Flash+Memory

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 * overview of flash memory Technology
 * flash memory history
 * Differences between NOR and NAND memory
 * Quantum Tunneling
 * Quantum Tunneling in flash memory
 * Electrons and Flash memory

Flash Memory and Quantum Mechanics Flash Memory is a technology used in many modern electronics, such as digital cameras, MP3 players such as the Apple iPod or Microsoft Zune, cell phones, and video game consuls. Although it's also referred to as 'Flash RAM (Random Access Memory), flash memory is different in that it can store information without using a power source. It's a form of non-volatile computer memory that is electrically programmed and erased. It has a grid of columns and rows with transistors at each intersection which are separated by a thin layer of oxide. One transistor is called the floating gate and the other is called the control gate. The link between the two gates is called the wordline, and when this is in place the cell has a value of 1. If the link is broken, the cells value becomes 0. The link is broken in a process called Fowler-Nordheim (Quantum) tunneling, where electrons in the cell are altered, either programming or erasing the information in the cell.  **Flash Memory History** Flash Memory was invented in 1984 by Dr. Fujio Masuoka while he was working for the company Toshiba. He prese nted the technology at the 1988 IEEE meeting in San Jose, California, where Intel took interest in his creation. Later, in 1988, Intel produced the first flash chip for consumer use. There are two types of flash memory. The type created first is called NOR flash. It has long erase and write times but has a full memory interface allowing random access to any location within the memory of the device. This makes it practical for data that doesn’t need to be frequently updated, such as a computer’s basic input/output system (BIOS). It’s endurance is 10,000 to 100,000 erase cycles. NOR based-flash is the base of early flash-based removable data. NAND flash memory was introduced in 1989 by Samsung and Toshiba. It has faster erase and write times, higher density, and a lower cost per bit than NOR flash. It only allows sequential access to data, meaning a group of elements can only be accessed in a predetermined order. It can’t skip certain bits of information to go to a different one. This makes NAND Memory more suitable for memory cards such as in USB Flash drives and camera memory cards instead of computer memory. The first NAND-based removable media format was known as SmartMedia, followed by MMC, Security Digital, Memory Stick and xD-Picture cards. ** **Quantum Tunneling**
 * Overview of flash memory technology **
 * Differences between NOR and NAND Flash Memory **
 * NOR memory requires that all bytes in the target block be written as zero before they can be erased, whereas NAND does not require this. The size of erase blocks in NOR memory ranges from 64 to 128 kilobytes, resulting in longer write or erase times of up to 5 seconds. The erase blocks in NAND memory are smaller, ranging from 8 to 32 kilobytes, producing write/erase times of only 4 milliseconds. The difference results in NOR-based units needing to do more erase operations for any write/erase action (especially for updating small files). Because of NAND memories smaller erase blocks, fewer actions are needed per block, creating the quicker write/erase time. NOR memory, however, has an SRAM interface (SRAM stands for Static Random Access Memory) which gives the memory device enough address pins to map its entire media, allowing for easy access to every byte within the device. NOR also has a more straightforward user process; it is connected like other memory devices and allows for codes to be taken directly from it. NAND is complicated, however, with its need for an Input/Output interface. NAND memory devices are also produced with bad blocks randomly scattered about in them. Producing a device with no bad blocks was found to be economically impractical because of a large price tag caused by low-production yield rates. Because of these bad blocks, NAND devices require initial scanning of the media within the device to detect bad blocks, resulting in NAND devices having virtual mapping active on them at all times.
 * Quantum Tunneling is when a wave particle of a common object passes through a barrier of a item. For example, it is like a ball being rolled up a hill. The ball in the real world will gain potential energy until it reaches the top, then it will transfer back into kenetic energy. With the concept of quantum tunneling the ball will produces particle waves. These waves could possibly pass through the hill ( the barrier) and reach the other side. When a object crosses through another this is quantum tunneling. [[image:http://images.intomobile.com/wp-content/uploads/2007/08/quantum-tunneling-speed-of-light-broken.jpg align="left"]] **

Quantum Tunneling in Flash Memory ** Quantum tunneling happens with in flash memory. Electrons travel through transistors and some electrons are lost in the middle of the oxide layer. This layer is held together by magnets. How the electrons got there is the quantum tunneling because they had to go through a barrier. The electrons that are leaked in are the oxide layer are the ones that allow you to store files and information on a flash drive. **

**Electrons and Flash memory**
 * The floating gate is very similar to an "electron gun". It makes excited electrons which are then basically shot through the oxide layer. This traps the electrons on the other side of the barrier. This creates negatively charged electrons. There is a magnetic field which keeps the electrons between the transistors in the barrier. This magnetic field keeps the electrons negatively charged. The negatively charged electrons store more information over a longer period of time. Since two parts of the transistor are able to be turned off, the flow will still go through the third and final part. The transistor can be off. When this happens "the gate is closed" and electricity can not flow through that part. When the transistor is on the Gate is open and the transistor allows the electrons to flow through. In flash memory there are many different gates, some of which are stacked on top of each other. These gates will leak electrons with a negative charge. The electrons are then trapped between two different gates. This causes memory to be stored. This concept is very similar to pipes with a water source. You have a tap when it is turned on the water flows. Think of this as a gate. When you turn the tap off the water stops flowing. There is still water in the tap waiting to be let out. That is why it takes so little time to get water out of the tap. This works the same way with Flash memory.  [[image:http://www.semiconductor.net/photo/100436-six0903high2.gif width="450" height="255"]] **