Plastic Memory

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ABSTRACT

A conducting plastic has been used to create a new memory technology which has the potential to store a mega bit of data in a millimeter- square device-10 times denser than current magnetic memories. This device is cheap and fast, but cannot be rewritten, so would only be suitable for permanent storage.

The device sandwiches a blob of a conducting polymer called PEDOT and a silicon diode between perpendicular wires.

The key to the new technology was discovered by passing high current through PEDOT (Polyethylenedioxythiophene) which turns it into an insulator, rather like blowing a fuse .The polymer has two possible states- conductor and insulator, that form the one and zero, necessary to store digital data.

However tuning the polymer into an insulator involves a permanent chemical change, meaning the memory can only be written once.

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1. INTRODUCTION

A new form of permanent computer memory which uses plastic and is much cheaper and faster than the existing silicon circuits was invented by Researchers at Princeton University working with Hewlett-Packard.

This new memory technology is created by using a conducting plastic which has the potential to store a megabit of data in a millimeter-square device - 10 times denser than current magnetic memories.

This utilizes a previously unknown property of a cheap, transparent plastic called PEDOT - short for polyethylenedioxythiophene. The inventors say that data densities as high as a megabit per square millimeter can be possible. By stacking layers of memory, a cubic centimeter device could hold as much as a gigabyte and be cheap enough to compete with CDs and DVD.

2. MEMORY
In order to enable computers to work faster, there are several types of memory available today. Within a single computer there are more than one type of memory.

Memory

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Figure 1: Common memory types in embedded systems

2.1 TYPES OF RAM

The RAM family includes two important memory devices: static RAM (SRAM) and dynamic RAM (DRAM). The primary difference between them is the lifetime of the data they store. SRAM retains its contents as long as electrical power is applied to the chip. If the power is turned off or lost temporarily, its contents will be lost forever. DRAM, on the other hand, has an extremely short data lifetime-typically about four milliseconds. This is true even when power is applied constantly.

In short, SRAM has all the properties of the memory you think of when you hear the word RAM. Compared to that, DRAM seems useless. However, a simple piece of hardware called a DRAM controller can be used to make DRAM behave more like SRAM. The job of the DRAM controller is to periodically refresh the data stored in the DRAM. By refreshing the data before it expires, the contents of memory can be kept alive for as long as they are needed. So DRAM is also as useful as SRAM. When deciding which type of RAM to use, a system designer must consider access time and cost. SRAM devices offer extremely fast access times (approximately four times faster than DRAM) but are much more expensive to produce. Generally, SRAM is used only where access speed is extremely important. A lower cost-per-byte makes DRAM attractive whenever large amounts of RAM are required. Many embedded systems include both types: a small block of SRAM (a few kilobytes) along a critical data path and a much larger block of dynamic random access memory (perhaps even in Megabytes) for everything else.

Thus DRAM can only hold data for a short period of time and must be refreshed periodically. DRAMs are measured by storage capability and access time.

Storage is rated in megabytes (8MB. 16MB etc). Access time is rated in nanoseconds (60ns, 70ns. 80ns, etc) and represents...
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