Advanced low-power SRAM improves reliability & backup battery life

The recent demands for highly secure and reliable user systems are driving increased demand for highly reliable SRAM, which is used to store important information such as system programs and financial transaction data. The prevention of soft errors caused by alpha rays and cosmic neutron rays is a significant issue. Typical measures to deal with this problem include embedding an Error Correcting Code (ECC) circuit in the SRAM or user system to correct any soft errors that occur. There are limits, however, to the error correction capabilities of ECC circuits. For example, some cannot correct simultaneous errors affecting multiple bits.

Renesas’ Advanced LP SRAM devices feature exclusive technology in their memory cells that achieves soft error resistance over 500 times that of conventional Full CMOS memory cells. This makes it desirable for use in fields requiring high reliability, including FA, measurement devices, smart grid-related devices, and industrial equipment, in addition to many other fields, such as consumer devices, office equipment, and communication devices.

In the Renesas Advanced LP SRAM structure, a stacked capacitor is added to each memory node within the memory cells. This configuration suppresses the generation of soft errors to a level that is effectively soft error free. In addition, the load transistor (P-channel) of each SRAM cell is a polysilicon Thin-Film Transistor (TFT) that is stacked on top of the N-channel MOS transistor formed on the silicon. Only the N-channel MOS transistor is formed on the silicon substrate below. This means that no parasitic thyristors are formed in the memory area and theoretically makes latch-up impossible. Therefore, the Advanced LP SRAM is suited to applications requiring high reliability, such as FA, measurement devices, smart grid related devices, traffic systems, and industrial equipment.

The standby current of the RMLV1616A Series and RMWV3216A Series is only 0.5μA (typical) for 16Mb devices and 1μA (typical) for 32Mb devices. These low current consumption levels are less than half the levels of comparable earlier Renesas SRAM products, making it possible to extend the service life of backup batteries. The minimum power supply voltage when retaining data is 1.5V, lower than the 2.0V of comparable earlier Renesas products. This helps customers designing systems that retain data using battery power.

The 16 Mb RMLV1616A Series is available in three packages: 48-ball FBGA, 48-pin TSOP, and 52-pin μTSOP, allowing customers to select the package that best matches their application. The 32Mb RMWV3216A Series is available in a 48-ball FBGA package.

Samples of the RMLV1616A Series and RMWV3216A Series will be available in September. Mass production of the two series is scheduled to begin in October 2015. Mass production using the 110nm process has already begun for Advanced LP SRAM products with 4Mb and 8Mb capacities.