Dynamic random access memories DRAMS

Today, dynamic random-access memories (DRAMs) are transistor/capacitor-based semiconductor devices, with access times measured in nanoseconds and very low costs. Core memories were made of magnetic rings not less than a millimetre in diameter, so that a megabyte of memory would have occupied square metres, while a corresponding DRAM would occupy a few square millimetres. Another version of a DRAM is the read-only memory (ROM), essential for the operation of any computer, and unalterable from the day it is manufactured. We see that developments in magnetic memories involved dramatic reductions in cost and... 

Dynamic random access memory (DRAM) silicon-based semiconductors and, 22 229, 230, 231, 250, 257, 258 vitreous silica in, 22 443 Dynamic random access memory devices, 10 3... 

Fig. 4.15 The use of etch stops to visualize defects in a dynamic random access memory (DRAM) structure for subsequent electron microscopy inspection. If a bias is applied to the silicon substrate, as shown in (a), the polysili-...

Capacitors are charge storage devices that are essential in many circuit families, including dynamic random access memory, DRAM, and RF chips. For example, in RF chips, capacitors occupy a large fraction (at present about 50 %) of the area of the... 

Mass production poses strict requirements on resist materials, most important of which are sensitivity, spatial resolution, contrast, and etch resistance. The sensitivity of the next-generation resists is required to be less than 10 pC/cm (EB), 100 mJ/cm (x-ray), and 25 mJ/cm (EUV) [89]. It should be noted that the resist sensitivity is traditionally expressed not by absorbed dose but exposure charge or energy per unit area. As for the spatial resolution, 45 nm is needed for the production of dynamic random access memory (DRAM) in 2010 [89]. Although resist patterns below 10 nm are presently fabricated by some kinds of resists, they do not have enough sensitivity required for the mass production [90,91]. 

As an example of Si technology, Figure 1 illustrates a packaged 1-megabit dynamic-random-access-memory (DRAM) chip on a 150-mm-diameter Si substrate containing fabricated chips. Each of the chips will be cut from the wafer, tested, and packaged like the chip shown on top of the wafer. The chip is based on a l- xm minimum feature size and contains 2,178,784 active devices. It can store 1,048,516 bits of information, which corresponds to approximately 100 typewritten pages. 

Figure 1. A packaged 1-megabit dynamic-random-access-memory (DRAM) silicon chip on a processed 150-mm-diameter Si wafer. (Used by courtesy of G. B. Larrabee, Texas Instruments.)...

In the case of dynamic random access memories (DRAMs) the cell is a thin film capacitor. The state of the cell ( 0 or T ) is read by the current pulse following an addressing voltage pulse. Because the charge stored in the capacitor leaks away in time (z = RC) then, for the information to be retained it must be periodically refreshed, the rate of leakage determining the necessary refresh interval. 

Over the past three decades, enormous progress has been made in materials and materials processing used to fabricate electronic devices. This progress has made possible an astonishing increase in device complexity and decrease in the dimensions of features used to fabricate the circuit, which, in turn, has led to improved performance and reduced cost per function. Figure 1 illustrates these trends for dynamic random access memory (DRAM), historically the most complex chip produced in terms of feature size and components per chip. 

Ferroelectrics are high dielectric materials that are easily polarized in an electric field and can remain polarized to some degree after the field is removed. Such properties make them ideal candidates for computer memory applications and they have been used in the form of thin films as ferroelectric random access memories (FeRAMs) and as high permittivity dielectrics for Dynamic Random Access Memory DRAMs. They have also been looked at as a replacement for silicon dioxide in certain MOS applications. 

This increase in circuit density is made possible only by decreasing the minimum feature size on the chip. Figure 2 illustrates the decrease in minimum feature size as a function of time for dynamic random access memory (DRAM) devices. In 1975, the 4-kilobit DRAM (4 X 10 memory cells or about 8.2 X 10 transistors) had features in the 7-9-(xm range, and by 1987,... 

On the other hand, there are applications shown in Figure 27.1 that are not effectively met by CSD. For example, integrated capacitors for dynamic random access memory (DRAM) node elements require a much higher capacitance density, extremely small lateral dimensions, and three-dimensional architectures. For... 

Dynamic random access memory (DRAM) was an improvement over SRAM. DRAM uses a different approach to storing the Is and Os. Instead of transistors, DRAM stores information as charges in very small capacitors. If a charge exists in a capacitor, it s interpreted as a 1. The absence of a charge will be interpreted as a 0. 

A. Dynamic Random Access Memory (DRAM) is the type of memory that is expanded when you add memory. Static Random Access Memory (SRAM) is often used for cache memory. See Chapter 2 for more information. 

The dynamic random access memory (DRAM) device, a two-element circuit, was invented by Dennard in 1967. The DRAM cell contains one MOSFET and one charge-storage capacitor. The MOSFET functions as a switch to charge or discharge the capacitor. Although a DRAM is volatile and consumes relatively high power, it is expected that DRAMs will continue to be the semiconductor memory of choice for nonportable electronic systems in the foreseeable future. ... 

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