Not so long ago the thought of keeping all your data at one place and be able to take it along seemed difficult. Backups of all your office files, pictures of your one week family holiday and your entire music collection traveling with you all the time sounded impossible.
But as it is said nothing is impossible. It took decades to develop but fortunately today we can keep all our data with us in a small memory storing devise.
Even now it is difficult to keep large amounts of high definition or huge amounts of data on a single chip called the “Flash”. Where you are reading this article, around the world work is being done to overcome this problem and our dreams to keep extremely heavy data on a single chip can come true.
To accomplish this few hurdles have to be covered by the technology developers.
The biggest competitor of flash right now is the “Magnetic Random Access Memory” or simply MRAM.
This memory device stores information onto two thin layers of magnetic material each divided into several cells. The bit set to 1 or 0 in the device is determined by the relative alignment of the magnetization of the two layers. One of these layers has a fixed polarity and that of the other can be flipped 180 degrees by applying small electric current or magnetic charge.
MRAM dependency to work using the magnetization is both a plus and a negative for it. Plus because it is easy and fast to control and the operations can be done in as little as nanosecond whereas the negative aspect is that while changing the magnetization of one cell can/does affect the magnetization of its neighbor as well.
This problem is holding the MRAM technology to a maximum capacity of 32 megabytes, less than one thousandth of the capacity if the best flash memory devices.
“Ferroelectric Random Access Memory” or “FeROM” has a close resemblance with the conventional flash. Both uses electrical effects to control the transistor like structure. Rather FeROM takes advantage of the strange distribution of electric charge in ferroelectrics (Complex crystals). Positive and negative ions in these crystals are brought into right position by a small external electrical field to create a stable electric polarization rather than the polarization techniques like that of magnets north and south poles. The polarization can be changed thus causing the bits to flip by the application of an additional charged caused by a small voltage applied to the crystals. Two advantages of FeRAM are that firstly it has a fast processing time, even less than nanosecond and secondly required very little power.
Now for the negatives, the problem with FeRAM is that it is charged based and to start it with sufficient speed additional charge needs to be stored near by. So every FeRAM memory cell with a capacitor attached. This capacitor does not only increase the size of the device but also limits the storage capacity. "The capacitor footprint limits storage density," admits Scott, who has studied ferroelectric materials for three decades. "I can’t see FeRAMs going to gigabyte devices like flash."
FeRAM can only be sued where economy is more important than capacity. This is because of its straight forward design and low power demands.
FeRAM was first produced commercially in 1992, according to Alwais. "It is a well-proven technology. It just isn’t widely produced, and so doesn’t have the economies of scale of other memory technologies."
Some of the applications of FeRAM are handheld glucometers, GPS receivers and cordless phones.
One option that looks good when talking about decreasing the size increasing the capacity of a memory device is phase change random access memory or PCRAM.
The technology used in this is similar to the one used in the rewritable CDs and DVDs. It has two distinctive solid phases, an amorphous phase in which the atom are randomly arranged like that of a window glass, it is an insulator and a crystalline phase like that found in the metals. This phase is electrically conducting.
The material is held between two electrodes. To change the state of the material to either amorphous or crystalline depends upon the duration of the pulse. If the pulse is long the material melts thus ordering itself into crystalline form and if the pulse is short the material cools abruptly into amorphous state.
The advantage of PCRAM being its size and the speed but speed itself is also a negative aspect. Speed and stability are inversely related to each other in PCRAM. The faster the state of the material changes the less stable its crystalline form tends to be. The problem now is to find a trade off between speed and stability by selecting the best combination of different atoms.
PCRAM and RRAM are somewhat interrelated, both of them have to potential to work at the tiniest of the scales. RRAM or ‘Resistive Random Access memory” uses electrochemical reactions to change the bonding structure of the crystalline solids whereas PCRAM uses heat from a pulse.
Raw material of RRAM is a naturally insulating oxide. When high voltage is applied to the crystal, oxygen atoms start to move away thus creating both holes and leaving behind excess electrons which are then available for conduction. The holes created move in line making a channel which is electrically conductive in the crystal. This can be reversed by reversing the voltage which will make the oxygen atoms to move back thus filling the empty holes and making the crystal and insulator once again.
This ability of RRAM to interconvert between conductive and insulator state by the movement of a few oxygen vacancies by the application of high voltage only at the right polarity makes it a fast low-powered technology.
The size, speed and power consumption of RRAM are all in the acceptable range, he only concern is the stability. Electrical current has the tendency to bypass the high-resistance region and take a detour through the neighboring element. This is the problem faced by the manufacturers of RRAM while placing the high resistance bit right next to the low resistance bit.
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