TECH CORNER

Static random access memory: A memory technology with a future

by Chen Grace Wang, Corporate Product Manager Digital, Rutronik

Many providers have pulled out of the static random access memory (SRAM) market to focus on high-end, high-margin technologies. But there are still numerous applications where SRAMs are ideal.

There is reason enough to take a closer look at these memory solutions. Memory technologies fall into two main categories:

1.) Non-volatile or read-only memory (ROM) — memory data is retained when the power supply is turned off. The most familiar type of non-volatile memory is flash memory (NOR flash, NAND flash).

2.) Volatile or random access memory (RAM) — memory data is lost as soon as the power supply is turned off. A distinction is made here between dynamic random access memory (DRAM) and SRAM.

SRAM provides the fastest access to memory in electronic applications. However, the manufacturing cost per bit is higher than DRAM because each memory cell consists of four or six transistors (4T or 6T architecture).

In contrast, DRAM has only one transistor and capacitor per memory cell. The disadvantage is that the data must be rewritten (refreshed) at certain intervals.

Table 1. Main differences between SRAM and DRAM.

Fast asynchronous SRAM: A sub-type of SRAM, asynchronous SRAMs are finding application as the main memory source for small embedded processors without cache, such as those used in the industrial electronics industry, as well as in measurement systems, hard drives and network communications equipment. Fast asynchronous SRAM is characterized by particularly short access speeds of 8 to 20ns. The trend here is toward lower operating voltages and away from parallel to serial interfaces.

Low-power SRAM: Another version of SRAM, low-power SRAMs have a similar design to fast asynchronous SRAMs but also have a longer access time, typically between 50 and 70ns. Thanks to their very low-level standby power consumption, they can support battery backup applications. They are also popular for their better data retention and lower failure probability (soft error rate). Low-power SRAMs are used in a wide range of applications, such as in industrial, communications devices and cell phones. As with fast asynchronous SRAM, the trend is toward lower operating voltages and serial interfaces.

Target applications for SRAM

Table 2. SRAMs are suitable for numerous applications in various markets.

In addition to industry and telecommunications, SRAMs are increasingly used in automotive applications. Due to the enormous popularity of apps, the smartphone is set to remain a source of infotainment and connectivity in vehicles for the foreseeable future. The greatest opportunity lies with companies offering application processors, WiFi/Bluetooth/GPS/FM combo chips and wearables/hearables.

In summary, while suppliers continue drive new memory technologies, providing faster, higher end devices, there remains a vibrant market where fast, low-power legacy SRAM products with long-term availability are required.