation systems.
Furthermore, Renesas Advanced LP SRAM achieves an even more compact cell size by combining polysilicon TFT stacking technology with stacked transistor technology. For example, the cell size in Renesas 110 nm Advanced LP SRAM is comparable to that in a full CMOS type SRAM fabricated in a 65 nm process.