Dynamic capacitors

The MOSEET has three regions of operation. The cutoff region occurs for V g < Up. In this region, the drain-to-source current is the reverse saturation current of the back-to-back source and drain junctions. This leakage current is small but nonzero and allows charge to leak off capacitors which are isolated by cutoff MOSFETs. Because this is how bits are stored in dynamic memory (DRAM) ceUs, DRAMs must be regularly refreshed to retain their memory. 

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... 

These cause dynamic issues to the switching power supply, and usually the only solution to that is to have enough bulk capacitance present on the 12V output rail. Luckily, since the main feedback loop is derived from the primary 5V/3.3V rails of the power supply, there is no minimum ESR requirement for the 12V rail output capacitance, and we can freely add several electrolytic capacitors in parallel. However, modern core processors can place very fast transient load demands on the primary regulated rail, too, and for that we need a whole bunch of ceramic capacitors sitting right at the point of load. In that case we must ensure the converter is designed to accept ceramic loads. Otherwise it will break up into oscillations. 

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... 

In addition to requiring high dielectric films for DRAM capacitors (dynamic random access memories) and for the active memory elements in FRAMs, the microelectronics industry has a stated demand for a replacement for Si02 gate oxides very soon. The leading candidate is hafnia (Hf02), and there are significant opportunities for the ferroelectrics community to contribute to the solution of this problem. 

In routine spectrophotometers, photomultiplier tubes are replaced by photodiodes (Fig. 11.11), which have excellent sensitivity, linearity and dynamic range. The photoelectric threshold, in the order of 1 eV, allows detection up to wavelengths of 1.1 pm. In diode array systems, each rectangular rectangular diode (15 pm x 2.5 mm) is associated with a capacitor. The electronic circuit sequentially samples the charge of each capacitor. While a photomultiplier tube measures the instant intensity in watts, a diode measures the emitted energy in joules over a time interval. 

To obtain the dynamic hysteresis loop of a ferroelectric capacitor the polarization is measured versus the applied voltage. Since the hysteresis is neither a linear nor a time invariant property, the hysteresis loop is dependent on the sample history and on the measurement method. To have a standardized and comparable hysteresis loop, certain parameters are commonly fixed. One is the absolute position of the loop on the polarization axis, since the initial (virgin) state of the polarization is unknown in almost all cases, the hysteresis loop is balanced to a reference value. Most commonly the positive and negative saturation polarization are set to... 

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. 

Fig. 7. Circuit and waveforms used to study the dynamic behavior of the FET and the simulated liquid crystal element. VD, potential applied to drain Va, gate pulses V, observed potential across 10-pF capacitor simulating liquid crystal element. The dashed lines indicate 0 V.

DRAM (dynamic random access memory) — A type of a commonly used random access memory that allows the stored data to be accessed in any order, i.e., at random, not just in sequence. That type of computer memory stores each bit of data in a separate capacitor charged and discharged by only one logic element transistor. However, the DRAM capacitors are not ideal and hence leak electrons the information eventually fades unless the capacitor charge is periodically refreshed (circa every 64 ms). This makes this type of memory more power... 

Since the early suggestion that ferroelectric thin film materials could be the high dielectric layer in the capacitor of the ultra large scale integrated dynamic random access memory devices (ULSI DRAMS) made by Parker and Tasch, there has been a great deal of research effort to deposit multi-component ferroelectric oxide thin films as well as more recent industrial activity. The term ferroelectric indicates the property of certain materials that have remnant... 

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