Ultra-Fast, High-Capacity, Non-Volatile RAMs with Quantum Dots

There are basically two types of random access memories currently marketed all over the world. The Flash memories, most commonly known as portable memory sticks and dynamic random access memories, those used in personal computers. Both types have disadvantages, however they complement each other. For example, Flash memories are non-volatile but they are rather slow at writing data. On the other hand, DRAMs are volatile and have high write speed.

The problem is that there is no solution to create fast Flash memories by using the technologies in the semiconductor industry. Alternatively, a collaboration between the Technical University of Berlin and Istanbul University claims to have created the ultimate Flash memory, able to write information in just a couple nanoseconds. Martin Geller, from the Technical University of Berlin, states that: "Flash memory, which is today's market-driver in the semiconductor industry, and which everybody knows from memory sticks, digital cameras, and mp3-players, has a slow write time. Our quantum-dot-based memory may provide long storage time without power consumption of Flash memory, as well as a fast write time and better scalability to real-life devices."

Andreas Marent, a colleague of Geller related that the first prototype they have developed was nearly as fast as a DRAM device, however by improving it, a quantum dot memory could write information in only one picosecond, making it 100 times faster than the fastest DRAM device.

Prototype design

The device was constructed out of indium arsenide semiconductor on a gallium arsenide substrate. While the substrate is 'p-doped', a second layer of gallium arsenide covering the indium arsenide quantum dots is 'n-doped', thus reconstructing the basic structure of a p-n junction inside diodes, while permitting the flow of electrical current in only one direction. Further still, this property of the diodes makes them act as capacitors as well, in certain conditions.

For example, if an electrical current is applied across the quantum dot 'diode-capacitor', it will become electrically charged. The level of store charge indicates what bit of information the quantum dot is holding, either a '1' or a '0'. A small electrical charge represents the '1' bit, while '0' is represented through a high charge storage capacity.

Although the speed of the device is practically 100 times greater than that of a typical PC RAM, its speed is in fact slower than that due to experimental setup. Geller speculates that near future improvements could bring it to a speed of one nanosecond – 20 times faster than a RAM, or even to a few picoseconds once the physical characteristics are all sorted out.



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