The words "flash memory" are now on everyone's lips. Even first-graders often use the term "flash drive" in conversation. This technology with incredible speed has gained popularity. Moreover, many analysts predict that soon flash memory will completely replace the storage devices based on magnetic disks. Well, it remains only to observe the progress and enjoy its benefits. Surprisingly, many people, speaking about this novelty, practically do not know anything about flash memory. On the one hand, the user needs the device to work, and how it performs its functions is the tenth thing. However, to have at least a general idea is necessary for every educated person.
What is flash memory?
As is known, in computers there are several types of storage devices: RAM modules, hard drives and optical disks. The last two are electromechanical solutions. But the RAM is a completely electronic device. It is a set of transistors, assembled on a chip of a special microcircuit. Its feature is that the data is stored until voltage is applied to the electrode of the base in each controlled key. This point we will consider in more detail later. Flash memory of this lack is deprived. The problem of storing a charge without external voltage was solved with the help of transistors with a floating gate. In the absence of external influence, the charge in such a device can be kept for a sufficiently long time (not less than 10 years). To explain the principle of work, you need to remember the basics of electronics.
How is the transistor arranged?
These elements have become so widely used that rarely, where they are not used. Even in the banal light switch, you sometimes install controlled keys. How is the classical transistor arranged? It is based on two semiconductor materials, one of which has electronic conductivity (n), and the other is p-type (p). To get the simplest transistor, you need to connect the materials, for example, in the form of npn and connect each electrode to each block. One voltage (emitter) is applied to one end electrode. It can be controlled by changing the value of the potential at the middle output (base). Removal occurs on a collector - the third extreme contact. Obviously, if the base voltage disappears, the device will return to the neutral state. But the device of a transistor with a floating gate, underlying the flash drives, is slightly different: before the semiconductor material of the base is placed a thin layer of dielectric and a floating gate - together they form the so-called "pocket". When applying positive voltage to the base, the transistor will be opened, skipping the current, which corresponds to zero in the logic. But if you place a single charge (electron) on the gate , then its field neutralizes the influence of the base potential - the device will refuse closed (logical unit). By measuring the voltage between the emitter and the collector, one can determine the presence (or absence) of the charge on the floating gate. The charge is placed on the gate using the tunnel effect (Fowler - Nordheim). To remove the charge, it is necessary to apply a high (9 V) negative voltage to the base and a positive voltage to the emitter. The charge will leave the shutter. As the technology is constantly evolving, it was suggested to combine a conventional transistor and a floating gate option. This allowed to "wipe" the charge with a lower voltage and produce more compact devices (there is no need to isolate). USB flash memory uses this principle (NAND structure).
Thus, by combining such transistors into blocks, it was possible to create a memory in which the recorded data is theoretically saved without changing for decades. Perhaps the only drawback of modern flash drives is the limitation on the number of rewriting cycles.