If used as RAM, PCM phase change memory will be thousands of times faster

Phase Change Memory (PCM) is a non-volatile memory technology that promises to be used on next generation SSD drives. However, it is not only hard drives that PCM can potentially be used as volatile DRAM memory to exploit its high-speed access advantages. Stanford University has demonstrated that PCM can achieve speeds thousands of times higher than conventional DRAM.

Before coming to Stanford's research, we need to understand that silicon memory chips generally have two forms: volatile memory such as RAM on a computer with the characteristic that data will be lost when power is lost ( shutdown) and non-volatile as flash memory types (memory chips on phones or SSDs on computers) can store data even when the computer is turned off.

Variable memory has a higher access rate than non-volatile memory, but non-volatile memory can store data for long periods of time. This is also the reason why flash memory technologies are used for storage devices while RAM works in conjunction with the CPU to store data temporarily during the calculation by its speed. measured in nanoseconds (10 ^ -9 seconds).

PCM is a unique, non-volatile memory technology, made with special semiconductor materials (such as chalcogenide glass) and has been studied by Stanford University engineers since the 1960s, 70 of the last century. PCM memory technology is also being developed by many companies but the main application in hard drive technology, such as IBM, HGST and even Intel with Optane / 3D Xpoint memory technology is also said to be developing. based on PCM.

Stanford University has demonstrated that PCM can achieve speeds thousands of times higher than conventional DRAM.

But researchers at Stanford have demonstrated that PCM can bring advantages to both types of memory, both to store permanent data, and to provide thousands of times faster access speeds. With current memory types, not to mention more power saving.

The common silicon memory chip operates according to the mechanism of turning on and off electron currents corresponding to signals 1 and 0 digitally. Scientists are still looking for new materials and new processing processes to save more electricity and less space than silicon. PCM is one of the potential solutions because it uses materials that possess a flexible atomic structure. PCM has two states: amorphous with high impedance and crystalline state (crystalline) with low impedance. In the crystalline state (or chaos), the atomic structure will block the flow of electrons while in crystalline state (or order), the atomic structure will allow the flow of electrons to pass through.

The reason that phase change material is considered a potential alternative to current silicon memory is that it can maintain any charge state that adapts to its structure. Once the material atom moves back and forth between the two states to form a 1 or 0 signal, the material can store that data until another energy source causes it to change. This data storage capability makes non-volatile phase change memory possible as NAND flash memory on phones or SSD drives.

However, in order to use the inherently variable DRAM memory, in addition to data storage, PCM needs to be fast and consume less power. The inherent disadvantage of DRAM memory is the memory gap (memory gap or memory wall) so we can see that although the DRAM memory clock has been constantly increasing during the past 30 years, the time of launching is only Marketing and feedback (or latency) of memory is still not much improved. And this drawback can be overcome by PCM.

Prototype PCIe SSD Onyx Moneta.

The research team is composed of 19 members led by photon science and photology assistant professor Aaron Lindenberg who has found a way to quickly switch between non-crystalline and crystalline states of the corresponding material from 0 to 1 and 1 return to 0 by applying electrical or optical pulses.

They put a sample of crystalline material into an electric field that has the same power as a lightning bolt. Based on a measuring device, the researchers measured the atomic structure of the state-changing material from crystallization (0) to crystallization (1) in less than 1 pico second (10 ^ -12 seconds). This means that PCM can store data many times faster than silicon-based RAM for tasks that require memory and the processor must operate at the same high speed. Thus, it can be said that PCM will eliminate the distance gap between RAM and CPU.

However, there are still many obstacles on the way to apply PCM technology to DRAM memory because high-energy pulses cannot be generated on PCB circuits and signals are difficult to transmit through printed circuits. bronze on modern board design. What we know now is that PCM can switch state very quickly. The ability to operate at pico seconds does not guarantee that this technology will replace DRAM, but it proves that PCM has the potential to operate at frequencies that DRAM cannot reach.