The words "flash memory" are now on everyone’s lips. Even first graders in conversation often use the term "flash drive". This technology with incredible speed has gained popularity.
Moreover, many analysts predict that in the near future flash memory will completely replace storage devices based on magnetic disks. Well, it remains only to observe the development of progress and enjoy its benefits. Surprisingly, many people, speaking about this new product, know almost nothing what flash memory is. On the one hand, the user needs the device to work, and how exactly it performs its functions is the tenth thing. However, at least a general idea is necessary for every educated person.
What is flash memory?
As you know, computers have several types of storage devices: RAM modules, hard drives and optical disks. The last two are electromechanical solutions. But the RAM is a fully electronic device.
It is a set of transistors assembled on a chip of a special chip. Its peculiarity lies in the fact that the data is stored until voltage is applied to the base electrode in each controlled key. This moment we will consider in more detail later.
Flash memory is devoid of
this drawback. The problem of storing the charge without supplying external voltage was solved using transistors with a floating gate. In the absence of external influence, the charge in such a device can remain for a sufficiently long time (at least 10 years). To explain the principle of operation, it is necessary to recall the
basics of electronics.
How is the transistor arranged?
These elements are so widely used that it is rare where they are not used.
Even in a commonplace
light switch, sometimes controlled keys are installed. How does a classic transistor work? It is based on two semiconductor materials, one of which has electronic conductivity (n), and the other hole (p). To get the simplest transistor, you need to connect the materials, for example, in the form of npn and connect an electrode to each block. A voltage is applied to one extreme electrode (emitter). It can be controlled by changing the magnitude of the potential at the middle terminal (base). Removal occurs on the collector - the third extreme contact. Obviously, when the base voltage disappears, the device will return to a neutral state. But the device of the transistor with the floating gate underlying the flash drives is slightly different: a thin layer of dielectric and a floating gate are placed in front of the semiconductor material of the base - together they form the so-called “pocket”. When positive voltage is applied to the base, the transistor will open, passing current, which corresponds to zero in logic. But if a single
charge (electron) is placed on the gate
, then its field neutralizes the influence of the base potential - the device will refuse to be closed (logical unit). By measuring the voltage between the emitter and the collector, it is possible to determine the presence (or absence) of charge on a 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 positive to the emitter. The charge will go off the shutter. Since the technology is constantly evolving, it was proposed to combine a conventional transistor and a version with a floating gate. This made it possible to “erase” the charge with a lower voltage and produce more compact devices (there is no need for isolation). USB flash memory uses exactly 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 stored without changing for decades. Perhaps the only drawback of modern flash drives is the limitation on the number of rewriting cycles.