Memory chips

FIGURE 15.29 These micrographs show that a block < opolymcr on its own > rystallizes in a chaotic pattern a) nanoscale techniques wcr used to produce the self-assi mbled parallel array o the same copolymer in (b) Such n gular arrays could be used to make ultra-high density memory chips to store information in miniature computers... 

FIGURE 4.1 Chemical reactions are used to achieve the fine structures seen in modern integrated circuits. This electron micrograph shows a transistor in a "cell" of a 1-mega-bit dynamic random access memory chip. The distance between features is about 1 pm. Courtesy, AT T Bell Laboratories. 

The production of memory chips requires highly pure silicon, which is grown as a single crystal (Czochrabki process). 

Due to the statistical nature of split synthesis, an average 20 beads per member must be used to ensure that all library members are prepared successfully This requirement results in increased reagent consumption and extra effort in screening and structural determination. One of the most powerful aspects of the rf memory chips is the ability to perform automated sorting of library members. Thus a complete library may be prepared with each member synthesized only once... 

Gallium arsenide for solid-state lasers and fast memory chips can be formed by molecular beam epitaxy through the reaction... 

A coating of polyimide with a thickness of no less than 3 mil over the memory chip will practically eliminate this problem. 

Much of the recent research in solid state chemistry is related to the ionic conductivity properties of solids, and new electrochemical cells and devices are being developed that contain solid, instead of liquid, electrolytes. Solid-state batteries are potentially useful because they can perform over a wide temperature range, they have a long shelf life, it is possible to make them very small, and they are spill-proof We use batteries all the time—to start cars, in toys, watches, cardiac pacemakers, and so on. Increasingly we need lightweight, small but powerful batteries for a variety of uses such as computer memory chips, laptop computers, and mobile phones. Once a primary battery has discharged, the reaction cannot be reversed and it has to be thrown away, so there is also interest in solid electrolytes in the production of secondary or storage batteries, which are reversible because once the chemical reaction has taken place the reactant concentrations can be... 

The importance of eliminating these contaminants can be understood by comparing the size of human hair (50 im diameter) and a bacterium ( 5 /xm) to a 1-jlm line such as used in a memory chip. To keep particulates from contacting the coating, all machines are maintained in dean rooms where air is filtered to remove contaminants also, people entering the room wear protective dothing that does not shed particulates into the air. The dean rooms are rated by the number of particles present in the air. A dass 100 rating indicates 100 or fewer particles >0.5 fim are present in 1 ft3 (2.83 x 10-2 m3 ) of air a dass 10,000 would have 10,000 or fewer 0.5 im partides. The exact specification depends on need, but class 100 rooms are in routine use. 

Figure 5. Characteristic chip length scales illustrated by comparison to a ladybug. The magnification increases for each picture in the clockwise direction starting with the upper left corner, which shows a ladybug on 62-kilobit random-access-memory chips on a 75-mm-diameter silicon wafer. The final magnification in the lower left corner shows the metal lines (2 fim) at the device level. (Reproduced with permission from reference 3.

IBM. Promising New Memory Chip Technology Demonstrated by IBM, Macronix and Qimonda Joint Research Team. IBM... 

Figure 4.13. Scaling of transistor size. The top line indicates the technology node, whereas the bottom line indicates the physical size of the gate. It should be noted that the technology node no longer refers to physical dimensions of the transistor, but is rather an industry term related to a new fabrication process every 2 years, in accord with Moore s Law. By definition, the technology node refers to half the distance (half-pitch) between cells in a DRAM memory chip. It is noteworthy that the gate length, L, officially moved into the nanoregime in the year 2000. Reproduced with permission from Intel Corporation (http //www.intel.com).

Computer memory chips are mounted on a finned metallic mount to protect them from overheating. A 1.52 MR memory cliip dissipates 5 W of heat to air at 25 C. If the temperature of this chip is to not exceed 50°C, the overall heat transfer coefficient-area product of the finned metal mount must be at least... 

Interleaving memory banks mean that the memory is organized into B banks. Consecutive memory locations are stored in adjacent memory banks a word with address a is stored in bank number a mod B. The memory cycle time is the minimum time between accesses to a memory chip. This means that there is a maximum rate at which a memory chip can receive requests and consequently a minimum time between two accesses to the same memory bank, the bank busy time. This has performance implications for a program that has a memory access pattern that hits the same bank more often than the bank busy time. This is called... 

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